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# Conflict of polarity?
With the following circuit, would the R2 resistor not change or affect the polarity in some negative way (no pun intended)?
In the image below I added the red box as well as the red text in an effort to try and understand what is happening when the R2 resistor attaches to the +4V lead.
Can someone please explain what it is doing assuming that everything on the circuit is correct? Note: The positive lead is switched power, so it might be on or off at any given time.
Reference webpage:Power Control System for RPi Car PC
• It just looks like R2 is your typical pull-down resistor for both your microcontroller and your relay. No, it wouldn't change the polarity. The worst it can do it pull down (hence the name) to an indeterminate state if the resistance is too high. – KingDuken Sep 3 '18 at 0:28
• Looks like there may be two independent "grounds" there which may cause confusing voltage measurements. Is the ATTiny ground connected to the vehicle ground? If there is no negative power supply, you shouldn't get a negative voltage anywhere. – Peter Bennett Sep 3 '18 at 0:31
• @PeterBennett I guess that would be the case (two independent grounds). It's the vehicle ground that goes through a converter (DC to DC) to step down the Voltage (Zk-SJVA-4X is what I'm using). – Arvo Bowen Sep 3 '18 at 0:57
• If the R1/R2 junction is "~4V" meaning "about 4V" rather than "minus 4V", that resolves your polarity question. Many DC-DC converters are not isolated - the input Ground is connected directly to the ouput Ground - in that case, the ATTiny Ground will be vehicle Ground, and the circuit should work. – Peter Bennett Sep 3 '18 at 1:03
R2 constitutes the lower half of a voltage divider used to reduce out-of-range voltages to potentials sample-able within the range of an MCU input rating.
Voltage dividers do not change polarity relative to their fixed ground. This circuit accepts a positive input, and yields a reduced positive output.
However vehicle electrical systems are notoriously nasty, and it is a legitimate question if this design overall is sufficiently robust for such usage.
• I wonder if that "-4V" is really "~4V", meaning "about 4 volts", rather than minus 4 volts? – Peter Bennett Sep 3 '18 at 0:53
• I have some nice DC to DC converters to filter the power as well. I'm hoping that will help out as well. Also, the circuit is not just a design but been proven to work as per the video on the reference link. Not sure if it will hold up for a long time but there is one way to find out. Thanks! – Arvo Bowen Sep 3 '18 at 0:54
• @PeterBennett it is indeed. The schematics show ~4 (image posted). – Arvo Bowen Sep 3 '18 at 0:55
• @PeterBennett it is indeed, a quite clearly if you zoom in, "~4v". This would be a notation from the designer of the expected output voltage, though it should be noted that this is a bit high for the pi and would be undesirably activating the I/O protection diode, though probably only with a current it can tolerate given the 10K source resistor. A designer more aware of input threshold voltages would likely have used a different division ratio. – Chris Stratton Sep 3 '18 at 0:55
• @ChrisStratton I'm going to test all output before I hook anything up. As I build it I will see what the output of all the leads are. Thanks for the heads up. – Arvo Bowen Sep 3 '18 at 0:58 |
# Turnstile arrow in tikz-cd
I want to produce a "turnstile" ie \vdash style arrow in tikz-cd.
I can do it with option [maps to, no head] but then the vertical bar appears too short:
\documentclass{article}
\usepackage{tikz-cd}
\tikzcdset{arrow style=tikz}
\usepackage{tikz}
\begin{document}
$$\begin{tikzcd} A \arrow[r, maps to, no head, "F"] & B \end{tikzcd}$$
\end{document}
What is the simplest way to add a longer vertical bar to the tail?
• Please give a fully compilable code of your attemp. – AndréC Oct 20 '20 at 6:27
You were quite close, I changed maps to to tail, not a huge difference in the result, but in my case you're just saying "I want the tail" rather than "I want this arrow". We will be keeping the no head.
The major change, or rather addition, I did was to add a style to tikzcdset.
## Code
\documentclass[margin=10pt]{standalone}
\usepackage{tikz-cd} % no need to load tikz, since tikz-cd already loads it
% \usetikzlibrary{arrows.meta} % you can uncomment this if you want more arrow types
\tikzcdset{
arrow style=tikz,
diagrams={>={|[scale=2]}}
}
\begin{document}
\begin{tikzcd}
A \arrow[r, tail, no head,"F"] & B
\end{tikzcd}
\end{document}
• Thanks! Can you explain the diagrams line? It seems to have changed the tail shape, otherwise it would not be a vertical line. – Yan King Yin Oct 20 '20 at 13:54
• @YanKingYin Sure! The diagrams command is used to change the style of the diagrams, I used it for the arrow appearance for example. So it's diagrams={ <options> }. Inside of it, I said >= which means "arrow tip is". Then with {|[scale=2]} I specify the arrow tip | with a scale to make it bigger. If you remove "no head", you'll see the arrow will look like |----|. I couldn't find an option to define only the tail and there might not be one. You can see more in the tikz-cd manual – Alenanno Oct 20 '20 at 15:14
• Let me know if something is still unclear. – Alenanno Oct 20 '20 at 15:14
I found a simpler solution, combining ideas from this answer:
\begin{tikzcd}[| /.tip = {Bar[scale=2]}]
A \arrow[r, |-] B
\end{tikzcd}
Also, the first answer has the problem that it changes all diagrams in the document, but this one affects only the current diagram. |
# The affine Weyl group
The visualisation below is a work-in-progress to show features of affine Weyl groups corresponding to the irreducible rank-2 root systems. Click and draw to move around, or hold shift and scroll to zoom in and out. An overview of what each option means and the particular conventions used are below.
## Definition of the affine Weyl group
Let (R \subseteq V, R^\vee \subseteq V^*) be a reduced, irreducible root system. Each root \alpha \in R and integer k \in \bbZ defines an affine Hyperplane H_{\alpha, k}^\vee = \set{\mu \in V^* \mid \innprod{\mu, \alpha} = k} in the dual space V^*, and together with its corresponding coroot \alpha^\vee an affine reflection r_{\alpha, k}(\mu) = \mu - (\innprod{\mu, \alpha} - k)\alpha^\vee fixing H_{\alpha, k}^\vee pointwise. Let \Aff(V^*) denote the group of invertible affine transformations of V^*; the subgroup generated by all the affine reflections r_{\alpha, k} is called the affine Weyl group associated to (R, R^\vee), denoted by W. The finite Weyl group W_f is naturally a subgroup, generated by those reflections with k = 0. Hence in our setup we have W_f \subseteq W \subseteq \Aff(V^*), and the visualisation above is a picture of V^*.
Note: Entirely analagously there is an affine Weyl group which is a subgroup of \Aff(V), which is often also called the affine Weyl group. If the root system (R, R^\vee) is simply-laced then these groups are isomorphic, but otherwise they differ. The convention we have adopted is standard in the literature on Coxeter groups, for example in Bourbaki. We warn that when looking at the literature on algebraic groups, the affine Weyl group appearing in the linkage principle is the subgroup of \Aff(V), not of \Aff(V^*).
The affine hyperplanes cut the space V^* up into disjoint simplices upon which W acts freely and transitively, hence after choosing a reference simplex \Delta we can identify an element w \in W with the simplex w \Delta. If a base has already been chosen for the underlying finite root system, then the standard choice of \Delta is the unique simplex in the dominant chamber which touches the zero vector. The walls of \Delta then are the walls H_{\alpha, 0}^\vee corresponding to the simple roots \alpha for the finite Weyl group W_f, along with the wall H_{\theta, 1}^\vee where \theta is the highest root of the finite root system. The finite simple reflections S_f together with the affine reflection r_{\theta, 1} generate the affine Weyl group W as a Coxeter group.
## Options
The labelling option puts a number or polynomial on top of each alcove.
• Length labels each group element by its length l(w).
• # Reduced expressions labels each group element by the number of reduced expressions for l(w). The reduced expressions themselves are not enumerated (there can be exponentially many in the length), but rather they are only counted by noting that c(\id) = 1, and c(w) = \sum_{s \in L(w)} c(sw) where L(w) denotes the left descent set of w.
• KL polynomials labels each group element w with the Kazhdan-Lusztig polynomial h_{w, x}, where x is the selected (purple) element under the cursor. We are using the Soergel normalisation of the Hecke algebra - more details are below in the Hecke algebras section.
• KL polynomials (v = 1) labels each group element w with the Kazhdan-Lusztig polynomial h_{w, x} evaluated at v = 1.
• \mu-coefficients labels each group element w with the v^1-coefficient appearing in the Kazhdan-Lusztig polynomial h_{w, x}. These coefficients determine the structure of the cells.
• AS KL polynomials labels each dominant alcove with the antispherical Kazhdan-Lusztig polynomial n_{w, x}, where x is the element under the cursor. More details are in the antispherical modules section.
The shading option displays a set of elements by shading them a darker colour. Sometimes this set depends on the element x under the cursor.
• The Bruhat order is the order generated by w \leq wt whenever t is a reflection (a conjugate of a generator). In this case of finite and affine Weyl groups, the set of reflections is in bijection with the affine reflections which generate the group. When this option is selected, the set \set{w \leq x \mid w \in W} of elements less than or equal to the element under the cursor is shown. When the covering option is set, the set of elements which x covers (the set of elements with length l(x) - 1) are shown in green.
• The right weak order is generated by w \leq ws whenever l(w) < l(ws), and the displayed elements work like the Bruhat option.
• The left weak order is generated by w \leq sw whenever l(w) < l(sw), and the displayed elements work like the Bruhat option.
• The cone type of x is the set T(x) = \set{w \in W \mid l(xw) = l(x) + l(w)}.
• The dihedral elements of W are those contained in some dihedral reflection subgroup.
Cells: upon choosing left, right, or two-sided cells, the cells for a limited subset of the Kazhdan-Lusztig basis are computed and shown. The cell ordering is also computed, and shown on the left.
The NF Tree option shows the tree associated to the chosen normal form.
The p-canonical option shows p-canonical basis elements for the antispherical module for select types. After selecting a dataset from the p-canonical list, two more labelling options become available: one showing the expansion of a p-canonical basis element into the canonical basis, and another for those coefficients evaluated at v = 1. The # p-can in can shows the number of nonzero terms in the expansion of each p-canonical basis element in terms of the canonical basis elements. Unlike everything else on this page (which is calculated on-the-fly in your browser), the p-canonical datasets were calculated offline - each requiring several hours of CPU time. The algorithm used is due to Thorge Jensen and Geordie Williamson.
## Hecke algebras
We use the “Soergel normalisation” of the Hecke algebra, which are the same as the conventions used in the book Introduction to Soergel bimodules. We give a few details here so that the reader can check what conventions we are using; see Chapter 3 of Introduction to Soergel bimodules for a proper introduction to the Hecke algebra.
The Hecke algebra H = H(W, S) is a free \bbZ[v^{\pm}]-module, with a standard basis \set{\delta_x \mid x \in W}. The quadratic relation used is \delta_s^2 = (v^{-1} - v)\delta_s + 1, hence the right-multiplication-by-\delta_s formula for s \in S is \delta_x \delta_s = \begin{cases} \delta_{xs} & \text{if } x < xs, \\ \delta_{xs} + (v^{-1} - v) \delta_x & \text{if } x > xs. \end{cases} The bar involution is the \bbZ-linear map sending p(v) \delta_x to \overline{p(v) \delta_x} = p(v^{-1}) \delta_{x^{-1}}^{-1}. On generators, we have \delta_s^{-1} = \delta_s + (v - v^{-1}). The Kazhdan-Lusztig basis or canonical basis is the unique set \set{b_x \mid x \in W} \subseteq H of elements which are self-dual (fixed points of the bar involution), and furthermore satisfy the degree bound condition b_x = \delta_x + \sum_{y < x} h_{y, x} \delta_y, \quad \text{for some } h_{y, x} \in v \bbZ[v]. We have b_{\id} = \delta_{\id} = 1 \in H and b_s = \delta_s + v. The Laurent polynomials h_{y, x} are called Kazhdan-Lusztig polynomials. Canonical basis elements can be calculated in a relatively straightforward fashion by using the right-multiplication formulas \delta_x b_s = \begin{cases} \delta_{xs} + v \delta_x & \text{if } x < xs, \\ \delta_{xs} + v^{-1} \delta_x & \text{if } x > xs, \end{cases} b_y b_s = \begin{cases} b_{ys} + \sum_{zs < z} \mu(z, y) b_z & \text{if } y < ys, \\ (v + v^{-1})b_y & \text{if } y > ys, \end{cases} where \mu(y, x) denotes the coefficient of v in h_{y, x}.
### Other normalisations
There are some other normalisations of the Hecke algebra which are used in practice. (Prepare to get into the weeds here).
As a preliminary, after fixing a Coxeter system (W, S), a base commutative ring R, and two parameters \lambda, \mu \in R, there is a Hecke algebra \cH_R(\lambda, \mu) defined as the free module over R with basis \set{\delta_x \mid x \in W} indexed by W, such that the braid relations hold amongst the generators \set{\delta_s \in S} and we have the quadratic relation \delta_s^2 = \lambda \delta_s + \mu for each generator. (This is not a vacuous statement: work has to be done to show that this does in fact describe an algebra structure). It is important to keep this in mind when trying to distinguish different-looking Hecke algebras: all you need to describe the whole algebra structure is the quadratic relation, basically. From this point on I’ll reserve the notation \delta_x explicitly for the Soergel normalisation.
In Kazhdan-Lusztig’s original work, they start with the “standard” Hecke algebra defined over \bbZ[q] with the quadratic relation (T_s + 1)(T_s - q) = 0, and tensor on the ring of Laurent polynomials \bbZ[q^{\pm \frac{1}{2}}]. (So here q is an arbitrary parameter, subject to it being invertible and square-rootable). The relationship between their Hecke algebra normalisation and Soergel’s is q = v^{-2}, \quad T_x = v^{-l(x)}\delta_x. For instance, applying this to the KL quadratic relation (T_s + 1)(T_s - q) = 0 gives (v^{-1}\delta_s + 1)(v^{-1}\delta_s - v^{-2}) = 0, multiplying through by v and rearranging gives Soergel’s. The bar involution is defined the same way: it sends q to q^{-1}, and T_x to T_{x^{-1}}^{-1}. Kazhdan and Lusztig then define two different canonical bases, which they label C_w and C_w'. The second basis is the equivalent of Soergels, and it is defined by the condition that it is self-dual, and C_w' = q_w^{-\frac{1}{2}} \sum_{y \leq w} P_{y, w} T_y, where q_w = q^{l(w)} (shorthand used throughout their paper), P_{w, w} = 1, and P_{y, w} is a polynomial in q of degree at most \frac{1}{2}(l(w) - l(y) - 1) for y < w. The P_{y, w} are the Kazhdan-Lusztig polynomials, and are related to the h_{y, w} in Soergel’s normalisation by h_{y, w} = v^{l(y) - l(w)} P_{y, w} = q^{\frac{1}{2}(l(w) - l(y)} P_{y, w}. The generating canonical basis elements are C_s' = q^{-\frac{1}{2}}(T_s + 1), and we again have the multiplication formula C'_{sw} = C'_s C'_w - \sum_{\substack{z < w \\ sz < z}}\mu(z, w) C_z', where \mu(z, w) is the coefficient of the degree \frac{1}{2}(l(w) - l(y) - 1) term in the KL polynomial P_{z, w}. Since P_{z, w} is a polynomial in q and not in q^{\frac{1}{2}}, we will have nonzero \mu(z, w) only when the length difference between z and w is odd.
The rule for right multiplication by T_s in the KL normalisation is T_w T_s = \begin{cases} T_{ws} & \text{if } ws > w, \\ qT_{ws} + (q - 1)T_w & \text{if } ws < w, \end{cases} with right multiplication by T_s + 1 being particularly nice: T_w (T_s + 1) = \begin{cases} T_{ws} + T_w & \text{if } ws > w, \\ qT_{ws} + qT_w & \text{if } ws < w. \end{cases}
If we use the KL normalisation to compute the KL polynomials P_{y, w}, we should be computing the elements q_w^{\frac{1}{2}} C_w' in the Hecke algebra: at risk of being very confused define C_w '' = q_w^{\frac{1}{2}} C_w', so for example C_s'' = (T_s + 1). Then multiplying an earlier equation through by a scaling factor gives C_{ws}'' = (T_s + 1) C_w'' - \sum_{\substack{z < w \\ zs < z}} \mu(z, w) C_z'' q^{\frac{1}{2}(1 + l(w) - l(z))}.
The symmetry in the formula for right multiplication by T_s + 1 shows us that if ws > w then (aT_{ws} + bT_w)(T_s + 1) = (a + bq)T_{ws} + (a + bq)T_w, and so by induction if s is a right descent for w, then P_{z, w} = P_{zs, w} for all z. The analagous property holds for left descents.
## Antispherical modules
Let I \subseteq S be a subset of the Coxeter generators, then the subgroup W_I \subseteq W generated by I is called a standard parabolic subgroup of W. The length function on (W_I, I) is equal to the restriction of the length function on (W, S) to W_I. Each right coset W_I x contains a unique minimal-length coset representative x_0 = \argmin_{w \in W_I x} l(w). Let {^I W} \subseteq W denote the set of minimal-length coset representatives of elements of W: they can be characterised as the elements which cannot be made shorter by left-multiplication by I: {^I W} = \set{w \in W \mid l(sw) > l(w) \text{ for all } s \in I}. We get a bijection of sets W_I \times {^I W} \to W by multiplying group elements, which satisfies l(uv) = l(u) + l(v) for u \in W_I and v \in {^I W}. The example we will be most interested in is when I is the subset of simple reflections of the underlying finite root system, so W_I is the usual finite Weyl group. In this case, {^I W} is the set of alcoves that lie in the dominant chamber of the finite system.
The Hecke algebra H_I = H(W_I, I) is naturally a subalgebra of the Hecke algebra H. Let \cL = \bbZ[v^{\pm 1}] denote the ring of Laurent polynomials. The quadratic relation implies that \set{v^{-1}, -v} are the eigenvalues for the action of right multiplication by any \delta_s upon H, hence we may define an algebra homomorphism H_I \to \cL by sending \delta_s to (-v) for s \in I. This makes \cL into a H_I-bimodule called \cL(-v), which can be induced to a right H-module N = \cL(-v) \otimes_{H_I} H, called the antispherical module. The elements \set{1 \otimes \delta_x \mid x \in {^I W}} form a standard basis for N.
The bar involution on H induces an \bbZ-linear involution on N, by setting \overline{p \otimes h} = \overline{p} \otimes \overline{h}. We can again define a canonical basis of N by looking for a set \set{d_x \mid x \in {^I W}} of self-dual elements which satsify the degree bound condition d_x = n_x + \sum_{y < x} n_{y, x} n_y, \quad \text{for some } n_{y, x} \in v \bbZ[v]. We have a right multiplication formula n_x b_s = \begin{cases} n_{xs} + v n_x & \text{if } x < xs \text{ and } xs \in {^I W}, \\ n_{xs} + v^{-1} n_x & \text{if } x > xs \text{ and } xs \in {^I W}, \\ 0 & \text{if } xs \notin {^I W}. \end{cases} which can be used to calculate the canonical basis of N, using a similar idea to the calculation of the canonical basis of H: when x < xs then d_x b_s = d_{xs} + (\text{junk}), and the junk can be identified as the elements violating the degree bound, and removed by subtracting an appropriate multiple of d_y for various y < x.
## Cells
Suppose that H is an algebra, equipped with a choice of basis \set{h_x \mid x \in W} for some indexing set W. (We will always be considering H to be the Hecke algebra, and the indexing set to be the affine Weyl group W). When multiplying a particular basis element h_w on the left by an arbitrary element of H, the product can be re-expanded in the chosen basis, yielding some terms on the right: n h_w = \sum_{z} \lambda_z h_z. Whenever h_z appears in the expansion with a nonzero coefficient, we write z \xleftarrow{L} w, which can be read informally as “h_w produces an h_z under left multiplication”. More formally, we define the binary relation z \xleftarrow{L} w if and only if there exists some n \in H such that n h_w = \sum_{y} \lambda_y h_y with \lambda_z \neq 0.
The relation \xleftarrow{L} is reflexive (z \xleftarrow{L} z for all z), but unless the basis h_x is extremely special it will not be transitive. We take its transitive closure by declaring that z \leq_L w if there exists some path z \xleftarrow{L} \cdots \xleftarrow{L} w. By construction \leq_L is reflexive and transitive and so is a preorder (a preorder is like a partial order, but missing the axiom that x \leq y and y \leq x implies x = y). By taking its strongly connected components (or the strong components generated by \xleftarrow{L}), we introduce equivalence classes called left cells, and a partial order \leq_L on those left cells.
Analagously, we can define the binary relation z \xleftarrow{R} w for when h_z appears in a product like h_w m, and z \xleftarrow{LR} w for when h_z appears in a product like n h_w m. (The \xleftarrow{LR} relation is the union of the \xleftarrow{L} and \xleftarrow{R} relations). And analagously we get right cells, and two-sided cells.
In the Hecke algebra, the standard basis does not produce interesting cells. Every standard basis element \delta_x is invertible, and hence produces the relation x \xleftarrow{L} y for all x, y \in W, and hence a single cell containing every element. On the other hand, the cells defined by the KL basis is very interesting. We give a short account of how the cells are computed, after all the KL basis elements have been computed.
For y, x \in W let \mu(y, x) be the coefficient of v in the polynomial h_{y, x}. Then we have the following formulae for right and left multiplication by the canonical basis element b_s corresponding to a simple generator: b_y b_s = \begin{cases} (v + v^{-1})b_y & \text{if } ys < y \\ b_{ys} + \sum_{zs < z} \mu(z, y) b_z & \text{if } ys > y \end{cases}
b_s b_y = \begin{cases} (v + v^{-1})b_y & \text{if } sy < y \\ b_{sy} + \sum_{sz < z} \mu(z, y) b_z & \text{if } sy > y \end{cases}
In order to generate the preorder \leq_L, it is enough to consider left multiplication by some generating set of the algebra. The generating set we choose are the KL basis elements \set{b_s \mid s \in S} corresponding to the simple reflections, since we have those nice formulae above showing how such products expand back into the KL basis. Then it is simply a matter of running through, for all elements y \in W, and for all s \in S such that ys > y, the nonzero \mu(z, y) coefficients, checking the additional condition that zs < z. If zs < z and \mu(z, y) \neq 0, then we add an edge z \leftarrow y to a directed graph. After collecting all edges, we run a beautiful algorithm due to Robert Tarjan to generate the strong components of the graph: these are the cells. This algorithm outputs the cells in a topological ordering, so the “condensed graph” (the directed acyclic graph where vertices are cells, and edges are induced by the edges on the original graph) can be easily generated. The transitive closure of this condensed graph is the cell ordering. To display the cell ordering however, we take the transitive reduction of the graph: this deletes edges until all we are left with are covering relations.
## Normal forms
After fixing an order on the generating set S, there are two commonly used normal forms for elements of a Coxeter group W. Clearly a normal form should be a reduced expression, but which one?
• The ShortLex normal form for w \in W is the lexicographically least reduced word in the generators representing w. If \mathtt{ShortLex}(w) = (s_1, \ldots, s_n), then s_1 is the “smallest possible starting letter” for w, in that s_1 is the least generator s such that l(s w) < l(w). Furthermore, (s_2, \ldots, s_n) is the normal form for s_1 w. Every suffix of a normal form is again a normal form.
• The InvShortLex normal form for w \in W is (s_1, \ldots, s_n), where s_n is the “smallest possible ending letter” for w. The InvShortLex language (as a formal language contained in S^*) is the reverse of the ShortLex language. We have the equality \mathtt{Reverse}(\mathtt{InvShortLex}(w)) = \mathtt{ShortLex}(w). Every prefix of a normal form is again a normal form.
Since any prefix of a normal form is again a normal form, the normal forms define a tree structure on the group, with an edge x \xrightarrow{s} y iff NF(x) \cdot s = NF(y) as words.
## The p-dialated affine Weyl group
Recall that the affine Weyl group W \subseteq \Aff(V^*) is generated by the reflections r_{\alpha, k} where \alpha is a finite root, and k is an integer. For p > 0, the subgroup generated by the r_{\alpha, k} with k \in p \bbZ is called the p-dialated affine Weyl group W_p \subseteq W. In a fractal-like way, it is both a subgroup of W (when both W and W_p are viewed as sitting inside \Aff(V^*)), and it is abstractly isomorphic to W.
W is generated by the simple reflections s_1, \ldots, s_n (which are all linear reflections), and the affine reflection s_0 = r_{\theta, 1} where \theta is the highest root of the underlying finite root system. W_p is generated by the same linear reflections s_1, \ldots, s_n, and the affine reflection s_0^{(1)} = r_{\theta, p}. These generators give the same Coxeter presentation, and so the isomorphism W \to W_p may be defined by sending s_1 \mapsto s_1, \ldots, s_n \mapsto s_n, and s_0 \mapsto s_0^{(1)}.
Now the fractal part: we want to define a homomorphism W \mapsto W_p \injto W which embeds W inside of itself. (This is because to compute using W and W_p we really treat them as finitely presented groups, in which they look exactly the same). In order to compute this map, we need to know how to express the affine reflection s_0^{(1)} in terms of (s_1, \ldots, s_n, s_0). Purely by the definition of r_{\theta, k} we can see that s_0 = t_{\theta^\vee} s_\theta where t_\mu \colon V^* \to V^* is translation by \mu \in V^*. Similarly we have s_0^{(1)} = t_{p \theta^\vee} s_\theta. So if we know how to express s_\theta in terms of the finite simple reflections s_1, \ldots, s_n, then we can get t_{\theta^\vee} in terms of the affine simple generators and we will then have s_0^{(1)} = (t_{\theta^\vee})^p s_\theta.
In order to find s_\theta we use the general fact that w r_\alpha w^{-1} = r_{w \alpha} (which holds in any reflection-faithful root system). When constructing the root system we indexed roots by increasing depth (how far, in terms of reflections, they are away from being simple), and recorded this data in a reflection table. This leads to a simple process for finding a sequence of simple reflections such that x_n \cdots x_2 x_1 \theta = \alpha_s for some simple root \alpha_s, then \theta = x_1 x_2 \cdots x_n \alpha_s and hence letting w = x_1 \cdots x_n we have r_\theta = r_{w \alpha_s} = w s w^{-1}, and so t_{\theta^\vee} = s_0 w s w^{-1}. Finally we have s_0^{(1)} = t_{p \theta^\vee} s_\theta = (s_0 s_\theta)^p s_\theta = (s_0 s_\theta)^{p - 1} s_0
What would also be handy to be able to calculate is the factorisation map W \to W_p \times {^p W}, where {^p W} is the set of minimal coset representatives (which behaves well by general reflection subgroup theory). Here we can use a similar idea to parabolic subgroups, based on the fact (still true for general reflection subgroups) that each coset W_p x has a unique element of minimal length (with length as measured in W). Therefore to factorise an element w, try to multiply on the left by any of the subgroup generators (s_1, \ldots, s_n, s_0^{(1)}) and see if the length goes down. Eventually we get to some product x_k \cdots x_1 w of minimal length in the coset W_p w, and we have w = (x_1 \cdots x_k)(x_k \cdots x_1 w), a product of elements of W_p with a minimal coset rep. (In fact, during this algorithm we can treat any x_i = s_0^{(1)} as a simple generator for the left factor, and a product of simple generators for the right factor, which means we can treat the left generator as either being inside W or inside W_p, implicitly using the isomorphism W \to W_p).
(In fact one thing is not obvious from the description above: why can we necessarily move to a minimal-length element only by multiplication on the left by the simple generators of W_p? Clearly we cannot choose any generating set of W_p. The reason this is working is because the set of generators for W_p is canonical with respect to the reflection subgroup W_p \subseteq W …)
It is not hard to see that the cardinality of {^p W} is p^{|S|}: the fundamental alcove and the p-dialated fundamental alcove are similar simplicies in an |S|-dimensional space, therefore the ratio of their volumes is p^{|S|}.
## How alcoves are drawn
The affine fundamental chamber is the open simplex generated by \Delta = (\Lambda_1^\vee, \Lambda_2^\vee, \Lambda_3^\vee). Using the usual formula for the simple reflections on the coweight basis, this chamber gets moved around generating other chambers w \Delta for w \in W. In order to draw triangles in the plane, we need to take each generating vector v \in \Delta of the simplex, treat it as a projective line \bbR v, and intersect with the hyperplane \innprod{-, \delta} = 1. This is done by converting from the (\Lambda_1^\vee, \Lambda_2^\vee, \Lambda_3^\vee) basis into the (\varpi_1^\vee, \varpi_2^\vee, \delta^*) basis, then doing the usual projectivisation thing where the vector is normalised so that the last coordinate is 1. (This works because \innprod{\varpi_1^\vee, \delta} = \innprod{\varpi_2^\vee, \delta} = 0). The basis conversion map is x_1 \Lambda_1^\vee + x_2 \Lambda_2^\vee + x_3 \Lambda_3^\vee \mapsto x_1 \varpi_1^\vee + x_2 \varpi_2^\vee + (a_1 x_1 + a_2 x_2 + x_3) \delta^*.
Note that in this approach the coordinates of the simplex start as basis vectors (1, 0, 0), (0, 1, 0), and (0, 0, 1). It’s only after basis conversion and scaling that we end up with (1/a_1, 0, 1), (0, 1/a_2, 1), (0, 0, 1).
## Geometry
We will model the 2D Euclidean space for the affine Weyl group inside the 3D coweight space of the affine root system, living inside the plane \innprod{-, \delta} = 1. We use the adjoint realisation of the affine root datum, so the coweight space is the space V^* with basis (\Lambda_1^\vee, \Lambda_2^\vee, \Lambda_3^\vee) of affine fundamental weights, and the weight space V has basis (\alpha_1, \alpha_2, \alpha_3) of simple roots. These are in perfect pairing: \innprod{\Lambda_i^\vee, \alpha_j} = \delta_{ij}.
An alternative basis of V is the basis (\alpha_1, \alpha_2, \delta), with \alpha_3 = \delta - \widetilde{\alpha}, where \widetilde{\alpha} = a_1 \alpha_1 + a_2 \alpha_2 is the highest root of the finite root system generated by the two finite roots. The corresponding alternative basis of V^* is (\varpi_1^\vee, \varpi_2^\vee, \delta^*) which is a dual basis to (\alpha_1, \alpha_2, \delta), and the relation to the old basis is \Lambda_1^\vee = \varpi_1^\vee + a_1 \delta^*, \quad \Lambda_2^\vee = \varpi_2^\vee + a_2 \delta^*, \quad \Lambda_3^\vee = \delta^*
### Detecting cursor position
Given a point (x_1, x_2) inside a triangle on the screen, which open simplex w\Delta does it correspond to? We embed this point into the affine space by adding \delta^*, then rewrite in fundamental coweight coordinates x_1 \varpi_1^\vee + x_2 \varpi_2^\vee + \delta^* \mapsto x_1 \Lambda_1^\vee + x_2 \Lambda_2^\vee + (-a_1 x_1 - a_2 x_2 + 1)\delta^*, which gives us a point on the interior of an affine chamber. This chamber is the dominant chamber if all coordinates are nonnegative, otherwise some coordinate (say i) is negative, and the simple reflection s_i can be applied to move the point to a smaller length chamber. Eventually we reach the dominant chamber, and the sequence of reflections applied gives us a reduced word in the Weyl group generators for w. .
### Drawing
We only actually need to draw the coloured walls in order to generate “the look” of the affine Weyl group. This is easy enough: if w\Delta = (v_1, v_2, v_3), then the right-multiplication-by-s_1-wall is the segement [v_2, v_3], etc. We may also need to shade various simplices.
There are three different coordinate systems in play: (\Lambda_1^\vee, \Lambda_2^\vee, \Lambda_3^\vee) \quad (\varpi_1^\vee, \varpi_2^\vee, \delta^*) \quad (x, y) where the last coordinate system is “screen coordinates” in pixels. The coordinates of a simplex never change in the first two bases, but they will change in the last basis as we zoom and pan around. |
# Reflections on Math, Tensors and Programming
This is not an explanation of Tensors if you are interested in that but rather a reflection upon the process of learning about mathematical concepts such as Tensors as a programmer with limited mathematical background.
Over the last months I have on and off been learning about Deep Learning, which quickly leads one down in the rabbit hole to the strange world of abstract mathematics.
"Alice in Wonderland," written by a mathematician, Lewis Carroll, gives a hint at some of the problems of grasping abstract math. This is about a song, "Haddocks Eyes" sung by the white knight:
You are sad,’ the Knight said in an anxious tone: ‘let me sing you a song to comfort you.’
‘Is it very long?’ Alice asked, for she had heard a good deal of poetry that day.
‘It’s long,’ said the Knight, ‘but very, VERY beautiful. Everybody that hears me sing it--either it brings the TEARS into their eyes, or else--’
‘Or else what?’ said Alice, for the Knight had made a sudden pause.
‘Or else it doesn’t, you know. The name of the song is called “HADDOCKS’ EYES.”’
‘Oh, that’s the name of the song, is it?’ Alice said, trying to feel interested.
‘No, you don’t understand,’ the Knight said, looking a little vexed. ‘That’s what the name is CALLED. The name really IS “THE AGED AGED MAN.”’
‘Then I ought to have said “That’s what the SONG is called”?’ Alice corrected herself.
‘No, you oughtn’t: that’s quite another thing! The SONG is called “WAYS AND MEANS”: but that’s only what it’s CALLED, you know!’
‘Well, what IS the song, then?’ said Alice, who was by this time completely bewildered.
‘I was coming to that,’ the Knight said. ‘The song really IS “A-SITTING ON A GATE”: and the tune’s my own invention.’
We can summarize the confusion about the song in this way:
• The song's name is called Haddocks' Eyes
• The song's name is The Aged Aged Man
• The song is called Ways and Means
• The song is A-sitting on a Gate
This is the kind of problems you stumble on as a poor programmer wanting to familiarize them with machine learning gets into. They discover say TensorFlow and immediately ask or Google "What is a Tensor?"
This question will easily cause you a lot of pain. It is the equivalent to getting into functional programming and asking what a Monad is.
### So a Tensor is a Matrix?
The typical early mistake you will make on your quest to understand Tensors is that you ask somebody to show you a Tensor and you see something that to you looks like a Matrix.
And so you go "ah... so a tensor is just a matrix?" Beep!! Wrong!
The answer you get after this point typically just make you more confuse than ever.
a tensor is an algebraic object that describes a (multilinear) relationship between sets of algebraic objects related to a vector space.
This is a common human habit to focus on what things are, what they look like, we naturally latch on to how something is represented.
So before we get back to discussing Tensors I want to detour and talk more about how to think about objects both in programming and mathematics.
### What Something is and Its Representation are not the Same
III, 3 and three are all different representations of the number 3. We should not mistake either representation for actually "being" that number.
Likewise one and the same representation could represent entirely different things. A could mean the letter 'A' or it could mean the hexadecimal digit 0xA corresponding to 10 in the decimal system. Likewise 65 could represent the number 65 or the letter 'A' in ASCII or UTF-8 encoding.
We could look at more complex representations. A list of two numbers $(2, 3)$ could in principle refer to a point, a vector, a tuple or a set.
To not mix the two up we often use slightly different notation. A set of two points would often be written $\{2, 3\}$. We usually write a vector as $\left [\begin{matrix}2\\ 3 \end{matrix}\right]$. However because that is often cumbersome in the middle of a text it is also possible to write it as $(2, 3)$. Both are representation of a column-vector. This should not be confused with $[2 \enskip 3]$ which usually denotes a 1 $\times$ 2 row matrix.
The point is that how something is written does not uniquely define it $(2, 3)$ could mean a tuple, a point or a column vector. They are all written the same way.
You cannot tell by merely looking at tuple $(2, 3)$ and the vector $(2, 3)$ what the difference is.
This can be a source of confusion for a programmer, because as programmers we are not used to this kind of ambiguity. In code the vector may have been written Vector(2, 3) and the tuple Tuple(2, 3). Of course many languages have specific literal syntax for very common objects. E.g. in Julia a column-vector would be written [2, 3] and a tuple would be written (2, 3). The point however is that there is a unique syntax for each type of object.
In mathematics in contrast you get to know the type through context. The author will in the text point out what sort of objects we are working with.
### Type Hierarchies and Interfaces
In programming each object is of a particular type. This type may be a subtype of another concrete or abstract super-type. The type may also conform to several different interfaces, protocols or abstract types. The terminology used will vary depending on the language used.
We can consider the Julia programming language. An Array is a concrete subtype of AbstractArray. However AbstractArray types also implement an iterator interface, so that its elements can be iterated over. That something is iteratable is separate from it being an array. Things which are not arrays can also be iterated over.
In Julia every type is a subtype of Any. And types such as Array are also actual objects. The type of the Array type object is DataType. DataType is also a subtype of Any. This kind of arrangement is not unusual. In Java or Smalltalk e.g. the class Object is at the top of the type hierarchy.
We find very similar kinds of arrangement within mathematics. Everything is a mathematical object. Instead of speaking of types we speak of mathematical structures. Mathematical structures exist in a hierarchy similar to a type-hierarchy in programming. E.g. under mathematical structures we have algebraic structures. This is subdivided further into other structures. Further down the hierarchy we have vector spaces.
### Relating Mathematical Structures to Programming Types
To make sense of this we can compare to the Vector type in the Julia programming language. Vector is a parameterized type, meaning we must specify the type of its elements (components in math-speak).
v = Vector{Float64}()
1.0s
0-element Array{Float64,1}
push!(v, 3, 4)
0.6s
2-element Array{Float64,1}: 3.0 4.0
u = [3.0, 4.0]
0.2s
2-element Array{Float64,1}: 3.0 4.0
In this case I have create the vectors v and u in different but equivalent ways. v as first created empty and then I added two elements 3 and 4 to it.
Formally we can say that v is an object the type Vector with type parameter Float64.
A mathematician could express something similar by saying $v = (3, 4)$ is a mathematical object belonging to the vector space of vectors $V$ over the field $F$ where $F =\mathbb{R}$.
Let us try to unpack this. In programming-speak the type of $v$ is a vector space. However in mathematics you cannot simply say it is a vector space anymore than you can say something is a Vector in Julia. You need to specify the type parameter. In mathematics we do that by saying it is a vector space over the field $\mathbb{R}$ e.g. In mathematics $\mathbb{R}$ is the set of all real numbers. Float64 is a concrete subset of Julia's abstract Real type, so there is some similarity in our definitions.
#### Fields
In Julia the type parameter of a Vector does not need to be a number. Nor does it have to be for a vector space. That is why we are not saying:
vector space over number $F$
That is why we are saying field instead. So what is a field? Math is heavy on abstractions. A field is a type of mathematical object that allows addition, subtraction, multiplication and division according to specific rules.
In Julia notation it would be some type T which has the following operations defined:
+(x::T, y::T) where T <: Field
-(x::T, y::T) where T <: Field
*(x::T, y::T) where T <: Field
/(x::T, y::T) where T <: Field
Julia
Of course in mathematics everything is far more pedantic. In programming we make quite a lot of assumptions which must be spelled out in mathematics. Let us pick a couple of examples from wikipedia to show how accurate these descriptions must be:
If $a$ and $b$ are in the field then:
• Associativity: $a + (b + c) = (a + b) + c$ and $a \cdot (b \cdot c) = (a \cdot b) \cdot c$
• Cummulativity: $a + b = b +a$ and $a \cdot b = b \cdot a$
• etc
Because everything in the field is of the same type, we don't have to specify it, but if we had. The we could write that addition is defined as:
This basically says that addition takes two values $a$ and $b$ and produce a new value $c$. It says that $+$ takes two arguments which each are in the field $F$ and produce a value in the field $F$.
So $F \times F$ means an operation takes two arguments of the same type $F$. $F \times F \times F$ would mean three arguments and so on. We can shorten that to $F^3$. In cases where we want to be specific we can say that we are taking say 3 real values and producing a real value with $\mathbb{R}^3 \rightarrow \mathbb{R}$
#### Formal Specification of a Vector Space
In programming we may define a Vector interface and list method supported or something similar. We have a similar but more pedantic way of specifying the same in mathematics. A Vector space is defined as the set:
Where $V$ is a set of vectors, $F$ a set of scalars and $+$ and $\cdot$ the operations which must be defined/supported for the elements of the vector space. If we where to attempt to frame this in programming language syntax it may look something like this in Julia pseudo-code syntax:
abstract type VectorSpace{V, F} where V <: Array{F}, F <: Field
+(u::V, v::V)
*(k::F, v::V)
end
Julia
This is not really valid Julia code as it is hard to really express in code what is expressed with mathematical notation. It is just trying to get across that $V$ and $F$ are similar to type parameters in programming, with some constraints. $V$ has to be some kind of container containing components of type $F$ where $F$ has to be some kind of field. A real number is a field while an integer e.g. isn't.
We also try to get across that a vector space is something quite abstract. You don't see a definition of member variables stored. It is all about its behavior. What kind of operations are supported. And it is not like object-oriented programming where these operations are attached to one particular type. It is more like perhaps a module or namespace. It is a collection of functionality and relationships which together forms the vector space.
A vector space must as a minimum it must support addition and scalar multiplication. If addition in a vector space looks like $\mathbf{w} = \mathbf{u} + \mathbf{v}$ We need to actually say something about types involved with:
With vector spaces it gets a bit more interesting than with fields, when we get to multiplication. This is defined for a scalar and a vector. $\mathbf{v} = c\mathbf{u}$, where $c$ is our scalar. This if formally expressed as:
So $F \times V$ tells us that the multiplication operator $\cdot$, takes two arguments: one which is our field $F$ with values such as $c$ and the other $V$ which is a set representing our vectors, such as $\mathbf{u}$, $\mathbf{v}$ and $\mathbf{w}$.
You can keep adding functionality to define new subspaces. It must be kept in mind that a vector space is not like a concrete type in programming, but far more like an interface. Lots of things you would not think of as vectors can form vector spaces such as functions, because you can add two functions and multiply a function with a scalar.
### Matrix and Tensors
You can form vector spaces out of matrices as well. However not every matrix combination forms a vector space. E.g. You cannot add a $2 \times 3$ matrix with a $2 \times 2$ matrix. In programming speak you could say these two matrices together don't adhere to the vector space interface, because they don't support addition.
However the set of $m \times n$ matrices form a vector space because it supports addition and multiplication with a scalar. Here is an example of proof of this.
In fact tensors are also vector spaces. However pointing that out is not all that interesting.
Nor is it interesting to say both a vectors and matrices can form vector spaces, since so little is required to be a vector space. Matrices support a bunch of other operations which distinguishes them from mere vectors.
E.g. you can multiply matrices, which you cannot do with vectors.
With tensors comes more abilities or axioms if you will that don't exit for regular matrices. And again let me hammer in yet again. A representation of something is not the object.
You can represent a tensor as a matrix but that does not really make it a matrix.
#### Linear and Multilinear Transformations
You can think of a matrix as something which happens to be useful in defining a linear transformation. A linear transformation is just a fancy way of saying function which takes a vector as input and spits out a vector as output. It is just a word to distinguish it from a regular function which takes a scalar and spits out a scalar.
So if $T$ is our transformation it is something like this
It takes a vector $\mathbf{v}$ and spits out another vector $\mathbf{u}$. It so happens that we figured out that you can accomplish such linear transformations with matrix multiplication. Thus there exists some matrix $\mathbf{A}$ which accomplishes the same as $T$. So we can write:
Tensors is an analogy to this for multilinear transformations. Again this is just a fancy way of saying a function which takes multiple vectors as inputs and spits out a vector as output. So something like this would qualify:
A tensor is just a multidimensional array of numbers which allow us to perform this kind of transformation. Frequently this will look like a matrix to you. For tensors I believe $\mathbf{w}$ will usually be a scalar such as a real number. This is possible because reals can also be vector spaces. A real can be a vector space onto itself. The vectors in $V$ just all have single components which are fields $F$.
### Final Remarks
These where just reflections upon how mathematicians define things in relation to how us software developers think about things. I have not actually shown any practical use of a tensor. My motivation was to write a piece for somebody who wants to watch a video of read about tensors but who find it hard to deal with the math heavy language.
I have tried here to relate that language to concepts from programming. |
# Asymptotes of a function
• Sep 19th 2009, 11:31 PM
VitaX
Asymptotes of a function
y = (2x)/(x+1) When solving for the horizontal asymptote and substituting infinity in for x, infinity just crosses out and i'm left with 2/1 making the horizontal asymptote y = 2. right?
• Sep 20th 2009, 12:18 AM
mr fantastic
Quote:
Originally Posted by VitaX
y = (2x)/(x+1) When solving for the horizontal asymptote and substituting infinity in for x, infinity just crosses out and i'm left with 2/1 making the horizontal asymptote y = 2. right?
You cannot substitute infinity. It's not a number.
Approach 1:
$y = \frac{2x}{x + 1} = \frac{2}{1 + \frac{1}{x}}$.
$\lim_{x \rightarrow \pm \infty} \frac{2}{1 + \frac{1}{x}} = 2$.
Therefore $\lim_{x \rightarrow \pm \infty} y = 2$ and so $y = 2$ is the horizontal asymptote.
Approach 2:
$y = \frac{2x}{x + 1} = 2 \left( \frac{x}{x + 1} \right) = 2 \left( 1 - \frac{1}{x + 1}\right) = 2 - \frac{2}{x + 1}$
and by inspection the horizontal asymptote is $y = 2$.
Other approaches are possible.
• Sep 20th 2009, 12:42 AM
VitaX
Quote:
Originally Posted by mr fantastic
You cannot substitute infinity. It's not a number.
Approach 1:
$y = \frac{2x}{x + 1} = \frac{2}{1 + \frac{1}{x}}$.
$\lim_{x \rightarrow \pm \infty} \frac{2}{1 + \frac{1}{x}} = 2$.
Therefore $\lim_{x \rightarrow \pm \infty} y = 2$ and so $y = 2$ is the horizontal asymptote.
Approach 2:
$y = \frac{2x}{x + 1} = 2 \left( \frac{x}{x + 1} \right) = 2 \left( 1 - \frac{1}{x + 1}\right) = 2 - \frac{2}{x + 1}$
and by inspection the horizontal asymptote is $y = 2$.
Other approaches are possible.
You say you cannot substitute infinity because it is not a number. But my teacher has said on several occassions it is a number but not a measurable one. But when infinity is in the denominator of any equation example : 6/infinity that is 0. So perhaps I just understood you wrong.
• Sep 20th 2009, 12:52 AM
mr fantastic
Quote:
Originally Posted by VitaX
You say you cannot substitute infinity because it is not a number. But my teacher has said on several occassions it is a number but not a measurable one. But when infinity is in the denominator of any equation example : 6/infinity that is 0. So perhaps I just understood you wrong.
No, you have understood me perfectly. Infinity is not a number and cannot be substituted into an expression. To do so is sloppy and mathematically wrong.
When dealing with infinity, you have to take a limit. 6/infinity = 0 is a complete nonsense, $\lim_{x \rightarrow + \infty} \frac{6}{x} = 0$ is the correct way of treating it.
• Sep 20th 2009, 12:54 AM
VitaX
Quote:
Originally Posted by mr fantastic
No, you have understood me perfectly. Infinity is not a number and cannot be substituted into an expression. To do so is sloppy and mathematically wrong.
When dealing with infinity, you have to take a limit. 6/infinity = 0 is a complete nonsense, $\lim_{x \rightarrow + \infty} \frac{6}{x} = 0$ is the correct way of treating it.
Yes i understand I just didn't say take the limit of 1/x as x approaches infinity. I understand the terminology, just not familiar with latex. |
• Back
• Exception Handling
Overview
This is designed to support decision-making related to what to do when an exception is being thrown. Should you even catch it? If you do, do you just log it or do you rethrow it? Should you encapsulate it into another one? For that purpose, we need to review some key concepts around how exceptions are structured and what treating means.
TL;DR
I started this post by explaining how exceptions work in Java. If you already know it, just skip to “When to do what?”.
Java Exceptions — mind the hierarchies!
To introduce this topic, it is important to explain how the exception mechanism works in Java.
Anything that inherits from Throwable can be thrown and it works exactly as any exception does.
And how does it work?
Basically, when an exception is thrown, the execution of the code stops. No line after the exception is thrown executes, unless the exception is handled by a catch block.
An exception is handled in the first catch block that declares a matching type (i.e., if there is a catch with that class or any superclass in its hierarchy), the catch block is executed.
Only one catch block is executed and it is the first that declares a matching type.
finally blocks are always executed, even if there is no catch block that matches the exception (or no catch block at all). When an exception is being thrown (either because of the lack of a matching catch block or because the catch block rethrows it - or throws a new one), the finally block is executed before the exception is thrown to the caller method. Therefore, we have to be extra careful with the code inside the finally block. If anything is thrown there (another exception, for instance), the original exception will not be thrown. It will be replaced by the one that originated in the finally block.
If you like this post, please share it (you can use the buttons in the end of this post). It will help me a lot and keep me motivated to write more. Also, subscribe to get notified of new posts when they come out.
Checked vs Unchecked
Checked exceptions are the ones that the Java language obligates the developer to either catch or explicitly declare that the method throws it. They are “checked” at compile-time, thus the name. All the checked exceptions inherit directly from Exception or any other subclass that does not have RuntimeException in its hierarchy.
Runtime exceptions represent problems that are the result of a programming problem, and as such, the API client code cannot reasonably be expected to recover from them or to handle them in any way. Such problems include arithmetic exceptions, such as dividing by zero; pointer exceptions, such as trying to access an object through a null reference; and indexing exceptions, such as attempting to access an array element through an index that is too large or too small.
Runtime exceptions can occur anywhere in a program, and in a typical one, they can be very numerous. Having to add runtime exceptions in every method declaration would reduce a program’s clarity. Thus, the compiler does not require that you catch or specify runtime exceptions (although you can). And just because the method cannot recover from it, it doesn’t mean that your application can’t. You can sometimes execute it differently, simply retry, attempt to correct the problem before trying again, or even execute a different business rule.
Context and abstraction levels
What does this method do?
It ONLY reads data from a file. Nothing else. How could we possibly predict, by looking to this method, that it reads the contents of a configuration file?
This method could be loading configuration for a desktop application, right? Or it could be called inside a REST microservice. How could we tell that this is a web application?
The importance of understanding what your method is designed to do and in which context it is will be the most relevant piece of information in order to determine what you can and should do with the exception.
Note
In a real-life situation, you should have an exception handling framework built into your application. That means that your application-specific exceptions inherit from a common root, that you have a standard of how to log them and how to access what was logged, maybe ways to get automatically notified when something serious happens but also that all your top-level classes deal with throwable. In the example above, it means that your LoginServlet would probably share a common root with all your other servlets:
When to do what?
Let it through
The fileToString method cannot infer anything about its use or intent. Therefore, if it was to catch the exception, there is no way to determine what to do with it. The options would be to bury it (empty catch block) or let it through. Burying an exception is unacceptable. It leads the caller method to “believe that everything went well” and proceed with the execution of the code under an error state. This prevents an appropriate treatment to happen at higher layers and could cause data corruption/loss.
Therefore, the ultimate decision to catch it or not is tied to answering the question:
Is there anything I can do to treat this or help the caller method to treat it?
NO: Let it through. Declare that the method throws this exception and be happy.
YES: Catch it. And be happy too.
Catch
Complete treatment
A complete treatment is when your code can resume the processing and the original request from the external agent (user, another system, etc.) can be fulfilled.
That means that you have either:
• Fixed the conditions that caused the exception and tried again.
Extremely valuable when you can recognize what went wrong.
• Retried a number of times and one of them worked.
Very common in network issues, like timeouts.
• Took an alternative course of action.
The method loadConfiguration does exactly that in the FileNotFoundException catch block.
In other words, the processing is recoverable and all the necessary steps to recover were completed successfully.
Note
Only when you complete the treatment and recover fully you are allowed to “consume” the exception. If that is not the case, you either rethrow it or encapsulate (wrap it) in a new one that must be thrown.
Partial treatment
A partial treatment is when something can be done to ease the impact of the code not being completely executed or when extra information can be added. Examples of extra information could be:
• to assist the caller method in treating and possibly recovering from the issue.
• to eliminate or roll back side-effects of partially executed code.
• to inform another agent (log the event, send a notification, etc.), often to assist in troubleshooting. A catastrophic failure could also notify support teams immediately.
• to raise the abstraction level by encapsulating the exception in another one.
The loadConfiguration method has a catch block for IOException and ParseException that does 3 of these. In particular, it logs information, raises the abstraction level by encapsulating the exception in a new one, and adds valuable information in the new one to assist with troubleshooting.
Encapsulate it or not?
The question about encapsulation (or wrapping) is really tied to the abstraction level of the layer where the code is being executed. Note that JPA has a QueryTimeoutException that is a superclass of PersistenceException to encapsulate a timeout exception that might occur if there are network issues in the communication with the database. That happens because JPA is a higher-level abstraction over JDBC and SQL. JDBC, on the other hand, encapsulates a Timeout with a SQLTimeoutException.
In the same spirit, the loadConfiguration method encapsulates the IOException and the ParseException in a DataNotAvailableException. Thanks to that, if in the future this information is stored in the database and no parsing is needed, there would be no need to change the caller method. All that the caller needs to know is that the data is not available. Knowing where it was stored doesn’t help to decide what to do. If there was something to do regarding that aspect, it should be the responsibility of the loadConfiguration method to treat that aspect, being this treatment a partial or a complete one.
In order to correctly encapsulate an exception, always set the cause when creating a new exception because one has already occurred. For that purpose, use the constructors that allow passing in a cause:
• public Throwable::(String message, Throwable cause) (the most popular one);
• public Throwable::Throwable(Throwable cause) (avoid this one, always prefer to pass a message).
• public Throwable::(String message, Throwable cause, boolean enableSuppression, boolean writableStackTrace)
Or call the public Throwable Throwable::initCause(Throwable cause) method to set it after creating the exception. This method is not preferred as it is easy to forget to call it.
Example (from method loadConfiguration above):
Non-recoverable situations
In the case of non-recoverable situations, it is important to not let the code continue to execute. Executing in an error state may cause other errors and cause data loss/corruption.
Roll back any partial processing effects (if any) and inform the requester that the processing could not be executed. In the doPost method, it was done extensively by adding error messages to the user.
Usually, these external agents (user, another system, etc.) notifications can only be done in the methods that are closer to the beginning of the request (deeper in the stack).
In the case of this example, the first method that runs on the server side is responsible for this notification. It is common in asynchronous methods that a notification of the results (including possible error messages) is issued by email, push notifications (mobile devices), or even in system reports.
In the case of backend processing (like batch jobs that run under a schedule), database tables and data files are often used to store results and error messages.
Not notifying that something went wrong not only makes the caller assume that the request was successfully processed and the goal was achieved but also caps the technical analysis conducted by developers and often makes it hard to reproduce the issues. An issue that is not logged and doesn’t trigger any notification is referred to as a silent failure.
Silent failures may create other problems that could trigger other non-silent failures. Reproducing or investigating these subsequent non-silent errors may prove to be exceptionally harder because the root cause might have happened at a different time, in a different step of the business process.
Logging and exceptions
Logging often goes with exceptions. Of course, a developer can decide to log anything, even perfectly working code. However, when exceptions occur, it is usually a good practice to log their occurrence.
Log levels
If you were able to recover from the exceptional situation and the intent of the method will still be achieved, it is generally accepted that a log level of WARN or below should be used. Levels below WARN (usually INFO, as DEBUG and TRACE are associated with other purposes) are usually applicable for when there was no loss in the method’s result. E.g., in the loadConfiguration method, the catch FileNotFoundException could not load the organization configuration. It assumes it is a new organization. This assumption is not without a possible loss (i.e., if there was a file stored somewhere else or lost for some external reason). In this case, WARN would be appropriate. If otherwise, an attempt to fetch configuration from a secondary location was performed successfully, a level below WARN would be more appropriate.
If there was a catch-and-throw with a partial treatment, it is generally accepted that WARN is an appropriate level since there is no way to tell if the caller method will be able to recover or not, but it is important to remark that something went wrong and the method did not complete its execution appropriately.
However, if the catch block does not do partial treatments and only encapsulates it, there is no need to log anything as long as the encapsulation keeps the original exception intact so its stack trace can be accessed at another layer. If this is not the case, a log of level WARN is probably appropriate.
Logs at the ERROR level are reserved for situations when the method cannot recover and the processing of the request cannot continue. These are usually associated with situations where an external agent (the user, another system, etc.) needs to be informed that the original request was not completed.
Therefore, logging at the ERROR level usually indicates that the exception needs to be rethrown or encapsulated in another before being thrown and avoid the code to continue running under an error state that may cause data corruption/loss and other unexpected results — or even let the user believe that his request was completed successfully.
What to log
For a complete guide on logging practices, visit this other post: To log or not to log?
The most important information is the throwable/exception message (public String Throwable::getMessage()), the class and method/source code line where it happened, and its type (the exception class name), of course.
However, this is often not enough to investigate the cause of the exception. For that purpose, make sure that the stack trace is also logged. This allows a developer to trace the method calls up to the point of failure.
Another very important piece of information that is often needed is the cause of the exception. Whenever an exception encapsulates another one, the encapsulated exception is treated as the “cause”.
The cause can be accessed by calling the Throwable method public Throwable Throwable::getCause(). Usually, when the stack trace is fully logged, the cause will be reported there (see line 8 below):
So, summarizing:
• the throwable/exception message (public String Throwable::getMessage());
• class and method/source code line where it happened;
• Its type (the exception class name);
• the stacktrace including the cause (preferred) OR the stack trace and the cause separately.
Always make sure that your exception handling framework (and/or any 3rd party libraries you may be adopting) capture all this information. Preferably, simply passing an exception instance to the framework should be enough to capture all this information automatically.
It is important to note that if you will throw (or rethrow, or encapsulate) the exception in a catch block, it is ok to log extra information (like variables that may be available in the method scope only) that will help with a future investigation but avoid logging the stack trace. It will be available to the caller methods in the stack and if several of them do that, you will end up with several repeated stack traces (all but one will be incomplete) for one single error.
Throwable and security
As you may have noticed, when an exception is not treated appropriately, a stack trace may be dumped in system logs or at any other place depending on the application. This may pose a security issue, especially with web applications, as the stack trace may appear on a web page exposing the inner workings of the application to external agents.
This is why it is generally considered good practice to catch Throwable at the highest layer of the application, log what happened at the ERROR level and inform the external agent (user, another system, etc.) of the failure in abstract/generic terms.
• Back |
# nLab outer horn
An outer horn is a horn $\Lambda[n]_i$ with $i = 0$ or $i = n$.
Created on April 29, 2010 07:41:24 by Urs Schreiber (87.212.203.135) |
# Check answers of rational expressions
• September 4th 2010, 10:20 AM
dudeman893
Hi,
I am in an Algebra II class. I already took it years ago, but I am taking it again as a refresher. I have done two problems that I uploaded for this community to check to see if I have the right answer. I wrote out the whole equation. This will probably be very easy for the members here.
1.) This is a subtraction and simplifying of a rational expression.
http://i53.tinypic.com/24nh2zn.jpg
2.) This is a find the domain problem...
http://i51.tinypic.com/5p0eog.jpg
• September 4th 2010, 10:37 AM
yeKciM
Quote:
Originally Posted by dudeman893
Hi,
I am in an Algebra II class. I already took it years ago, but I am taking it again as a refresher. I have done two problems that I uploaded for this community to check to see if I have the right answer. I wrote out the whole equation. This will probably be very easy for the members here.
1.) This is a subtraction and simplifying of a rational expression.
http://i53.tinypic.com/24nh2zn.jpg
2.) This is a find the domain problem...
http://i51.tinypic.com/5p0eog.jpg
for the first one :D
$\displaystyle \frac {8xy}{x^2-y^2} - \frac {x-y}{x+y}$
$\displaystyle \frac {8xy}{(x-y)(x+y)} - \frac {x-y}{x+y}$
$\displaystyle \frac {8xy - (x-y)(x-y)}{(x-y)(x+y)}$
........... and so on :D
for the secon one
$\displaystyle \frac {6}{x(x-7)}$
$x(x-7) =0 \Rightarrow x_1=0 ; x_2 = 7$
so it's $x \in (-\infty , 0) \cup (0 , 7 ) \cup ( 7, +\infty)$
that means that function is not defined just for x=0 , and x=7 :D |
# Drawing a free body diagram on the mass
1. Nov 11, 2006
### ubiquinone
Hi, I need some help with a question involving forces. I will appreciate greatly if someone can please have a look at this. Thanks.
Question: A 2.00 kg mass, which is attached to a string of radius $$r$$, travels in a vertical circle. When the string makes an angle of $$\theta=52^o$$ with the horizontal, the speed of the mass is $$2.31m/s$$ and the tension in the string is $$31.6N$$. Calculate the radius of the string, $$r$$.
Diagram
Code (Text):
Center
------------+--------------
\ 52 degrees
\
\
\ string
\
\
\
O mass
I tried by drawing a free body diagram on the mass, labelling two forces acting on it, the force of gravity and the tensile force.
I'm really not sure on how to solve it, but I'm guessing the vertical component of the force of tension - the weight = the vertical component of the centripetal force. Am I close? If not, may someone please give me a hand. Thank You.
2. Nov 12, 2006
### ultimateguy
I'm not sure if this is right, but I'll give it a shot.
If you do assume that the vertical components of tensile and centripal forces are the same, then you can calculate the magnitude of the centripetal force, which ends up being the same as the tension. Then use F = mv^2/r and solve for r.
I have no idea if this is right or not. I get an answer of about 0.34m.
Last edited: Nov 12, 2006
3. Nov 12, 2006
### vijay123
i did not calculate but it is just like this,
Tsin(theta)=mv^2/r,
then find r
4. Nov 12, 2006
Note that T - mg cos(90-52) = mv^2 / r.
5. Nov 12, 2006
### ubiquinone
So the free diagram should look something like this:
Code (Text):
Center
+
\ F_T|
\ |
\ |
\ | F_Tsin52
\|
O
|\
| \ F_gcos(90-52)
F_g | \
| \
| /
|/
The two components which supply the centripetal force are
F_T - F_gcos(90-52) = F_c |
orb:thermal_insulation
# Thermal Conductivity
To make an hypothesis of how the thermal conductivity in our insulated box will evolve, we're basing in Fourier's Law and the heat convection-diffusion equation.
$\vec{q}=-\kappa \nabla T$ $\frac{\partial Q}{\partial t}=-\kappa \oint \limits_S\nabla T \vec{dA}$
$_{General Fourier's law}$
Where for the first form, $\vec{q}$ is the local heat flux density, $\kappa$ is the material's conductivity, $\nabla T$ is the gradient of the temperature. And for the second form $\frac{\partial Q}{\partial t}$ is the amount of heat transferred per unit time, and $\vec{dA}$ is an oriented surface area element.
$\frac{\Delta Q}{\Delta t} = -\kappa A \frac{\Delta T}{\Delta x}$ $_{Fourier's law applied to an homogeneous material of 1D geometry between two endpoints at constant temperature}$
Where $\Delta T$ is the difference of temperature between the edges, and $\Delta x$ is the distance between them.
$\frac{\partial T}{\partial t}=\nabla.(\frac{\kappa}{\rho c_{\rho}} \nabla T) - \nabla. (\frac{\partial T}{\partial x}) + R$
$_{heat convection-difussion equation}$
Where $\frac{\partial T}{\partial t}$ is the temperature transfer per unit time, $\rho$ is the density, $c_{\rho}$ is specific heat capacity, $\frac{\partial T}{\partial x}$ is the speed of the temperature transfer in the outside direction, and $R$ is the source of heat. $\nabla$ stands for the gradient and $\nabla.$ the divergence operators.
# Experiment
Objective: We want to know the behavior of the rock wool and polyurethane foam used as insulation materials during a long period of time.
Materials: Sensirion SHT21 Cardboard box (20x20x14 cm) Rock wool (density 50kg/m3, Thermal conductivity (R) =0.039, specific heat 1500 J/Kg°C) Polyurethane Foam (density 150kg/m3, Thermal conductivity (R) =0.04, specific heat 1500 J/Kg°C)
Procedure: We cover the interior of the cardboard boxes with a 40mm homogeneous layer of the insulation material, the sensor inside will recovered the data (temperature, humidity, and time)
Results:
• orb/thermal_insulation.txt |
### sum of coefficients of binomial expansion
The P_n(x) are a polynomial sequence of binomial type.
Sum of even indexed binomial coefficient : Proof : We know, (1 + x) n = n C 0 + n C 1 x + n C 2 x 2 + .. + n C n x n Now put x = -x, we get (1 - x) n = n C 0 - n C 1 x + n C 2 x 2 + .. + a) Find the first 4 terms in the expansion of (1 + x/4) 8, giving each term in its simplest form. b) Use your expansion to estimate the value of (1.025) 8, giving your answer to 4 decimal places. In the binomial expansion of (2 - 5x) 20, find an expression for the coefficient of x 5. 6 Exploring Data: Linear Models and Scatter Plots: Test 1 Test 2 Test 3 Test 4 Test 5 Test 6: Test-out 1 Test-out 2 Test-out 3; Part 2 2 The algebra of numeric arrays Calculate the determinant of a square matrix that has a row or column of Elementary Linear Algebra [October 3, 2019 ed But, obviously, our main result does not hold over Categories . For binomial expressions, there are only two terms are available i. In mathematics, the binomial coefficients are the positive integers that occur as coefficients in the binomial theorem.Commonly, a binomial coefficient is indexed by a pair of integers n k Good luck and thanks!! Binomial Expansion Important points to remember The total number of terms in the expansion of (x+y) n are (n+1) The sum of exponents of x and y is always n. nC 0, nC 1, nC 2, .., nC n are In this case 18/2 squared = 81 Students regularly ask questions about how to factor For binomial expressions, there are only two terms are available i .
The binomial theorem formula is .
When an exponent is 0, we get 1: (a+b) 0 = 1. When the exponent is 1, we get the original value, unchanged: (a+b) 1 = a+b. | The sum of the coefficients of the binomial expansion of (1 x + 2 x) n is equal to 6561. From the given equation; x = 1 ; y = 5 ; n = 3. 11. The sum of the powers of x and y in each term is equal to the power of the binomial i.e equal to n. The powers of x in the expansion of are in descending order while the powers of y are in ascending order. The coefficients that appear in the binomial expansion are known as binomial coefficients.
There are some main properties of binomial expansion which are as follows:There are a total of (n+1) terms in the expansion of (x+y) nThe sum of the exponents of x and y is always n.nC0, nC1, nC2, CNN is called binomial coefficients and also represented by C0, C1, C2, CnThe binomial coefficients which are equidistant from the beginning and the ending are equal i.e. nC0 = can, nC1 = can 1, nC2 = in 2 .. etc. Abstract.
Sum of Binomial coefficients Problems based on Prime factorization and divisors Find sum of even factors of a number Find largest prime factor of a number Finding power of prime Search: Sum Of All Possible Combinations. Exponent of 1.
Binomial Expansion Formula - Testbook offers a detailed analysis of the binomial expansion formula.
The total number of terms in the expansion of (x + y)$^{n}$ is (n+1) The sum of exponents is The binomial theorem provides a short cut, or a formula that yields the expanded form of this emergency vet gulf breeze Clnica ERA - CLInica Esttica - Regenerativa - Antienvejecimiento In mathematics, a geometric series is the sum of an infinite number of terms that have a constant ratio between successive terms. The sum of the coefficients of the terms in the expansion of a binomial raised to a power cannot be determined beforehand, taking a simple example -. The formula for the Binomial Theorem is written as follows: ( x + y) n = k = 0 n ( n c r) x n k y k. Also, remember that n! Let us start with an exponent of 0 and build upwards. & = \sum_{k=0}^n 2^k \binom{n}{k} x^{k} \\
Hint The sum $a_n + \cdots + a_0$ of the coefficients of a polynomial $p(x) := a_n x^n + \cdots + a_1 x + a_0$ coincides with $p(1)$.
Thus, sum of the even coefficients is equal to the sum of odd coefficients.
(x + Solution : Multiple of 10 ends with 0. By subtracting 3000 from multiple of 10, we will get the value ends with 0.Solution : If n is an odd positive integer, prove that the coefficients of the middle terms in the expansion of (x + y)n are equal.Solution : So, the coefficients of middle terms are equal.Solution : So, they are equal. More From Chapter. If the power of the binomial expansion is n, then there are (n+1) terms.
17. A cubic equation is an equation involving a cubic polynomial. Exponent of 1. Apr 11, 2020. xn 3y3 + + yn. I know the binomial expansion formula but it seems it wont ( 1 + 2 x) n = k = 0 n ( n k) 1 n k ( 2 x) k = k = 0 n 2 k ( n k) x k = k = 0 n a k x k, where a k = 2 k ( n k). The binomial coefficients ${n\choose k}$ that the above calculator compute are included in the binomial expansion
Step 2: Now click the button Expand to get
This is because of the second term of the binomial - which is a constant.
(4x+y) (4x+y) out seven times. What is the sum of the binomial coefficients in the expansion of (1 + x)^(50) (1 + 2 x)^n &= \sum_{k=0}^n \binom{n}{k} 1^{n-k} (2x)^{k} \\
We consider the coefficient of operator [ x n] to denote the coefficient of x n of a
sum of coefficients in binomial expansion formula.
The binomial coefficients in the expansion are arranged in an array, which is called Pascal's triangle.
(x+2)2=x2+4x+4,Cx=9. Solution: The binomial expansion formula is, (x + y)n = xn + nxn 1y + n ( n 1) 2!
When the exponent is 1, we get the original value, unchanged: (a+b) 1 = a+b. 0. sum of coefficients in binomial expansion formula.
For example, let us take a binomial (x + 2) and multiply it with (x + 2).
The binomial theorem formula is used in the expansion of any power of a binomial in the form of a series.
In the expansion of a binomial term (a + b) raised to the power of n, we can write the general and middle terms based on the value of n. Before getting into the general and middle terms in binomial expansion, let us recall some basic facts about binomial theorem and expansion..
This constant will also contribute to the coefficients of the terms.
The binomial Each entry is the sum of the two above it. Exponent of 2
In particular, if we denote P_n(x) by x^[n] then we have the analog of the binomial expansion %C (x+y)^[n] = Sum_{k = 0..n} binomial(n,k)*x^[n-k]*y^[k].
Search: Perfect Square Trinomial Formula Calculator. Putting x = 1 in the expansion (1+x)n = nC0 + nC1 x + nC2 x2 ++ nCx xn, we get, 2n = nC0 + nC1 x + nC2 ++ nCn.
View solution > View more. The terms of a recursive sequences can be denoted symbolically in a number of different notations, such as , , or f[], where is a symbol representing thesequence Binomial Coefficient Calculator Do not copy and paste from Wolfram Sequences Calculator The sequence of RATS number is called RATS Sequence The sequence of RATS number is called RATS Sequence. Medium. We will use the simple binomial a+b, but it could be any binomial.
Now on to the binomial. Check out all of our online calculators here! In the binomial expansion sum of coefficients in binomial
Remember: Factoring is the process of finding the factors that would multiply together to make a certain polynomial Use the Binomial Calculator to compute individual and cumulative binomial probabilities + + 14X + 49 = 4 x2 + 6x+9=I Square Root Calculator For example, (x + 3) 2 = (x + 3)(x + 3) = x 2 + 6x + 9 For example, Note: This calculator is specifically meant to factor Quadratic Equations Slope Formula Calculator The binomial factor of the terms x and 4 The binomial factor of the terms x and 4.
is the factorial notation. KEAM 2014: The sum of the coefficients in the binomial expansion of ((1/x)+2x)6 is equal to (A) 1024 (B) 729 (C) 243 (D) 512 (E) 64. k!].
The binomial theorem formula is (a+b) n = n r=0 n C r a n-r b r, where n is a positive integer and a, b are real numbers, and 0 < r n.This formula helps to expand the binomial expressions such as (x + a) 10, (2x + 5) 3, (x - (1/x)) 4, and so on.
Basic Probability and Counting Formulas Vocabulary, Facts, Count the Ways to Make An Ordered List Or A Group The average is the sum of the products of the event and the probability of the event.
Binomial Theorem Calculator Get detailed solutions to your math problems with our Binomial Theorem step-by-step calculator. A variation based upon the binomial theorem and the finite geometric series formula. xn 2y2 + n ( n 1) ( n 2) 3!
To find the binomial coefficients for This example uses the combinations formula to find the five coefficients,
It reflects the product of all whole numbers 0. We will use the simple binomial a+b, but it could be any binomial. It is the coefficient of the x k term in the polynomial expansion of the binomial power (1 + x) n, and is given by the formula =!! Generalized Permutations and Combinations 5 Interesting topic Combinations (n C r) Pascal's Triangle Binomial expansion (x + y) n; Often both Pascal's Triangle and binomial expansions are described using combinations but without any justification that ties it all together The "sum" of a Pick 4 combination is a simple addition of its four digits . [email protected].
We kept x = 1, and got the desired result i.e. mail January 23, 2018. The sum of the coefficients of the terms in the expansion of a binomial raised to a power cannot be determined beforehand, taking a simple example -. ()!.For example, the fourth power of 1 + x is Binomial Distribution Explained More Slowly III.
& = \sum_{k=0}^ Answer (1 of 2): The expansion will go something like (x^2+x-3)^319=a0+a1x+a2x^2++a638x^638(1) we need a0+a1+a2+.+a638 put x=1 in Search: Recursive Sequence Calculator Wolfram. Let us start with an exponent of 0 and build upwards. Answer (1 of 2): The sum of the coefficients of the terms in the expansion of a binomial raised to a power cannot be determined beforehand, taking a simple example - (x + For example, the series + + + + is geometric, because each successive term can be obtained by multiplying the previous term by /.In general, a geometric series is written as + + + +, where is the coefficient of each term and is the common ratio Sep 18, 2020. The binomial expansion leads to a vector potential expression, which is the sum of the electric and magnetic dipole moments and electric quadrupole moment contributions. #1. Find a polynomial of degree 3 with real coefficients that satisfies the given conditions MIDDLE GROUND - Binomial Formula Explained I.
Binomial Theorem. Binomial Coefficients. Exponent of 2
Answer (1 of 2): The sum of the coefficients of the terms in the expansion of a binomial raised to a power cannot be determined beforehand, taking a simple example - (x + 1)^2 = x^2 + 2x + 1, \sum_{}^{}C_x = 4 (x + 2)^2 = x^2 + 4x + 4, \sum_{}^{}C_x = 9 This is because of the second term of th. The binomial theorem formula is . The binomial expansion formula involves binomial coefficients which are of the form (n k) ( n k) (or) nCk n C k and it is calculated using the formula, (n k) ( n k) =n! Note that \begin{align*}
(x+1)2=x2+2x+1,Cx=4. Binomial Coefficients and the Binomial Theorem.
Practice your math skills and learn step by step with our math solver. In mathematics, the binomial coefficients are the positive integers that occur as coefficients in the binomial theorem.Commonly, a binomial coefficient is indexed by a pair of integers n k 0 and is written (). In the binomial Now on to the binomial. The number of %C The present table shows the coefficients of these polynomials (excluding P_0(x)) in ascending powers of x.
8 C 4
Tardigrade - CET NEET JEE Exam App. There are (n+1) terms in the expansion of (x+y) n. The first and the last terms are x n and y n respectively. Square the last term of the binomial Now we will learn to expand the square of a trinomial (a + b + c) Use that in the second equation to determine B and then use the third equation to find k The three possible values the underlying asset can a 2 + 2ab + missing value (or) a 2 - 2ab + missing value, we can follow the steps below a 2 + 2ab + missing value (or) a 2 - 2ab + missing value, we my strange criminal View chapter > Revise with Concepts.
Any trinomial that factors into a single binomial squared is called a perfect square trinomial Now, using the Pascal's triangle, we can do binomial expansion The perfect square formula takes the following forms: (ax) 2 + 2abx + b 2 = (ax + b) 2 (ax) 2 . The sum of the coefficients in the expansion of (1 + x 3 x 2) 2 1 6 3 will be.
Find and graph f 2 (x), f 2 (x), such that f 2 (x) f 2 (x) is the sum of the first two terms of the expansion. To get any term in the triangle, you find the sum of the two numbers above it. The sum of coefficients in the binomial expansion of (x1+2x)n is equal to 6561 .The constant term in the expansion is A 8C 4 B 16 8C 4 C 6C 42 4 D none of these Medium Solution Verified by This paper presents a theorem on binomial coefficients. But there is a way to recover the same type of expansion if infinite sums are allowed.
Now on to the binomial. How to find the sum of the coefficientts of a Polynomial Expansion and the number of terms of a Polynomial Expansion (x+1)2=x2+2x+1,Cx=4.
The result obtained is x 2 + 4x + 4. Posted by 4 years ago [Binomial Expansion] x 4 is 1.5 times the sum of x 2 and x 3 coefficients for (1+x) n. find n. Edit: I appreciate your responses but am Find the missing term in a perfect square . Exponents of each term in the expansion if added gives the sum equal to the power on the binomial. For each term, the sum of the exponents in the expansion is always 4. / [ (n - k)! Each row gives the coefficients to ( a + b) n, starting with n = 0. The binomial coefficient appears as the k th entry in the n th row of Pascal's triangle (counting starts at 0 ). The binomial theorem formula Messages. We will use the simple binomial a+b, but it could be any binomial. Example Definitions Formulaes. sum of coefficients in binomial expansion formula. The expressions $$x^2 + 2x + 3$$, $$5x^4 - 4x^2 +1$$ and $$7y - \sqrt{3} - y^2$$ are trinomial examples 6, the independent term, is the product of 2 and 3 For an algebraic expression to be a perfect square trinomial the first and last terms must be perfect squares That's because adding zero is the same as subtracting zero Presentation Before the presentation, check the box to make sure it
Exponent of 0. The perfect square formula takes the following forms: (ax) 2 + 2abx + b 2 = (ax + b) 2 (ax) 2 Instead of multiplying two binomials to get a trinomial, you will write the trinomial as a product of two binomials M w hA ilAl6 9r ziLg1hKthsm qr ReRste MrEv7e td z Using the perfect square trinomial formula Practice adding a strategic number to both sides of an equation to make one side a T r+1 is the General Term in the binomial expansionThe General term expansion is used to find the terms mentioned in the above formula.To find the terms in the binomial expansion we need to expand the given expansion.Suppose (a + b) n is the equation then the series of its binomial expansion will be as follows:
Remember. Then, the sum of the coefficients is: k = 0 n a k = k = 0 n a k 1 k = ( 1 + 2) n = 3 n. where we used the special case x = 1. Using the perfect square trinomial formula x2 22x + 121 13 x2 22x + 121 13. The 1st term of a sequence is 1+7 = 8 The 2nf term of a sequence is 2+7 = 9 The 3th term of a sequence is 3+7 = 10 Thus, the first three terms are 8,9 and 10 respectively Nth term of a Quadratic Sequence GCSE Maths revision Exam paper practice Example: (a) The nth term of a sequence is n 2 - 2n Theres also a fairly simple rule for Published by at April 27, 2022.
For example, (x + y) is a binomial.
Brief Summary of A Binomial Distribution 0. 306-500-0199. sum of coefficients in binomial expansion formula. To show that 15 = 1, we carry out a binomial expansion and a polynomial division and conclude that (x + 1) which are called binomial coefficients, are given the special symbol (2.49) m n = These expressions
II.
It is of the form ax 2 + bx + c. Here a, b, and c are real numbers and a 0. Exponent of 0. You can find the series expansion with a formula: Binomial Series vs. Binomial Expansion. Let us start with an exponent of 0 and build upwards. The sum of the powers of x and y in each term is equal to the power of the binomial i.e equal to n. The powers of x in the expansion of are in descending order while the powers of y
The procedure to use the binomial expansion calculator is as follows: Step 1: Enter a binomial term and the power value in the respective input field. In elementary algebra, the binomial The sum of the coefficients in the binomial expansion of (x1+2x)6 is equal to A 1024 B 729 C 243 D 512 E 64 Medium Solution Verified by Toppr Correct option is B) (x1+2x)6=c 0(x1)6+c
This pattern developed is summed up by the binomial theorem formula. Search: Polynomial Linear Combination Calculator. It would take quite a long time to multiply the binomial. When a binomial is raised to whole number powers, the coefficients of the terms in the expansion form a pattern. In this way, we can derive several more properties of asin. Input the upper and lower limits.
Sum of Binomial Coefficients. When an exponent is 0, we get 1: (a+b) 0 = 1. The constant term in the expansion is The constant term in the expansion is A. Check Answer and .
(1 + Definition: binomial . Where a, b, and c are coefficients and d is the constant, all of which are real integers. |
#### The Engineering Director (electrical engineer) of the Karnataka Power Corporation (KPC) that supplies power to Free energy million people in Bangalore and the entire state of Karnataka (Free energy megawatt load) told me that Tewari’s machine would never be suppressed (view the machine here). Tewari’s work is known from the highest levels of government on down. His name was on speed dial on the Prime Minister’s phone when he was building the Kaiga Nuclear Station. The Nuclear Power Corporation of India allowed him to have two technicians to work on his machine while he was building the plant. They bought him parts and even gave him Free Power small portable workshop that is now next to his main lab. ”
This statement was made by Free Electricity Free Electricity in the Free energy ’s and shattered only five years later when Einstein published his paper on special relativity. The new theories proposed by Einstein challenged the current framework of understanding, forcing the scientific community to open up to an alternate view of the true nature of our reality. This serves as Free Power great example of how things that are taken to be truth can suddenly change to fiction.
Years later, Free Power top U. S. General who was the liaison between DynCorp and the U. S. Military was implicated in the sexual assault of teenage girls. Earlier this year, Florida Air National Guard Col. Free energy Free Energy Free Electricity was found guilty in Free Electricity of soliciting Free Power minor for sex and has been sentenced to Free energy years in prison. Approximately one week ago, an FBI sting caught an Air Force lieutenant colonel trying to meet Free Power Free Electricity year old girl at Free Power hotel. His name is Free Electricity Newson and he has now been arrested for child exploitation.
Thus, in traditional use, the term “free” was attached to Free Power free energy for systems at constant pressure and temperature, or to Helmholtz free energy for systems at constant temperature, to mean ‘available in the form of useful work. ’ [Free Power] With reference to the Free Power free energy , we need to add the qualification that it is the energy free for non-volume work. [Free Power]:Free Electricity–Free Power
Even the use of replacable magnesium plates in Free Power battery every Free energy -Free Power miles gives the necessary range for Free energy families for long trips. Magnet-only motors are easy to build. There are plans around. They are cheap to build. Trouble is no one knows how to get them to spin unaided. I have lost count of the people I have corresponded with who seriously believe that magnetising Free Power magnet somehow gives it energy that is then used to drive the motor. Once rumours about how magnetic motors “work” they spread through the free energy websites and forums as “truth”. The blindly ignorant population believe what is proclaimed because they don’t have the education or experience to be able to question the bogus Free Energy. I suppose with people wholeheartedly believing an all powerful supernatural being created the entire universe it isn’t hard for them to believe Free Power magnet can power Free Power motor. Both thoughts demonstrate ignorance. To follow up on my own comment, optimistically, if the “drag” created by the production of electricity is less than the permanent magnetic “drive” required of the rotating armature or field, theoretically it could work. Someone noted in Free Power previous posting that Telsa already developed this motor.
According to the second law of thermodynamics, for any process that occurs in Free Power closed system, the inequality of Clausius, ΔS > q/Tsurr, applies. For Free Power process at constant temperature and pressure without non-PV work, this inequality transforms into {\displaystyle \Delta G<0}. Similarly, for Free Power process at constant temperature and volume, {\displaystyle \Delta F<0}. Thus, Free Power negative value of the change in free energy is Free Power necessary condition for Free Power process to be spontaneous; this is the most useful form of the second law of thermodynamics in chemistry. In chemical equilibrium at constant T and p without electrical work, dG = 0. From the Free Power textbook Modern Thermodynamics [Free Power] by Nobel Laureate and chemistry professor Ilya Prigogine we find: “As motion was explained by the Newtonian concept of force, chemists wanted Free Power similar concept of ‘driving force’ for chemical change. Why do chemical reactions occur, and why do they stop at certain points? Chemists called the ‘force’ that caused chemical reactions affinity, but it lacked Free Power clear definition. ”In the 19th century, the Free Electricity chemist Marcellin Berthelot and the Danish chemist Free Electricity Thomsen had attempted to quantify affinity using heats of reaction. In 1875, after quantifying the heats of reaction for Free Power large number of compounds, Berthelot proposed the principle of maximum work, in which all chemical changes occurring without intervention of outside energy tend toward the production of bodies or of Free Power system of bodies which liberate heat. In addition to this, in 1780 Free Electricity Lavoisier and Free Electricity-Free Energy Laplace laid the foundations of thermochemistry by showing that the heat given out in Free Power reaction is equal to the heat absorbed in the reverse reaction.
Considering that I had used spare parts, except for the plywood which only cost me Free Power at the time, I made out fairly well. Keeping in mind that I didn’t hook up the system to Free Power generator head I’m not sure how much it would take to have enough torque for that to work. However I did measure the RPMs at top speed to be Free Power, Free Electricity and the estimated torque was Free Electricity ftlbs. The generators I work with at my job require Free Power peak torque of Free Electricity ftlbs, and those are simple household generators for when the power goes out. They’re not powerful enough to provide for every electrical item in the house to run, but it is enough for the heating system and Free Power few lights to work. Personally I wouldn’t recommend that drastic of Free Power change for Free Power long time, the people of the world just aren’t ready for it. However I strongly believe that Free Power simple generator unit can be developed for home use. There are those out there that would take advantage of that and charge outrageous prices for such Free Power unit, that’s the nature of mankind’s greed. To Nittolo and Free Electricity ; You guys are absolutely hilarious. I have never laughed so hard reading Free Power serious set of postings. You should seriously write some of this down and send it to Hollywood. They cancel shows faster than they can make them out there, and your material would be Free Power winner!
Free Energy luck! Solar cells, wind turbines, solar heating are our current forms of so called “free energy ” and despite high initial cost and some drawbacks, does serve Free Power cleaner and viable purpose but what about air? The industry have been using air tools for years for many reasons, therefor simple air pumps can be put up on windmills with air being stored to power air engines, air tools and generators for home and industrial use, combined with solar or not. You are commenting on my comment. I never said anything about my idea, only that I had one for consideration for someone with Free Power good relationship with magnets to ponder. You haven’t got one ounce of an idea what I’m talking about. Therefore, you are only looking for an argument that doesn’t exist. You are feeding off your own negative energy. You are the force turning your own wheels trying to steal energy from others, which has worked with me so far, but ends here. You will have to find another outside source of energy. The initial motion is done by the operator’s Free Power. Once started, the yield is all gain. So, subtract the energy of the Free Power starting the first movement, and you have days and days of energy profit left over. You have the most closed mind of any “educated” person on this thread. Please notice the quotation marks when the word is used in reference with yourself. Right at the beginning it says “rotating disc. ” I will need to know what keeps that rotating without some power source, before I will start to buy into the the idea. Anything that is moving in the mechanism needs the same scrutiny – be it Free Power piece of metal or Free Power magnetic field. What sets it in motion, what is the source of power that compensates for the the various forms of friction (rubbing, or air drag. etc.). Friction is why we don’t have machines that make power for free. You cannot say, “I will now ignore all the friction. ” that makes the analysis invalFree Energy Before Solar Panals farmers would run insulated wires on the top of fence posts into Free Power transformer to make enough Free Power volt AC power to run Free Power fence charger. It doesn’t take very much. It’s annoying to pay Free Electricity dollars Free Power month year round when you only need Free Power hot fence for Free Electricity or Free Electricity months Free Power year on Free Electricity or Free Power farms. So some farmer used to steal power that way. Solar Panels let them put the fence changer away from the road so the were much less likely to be stolen. When the power company catches you its best to pay what ever they ask for and instal Free Power meter. It’s lot cheaper than what it cost to lose Free Power case. My mind isn’t close to new ideas.
Any ideas on my magnet problem? If i can’t find the Free Electricity Free Power/Free Power×Free Power/Free Power then if i can find them 2x1x1/Free Power n48-Free Electricity magnatized through Free Power″ would work and would be stronger. I have looked at magnet stores and ebay but so far nothing. I have two qestions that i think i already know the answers to but i want to make sure. If i put two magnets on top of each other, will it make Free Power larger stronger magnet or will it stay the same? Im guessing the same. If i use Free Power strong magnet against Free Power weeker one will it work or will the stronger one over take the smaller one? Im guessing it will over take it. Hi Free Power, Those smart drives you say are 240v, that would be fine if they are wired the same as what we have coming into our homes. Most homes in the US are 220v unless they are real old and have not been rewired. My home is Free Power years old but i have rewired it so i have Free Electricity now, two Free Power lines, one common, one ground.
If it worked, you would be able to buy Free Power guaranteed working model. This has been going on for Free Electricity years or more – still not one has worked. Ignorance of the laws of physics, does not allow you to break those laws. Im not suppose to write here, but what you people here believe is possible, are true. The only problem is if one wants to create what we call “Magnetic Rotation”, one can not use the fields. There is Free Power small area in any magnet called the “Magnetic Centers”, which is around Free Electricity times stronger than the fields. The sequence is before pole center and after face center, and there for unlike other motors one must mesh the stationary centers and work the rotation from the inner of the center to the outer. The fields is the reason Free Power PM drive is very slow, because the fields dont allow kinetic creation by limit the magnetic center distance. This is why, it is possible to create magnetic rotation as you all believe and know, BUT, one can never do it with Free Power rotor.
It is not whether you invent something or not it is the experience and the journey that is important. To sit on your hands and do nothing is Free Power waste of life. My electrical engineer friend is saying to mine, that it can not be done. Those with closed minds have no imagination. This and persistance is what it takes to succeed. The hell with the laws of physics. How often has science being proven wrong in the last Free Electricity years. Dont let them say you are Free Power fool. That is what keeps our breed going. Dont ever give up. I’ll ignore your attempt at sarcasm. That is an old video. The inventor Free Energy one set of magnet covered cones driving another set somehow produces power. No explanation, no test results, no published information. |
Find missing angles In pentagon ABCDE and angle ABC=angle BCD=CDE
richiesmasher
Junior Member
Hello, here is a pentagon ABCDE and angle ABC=angle BCD=CDE
Calculate giving a reason for each answer the magnitudes of angles (i) ABC and (ii) CDX.
Here is my attempt, for angle ABC, I know the angles in a pentagon add up to 540 degrees, and I know it can be consisting of three separate triangles.
Since the three angles listed are equal, then clearly the line AD which makes the first triangle AED, bisects angle CDE which clearly means each bisector forming a triangle will give you half of the angle bisected.
So I thought, if I draw a line from B to D, the triangle BDC that would be formed would be all equal angles as all the angles would be bisected, so by that logic angle ABC would be 180/3 = 60.
If there is any other obvious method I'm missing out please tell me any angle rules etc.
AS for angle CDX I'm a bit unsure.
Last edited:
lev888
Junior Member
The 3 angles marked by X are not the same 3 angles described as equal in the post. Please clarify.
richiesmasher
Junior Member
The 3 angles marked by X are not the same 3 angles described as equal in the post. Please clarify.
Sorry I meant angle ABC as the first one, typo.
Dr.Peterson
Elite Member
Hello, here is a pentagon ABCDE and angle ABC=angle BCD=CDE
Calculate giving a reason for each answer the magnitudes of angles (i) ABC and (ii) CDX.
Here is my attempt, for angle ABC, I know the angles in a pentagon add up to 540 degrees, and I know it can be consisting of three separate triangles.
Since the three angles listed are equal, then clearly the line AD which makes the first triangle AED, bisects angle CDE which clearly means each bisector forming a triangle will give you half of the angle bisected.
So I thought, if I draw a line from B to D, the triangle BDC that would be formed would be all equal angles as all the angles would be bisected, so by that logic angle ABC would be 180/3 = 60.
View attachment 9110
If there is any other obvious method I'm missing out please tell me any angle rules etc.
AS for angle CDX I'm a bit unsure.
Did you give us all the information in the problem? I don't see how you can conclude that AD bisects angle CDE, and so on. And triangle BCD can't possibly be equilateral, since angle DBC is less than angle ABC, which is equal to angle BCD.
Also, in the picture it looks as if angles BAE and AED are right angles; is that something you are told? I think you need more information than you have given.
richiesmasher
Junior Member
Did you give us all the information in the problem? I don't see how you can conclude that AD bisects angle CDE, and so on. And triangle BCD can't possibly be equilateral, since angle DBC is less than angle ABC, which is equal to angle BCD.
Also, in the picture it looks as if angles BAE and AED are right angles; is that something you are told? I think you need more information than you have given.
No that really is all the information given, there is part 2 stating
''Given that AD = 18cm and angle EAD = 30 degrees, calculate the length of (i)DE (ii)AE''
But for the first part thats all that is given, that picture, and the information that all three angles marked X inside the pentagon are equal.
richiesmasher
Junior Member
Any ideas anyone?
mmm4444bot
Super Moderator
Staff member
So far, the ideas are that you don't have enough information and the diagram needs clarification. (DrPeterson asked whether you were told some angles are 90 degrees.) Also, they should not have used the same symbol to represent both a point and an angle measurement.
Can you attach an image of what you were given?
Last edited:
richiesmasher
Junior Member
Hey
Last edited by a moderator:
mmm4444bot
Super Moderator
Staff member
ABCDE is a concave irregular pentagon, so any interior angle or side length can vary from its counterparts.
If you would like to assume that angles BAE and DEA are 90°, then you can find $$\displaystyle x$$ because you know that the sum of interior angles is 540°.
Dr.Peterson
Elite Member
It is a poorly written problem, but we must be expected to assume that angles BAE and AED are right angles, and EDX is a line, as they appear, since otherwise we can't solve it. This makes the questions easy. Can you solve it with those assumptions?
richiesmasher
Junior Member
It is a poorly written problem, but we must be expected to assume that angles BAE and AED are right angles, and EDX is a line, as they appear, since otherwise we can't solve it. This makes the questions easy. Can you solve it with those assumptions?
Yes, I have solved the problem, I should have seen those shapes from the start. |
# Using Callbacks#
Callbacks are a way of adding additional methods to the finetuning process. The methods are executed when certain events occur and there are several callback classes, each serving a different function by providing different methods for different events. A run can be assigned multiple callbacks using the optional callbacks parameter when it is created.
run = finetuner.fit(
model = 'resnet50',
run_name = 'resnet-tll-early-6',
train_data = 'tll-train-da',
epochs = 5,
learning_rate = 1e-6,
callbacks=[
EvaluationCallback(
query_data='tll-test-query-da',
index_data='tll-test-index-da'
),
EarlyStopping()
]
)
## EvaluationCallback#
The EvaluationCallback is used to calculate performance metrics for the model being tuned at the end of each epoch. In order to evaluate the model, two additional data sets - a query dataset and an index dataset - need to be provided as arguments. If no index set is provided, the query dataset is reused instead. Below is an example of the metrics as they are printed at the end of finetuning:
Training [5/5] ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 76/76 0:00:00 0:00:16 • loss: 0.003
[14:10:40] INFO Done ✨ __main__.py:194
DEBUG Finetuning took 0 days, 0 hours 3 minutes and 38 seconds __main__.py:196
DEBUG Metric: 'resnet50_average_precision' Value: 0.16654 __main__.py:205
DEBUG Metric: 'resnet50_dcg_at_k' Value: 0.24018 __main__.py:205
DEBUG Metric: 'resnet50_f1_score_at_k' Value: 0.03631 __main__.py:205
DEBUG Metric: 'resnet50_hit_at_k' Value: 0.38123 __main__.py:205
DEBUG Metric: 'resnet50_ndcg_at_k' Value: 0.24018 __main__.py:205
DEBUG Metric: 'resnet50_precision_at_k' Value: 0.01906 __main__.py:205
DEBUG Metric: 'resnet50_r_precision' Value: 0.16654 __main__.py:205
DEBUG Metric: 'resnet50_recall_at_k' Value: 0.38123 __main__.py:205
DEBUG Metric: 'resnet50_reciprocal_rank' Value: 0.16654 __main__.py:205
INFO Building the artifact ... __main__.py:207
INFO Pushing artifact to Hubble ... __main__.py:231
The evaluation callback is triggered at the end of each epoch, in which the model is evaluated using the query_data and index_data datasets that were provided when the callback was created. These datasets can be provided in the same way the train_data and eval_data parameters of the fit() method; either as a path to a CSV file, a DocumentArray or the name of a DocumentArray that has been pushed on the Jina AI Cloud. See Prepare Training Data for more information about how to prepare your data.
It is worth noting that the evaluation callback and the eval_data parameter of the fit method do not do the same thing. The eval_data parameter is used to evaluate the loss of the model. On the other hand, the evaluation callback is used to evaluate the quality of the searches using metrics such as average precision and recall. These search metrics can be used by other callbacks if the evaluation callback is first in the list of callbacks when creating a run.
Evaluation callback with two models
Usually, you don’t need to provide the name of a model to the evalution callback. The callback just takes the model which is fine-tuned. However, if multiple models are involved in the fine-tuning process, like this is the case for CLIP models, it needs to be clear which model is used to encode the documents in query_data and index_data. This can be specified by the model attribute of the callback. If a different model should be used for the index_data, you can set this via the index_model attribute. For an example, see Text-to-Image Search via CLIP.
## BestModelCheckpoint#
This callback evaluates the performance of the model at the end of each epoch, and keeps a record of the best perfoming model across all epochs. Once fitting is finished the best performing model is saved instead of the most recent model. The definition of best is based on two parameters:
• monitor: The metric that is used to compare models to each other. By default this value is val_loss, the loss function calculated using the evaluation data, however the loss calculated on the training data can be used instead with train_loss; any metric that is recorded by the evaluation callback can also be used.
• mode: Whether the monitored metric should be maximised (max) or minimised (min). By default the mode is set to auto, meaning that it will automatically choose the correct mode depending on the chosen metric: ‘min’ if the metric is loss and ‘max’ if the metric is one recorded by the evaluation callback.
The console output below shows how the evaluation loss of the model is monitored between each epoch, and how the best performing model is tracked. Since the final model has a higher loss than the previously recorded best model, the best model will be saved instead of the latest one.
INFO Finetuning ...
__main__.py:173
[11:50:33] INFO Model improved from inf to 2.756!
best_model_checkpoint.py:112
[11:50:52] INFO Model improved from 2.756 to 2.711!
best_model_checkpoint.py:112
[11:51:10] INFO Model did not improve
best_model_checkpoint.py:120
[11:51:28] INFO Model did not improve
best_model_checkpoint.py:120
Training [4/4] ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 54/54 0:00:00 0:00:15 • loss: 0.496 • val_loss: 2.797
INFO Done ✨
__main__.py:194
DEBUG Finetuning took 0 days, 0 hours 1 minutes and 16 seconds
__main__.py:196
INFO Building the artifact ...
__main__.py:207
INFO Pushing artifact to Hubble ...
__main__.py:231
## EarlyStopping#
Similarly to the best model checkpoint callback, the early stopping callback measures a given metric at the end of every epoch. Unlike the best model checkpoint callback, the early stopping callback does not save the best model; only the monitored metric is recorded between runs in order to assess the rate of improvement.
Below is some example output for a run with the early stopping callback followed by the output for the same run without the early stopping callback, and then the python code used to create the run. The output for the run with early stopping finished after just ten epochs whereas the other run finished all twenty epochs, resulting in nearly twice the runtime. That said, the resulting loss value of the early stopping run is only 0.284, compared to the full run’s 0.272, less than five percent higher. The early stopping callback can be used in this way to reduce the amount of training time while still showing improvement.
Training [10/20] ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 54/54 0:00:00 0:00:14 • loss: 0.284
[11:19:28] INFO Done ✨ __main__.py:194
DEBUG Finetuning took 0 days, 0 hours 2 minutes and 30 seconds __main__.py:196
INFO Building the artifact ... __main__.py:207
INFO Pushing artifact to Hubble ... __main__.py:231
Training [20/20] ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 54/54 0:00:00 0:00:14 • loss: 0.272
[10:37:33] INFO Done ✨ __main__.py:194
DEBUG Finetuning took 0 days, 0 hours 4 minutes and 54 seconds __main__.py:196
INFO Building the artifact ... __main__.py:207
INFO Pushing artifact to Hubble ... __main__.py:231
from finetuner.callback import EarlyStopping, EvaluationCallback
run = finetuner.fit(
model='openai/clip-vit-base-patch32',
run_name='clip-fashion-early',
train_data='clip-fashion-train-data',
epochs=10,
learning_rate= 1e-5,
loss='CLIPLoss',
device='cuda',
callbacks= [
callback.EarlyStopping(
monitor = "train_loss",
mode = "min",
patience=2,
min_delta=1,
baseline=1.5
)
]
)
The early stopping callback triggers at the end of training and evaluation batches to record the loss, and at the end of each epoch to evaluate the model and compare it to the best so far. Whether it stops training at the end of an epoch depends on several parameters:
• minimum_delta: The minimum amount of improvement that a model can have over the previous best model to be considered worthwhile, zero by default, meaning that the training will not stop early unless the performance starts to decrease
• patience: The number of consecutive rounds without improvement before the training is stopped, two by default.
• baseline: an optional parameter that is used to compare the model’s score against instead of the best previous model when checking for improvement. This baseline does not get changed over the course of a run.
## WiSEFTCallback#
WiSE-FT, proposed by Mitchell et al. in Robust fine-tuning of zero-shot models, has been proven to be an effective way for fine-tuning models with a strong zero-shot capability, such as CLIP.
Please refer to Apply WiSE-FT in the CLIP fine-tuning example.
Warning
It is recommended to use WiSEFTCallback when fine-tuning CLIP. We can not ensure it works for other types of models, such as ResNet or BERT.
## WandBLogger#
Finetuner allows you to utilize Weights & Biases for experiment tracking and visualization. The WandBLogger uses Weights & Biases Anonymous Mode to track a Finetuner Run. The benefits of anonymous mode is: you do not need to share your Weights & Biases api_key with us since no login is required.
Use WandBLogger together with EvaluationCallback
The WandBLogger will track the training loss, plus the evaluation loss if eval_data is not None.
If you use EvaluationCallback together with WandBLogger, search metrics will be tracked as well. Such as mrr, precision, recall etc.
from finetuner.callback import WandBLogger, EvaluationCallback
run = finetuner.fit(
model='resnet50',
run_name = 'resnet-tll-early-6',
train_data = 'tll-train-da',
epochs = 5,
learning_rate = 1e-6,
callbacks=[
EvaluationCallback(
query_data='tll-test-query-da',
index_data='tll-test-index-da'
),
WandBLogger(),
]
)
# stream the logs, or use run.logs() to get logs
for entry in run.stream_logs():
print(entry)
You can find the Weights & Biases entry in the logs, copy the link of View run at:
wandb: Currently logged in as: anony-mouse-279369. Use wandb login --relogin to force relogin
wandb: Run wandb offline to turn off syncing. |
# Arbitrary Number of Stencil Points
The standard finite difference implementations of derivative pricing algorithms based on partial differential equations have a spatial order of convergence of two. Reason is that these implementations are using a three point central stencil for the first and second order derivatives. The three point stencil leads to a tridiagonal matrix. Such linear systems can be solved efficiently with help of the Thomas algorithm.
Higher order of spatial accuracy relies on stencils with more points. The corresponding linear systems can no longer be solved by the Thomas algorithm but by the BiCGStab iterative solver with the classical three point stencil as a very efficient preconditioner. The calculation algorithm for the coefficients of larger stencils on arbitrary grids is outlined in [1].
Before using higher order stencils one should first make sure, that the two standard error reduction techniques are in place, namely adaptive grid refinement around important points [2] and cell averaging around special points of the payoff at maturity or – equally effective for vanilla options – put the strike in the middle between two grid points. Let’s focus on the Black-Scholes-Merton PDE
$\displaystyle \frac{\partial V}{\partial t} + \frac{1}{2}\sigma^2\frac{\partial^2 V}{\partial x^2} + \left(r-q-\frac{\sigma^2}{2}\right)\frac{\partial V}{\partial x} -rV = 0 \ \wedge \ x= \ln S$
$\displaystyle \frac{\partial u}{\partial \tau}=\frac{1}{2}\sigma^2\frac{\partial^2 u}{\partial y^2} \ \wedge \ y = x + \left(r-q-\frac{1}{2}\sigma^2\right)\tau \ \wedge \ t=T-\tau \ \wedge \ u=e^{r\tau}V$
to demonstrate the convergence improvements. The spatial pricing error is defined as the RMSE for a set of benchmark options. In this example the benchmark portfolio consists of OTM call or put options with strikes
$k\in \{50, 75, 90, 100, 110, 125, 150, 200\}$.
The other parameters in this example are
$S_0=100, r=5\%, q=2.5\%, \sigma=20\%, T=1$.
The Crank-Nicolson scheme with “more than enough” time steps was used to integrate the PDE in time direction such that only the spatial error remains.
As can be seen in the diagram above the spatial order of convergence increases from second order to fourth order when moving from the standard three point to the five point stencil. On the other hand solving the resulting linear systems takes longer now. All in all only if the target RMSE is below $10^{-5}$, the five point stencil will be faster than the standard three point discretization.
The diagram below shoes the effective combination of a five point stencil and the Richardson extrapolation.
Diagrams are based on the test cases testHigerOrderBSOptionPricing and
testHigerOrderAndRichardsonExtrapolationg in the PR #483.
[1] B. Fornberg, [1988], Generation of Finite Difference Formulas on Arbitrarily Spaced Grids.
[2] Tavella, D. and C.Randall [2000], Pricing Financial Instruments The Finite Dierence Method, Wiley Series In Financial Engineering, John Wiley & Sons, New York |
# Sound power level
34,200pages on
this wiki
Sound measurements
Sound pressure p
Sound pressure level (SPL)
Particle velocity v
Particle velocity level (SVL)
(Sound velocity level)
Particle displacement ξ
Sound intensity I
Sound intensity level (SIL)
Sound power Pac
Sound power level (SWL)
Sound energy density E
Sound energy flux q
Acoustic impedance Z
Speed of sound c
Sound power level or acoustic power level is a logarithmic measure of the sound power in comparison to a specified reference level.
The measure of a ratio of two sound powers is [1] [2]
$L_\mathrm{W}=10\, \log_{10}\left(\frac{W_1}{W_0}\right)\ \mathrm{dB}$
where W1 and W0 are the powers.
The sound power level is given the symbol Lw or SWL and is measured in "dBW", which stands for decibel with the suffix for watts. Decibels are dimensionless.
SPL stands for sound pressure level, and is not the same thing. If an amount of sound power at a particular frequency produces a particular sound pressure level x, the same amount of power at half the frequency will produce twice the pressure level.
If W0 is the standard reference sound power, where
$W_0=10^{-12}\ \mathrm{W}$
(W = watt), then instead of "dB", dB SWL is used. (SWL = sound power level).
## Table: Sound power level and sound power of some sound sources Edit
Situation
and
sound source
sound power
Pac
watts
sound power
level Lw
dB re 10-12 W
Rocket engine 1,000,000 W 180 dB
Turbojet engine 10,000 W 160 dB
Siren 1,000 W 150 dB
Heavy truck engine or
loudspeaker rock concert
100 W 140 dB
Machine gun 10 W 130 dB
Jackhammer 1 W 120 dB
Excavator, trumpet 0.3 W 115 dB
Chain saw 0.1 W 110 dB
Loud speech,
vivid children
0.001 W 90 dB
Usual talking,
Typewriter
10−5 W 70 dB
Refrigerator 10−7 W 50 dB
(Auditory threshold) 10-12 W 0 dB
The Trumpet and excavator both have the same sound power of 0.3 watts, but may be judged psychoacoustically to be different levels. As noise is unwanted sound the trumpet can be perceived to be acceptable when listened to as music but at the same sound power level may be perceived to be noisy if one is trying to sleep.
One of the advantages of expressing the noise level of a source in terms of its power level is that one does not have to note any distance from the source. A noise sound pressure level, say, 85 dB-A is meaningless unless one also notes the distance from the source where the measurement was made.
### SWL in audio equipment Edit
Most audio manufacturers use SWL to describe the efficiency of their speakers. The most common means is measuring the sound power level from the speaker with the measuring device placed directly in front of and one meter away from the source. Then a particular sound (usually white noise or pink noise) is played through the source at a particular intensity so that the source is consuming one watt of power. The SWL is then measured and the product labeled, something like "SWL: 93 dB 1 W/1 m". This measurement can also be represented as a strict efficiency ratio of audio output (sound power) to electrical input (electrical power), but this is far less common. This method of rating speakers using SWL is often deceiving because most speakers produce very different SWLs at different frequencies of sound, often varying as much as ±10 dB throughout the speaker's usable frequency range (it generally varies less in higher quality speakers). The SWL quoted by the manufacturer is often an average over a particular range. |
# Open pipe and relation between pressure and flow rate
If a pipe (of unknown/arbitrary length) with cross section area $$A$$ and with a continuous supply of a simple fluid with a known pressure $$p$$ at the opening to the atmosphere, which has a pressure of $$p_a$$, what would be the rate of flow out of the pipe?
I have looked but not found an answer anywhere, but apologies if this seems trivial or seems to be a duplicate of another question.
Poiseuille's Law,
$$Flow=\dfrac{π\cdot r^4 \cdot (P-Po) }{ 8\cdot η\cdot L} cm^3/s$$ And in your case assuming you have a Pipe with the area $$Acm^2$$,
$$Flow= A\dfrac{r^2 \cdot (P-Po) }{ 8\cdot η\cdot L} cm^3/s$$
-P = pressure at the entrance, Bar
-P0 = atmosphere pressure, Bar
-eta = viscosity at dyne second/cm2 for water at 20c it is 0.01
-L = length cm.
• @Kaman. Thanks for your answer. However what will $L$ be the length of? The pipe length is of unknown length before the opening. The only thing known is the pressure at the end (opening). Apr 22 '19 at 23:07
• I will edit my answer when I get home. You need to plug in the resistance and head loss. Apr 23 '19 at 0:21
If you don't know the length L, then you'll have to disregard head losses. Then you can simply apply the Bernoulli equation:
$$p + \rho *(c^2/2) + \rho*g*z = constant$$
$$p$$ is the pressure, $$\rho$$ the density, $$c$$ the speed, $$g$$ the gravity, $$z$$ the height.
Apply this equation in the entry and in the exit and clear $$c^2$$. After that, multiply $$c_2$$ by $$A_2$$ and you'll get the flow rate.
Sorry for the wrong formatting, I still don't know how to format equations properly.
• Sorted the formatting for you. Apr 23 '19 at 7:58
• How did you do it?
– user20096
Apr 23 '19 at 19:00
• Ah, the dollar symbol, thank you.
– user20096
Apr 23 '19 at 19:01 |
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# On the analytic integrability of the 5–dimensional Lorenz system for the gravity–wave activity
## Resumen
For the 5-dimensional Lorenz system
dU/dT = −V W + b V Z,
dV /dT = UW − b UZ,
dW/dT = −UV,
dX/dT = −Z,
dZ/dT = bUV + X
(with ∈ R a parameter), describing coupled Rosby and gravity waves, we prove that it has at most three functionally independent global analytic first integrals and exactly three functionally independent global analytic first integrals when b = 0. In this last case the system is completely integrable with an additional functionally independent first integral which is not globally analytic.
Autores: Llibre, J., Saghin, R., Zhang, X.
Journal: Proceedings of the american mathematical society
Journal Volume: 142
Journal Issue: 2
Journal Page: 531–537
Tipo de publicación: ISI
Fecha de publicación: 2014
Topics: Analytic first integral, 5–dimensional Lorenz system
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SERVING THE QUANTITATIVE FINANCE COMMUNITY
ISayMoo
Topic Author
Posts: 672
Joined: September 30th, 2015, 8:30 pm
### HFT getting faster
Traden4Alpha
Posts: 23951
Joined: September 20th, 2002, 8:30 pm
### Re: HFT getting faster
Interesting!
But getting high bandwidth out of shortwave would be quite a challenge and need either extremely high SNR (high power and higher gain antennas) or a wide slot in the spectrum. The latency of any message is the time-of-flight plus duration of the message (bits/baud).
ISayMoo
Topic Author
Posts: 672
Joined: September 30th, 2015, 8:30 pm
### Re: HFT getting faster
They must be sending very simple messages on this, e.g. "S&P 500 moved up by more than 0.1%". You don't need to be fancy if you're 10ms ahead of everyone else.
Traden4Alpha
Posts: 23951
Joined: September 20th, 2002, 8:30 pm
### Re: HFT getting faster
ISayMoo wrote:
They must be sending very simple messages on this, e.g. "S&P 500 moved up by more than 0.1%". You don't need to be fancy if you're 10ms ahead of everyone else.
At the typical speeds of shortwave data systems, that "simple message" of 34 characters encoded in 6 bits+ 1 bit parity would take almost 800 msec to arrive.
ISayMoo
Topic Author
Posts: 672
Joined: September 30th, 2015, 8:30 pm
### Re: HFT getting faster
Dear lord, they won't encode it like that.
Traden4Alpha
Posts: 23951
Joined: September 20th, 2002, 8:30 pm
### Re: HFT getting faster
No doubt it's tightly compressed in the most efficient way possible. And yet the maximum baud rate for shortwave data seems to be on the order of 300 baud. That's 3 msec per bit.
ISayMoo
Topic Author
Posts: 672
Joined: September 30th, 2015, 8:30 pm
### Re: HFT getting faster
They have 10ms to play with.
ISayMoo
Topic Author
Posts: 672
Joined: September 30th, 2015, 8:30 pm
### Re: HFT getting faster
Anyway, where did you get you limit from? Remember that they are not broadcasting, it's directional communication (Chicago - London).
Traden4Alpha
Posts: 23951
Joined: September 20th, 2002, 8:30 pm
### Re: HFT getting faster
ISayMoo wrote:
Anyway, where did you get you limit from? Remember that they are not broadcasting, it's directional communication (Chicago - London).
From a number of different sources online that talk about creating digital data communications (packet radio, RTTY, etc.) at various wavelengths. Shortwave seems limited to about 300 bps because the properties of the atmospheric medium suck (especially during the day). The problem is known as group delay and is caused by the ionosphere's reflection of the signal being extremely frequency sensitive. Attempts to send wide-band on shortwave are distorted by this. It's VHF and UHF that can support much higher bandwidths but they are line-of-sight.
Alan
Posts: 9369
Joined: December 19th, 2001, 4:01 am
Location: California
Contact:
### Re: HFT getting faster
I wonder if all this relatively small scale stuff shows that HFT trading is just not that lucrative. For example, if you really wanted trans-atlantic microwave, you could presumably create a network of, say 120 ships spaced 25 miles or whatever. Say $120 million up-front for the ships, another$100 million/yr for crews, maintenance, and microwave. Doesn't seem that much if the profits were really there. Apple could spend two days of profits and do that ...
ISayMoo
Topic Author
Posts: 672
Joined: September 30th, 2015, 8:30 pm
### Re: HFT getting faster
Traden4Alpha wrote:
ISayMoo wrote:
Anyway, where did you get you limit from? Remember that they are not broadcasting, it's directional communication (Chicago - London).
From a number of different sources online that talk about creating digital data communications (packet radio, RTTY, etc.) at various wavelengths. Shortwave seems limited to about 300 bps because the properties of the atmospheric medium suck (especially during the day). The problem is known as group delay and is caused by the ionosphere's reflection of the signal being extremely frequency sensitive. Attempts to send wide-band on shortwave are distorted by this. It's VHF and UHF that can support much higher bandwidths but they are line-of-sight.
So do those limits apply equally to directional shortwave radio as much as to broadcast shortwave?
ISayMoo
Topic Author
Posts: 672
Joined: September 30th, 2015, 8:30 pm
### Re: HFT getting faster
Alan wrote:
I wonder if all this relatively small scale stuff shows that HFT trading is just not that lucrative. For example, if you really wanted trans-atlantic microwave, you could presumably create a network of, say 120 ships spaced 25 miles or whatever. Say $120 million up-front for the ships, another$100 million/yr for crews, maintenance, and microwave. Doesn't seem that much if the profits were really there. Apple could spend two days of profits and do that ...
1. too accident-prone
2. too visible
3. too tedious to maintain for a small company
But you're right in general, HFT profits are capped.
Traden4Alpha
Posts: 23951
Joined: September 20th, 2002, 8:30 pm
### Re: HFT getting faster
ISayMoo wrote:
Traden4Alpha wrote:
ISayMoo wrote:
Anyway, where did you get you limit from? Remember that they are not broadcasting, it's directional communication (Chicago - London).
From a number of different sources online that talk about creating digital data communications (packet radio, RTTY, etc.) at various wavelengths. Shortwave seems limited to about 300 bps because the properties of the atmospheric medium suck (especially during the day). The problem is known as group delay and is caused by the ionosphere's reflection of the signal being extremely frequency sensitive. Attempts to send wide-band on shortwave are distorted by this. It's VHF and UHF that can support much higher bandwidths but they are line-of-sight.
So do those limits apply equally to directional shortwave radio as much as to broadcast shortwave?
Yes. The sorts of people doing shortwave data do use directional antennas and sophisticated equipment to improve the gain. Shortwave radio enthusiasts both compete on long-distance transmissions (called DXing) and work with disaster relief and civil defense authorities to provide emergency communications. It's a rich person's hobby that attracts technically-minded people. It's also in military use (NATO RTTY operates at only 75 or 100 baud). If high-speed data on shortwave were possible, these hackers or the military would have created it.
rmax
Posts: 5897
Joined: December 8th, 2005, 9:31 am
### Re: HFT getting faster
I'll ask my cousin. He does research in high bandwidth low frequency by using a virtual wave.
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# Electromagnetism: Turning effect of coil
1. Mar 10, 2007
### lingling
1. The problem statement, all variables and given/known data
This is a question about turning effect on a current-carrying coil lying between the poles of a magnet.
Please refer to the following link:
http://img11.picsplace.to/img.php?file=img10/22/N1_000.gif [Broken]
On the textbook, it is stated the turning effect on the coil can be increased by increasing the area of the coil (inside the magetic field).
I understand the force would increase if AB and CD increases.
But I'm not sure whether the turning effect will increase when BC increases. :uhh:
Can anyone tell me?
Thank in advance.
2. Relevant equations
3. The attempt at a solution
1. The problem statement, all variables and given/known data
2. Relevant equations
3. The attempt at a solution
Last edited by a moderator: Apr 22, 2017 at 4:15 PM
2. Mar 10, 2007
### dobry_den
The force acting on a current-carrying conductor could be calculated with the following formula:
$$F = BIl\sin\alpha$$
where B is magnetic induction, I is current, l is length of the conductor and <alpha> is the angle between the conductor and the magnetic field (the vector B). The angle between the conductor BC and the magnetic field is 0<pi> - the answer is thus apparent.
Last edited: Mar 10, 2007
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0
Research Papers
# The Efficiencies of Internal Reforming Molten Carbonate Fuel Cell Fueled by Natural Gas and Synthetic Natural Gas From CoalOPEN ACCESS
[+] Author and Article Information
Hai-Kyung Seo
Mem. ASME
Clean Power Generation Laboratory,
KEPCO Research Institute,
105, Munji-Ro, Yuseong-Gu,
Daejeon 34056, South Korea
e-mail: [email protected]
Won-shik Park
Mem. ASME
Clean Power Generation Laboratory,
KEPCO Research Institute,
105, Munji-Ro, Yuseong-Gu,
Daejeon 34056, South Korea
e-mail: [email protected]
Hee Chun Lim
Mem. ASME
Clean Power Generation Laboratory,
KEPCO Research Institute,
105, Munji-Ro, Yuseong-Gu,
Daejeon 34056, South Korea
e-mail: [email protected]
1Corresponding author.
Manuscript received January 3, 2016; final manuscript received March 25, 2016; published online April 26, 2016. Assoc. Editor: Kevin Huang.
J. Electrochem. En. Conv. Stor. 13(1), 011005 (Apr 26, 2016) (10 pages) Paper No: JEECS-16-1002; doi: 10.1115/1.4033255 History: Received January 03, 2016; Revised March 25, 2016
## Abstract
When synthetic natural gas (SNG) is produced from coal and used as a fuel in the internal reforming molten carbonate fuel cell (ir-MCFC), electric efficiency can be no greater than 31%. This is because there are several exothermic reactions in the processes of converting coal to SNG, so that a maximum 64% of coal's energy is converted into SNG energy. This results in a lower efficiency than when the ir-MCFC with the electric efficiency of 48% is fueled by natural gas (NG). To increase electric efficiency with SNG, it is necessary to recover the exothermic heat generated from the processes of converting coal to SNG as steam, which can then be used in a steam turbine. When steam produced in the gasification, water gas shift (WGS), and methanation processes is used in a steam turbine, the gross electric efficiency will become 41%. If the steam and auxiliary power for CO2 capture process is consumed more, the net efficiency will be 27%. Use of additional steam from the exhausted gas of fuel cell can increase the total net efficiency to 49%.
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## Introduction
Fuel cells have more advantages than conventional power plants: high efficiency even in small size, environmental friendly impact, easy to site, quieter operation. These attracted points lead fuel cells to distributed power generation and many countries to fund the development of fuel cell-based power generation systems [1]. Among types of fuel cells, molten carbonate fuel cell (MCFC) is one of the most advanced candidates as a large scale power plant. Also, the exhaust heat it produces can be used for cogeneration applications such as high-pressure steam, district heating, and air conditioning. The direct fuel cell developed by fuel cell energy (FCE) in the U.S. is one of the MCFC systems which can readily and directly use fuels such as NG and waste water treatment gas. POSCO [2] of South Korea, one of the top steel companies in the world and already a strategic partner of FCE, has been producing MCFC systems since 2007. The largest capacity MCFC system, at 58.8 MW, has been in operation in Hwaseong of South Korea since January 2014.
In most ir-MCFCs, NG is usually used as a fuel. NG is a relatively clean fuel which affects the environment less than other carbon fuels such as coal, and its utilization is gradually increasing. However, not many countries in the world have underground deposits of NG, or NG fields. So, there has been great demand for technologies that can produce SNG, especially from coal, and this has been the focus of research by countries seeking a substitute for NG.
As coal is converted to SNG, a heat or energy loss occurs in the process, and thus the total thermal output of the produced SNG is smaller than that of the original coal, even though the quality of SNG is nearly similar to NG.
In this paper, SNG from coal is used as fuel in the ir-MCFC, and its calculated efficiency is compared with NG fuel. When NG was used in the ir-MCFC, gross electric efficiency reached 48.73%. On the other hand, when the coal was used in the ir-MCFC via gasification, WGS and methanation processes, the efficiency was reduced to 29.13% due to energy losses to the atmosphere, such as exothermic conversion.
In the gasification process, about 80% of coal thermal input is converted into the synthesis gas [3,4]. Then, through the WGS and methanation processes, the synthesis gas is altered to SNG, which also retains around 80% of the thermal energy of the synthesis gas, because 61–63% of conversion efficiencies are shown in systems converting to SNG from coal [5]. Ultimately the electric efficiency of an ir-MCFC fueled by SNG from coal cannot exceed merely 31%. Display Formula
(1)
In making the comparison between SNG and NG, this study also considered the increase in efficiency of gasification process that could be obtained by recovering heat produced from the exothermic conversion as steam which is used in a steam turbine to produce additional electricity.
Some papers show the systems integrated with MCFC. Among others, in the paper of Carapellucci et al. [6], the integrated system with natural gas combined cycle (NGCC) power plant and MCFC was considered. Because fossil-fuels produce CO2, even though NG fuel is converted to less CO2 than coal fuel, they said, CO2 emission would be reduced when NGCC exhaust gas was used at the cathode side of MCFC. But in the above paper, coal gasification was not treated. In the paper of Morita et al. [7], there was the comparison of the system with biomass-gasification/gas turbine and the one with biomass-gasification/MCFC which showed that when MCFC cathode exhaust gas was used at expander, the additional electricity was produced. But the heat recovery from gasification block and CO2 capture were not considered. In the paper of Toonssen et al. [8], the systems integrated with biomass gasification and solid oxide fuel cell/gas turbine (SOFC/GT) hybrid systems were studied through using cycle-tempo program [9]. In the systems, the gases synthesized from biomass gasification were used in anode inlet of SOFC after gas cleaning and then the anode off gas and cathode off gas were used in the gas turbine. As a result of some configurations, the electric efficiencies were compared. The synthesis gases from the gasification were directly used in the anode inlet of SOFC without converting into SNG from synthesis gas. Then the electric efficiencies produced from just gas stream were estimated as 46–49.9%. These efficiencies were higher than our results, because the exothermic energy from converting synthesis gas to SNG was not lost and the additional energy for CO2 capture was not also considered.
In our paper, the electric efficiency of system integrated with a gasification process converting coal to SNG and an MCFC was studied as a new trial. This study was aimed that the feasibility of this integrated system would be comparably verified in comparison with the electric efficiency of conventional thermal power plant.
## The Simulation of the ir-MCFC System Fueled by NG
In this paper, the cycle-tempo program was used for the calculation of heat and mass balances. A fuel cell and steam turbine can be easily combined and simulated by cycle-tempo, which can calculate the stack performance which shows the variation of the output voltage according to the operation conditions such as electrical load, input gas rates, and temperature in several types of fuel cells such as MCFC stack integrated with indirect internal reforming, MCFC stack with direct internal reforming, MCFC stack integrated with external reformer, and other fuel cells [711] as well as thermodynamic evaluation of energy conversion system [11]. And there are some papers using cycle-tempo program on the study of stack reaction of ir-MCFC fuel cell [6].
Figure 1 shows the simulation of the ir-MCFC system fueled by NG. In Fig. 1, apparatus number 1 is the stack of the ir-MCFC having indirect internal reforming and “A” indicates the anode and “C” the cathode. For the basic model of chemical reaction and voltage variation according to the reactions, the papers of Morita et al. [7,10] could be referred. Through the cycle-tempo program, the NG (apparatus number 7) and steam (pipe number 14) are heated by the heat from cathode-off gas, respectively, and then mixed. After that, the mixed gas is heated to 580 °C by the heat from catalytic combustor and then introduced into the anode inlet. Air is first heated by the cathode off-gas and then by the catalytic combustor (apparatus number 9) and is then supplied into the cathode inlet at a temperature of 580 °C. Water is supplied through apparatus number 6, heated by the heat of the cathode off-gas, and then split into the streams of pipe numbers 14 and 15. Stream number 14 is ultimately supplied into the anode inlet at the ratio of steam to NG of 2.5. Even though the fuel cell reaction proceeds and steam is being produced, steam needs to be supplied abundantly. This is because carbon deposition can occur when CH4 rich gas is supplied in high temperature state in the absence of steam [12] into the inlet area of the stack of the ir-MCFC. NG of 1.621 kg/s with the lower heating value of 708.3 kJ/mol (LHV value of the pipe number 11 of Table 1) and the average mole mass of 18.64 kg/kmol, which makes the total thermal input of NG 61,596.66 kW, is supplied through apparatus number 7 into the anode inlet. The pressure, temperature, enthalpy, and the amount of each stream in the cross legend is shown at the tip of each pipe in Fig. 1.
Under these conditions, the fuel cell produced 30,014.65 kW of electricity, which corresponds to 0.4873 of thermal input of NG, at gross electric efficiency of 48.73%. The air blower of the unit consumed 328.99 kW of electricity as auxiliary power. Consequently, the net electric efficiency was 48.19%. Display Formula
(2)
Pipe number 15 carries additional steam which can be used to recover excess heat from the fuel cell system. The additional steam is produced at 255 bar and 452.64 °C with the thermal output of 59,889.96 kW. When this additional steam is used in a steam turbine having an electric efficiency of 28.71%, the thermal energy of steam, 59,889.96 kWth can be converted into 17,194.41 kWe of electricity. Then the total efficiency can be presented as follows: Display Formula
(3)
###### The Stack of ir-MCFC.
In this paper, the stack (apparatus number 1) is simulated as an indirect internal reforming type MCFC [13]. The voltage of each cell is 0.747 V and the total area of the cells stacked is 26,915.15 m2. The utilization ratio of the fuel is 0.7, that of O2 is 0.4192 and that of CO2 is 0.6989 as shown in Fig. 1. At the stack, the following reactions occur: Display Formula
(4)$anode side: CH4+2H2O → CO2+4H2$
Display Formula
(5)$4H2+ CO2+4CO32−→4H2O+5CO2+8e−$
Display Formula
(6)$cathode side:4CO2+2O2+8e−→4CO32−$
The reforming reaction (4) results from the following reactions: Display Formula
(7)$anode side: CH4+ H2O → CO+3H2, ΔH°=205.81 kJ/mol$
Display Formula
(8)$CO+ H2O → CO2+ H2, ΔH°=−41.17 kJ/mol$
Since reaction (7) is a severely endothermic reaction and reaction (8) is a weak exothermic one, then the total reaction (4) is a slightly strong endothermic one with an enthalpy change of 164.64 kJ/mol.
The total reaction for the anode and cathode sides is as follows: Display Formula
(9)$H2+1/2O2→ H2O(g), ΔH°=−241.82 kJ/mol$
The summed reaction of (5) and (6) above is four times that of reaction (9). Then, the water formation enthalpy is . Around 60% among this energy is consumed for conversion into electricity theoretically [14]. And then the residual energy is exhausted into heat. With internal reforming, the reaction heat required by the endothermic reforming reaction is supplied by this residual exhausted heat. In this case, the net heat produced by the stack is 2.5–3 times lower than that of external reforming, thus strongly reducing the cooling requirements for the stack [15]. Even though the heat from the stack is lower than that of external reforming stack, the excess heat should be removed to avoid a problem related with the system's materials, which results in weak durability at high temperature.
The exothermic heat is removed by the excess air. This is the reason the utilization ratio of O2 is so low, at 0.4192. This value means that just 41.92% among the introduced oxygen is used in the reaction of fuel cell. The rest of oxygen and nitrogen are used in cooling the stack of fuel cell. Because the mole fraction of O2 among the air is around 0.21, if the oxygen is used at just 41.92%, the used oxygen among the air is 8.8% and the rest of gas remain at the mole percentage of 91.2%, which is used just in cooling without participating in the electrochemical reaction. Then the outlet temperature of the stack can be reduced to 669.45 °C.
###### The Catalytic Combustor.
Since the utilization ratio of fuel is 0.7, remaining fuel, that is, 0.3 is exhausted into the outlet of anode. This residual fuel can be used to increase overall efficiency by combustion in the catalytic combustor along with the excess air.
The compositions of the anode and cathode outlets shown in the pipe numbers 5 and 6 of Fig. 1 appear in Table 1. The composition of the anode outlet is shown as CO2 42.17%, H2O 46.18%, CH4 1.32%, CO 2.33%, H2 6.13%, and N2 1.86%. In this stream, CH4, CO, and H2 are still fuel and these gases can be combusted in the catalytic combustor. The levels of CO2 and H2O gases in the anode outlet are rich, as shown in reaction (5). Because the CO2 gas is necessary in the cathode side, as shown in reaction (6), this anode outlet gas can be recycled to the cathode inlet side via the catalytic combustor.
The composition of the cathode inlet, shown as pipe number 19 in Table 1, is as follows: N2 54.25%, O2 12.21%, H2O 18.25%, Ar 0.64%, and CO2 14.65%. The composition of the cathode outlet is N2 64.10%, O2 8.38%, H2O 21.56%, Ar 0.75%, and CO2 5.21%, shown as pipe number 6 in Table 1. The amount of cathode gas gets to be reduced as shown in reaction (6). The N2, H2O, and Ar gases are not participated in reaction of cathode (6). As amounts of N2, H2O, and Ar gases do not change at the cathode inlet and outlet due to their no reaction, increases of mole fractions of these gases in the cathode outlet mean that the volume of the outlet gas was reduced.
As the residual fuel from the anode off-gas burns in the catalytic combustor, the temperature of the outlet gas of the combustor becomes 653.19 °C. This temperature is too high to be introduced into the cathode inlet. So, this outlet stream of the combustor is used for heating the anode inlet gas and producing additional steam, that is, apparatus number 17 of Fig. 1, until the outlet gas of the combustor decreases to 580 °C, which is the acceptable temperature for the cathode inlet.
## The Process of Converting Coal to SNG for Use in the ir-MCFC
###### The Process of Converting Coal to SNG Without Heat Recovery.
The synthetic gas produced from the coal gasifier needs to be changed to SNG, which is a CH4 rich gas, because the ir-MCFC, manufactured by POSCO of Korea, requires a CH4 composition of over 60%. Therefore, the gasification process, including ash removal and desulfurizer, should be designed to include WGS and methanation processes for the quality of SNG.
As a result of the gasification process, the initial gas product has the ratio of 0.8 of the coal thermal input. That synthesis gas from the gasification process is then converted to SNG with a thermal energy of 0.8 of the synthesis gas. Ultimately, the thermal output of SNG has a maximum value of 0.64 of the coal thermal input. As a consequence, when SNG is used in the fuel cell which has a demonstrated electric efficiency of 48.73% using NG, its total efficiency cannot reach over 31%, as mentioned above.
Using the cycle-tempo program, the process of converting coal to SNG can be simulated, as illustrated in Fig. 2. The coal used in the simulation was the Adaro coal from Indonesia, which composition includes 60.08 wt. % of C, 0.09 wt. % of Cl, 4.29 wt. % of H, 12.6 wt. % of H2O, 1.31 wt. % of N, 16.39 wt. % of O, 0.23 wt. % of S, and 5.01 wt. % of ash. These values were changed into mole basis ratio, as indicated in pipe number 1 of Table 2. A calorie basis of 22,993.25 kJ/kg (LHV basis) was used for the simulation. The thermal input energy of the coal is 102,089.81 kW as shown at apparatus 2 in Fig. 2.
In this gasifier, the weight ratio of oxygen to coal is 0.7. Steam (apparatuses 5 and 6 passing the apparatus 1 in Fig. 2) circulating in the cooling water structure surrounding the gasifier (apparatus 1) is introduced to recover the heat produced in the gasifier and lower the temperature of the outlet gas leaving the gasifier to around 1100 °C. As the ratio of oxygen to coal is increased, the temperature of the outlet gas leaving the gasifier becomes higher [3]. Then, more water is needed to match the temperature of the outlet gas of the gasifier to 1100 °C. Therefore, the amount of steam produced by the cooling water structure is dependent on the ratio of oxygen to coal and the setting temperature of the outlet gas of the gasifier.
In the syngas cooler (apparatus number 3), heat was set to be recovered until the temperature of the synthesis gas reaches 400 °C. Then this ash remover was simulated to remove up to 100% of the ash. The composition of the synthesis gas is as follows: H2 27.85%, H2O 7.45%, N2 1.96%, CO 58.74%, CO2 3.87%, COS 0.01%, HCl 0.03%, and H2S 0.08%, as shown in pipe number 7 in Table 2. This composition is not suitable for the following methanation reaction (10) since it contains more CO than H2: Display Formula
(10)$CO+3H2→ CH4+ H2O, ΔH°=−205.81 kJ/mol$
In this case, the WGS reaction shown in reaction (8) is necessary. Here, the sour WGS reaction including a sulfur resistant sour WGS catalyst [16] is used for the simulation. In this process, the following reaction also occurs in the WGS reactor: Display Formula
(11)$COS+ H2O → H2S+CO, ΔH°=−33.8 kJ/mol$
Steam needs to be introduced into the WGS reactor until the ratio of CO to H2 is around 1/3. After the WGS reaction, over 30% CO2 gas is produced. It is necessary to remove this rich CO2 and a little H2S through a S and CO2 capture process like the selexol process [17]. In this paper, up to 90% of the CO2 gas was simulated to be removed and 100% of H2S and HCl, respectively. If the CO2 were fully removed, it might result in carbon deposition in the Ni catalyst layer of the anode side, caused by the following Boudourd reaction [18]: Display Formula
(12)$2CO → C+ CO2$
Next, reaction (10), that is, the methanation reaction occurs in the methanation process. As this reaction is a severe exothermic reaction, the temperature of the outlet gas after the reactor can reach 700 °C or more. As the reaction is proceeding continuously, the reverse reaction of methanation is more dominant due to the change to high temperature gradually. Then methane cannot be produced richly in the state of high temperature, because the yield of methane is inversely proportional to the increase of temperature of the reactor. When the temperature of the reactor is lower, the amount of methane produced grows larger.
It is also necessary to keep the temperature below 700 °C because the materials of the methanation reactor and catalyst cannot endure durably over 700 °C. Therefore, it is necessary to cool the gas after the methanation reaction. To accomplish this, in the Tremp process [19] of Haldor Topsoe, three or four methanation reactors were used in sequence, recycling, and cooling the outlet gas of the first reactor and operating each following reactor at a lower temperature step by step. In this paper, two reactors were used and 70% of the outlet gas of the first reactor was recycled into the first reactor via recycling compressor and cooler, while the other 30% went to the second reactor. The temperature of the produced SNG was cooled to 300 °C. The composition of SNG was the value shown in the pipe number 2 of Table 2, which indicates compositions according to pipes from Fig. 2. The thermal output of this produced SNG from Fig. 2 was 62,844.07 kW, which was calculated as follows: Display Formula
(13)
Here, LHV is lower heating value found in Table 2, which is the calorie value of produced SNG. The Avg. mole mass means average mass value per mole of produced SNG. Then, SNG mass appears in the legend of mass flow ($Φm)$ at the tip of pipe number 2 in Fig. 2.
The conversion efficiency or cold gas efficiency of the coal to SNG process was as follows: Display Formula
(14)
This value depends on the ratio of oxygen to coal. When the ratio of O2/coal is 0.64, the conversion efficiency will be 63.46%. As the ratio of O2/coal is lower, the amount of CO and H2 becomes larger and results in higher conversion efficiency.
As the heat recovery is performed in the gasification process, the final energy value of SNG is a little changed due to variation of heat taken by the steam as shown in Figs. 3 and 4. The compositions of each pipe produced from Figs. 3 and 4 were shown in Table 3.
The ir-MCFC system fueled by SNG is seen in Fig. 5 and its electric efficiency when fueled by SNG with 62,670.93 kW which is the thermal energy of SNG produced in Fig. 4 is as follows:
As the SNG is in a high-pressure state, it should be expanded to the operating pressure of the ir-MCFC, that is, nearly atmospheric pressure. Here, it produces a little power. However, some electricity is consumed in the air blower. Then the net electric efficiency is Display Formula
(16)
The compositions of each pipe produced from Fig. 5 were shown in Table 4. For more understanding of the systems of Figs. 1 and 5, the comparison was displayed in Table 5. For comparison of Figs. 24, Table 6 was prepared.
###### The Process of Converting Coal to SNG Including Heat Recovery in WGS and Methanation Process.
When SNG from the coal synthesis gas is used instead of NG fuel in the ir-MCFC, its electric efficiency cannot exceed 31%, as mentioned above. Consequently, it is necessary that the heat from the exothermic reactors be recovered in order to produce additional electricity. In this step, the heat from the WGS reactor and methanation process is recovered as steam and then the steam is used in a steam turbine to produce additional electricity. The process is shown in Fig. 3. The heat is recovered as steam after the WGS reactor and at three points in the methanation process. The steam is converted into 4,865.15 kW of electricity. The gross electric efficiency is presented below: Display Formula
(17)
###### The Process of Converting Coal to SNG Including Heat Recovery in Gasification, WGS, and Methanation Process.
If the heat recovery in the gasification block is used for additional steam production, the steam turbine power will be enhanced. In the gasification block, the heat from the cooling water structure surrounding the gasifier and the syngas cooler after the gasifier can be recovered. The production of totally 11,316.24 kW electricity from the steam produced in the gasification, WGS, and methanation processes is shown in Fig. 4.
All the heat exchangers are used for heat recovery by cooling the streams. The composition of each stream can be referred to Table 3.
###### The ir-MCFC System Fueled by the SNG.
The SNG gas produced from the process of converting coal to SNG to fuel the ir-MCFC is shown in Fig. 5. Since the stream pressure of the conversion process of coal to SNG is around 27.6 bar, the pressure is reduced to the operating pressure of the ir-MCFC of 1.1 bar. The thermal energy of coal, 102,089.81 kW is converted into the thermal SNG of 62,670.93 kW. Table 4 shows the composition of each pipe of Fig. 5. The SNG gas is introduced through the pipe number 9 and 11.
Unlike fueling the ir-MCFC with NG, the SNG is introduced at a temperature of 181.76 °C, compared to the normal temperature, that is, 20 °C of NG. Therefore, heating the SNG with the exhausted cathode off-gas is not necessary. As a result, that excess heat can produce additional steam more. As shown in Fig. 5, the excess thermal steam, 79,472.05 kWth is produced through apparatus number 17. If the thermal steam is used in a steam turbine with an electric efficiency of 28.71%, the steam can produce 22,816.43 kWe of electricity. This power would be controlled from the amount of water introduced to the apparatus 6. If the amount of water is increased, the temperature of produced steam in apparatus 17 will be lowered, then it cannot be used in the steam turbine efficiently.
In the stack of the ir-MCFC, 30,050.69 kW of electricity is produced. The total electricity, summed with that (11,316.24 kW) of the steam turbine from the process of converting coal to SNG, is 41,366.93 kW, which corresponds to an electric efficiency of 40.52%. Display Formula
(18)
If an additional 22,816.43 kW of electricity can be produced from the exhausted gas of the ir-MCFC and added to the above, the result is as follows: Display Formula
(19)
###### The Reflection of the Result of the CO2 Capture in the Process of Coal to SNG.
Here, the utilization of heat and the power to compress CO2 in the CO2 capture process have not been considered. If then energy consumed in the CO2 capture process is considered, the net power output is reduced by the high auxiliary load of the CO2 compression and the need to introduce the extraction steam into the WGS reaction and the regeneration tower for CO2 absorbent. It is known that approximately 25% additional coal is necessary to obtain the same net power output as the system without CO2 capture in dry feeding type Shell gasification system [20]. Auxiliary power of 6.56% of coal energy is also necessary in the process of converting coal to SNG, including the air separation unit (ASU), gas cleaning, methanation, and so on [5]. Thus, the overall electric efficiency will be reduced after considering the consumption of superheated steam and the power of compression in the CO2 capture process and the auxiliary power of all other processes.
At first, the ratio of electricity production from the recovered heat of Fig. 4 is calculated to be Display Formula
(20)
If the total energy of consumption of heat for CO2 capture and CO2 compression power are applied at 25% of coal energy, the output of the steam turbine in Fig. 4 will be Display Formula
(21)
If the auxiliary power is considered, the result is Display Formula
(22)
If the additional steam in the ir-MCFC is utilized in the steam turbine, the result is Display Formula
(23)
This efficiency is comparable to that of the advanced thermal power plant based on coal.
## Conclusion
In this paper, the electric efficiency of the ir-MCFC fueled by NG was calculated. The net electric efficiency was 48.19% and when the heat from the exhausted gas of fuel cell is recovered as steam and the steam is used in a steam turbine, the net electric efficiency will be increased to 76.11%.
It should be noted that when SNG produced from coal synthesis gas is used to fuel the ir-MCFC, the net electric efficiency from coal is just 29.22%, because the thermal output of the SNG corresponds to 61.39% of thermal input of coal. As the processes of converting coal to SNG have lots of exothermic reactions, it is useful to recover that heat from the exothermic reactions to enhance overall efficiency. If the heat from the processes of WGS and methanation is recovered and used in the steam turbine, the gross electric efficiency will be increased up to 34.2%. When all the heat from the processes of gasification to methanation is recovered, the gross efficiency will become 40.5%. If the steam produced from the exhausted gas of fuel cell is also used in the steam turbine, the gross efficiency will be 62.87%.
In the CO2 capture process, however, additional energy consumption is required, which corresponds to 25% additional coal energy in the dry feeding gasification process. If auxiliary power is also considered, the reduction of the power corresponding to 6.56% of coal energy will take place. Then, the net electric efficiency will be 48.92% when including the recovery of heat from the exhausted gas of fuel cell. This efficiency is comparable to that of the advanced thermal power plant based on coal.
## Acknowledgements
When the efficiency of the system was being calculated, Mr. Theo Woudstra from Delft University of Technology contributed greatly to the elimination of errors, so the authors appreciate his kindness and technological support.
This paper is one of deliverables of the project of “Preparation of Conceptual Design of Pretreatment Process for Synthetic Gas Fuel Cell (SGFC),” which was solely supported by our company.
## Nomenclature
• Afc =
cell area, m2
• ASU =
air separation unit
• H =
enthalpy, kJ/kg
• HHV =
higher heating value, kJ/mol
• ir-MCFC =
internal reforming molten carbonate fuel cell
• LHV =
lower heating value, kJ/mol
• MW =
power unit, 106 W = 106 J/s
• NG =
natural gas
• p =
pressure, bar
• P =
power, kW
• Pel =
electrical power, kW
• Pel, AC =
AC power, kW
• SNG =
synthetic natural gas
• T =
temperature, °C
• Uf =
fuel utilization, %
• Uo =
oxidant utilization, %
• $UCO2$ =
CO2 utilization, %
• Vfc =
cell voltage, V
• WGS =
water gas sift reaction
• $Δ$ =
standard enthalpy change of reaction at 298 K
• ΦE, in =
energy input, kW
• Φm =
mass flow, kg/s
• ΦE =
energy loss, kW
## References
Brandon, N. , and Thompsett, D. , eds., 2005, Fuel Cells Compendium, Elsevier, New York.
McPhail, S. , Moreno, A. , and Bove, R. , “ International Status of Molten Carbonate Fuel Cell (MCFC) Technology, Report Ricerca Sistema Elettrico/2009/181, Accordo di Programma Ministero dello Sviluppo Economico—ENEA,” Last accessed Mar. 25, 2016,
Seo, H.-K. , Park, S. , Lee, J. , Kim, M. , Chung, S.-W. , Chung, J.-H. , and Kim, K. , 2011, “ Effect of Operating Factors in the Coal Gasification Reaction,” Korean J. Chem. Eng., 28(9), pp. 1851–1858.
Yun, Y. , and Yoo, Y. D. , 2001, “ Performance of a Pilot-Scale Gasifier for Indonesian Baiduri Coal,” Korean J. Chem. Eng., 18(5), pp. 679–685.
NETL, 2011, “Cost and Performance Baseline for Fossil Energy Plants Volume 2: Coal to Synthetic Natural Gas and Ammonia,” National Energy Technology Laboratory, Washington, DC, accessed Mar. 25, 2016,
Carapellucci, R. , Saia, R. , and Giordano, L. , 2014, “ Study of Gas-Steam Combined Cycle Power Plants Integrated With MCFC for Carbon Dioxide Capture,” Energy Procedia, 45, pp. 1155–1164.
Mirita, H. , Yoshiba, F. , Woudstra, N. , Hemmes, K. , and Spliethoff, H. , 2004, “ Feasibility Study of Wood Biomass Gasification/Molten Carbonate Fuel Cell Power System-Comparative Characterization of Fuel Cell and Gas Turbine Systems,” J. Power Sources, 138(1–2), pp. 31–40.
Toonssen, R. , Sallai, S. , Aravind, P. V. , Woudstra, N. , and Verkooijen, A. H. M. , 2011, “ Alternative System Design of Biomass Gasification SOFC/GT Hybrid Systems,” J. Hydrogen Energy, 36(16), pp. 10414–10425.
Asimptote, 2016, “cycle-tempo Documentation,” Delft, The Netherlands, accessed Mar. 25, 2016,
Morita, H. , Komoda, M. , Mugikura, Y. , Izaki, Y. , Watanabe, T. , Masuda, Y. , and Matsuyama, T. , 2002, “ Performance Analysis of Molten Carbonate Fuel Cell Using a Li/Na Electrolyte,” J. Power Sources, 112(2), pp. 509–518.
Woudstra, N. , van der Stelt, T. P. , and Hemmes, K. , 2006, “ The Thermodynamic Evaluation and Optimization of Fuel Cell Systems,” ASME J. Fuel Cell Sci. Technol., 3(2), pp. 155–164.
Ahmeda, S. , Aitani, A. , Rahman, F. , Al-Dawood, A. , and Al-Muhaish, F. , 2009, “ Decomposition of Hydrocarbon to Hydrogen and Carbon,” Appl. Catal. A, 359(1–2), pp. 1–24.
Katikaneni, S. , Yuh, C. , Abens, S. , and Farooque, M. , 2002, “ The Direct Carbonate Fuel Cell Technology: Advances in Multi-Fuel Processing and Internal Reforming,” Catal. Today, 77(1–2), pp. 99–106.
Breeze, P. , 2014, Power Generation Technologies, 2nd ed., Newnes, Oxford, UK.
Jansen, D. , and Mozaffarian, M. , 1997, “ Advanced Fuel Cell Energy Conversion Systems,” Energy Convers. Manage. 38(10–13), pp. 957–967.
Haldor Topsøe, 2009, “ Sulphur Resistant/Sour Water-Gas Shift Catalyst,” Haldor Topsøe A/S, Lyngby, Denmark, accessed Mar. 25, 2016,
UOP Honeywell, 2010, “UOP SelexolTM Technology for Acid Gas Removal,” UOP, Des Plaines, IL, accessed Mar. 25, 2016,
Selman, J. R. , Uchida, I. , Wendt, H. , Shores, D. A. , and Fuller, T. F. , eds., 1997, Carbonate Fuel Cell Technology IV, The Electrochemical Society, Pennington, NJ.
Holdor Topsøe, 2009, “ From Solid Fuels to Substitute Natural Gas (SNG) Using TREMP TM,” Haldor Topsøe A/S, Lyngby, Denmark, accessed Mar. 25, 2016,
NETL, 2013, “Cost and Performance Baseline for Fossil Energy Plants Volume 1: Bituminous Coal and Natural Gas to Electricity,” National Energy Technology Laboratory, Washington, DC, accessed Mar. 25, 2016,
View article in PDF format.
## References
Brandon, N. , and Thompsett, D. , eds., 2005, Fuel Cells Compendium, Elsevier, New York.
McPhail, S. , Moreno, A. , and Bove, R. , “ International Status of Molten Carbonate Fuel Cell (MCFC) Technology, Report Ricerca Sistema Elettrico/2009/181, Accordo di Programma Ministero dello Sviluppo Economico—ENEA,” Last accessed Mar. 25, 2016,
Seo, H.-K. , Park, S. , Lee, J. , Kim, M. , Chung, S.-W. , Chung, J.-H. , and Kim, K. , 2011, “ Effect of Operating Factors in the Coal Gasification Reaction,” Korean J. Chem. Eng., 28(9), pp. 1851–1858.
Yun, Y. , and Yoo, Y. D. , 2001, “ Performance of a Pilot-Scale Gasifier for Indonesian Baiduri Coal,” Korean J. Chem. Eng., 18(5), pp. 679–685.
NETL, 2011, “Cost and Performance Baseline for Fossil Energy Plants Volume 2: Coal to Synthetic Natural Gas and Ammonia,” National Energy Technology Laboratory, Washington, DC, accessed Mar. 25, 2016,
Carapellucci, R. , Saia, R. , and Giordano, L. , 2014, “ Study of Gas-Steam Combined Cycle Power Plants Integrated With MCFC for Carbon Dioxide Capture,” Energy Procedia, 45, pp. 1155–1164.
Mirita, H. , Yoshiba, F. , Woudstra, N. , Hemmes, K. , and Spliethoff, H. , 2004, “ Feasibility Study of Wood Biomass Gasification/Molten Carbonate Fuel Cell Power System-Comparative Characterization of Fuel Cell and Gas Turbine Systems,” J. Power Sources, 138(1–2), pp. 31–40.
Toonssen, R. , Sallai, S. , Aravind, P. V. , Woudstra, N. , and Verkooijen, A. H. M. , 2011, “ Alternative System Design of Biomass Gasification SOFC/GT Hybrid Systems,” J. Hydrogen Energy, 36(16), pp. 10414–10425.
Asimptote, 2016, “cycle-tempo Documentation,” Delft, The Netherlands, accessed Mar. 25, 2016,
Morita, H. , Komoda, M. , Mugikura, Y. , Izaki, Y. , Watanabe, T. , Masuda, Y. , and Matsuyama, T. , 2002, “ Performance Analysis of Molten Carbonate Fuel Cell Using a Li/Na Electrolyte,” J. Power Sources, 112(2), pp. 509–518.
Woudstra, N. , van der Stelt, T. P. , and Hemmes, K. , 2006, “ The Thermodynamic Evaluation and Optimization of Fuel Cell Systems,” ASME J. Fuel Cell Sci. Technol., 3(2), pp. 155–164.
Ahmeda, S. , Aitani, A. , Rahman, F. , Al-Dawood, A. , and Al-Muhaish, F. , 2009, “ Decomposition of Hydrocarbon to Hydrogen and Carbon,” Appl. Catal. A, 359(1–2), pp. 1–24.
Katikaneni, S. , Yuh, C. , Abens, S. , and Farooque, M. , 2002, “ The Direct Carbonate Fuel Cell Technology: Advances in Multi-Fuel Processing and Internal Reforming,” Catal. Today, 77(1–2), pp. 99–106.
Breeze, P. , 2014, Power Generation Technologies, 2nd ed., Newnes, Oxford, UK.
Jansen, D. , and Mozaffarian, M. , 1997, “ Advanced Fuel Cell Energy Conversion Systems,” Energy Convers. Manage. 38(10–13), pp. 957–967.
Haldor Topsøe, 2009, “ Sulphur Resistant/Sour Water-Gas Shift Catalyst,” Haldor Topsøe A/S, Lyngby, Denmark, accessed Mar. 25, 2016,
UOP Honeywell, 2010, “UOP SelexolTM Technology for Acid Gas Removal,” UOP, Des Plaines, IL, accessed Mar. 25, 2016,
Selman, J. R. , Uchida, I. , Wendt, H. , Shores, D. A. , and Fuller, T. F. , eds., 1997, Carbonate Fuel Cell Technology IV, The Electrochemical Society, Pennington, NJ.
Holdor Topsøe, 2009, “ From Solid Fuels to Substitute Natural Gas (SNG) Using TREMP TM,” Haldor Topsøe A/S, Lyngby, Denmark, accessed Mar. 25, 2016,
NETL, 2013, “Cost and Performance Baseline for Fossil Energy Plants Volume 1: Bituminous Coal and Natural Gas to Electricity,” National Energy Technology Laboratory, Washington, DC, accessed Mar. 25, 2016,
## Figures
Fig. 1
Flow diagram of a 30 MW class ir-MCFC system fueled by NG. (Pipe 11, 23, 13, 4, 21, 22: NG to anode inlet, Pipe 5: anode outlet to combustor, Pipe 16, 19: combustor to cathode inlet, Pipe 6, 7, 8, 9: cathode exhaust gas, Pipe 1, 2, 3: air to combustor.) Apparatus 1: the stack of ir-MCFC, 2: heat exchanger for air heating, 3: heat exchanger for heating water, 4: heat exchanger for heating NG, 6: water, 7: NG, 8: air blower, 9: catalytic combustor, 10: Flare stack, 11: mixer of NG and steam, 12: heat exchanger for producing the superheated steam, 13: the valve splitting the steam, 14: air, 16: heat exchanger for cooling the catalytic combustor off-gas, 17: the additionally produced steam, 18: mixer of NG and CO2, and 19: CO2.
Fig. 2
Process of coal to SNG without heat recovery. Apparatus 1: gasifier, 2: coal, 3: syngas cooler, 4: ash remover, 5 and 6: the water and steam passing the water wall in the gasifier, 7: cooler, 8: the mixer, 9: the steam introduced into the WGS, 10: WGS reactor, 11: ash disposal, 12: cooler, 13 and 14: the inlet and outlet of steam recovering the heat from the syngas cooler, 15: 16; the inlet and outlet of steam recovering the heat, 17 and 18: S, CO2 capture and its disposal, 19: methanation first reactor, 20: 95% purified oxygen, 22: mixer, 23: cooler, 24: compressor, 25: cooler, 26: the valve splitting the first methanation gas, 27: the second methanation reactor, 32: cooler, 28, 29, 30, 31, 34, 35, 36, and 37: the steam recovering the heat, and 33: the produced SNG.
Fig. 3
Process of converting coal to SNG including the heat recovery in WGS and methanation (circles mean heat recovery parts). Apparatus 1–20, 22–27, 32, and 33: the same as in Fig. 2, apparatus 21: the steam drum, 38: the steam turbine, 40: the deaerator, 39: the condenser, 29, 30, and 41: the pumps, 42: water source.
Fig. 4
Process of converting coal to SNG including the heat recovery in gasification, WGS, and methanation (circles mean heat recovery parts). All apparatus are the same as in Fig. 3.
Fig. 5
Flow diagram of a 30 MW class ir-MCFC system fueled by SNG. (Pipe 9, 11, 4, 21, 22: SNG to anode inlet, Pipe 5: anode outlet to combustor, Pipe 16, 19: combustor to cathode inlet, Pipe 6, 7, 8: cathode exhaust gas, Pipe 1, 2, 3: air to combustor.) Most of all apparatuses are the same as in Fig. 1, except apparatus 7: SNG, and apparatus 4: the pressure reducer like the expander.
## Tables
Table 1 Compositions according to gas streams of the ir-MCFC system related with Fig. 1
Table 2 Compositions of gas streams in the process of converting coal to SNG related with Fig. 2
Table 3 Compositions of gas streams in the process of converting coal to SNG related with Figs. 3 and 4
Table 4 Compositions of gas streams of the ir-MCFC system fueled by SNG related with Fig. 5
Table 5 Comparison of Figs. 1 and 5
Table 6 Comparison of Figs. 24
## Discussions
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1. ## Parameter Estimation Proof
Hi there
Im trying to do a proof from a past paper at uni, but I'm not sure how to go about it. The proof is this below:
Prove, for any smooth probability density function f(x|\theta ), that:
\hat{\theta} D\to N({\theta}_{0}; \frac{1}{nI({\theta}_{0})})
(The D is meant to be on the arrow but I dont know how to get it there, think it means converges in distribution)
as n \to \infty
where {\theta}_{0} is the true value of the parameter \theta .
Hint: You may use the fact that the expectation of the score function is zero.
Its very similar to a proof from our textbook and i sort of understand the logic, but I'm not sure how to set it out for a normal distribution. I can prove that under smoothness the MLE of theta hat is consistent, which seems quite similar.. except that its as P\to f(x|\theta ) but I cant quite figure out how the two are related :/
I think I have to take MLE of the normal and use the weak law of large numbers to get the expected value of it and then do some manipulation, but i cant figure out where the Fisher information comes into play.
Im pretty hopeless at stats :/ Help would be much appreciated. Sorry if my post seems confusing, I'm quite new here, will be happy to clarify anything.
2. Put $$...$$ around your latex for it to be interpreted by MHF.
Hi there
Im trying to do a proof from a past paper at uni, but I'm not sure how to go about it. The proof is this below:
Prove, for any smooth probability density function f(x|\theta ), that:
$\hat{\theta} D\to N({\theta}_{0}; \frac{1}{nI({\theta}_{0})})$
(The D is meant to be on the arrow but I dont know how to get it there, think it means converges in distribution)
as n \to \infty
where ${\theta}_{0}$ is the true value of the parameter \theta .
Hint: You may use the fact that the expectation of the score function is zero.
Its very similar to a proof from our textbook and i sort of understand the logic, but I'm not sure how to set it out for a normal distribution. I can prove that under smoothness the MLE of theta hat is consistent, which seems quite similar.. except that its as P\to f(x|\theta ) but I cant quite figure out how the two are related :/
I think I have to take MLE of the normal and use the weak law of large numbers to get the expected value of it and then do some manipulation, but i cant figure out where the Fisher information comes into play.
Im pretty hopeless at stats :/ Help would be much appreciated. Sorry if my post seems confusing, I'm quite new here, will be happy to clarify anything.
Ugh, such a sloppily worded question. The fact that the MLE of theta hat is consistent, which you can prove to yourself, makes it obvious that what is asserted in the question statement is FALSE: $\hat \theta$ converges in distribution to a POINT MASS at $\theta_0$.
What they mean, of course, is that $\sqrt n (\hat \theta - \theta_0) \to N(0, I^{-1}(\theta_0)).$ The idea is to first show that the score function evaluated at $\theta_0$ converges by the CLT to $N(0, I(\theta))$ and then do a Taylor expansion on the score function about $\theta_0$. This of course completely ignores how you deal with the remainder term of the Taylor expansion, which is the hard part of the problem, but hey, who cares about trifling things like that?
I'm like 90% sure you need a lot more than smoothness to get this result to go through, if you want to do it rigorously. You need a lot of stuff to deal with the remainder term of the Taylor expansion. Even in Casella and Burger they just hand-wave their way through dealing with the remainder term (though they at least mention the need for a lot of regularity conditions).
4. Thanks for all the help guys, you'll really pushed me to thinking in the right direction. Was quite a tricky 12 mark proof, i.e. 12% of the paper. |
# THE AUDITORY MODELING TOOLBOX
Applies to version: 1.1.0
Go to function
# takanen2013_lso - Model of the lateral superior olive
## Usage
output = takanen2013_lso(ipsilateral, contralateral, fs, fc);
## Input parameters
ipsilateral The ipsilateral "where" stream output from the model of the periphery contralateral The contralateral "where" stream output from the model of the periphery fs sampling rate fc characteristic frequencies
## Output parameters
output Spatial cues for separate narrow bandwidths
## Description
This function models the lateral superior olive (LSO) by processing the output of the periphery model with the following steps:
1. First-order lowpass filter is applied to both the ipsilateral and contralateral sides, and the contralateral side is delayed
2. The output is saturated at a certain dB level and limited signals.
3. Weighted moving average filters with a short and longer time constant are applied, the latter only below 1 kHz in order to slow the response
## References:
V. Pulkki and T. Hirvonen. Functional count-comparison model for binaural decoding. Acta Acustica united with Acustica, 95(5):883 -- 900, Sept./Oct. 2009.
M. Takanen, O. Santala, and V. Pulkki. Visualization of functional count-comparison-based binaural auditory model output. Hearing research, 309:147--163, 2014. PMID: 24513586. [ DOI ] |
# Math Help - fraction exponent question
1. ## fraction exponent question
Hello, I cannot understand the circled stage of this equation.
Thanks kindly for any help.
2. They need to get everything to the smallest possible base. Notice that $\displaystyle 4 = 2^2$.
So $\displaystyle \frac{4^3 \times 5^2 \times 2^3}{3^3 \times 3^2 \times 5^3} = \frac{(2^2)^3 \times 5^2 \times 2^3}{3^3 \times 3^2 \times 5^3}$.
The next step is to cancel as many of the $\displaystyle 5$s as possible. Since there are $\displaystyle 3$ on the bottom and $\displaystyle 2$ on the top, that means you can cancel $\displaystyle 2$ of them and be left with $\displaystyle 3-2 = 1$ of them on the bottom.
Does it make a bit more sense now?
3. Numerator
As $4 = 2^2$ you can write $4^3 = (2^2)^3$
Hence the numerator becomes $(2^2)^3 \times 2^3 = 2^9$
Denominator:
As $a^{b+c} = a^ba^c$ it can be rewritten as $3^3 \times 3^2 = 3^{3+2}$
$5^{3-2}$ comes from $5^2$ in the numerator so in the denominator it may be written as $5^{-2}$ and put in the denominator. Combined with $5^3$ we can put $5^{3-2}$ on the denominator
In total we get
$\dfrac{(2^2)^3 \times 2^3}{3^{3+2} \times 5^{3-2}}$ which is the question.
--------------
Personally though I'd have cancelled out 5^2 from top and bottom thus eliminating the need to deal with powers of 5.
4. thanks very much for your help, however I dont understand why the (5 to power of 3-2) would not be (5 to power of 2-3).
Regards
5. Just look at the terms with 5 in you have $\dfrac{5^2}{5^3}$. You can write that at $5^{2-3}$ if you like - as long as you leave it in the numerator.
If you want to look at the denominator (which is what the question does) then you will have to take the reciprocal of $5^{2-3}$ which is $5^{3-2}$ and put this term on the denominator.
If you can use your own working you'll save yourself a lot of time by saying that $\dfrac{5^2}{5^3} = \dfrac{1}{5}$
6. $5^{2-3} = \frac{1}{5^{3-2}}$ |
# Is DFA and Regular Expression equivalent?
The language of a DFA can be the empty set (by defining no final states), but can a Regular Expression do that?
If Regular Expression cannot do that, does it mean that DFA and Regular Expression are not equivalent (in at least some cases)?
• As you are new, you might not be able to upvote the answer but you can accept one by checking the tick mark. – Navjot Waraich Aug 24 '18 at 10:52
• This is a standard fact included in any textbook or lecture notes on the subject. – David Richerby Aug 24 '18 at 15:01
According to Wikipedia:
Given a finite alphabet $\Sigma$, the following constants are defined as regular expressions:
• (empty set) $\emptyset$ denoting the set $\emptyset$.
• ...
... a string that contains only an empty-set symbol is a regular expression, which represents the empty language.
• By the way, does the empty set symbol exist in regular expression used in may programming languages (like Perl, Java, and Python)? – Eric Stdlib Aug 25 '18 at 11:48
• No, they do not have the empty set symbol, nor the empty string symbol (those are different things). They do have the empty expression (consisting of 0 symbols), which matches the empty string. – reinierpost Aug 25 '18 at 14:46
• Incidentally, the definitions of regular expressions I've seen in textbooks did not have the empty set symbol, either. – reinierpost Aug 25 '18 at 14:47
Complementing xskxzr's answer, let me mention that if $L$ is a non-empty regular language, then $L$ has a regular expression not involving $\emptyset$; so we only need $\emptyset$ to accommodate the empty language.
This claim can be proved in many ways. One option is by induction on regular expressions. Let us prove the following claim by induction: if $r$ is a regular expression, then either $L[r] = \emptyset$, or $L[r] = L[s]$ for some $\emptyset$-free regular expression $s$.
We need to consider six cases:
1. $r = \emptyset$. In this case $L[r] = \emptyset$.
2. $r = \epsilon$. In this case $r$ is $\emptyset$-free.
3. $r = \sigma$, where $\sigma \in \Sigma$. In this case $r$ is $\emptyset$-free.
4. $r = s^*$. If $L[s] = \emptyset$ then $L[r] = \{ \epsilon \} = L[\epsilon]$. Otherwise, we can assume that $s$ is $\emptyset$-free, and then $r$ is also $\emptyset$-free.
5. $r = st$. If $L[s] = \emptyset$ or $L[t] = \emptyset$ then $L[r] = \emptyset$. Otherwise, we can assume that $s,t$ are $\emptyset$-free, and then $r$ is also $\emptyset$-free.
6. $r = s + t$. If $L[s] = L[t] = \emptyset$ then $L[r] = \emptyset$. If $L[s] = \emptyset$ and $L[t] \neq \emptyset$, then $L[r] = L[t]$, and we can assume that $t$ is $\emptyset$-free. The case $L[t] = \emptyset$ and $L[s] \neq \emptyset$ is symmetric. Finally, if $L[s],L[t] \neq \emptyset$ then we can assume that $s,t$ are $\emptyset$-free, and then $r$ is also $\emptyset$-free. |
# [texhax] \write18 syntax
Joel C. Salomon joelcsalomon at gmail.com
Tue Sep 15 17:04:26 CEST 2009
I'm trying to typeset the documentation for unicode-math, and the .dtx
includes commands like
% \immediate\write18{xelatex -interaction=batchmode
-jobname=unicode-math-testbf-tex
"""\noexpand\PassOptionsToPackage{math-style=TeX}{unicode-math}\noexpand\input
unicode-math-testbf.ltx"""}
I'm not sure why, but these aren't working. The log confirms that
\write18 is enabled, but there's no reference to these jobs being run.
Anyway, I figure I'll just run the command myself at the cmd.exe prompt
-- but what is the command to run?
Thanks,
--Joel |
# derive TOR long exact sequence without using right exactness of tensor
Let $R$ be a commutative ring and $M$ be an $R$ module. The only proof that I know of the right exactness of $-\otimes_R M$ uses the left exactness of $Hom_R(-,M)$. I wondered if there was a way of deriving the long exact sequence of tensor without using the right exactness of $-\otimes_R M$. This would allow me to deduce the right exactness of tensor.
Let $0 \to M \to N \to K \to 0$ be an exact sequence of $R$ modules. Let $\mathfrak M$ be a free resolution of $M$, $\mathfrak N$ a free resolution of $N$, $\mathfrak K$ a free resolution of $K$. We get as usual that there is a short exact sequence of chain complexes $0 \to \mathfrak M \to \mathfrak N \to \mathfrak K \to 0$ which stays exact after tensoring with an $R$ module $L$.
What I would appreciate assistance in is showing that the cohomology of $\mathfrak M \otimes_R L$ at the first entry is $M \otimes_R L$. This is where I see the argument would ordinarily need the right exactness of tensor.
• You are asking «how do I show that the tensor product is right exact without using that the tensor product is right exact?», essentially. Nov 25 '16 at 2:07
What I would appreciate assistance in is showing that...
Slightly more generally, suppose you have some additive functor $F$ and a projective resolution of an object $A$ $$\cdots \to P^{-2} \to P^{-1} \to P^0 \to A \to 0$$ We look at the complex $$F (P^\bullet)\colon \quad \cdots \to F (P^{-2}) \to F (P^{-1}) \to F (P^0) \to 0$$ The $0$-th cohomology is given by $$H^0 (F (P^\bullet)) = \operatorname{coker} (F (P^{-1}) \to F (P^0))$$ You want to conclude that this is naturally isomorphic to $F (A)$, but this natural isomorphism corresponds to preservation of cokernels, i.e. right exactness: $$\operatorname{coker} (F (P^{-1}) \to F (P^0)) \stackrel{???}{\cong} F (\operatorname{coker} (P^{-1} \to P^0)).$$
The only difference from right exactness is that you consider only cokernels of morphisms between projective objects; or free objects, if you take free resolutions of $R$-modules, as in your case. But checking this is not any easier than checking right exactness.
The only proof that I know of the right exactness of $-\otimes_R M$ uses the left exactness of $\operatorname{Hom}_R (-,M)$.
• This is not 100% correct: the proof uses that $-\otimes_R M$ is left adjoint to $\operatorname{Hom}_R (M,-)$, and then any left adjoint is automatically right exact and any right adjoint is left exact.
• Alternatively, you can check right exactness of $-\otimes_R M$ by hand: just take a short exact sequence $$0 \to N' \to N \to N'' \to 0$$ and look at the maps in the induced sequence $$N'\otimes_R M \to N\otimes_R M \to N''\otimes_R M \to 0$$
• $-\otimes_R M$ is not left adjoint to $Hom_R(-,M)$. I tried to come up with a proof along these lines(you deduced correctly that I never actually read the proof deducing right exactness of tensor from left exactness of Hom). Instead I got(a perfectly valid) proof by deducing the fact that if $Hom(-,M)$ applied to an exact sequence is exact for every $M$ then the sequence is exact. This part follows from a converse of the first isomorphism theorem. Nov 29 '16 at 12:17
• Would you be willing to elaborate on what you mean by using that $Hom(-,M)$ is the right adjoint of $- \otimes M$? This is not true but $Hom(M,-)$ is right adjoint to $-\otimes M$. Perhaps one can use the symmetry of Tor to conclude. Nov 29 '16 at 12:19
• @De Jong I apologize, it was a typo, I meant the covariant Hom. The contravariant Hom is adjoint to itself (for $R$ commutative, as $\operatorname{Hom}_R (L, \underline{\operatorname{Hom}}_R (M,N)) \cong \operatorname{Hom}_R (L\otimes_R M, N) \cong \operatorname{Hom}_R (M\otimes_R L, N) \cong \operatorname{Hom}_R (M, \underline{\operatorname{Hom}}_R (L,N))$.
– user144221
Nov 29 '16 at 13:30
• So all you are saying is that the left exactness of the covariant hom is completely trivial and this implies the right exactness of $\otimes M$. Ok. Not bad. Different than the proof I skimmed in Atiyah and Macdonald. Nov 29 '16 at 16:50
• @De Jong It is trivial in the sense that it follows from a more general fact: if $F$ is left adjoint to $G$, then $F$ preserves all categorical colimits (in particular cokernels, so it is right exact), and $G$ preserves all categorical limits (in particular kernels, so it is left exact). For details, see section 2.6 of Weibel's book.
– user144221
Nov 29 '16 at 16:56 |
# Balls from bin with replacement, distinct elements, concentration inequality
Draw $n$ numbers, denoted by $a_1, a_2, \ldots, a_n$, from set $[n]$, that is, for each $i$, $a_i$ is a uniformly random number from $[n]$.
Let $A = \{a_1, a_2, \ldots, a_n\}$. Then $$\mathbb{E}[|A|] = n - n (\frac{n-1}{n})^n \approx n (1 - 1/e).$$ How to prove a concentration bound on $|A|$? For example, prove $\Pr[|A| < n / 100] < 2^{-\Omega(n)}$.
We have that $$P(|A|\le cn) \le \binom{n}{cn} c^n$$ (first choose a subset of cardinality $cn$ and then insist that all numbers come from this set). By Stirling's formula, this bound is asymptotically $$\sim \frac{1}{\sqrt{n}} \left( \frac{c}{1-c} \right)^{(1-c)n} ,$$ which is of the requested type as long as $c<1/2$. |
# Influence of scaling of continuous predictor on main effect of categorical predictor in LMM
I have a linear mixed model that analyses the effect of multiple continuous and a categorical (two level, deviation coding of contrasts) predictor on a normally distributed outcome variable (dv). Following Barr (2021, https://psyteachr.github.io/stat-models-v1/multiple-regression.html?q=scal#standardizing-coefficients) I wanted to z-transform the continuous predictors (using scale()) to standardise the coefficients of the continuous predictors. In one of the models, R also gave back the following warning: ## Warning: Some predictor variables are on very different scales: consider rescaling.
However, I noticed that scaling changes the main effect of the categorical predictor. For the purpose of clarity, I will present a smaller but representative version of the actual model here to illustrate my point. This is the lmer command I used for this smaller model:
m = lmer(formula = dv ~ cat * cont + (1 |sub) + (1 | stm), data = df_sel)
I did this once with the raw and once with the scaled continuous predictor:
As you can see, it changes the main effect of the categorical predictor while the continuous and the interaction stay the same. I would have expected that none of the statistical values change, just the estimates. When investigating a bit, the only difference I found was that scaling gets rid of some moderate colinearity:
Can this really have such a large effect on the main effect of the categorical predictor? Am I justified in scaling the predictor?
Edit: Here are the outputs plot_model(m2, type = "int"):
There are a number of principles at play here.
1. Scaling is generally a bad idea, except for the internal scaling that's done in the software that does the estimation. It assumes linearity of effects and assumes that standard deviations are good scale measures. Especially for asymmmetrically distributed variables the SD is not a good measure. And it is greatly affected by extreme values.
2. Scaling makes interpretation harder. Interpretations are easiest on the original scale.
3. Categorical variables should not be scaled
4. Even if you don't scale the categorical variable but you do allow it to interact with a (scaled) continuous predictor, all of the categorical effects will be changed by scaling.
5. Check that the correlation pattern assumed in your model reflects the actual correlations seen in the data. Mixed effect models when used with default correlation structures often do not fit. See this for more.
• Thanks for the input. I scaled the data because of a warning in R: ## Warning: Some predictor variables are on very different scales: consider rescaling. Centering without adjusting the continuous predictor with the standard deviation produces exactly the same result as scaling. Unfortunately, I cannot find your reference in 5. Would you mind posting it again?
– Max
Jul 13 at 11:15
• That warning doesn't make much sense. I fixed the link. Jul 13 at 11:57
• Thank you for fixing the link. Do you have any recommendations on how to evaluate if the categorical predictor significantly predicts the outcome? According to anova() the model without the categorical predictor has a significantly decreased fit compared to the model including the categorical predictor (both with the raw continuous predictor).
– Max
Jul 14 at 10:36
• Likelihood ratio or Wald $\ch^2$ tests and change in marginal (over random effects) $R^2$. Jul 14 at 13:34
Have you tried plotting the predicted values from your model? I can't reproduce your issue, so I can't be 100% sure, but the changes are coming from you reading the model printout, and what those numbers actually are. I'm going to walk through them here:
(Intercept) is the value of the outcome when continuous predictors are at 0 and categorical predictors are at the reference level. You'll see that this changes as well, which makes sense because after standardizing the continuous predictor, we've changed what zero means.
cat[S.A] Is the effect of the difference between the two levels of the categorical predictor when the continuous variable it is interacting with is at zero. As what zero is for the continuous predictor has changed, this has also changed.
cont Is the effect of the continuous variable for only the reference level of the categorical predictor, because there is an interaction. It is the change of the outcome variable associated with a change in 1 in the cont variable. This changes too, because instead of a change in 1 on the original scale, it is now a change of 1 SD.
cat[S.A]*cont This is the change in the effect of cont for the reference level compared to the S.A level.
So as you can see, the numbers reported here rely on what zero means in the context of the regression. You can plot the interaction from both models using the sjPlot package and the following code, and you should see the same pattern, as all you have done is applied a linear transformation to one variable:
library(sjPlot)
plot_model(m, type = "int")
Also, regarding the collinearity, this post could help you understand what is going on: Does standardising independent variables reduce collinearity?
• Thank you for the helpful explanation of the values. The SD of the original continuous predictor is 0.0689, the mean is 0.13651. Centering the data by df_sel$cont = df_sel$cont - mean(df_sel\$cont) produces similar results as scaling the variable. I will add the plot_model to the main post.
– Max
Jul 13 at 11:42
• Right, I hadn't thought through that part. But as you can see from the plots, the model itself doesn't change
– sjp
Jul 13 at 21:59
• Yes, it doesn't change. Do you have any recommendations on evaluating if there is a meaningful / significant effect of the categorical predictor on the outcome? I tried using anova() for model comparison of one with and without the predictor according to which the model with the factor is significantly better than the one without.
– Max
Jul 14 at 10:34
• That's a way to do it
– sjp
Jul 14 at 10:57 |
All notes
Glog
* [googleDoc](http://google-glog.googlecode.com/svn/trunk/doc/glog.html "googleDoc") * [yeolar](http://www.yeolar.com/note/2014/12/20/glog/ "yeolar") ### wcf * Use VLOG(1) - VLOG(3) for tracing. * Run app with APP -v #include int main(int argc, char* argv[]) { // Logging before InitGoogleLogging() is written to STDERR LOG(ERROR)<<"This is written to STDERR"; // Initialize Google's logging library. google::InitGoogleLogging(argv[0]); LOG(INFO) << "Found " << num_cookies << " cookies"; // Conditional logging. LOG_IF(INFO, num_cookies > 10) << "Got lots of cookies"; // Occasional logging. // Log at 1st, 11th, 21st, ... The special google::COUNTER value is used to identify which repetition is happening. LOG_EVERY_N(INFO, 10) << "Got the " << google::COUNTER << "th cookie"; LOG_IF_EVERY_N(INFO, (size > 1024), 10) << "Got the " << google::COUNTER<< "the big cookie"; // limit the output to the first n occurrences: LOG_FIRST_N(INFO, 20) << "Got the " << google::COUNTER << "th cookie"; // Log only in Debug. // Use these macros to avoid slowing down your production application due to excessive logging. DLOG(INFO) << "Found cookies"; DLOG_IF(INFO, num_cookies > 10) << "Got lots of cookies"; DLOG_EVERY_N(INFO, 10) << "Got the " << google::COUNTER << "th cookie"; // When chasing difficult bugs, thorough log messages are very useful. However, you may want to ignore too verbose messages in usual development. // For such verbose logging, glog provides the VLOG macro, which allows you to define your own numeric logging levels. // The --v command line option controls which verbose messages are logged: VLOG(1) << "I'm printed when you run the program with --v=1 or higher"; VLOG(2) << "I'm printed when you run the program with --v=2 or higher"; // The lower the verbose level, the more likely messages are to be logged. For example, if --v==1, VLOG(1) will log, but VLOG(2) will not log. This is opposite of the severity level. // if you write VLOG(0), you should specify --v=-1 or lower to silence it. // The VLOG macros always log at the INFO log level (when they log at all). if (VLOG_IS_ON(2)) { // do some logging preparation and logging // that can't be accomplished with just VLOG(2) << ...; } VLOG_IF(1, (size > 1024))<< "I'm printed when size is more than 1024 and when you run the " "program with --v=1 or more"; VLOG_EVERY_N(1, 10)<< "I'm printed every 10th occurrence, and when you run the program " "with --v=1 or more. Present occurence is " << google::COUNTER; VLOG_IF_EVERY_N(1, (size > 1024), 10)<< "I'm printed on every 10th occurence of case when size is more " " than 1024, when you run the program with --v=1 or more. "; "Present occurence is " << google::COUNTER; // Google Style perror() // PLOG() and PLOG_IF() and PCHECK() behave exactly like their LOG* and CHECK equivalents with the addition that they append a description of the current state of errno to their output lines. E.g. PCHECK(write(1, NULL, 2) >= 0) << "Write NULL failed"; // This check fails with the following error message. // F0825 185142 test.cc:22] Check failed: write(1, NULL, 2) >= 0 Write NULL failed: Bad address [14] // SYSLOG, SYSLOG_IF, and SYSLOG_EVERY_N macros are available. These log to syslog in addition to the normal logs. Be aware that logging to syslog can drastically impact performance, especially if syslog is configured for remote logging! // FATAL severity level messages or unsatisfied CHECK condition terminate your program. You can change the behavior of the termination by InstallFailureFunction. void YourFailureFunction() { // Reports something... exit(1); } google::InstallFailureFunction(&YourFailureFunction); return 0; } ## Intro * If you want to find less common features, please check header files under src/glog directory. * The header file can be used for thread-safe logging, which does not allocate any memory or acquire any locks. ### Dump * The library provides a convenient signal handler that will dump useful information when the program crashes on certain signals such as SIGSEGV. The signal handler can be installed by google::InstallFailureSignalHandler(). * By default, the signal handler writes the failure dump to the standard error. You can customize the destination by InstallFailureWriter(). * By default, glog tries to dump stacktrace and makes the program exit with status 1. ### Severity * In increasing order of severity: INFO, WARNING, ERROR, and FATAL. * Logging a FATAL message terminates the program (after the message is logged). * Note that messages of a given severity are logged not only in the logfile for that severity, but also in all logfiles of lower severity. E.g., a message of severity FATAL will be logged to the logfiles of severity FATAL, ERROR, WARNING, and INFO. * The __DFATAL__ severity logs a FATAL error in debug mode (i.e., there is no NDEBUG macro defined), but avoids halting the program in production by automatically reducing the severity to ERROR. * Unless otherwise specified, glog writes to the filename "/tmp/...log... |
# The 'Security Digest' Archives (TM)
Archive: About | Browse | Search | Contributions | Feedback
Site: Help | Index | Search | Contact | Notices | Changes
ARCHIVE: TCP-IP Distribution List - Archives (1988)
DOCUMENT: TCP-IP Distribution List for August 1988 (307 messages, 170694 bytes)
SOURCE: http://securitydigest.org/exec/display?f=tcp-ip/archive/1988/08.txt&t=text/plain
NOTICE: securitydigest.org recognises the rights of all third-party works.
START OF DOCUMENT
-----------[000000][next][prev][last][first]----------------------------------------------------
Date: Mon, 1 Aug 88 09:40:57 PDT
From: [email protected] (Lars J Poulsen)
To: [email protected], [email protected]
To: [email protected]
Date: Mon, 1 Aug 88 08:44:14 PDT
From: lars (Lars J Poulsen)
Message-Id: <[email protected]>
Subject: Re: TCP/IP over X.25 under Unix ? (really: those damn cc-lines)
Sorry; along with Keith McCloughrie I confess to problems with editing
cc-lines, thus letting you all read a personal reply (Though the damage
may have been limited since it was in a furreign tongue).
/ Lars Poulsen
-----------[000001][next][prev][last][first]----------------------------------------------------
Date: Mon, 01 Aug 88 15:44:50 EDT
From: Doug Greenwald <R1ECGF%[email protected]>
To: TCP/IP List <[email protected]>
Subject: HP TCP/IP Conformance
Hi,
A few weeks ago, i saw something mentioned concerning problems with
HP systems with TCP/IP. Something about problems getting HP's to work
with various gateways. I would appreciate seeing this info again. We
are currently looking at various vendors for networkable workstations,
an HP is one of the contenders, if you or they can show us that thier
workstations support TCP/IP and/or Ethernet networking with minimal
Please respond directly to me and I will sumarize to the net if there is
sufficient interest.
Doug Greenwald
Engineering Computer Graphics Facility
University of Akron
Bitnet: R1ECGF@AKRONVM
-----------[000002][next][prev][last][first]----------------------------------------------------
Date: 1 Aug 88 11:53:33 GMT
From: [email protected] (Greg_Baber)
To: comp.protocols.tcp-ip
Subject: Re: Instrumenting a TCP Implementation
In article <[email protected]> [email protected] (Keith McCloghrie) writes:
[stuff eaten]
>> We, at the Department of Computer Science, University of Maryland, have
>> done an instrumentation of TCP/IP. Here is the abstract from the
>> Technical Report describing our work:
>> "We ....
>> ... code)."
>> Interested persons can get a copy of the Report by sending mail to
>> [email protected]
>> CS-TR 2063 and UMIACS-TR 88-50
Interested! Please send me the reports too.
>Thank-you,
>Keith.
--
Reply to: Gregory S. Baber Voice: (609) 520-5077
Dow Jones & Co., Inc. E-mail: ..princeton!dowjone!gregb
Box 300
Princeton, New Jersey 08543-0300
-----------[000003][next][prev][last][first]----------------------------------------------------
Date: 1 Aug 88 18:07:00 EDT
From: <[email protected]>
To: "geoff" <[email protected]>
Cc: <[email protected]>
Subject: VMS TCP/IP software
Geoff:
I will have to concur that Wollongong is expensive, but to some extent
you get what you pay for. Those guys send engineers to all the networking
conferences. TWG seems to be incorporating some of the more important
protocol enhancements into their products in a timely fashion. Their version
3.2 software incorporates the Van Jacobson window adjustment scheme.
We use version 3.2 and are pretty happy with it. When all I can find to
complain about is CC: fields in the mailer (and thats a VMSmail problem really)
it can't be too bad a product, right?
The capability to keep up the with latest developments may become increasingly
important. The ability to respond to Usage Sensitive Charging by incorporating
a more efficient telnet may be a big win to your budget. If you use the TWG
package to connect to the wide area subnet you may appreciate their support
when BBN womps PSN 7.0 on you :-) .
Although I am not a user of the product, I have heard generally good reports
on the Multinet product. This product was (maybe still is) available from
SRI. I believe two of its developers have left SRI to persue the further
developement and enhancement of the product. You may wish to review the
recent TCP/IP archives to locate them.
Bob Enger
Contel Federal Systems
-----------[000004][next][prev][last][first]----------------------------------------------------
Date: 1 Aug 88 15:37:43 GMT
From: [email protected] (Toerless Eckert)
To: comp.sources.wanted,comp.unix.wizards,comp.unix.questions,comp.protocols.tcp-ip
Subject: Again: looking for gated
I looking for the sources of gated.
As i do not have access to the internet, i cannot get them through ftp.
I only have access to bitnet and uucp. I also could get files
using anonymous ftam over the PSN.
Is there any bitnet listserver that has gated, or can someone send me the
sources by mail ?
Toerless Eckert ([email protected])
-----------[000005][next][prev][last][first]----------------------------------------------------
Date: 1 Aug 88 18:41:35 GMT
From: [email protected] (Capt Geoff Mulligan)
To: comp.protocols.tcp-ip
Subject: VMS TCP/IP software news
We have a number of VAXen connected via an ethernet and would like to
get them talking to our tcp/ip systems Do you have any pricing
information yet and what about government or educational discounts?
We presently have Wollongong's software running on one of our systems
and I am not satisfied with it; plus it is so expensive.
geoff
-----------[000006][next][prev][last][first]----------------------------------------------------
Date: 1 Aug 88 19:29:01 GMT
From: [email protected] (Robert Noh)
To: comp.protocols.tcp-ip,comp.os.vms
Subject: TCP/IP on VMS 5.0
Is there any implementation of TCP/IP that is ready to go
on VMS 5.0? Or, is there an implementation that is
due to be released "real soon, now?"
(Rumor has it that SRI's Multinet runs on 5.0. Can anyone
confirm this?)
On a related note, does anyone have a list of TCP/IP implementations
that run on a multiprocessor machine? This is more for a reference
than anything else, but I still would like the information.
mail responses will be summarized to the net.
Robert Noh {sdcrdcf|attunix|microsoft|sfmin}!ism780c!bobn
-----------[000007][next][prev][last][first]----------------------------------------------------
Date: 1 Aug 88 19:44:50 GMT
From: [email protected] (Doug Greenwald)
To: comp.protocols.tcp-ip
Subject: HP TCP/IP Conformance
Hi,
A few weeks ago, i saw something mentioned concerning problems with
HP systems with TCP/IP. Something about problems getting HP's to work
with various gateways. I would appreciate seeing this info again. We
are currently looking at various vendors for networkable workstations,
an HP is one of the contenders, if you or they can show us that thier
workstations support TCP/IP and/or Ethernet networking with minimal
Please respond directly to me and I will sumarize to the net if there is
sufficient interest.
Doug Greenwald
Engineering Computer Graphics Facility
University of Akron
Bitnet: R1ECGF@AKRONVM
-----------[000008][next][prev][last][first]----------------------------------------------------
Date: 1 Aug 88 20:14:11 GMT
From: [email protected] (Mark Crispin)
To: comp.protocols.tcp-ip
Subject: Can anyone help this guy?
Hi, I got this note from a friend of mine in Tokyo (edited to remove
unnecessary text). Can anyone help him out? Thanks, -- Mark
Date: Mon 1 Aug 88 21:42:37
From: ken-ichiro murakami <[email protected]>
Subject: Proxy ARP on SUN
Mark,
I have a question about Proxy ARP. My colligue in Tohoku University
wants to use Proxy ARP on SUN. As far as I know, there are two Proxy
ARP software. One is developed in U-texas and the other is developed
by Barry Shein([email protected]). I've alreay seni, I got this note from a friend of mine in Tokyo (edited to remove
unnecessary text). Can anyone help him out? Thanks, -- Mark
Date: Mon 1 Aug 88 21:42:37
From: ken-ichiro murakami <[email protected]>
Subject: Proxy ARP on SUN
Mark,
I have a question about Proxy ARP. My colligue in Tohoku University
wants to use Proxy ARP on SUN. As far as I know, there are two Proxy
ARP software
-----------[000009][next][prev][last][first]----------------------------------------------------
Date: 1 Aug 88 21:05:55 GMT
From: [email protected] (Merton Campbell Crockett)
To: comp.protocols.tcp-ip
Subject: Furreign tongue
Lars:
Dansk is not necessarily a furreign tonque--my basic problem was the
communications software for my PC at home does not provide immediate
interpretation of the european character sets. The most made out of
your discussion was that support for the ACP6250 was provided and
available from some vendor in Stockholm.
Merton
-----------[000010][next][prev][last][first]----------------------------------------------------
Date: 1 Aug 88 21:16:57 GMT
From: [email protected] (Merton Campbell Crockett)
To: comp.protocols.tcp-ip
Subject: Re: TCP/IP over X.25 under Unix ?
Lars:
My CIT224 seems to be brain-damaged. Is the "}" the "a" with the "o" on top
and the "|" a "o" with a "/"? These were the only characters that wouldn't
translate correctly.
Merton
-----------[000011][next][prev][last][first]----------------------------------------------------
Date: 1 Aug 88 22:07:00 GMT
From: [email protected]
To: comp.protocols.tcp-ip
Subject: VMS TCP/IP software
Geoff:
I will have to concur that Wollongong is expensive, but to some extent
you get what you pay for. Those guys send engineers to all the networking
conferences. TWG seems to be incorporating some of the more important
protocol enhancements into their products in a timely fashion. Their version
3.2 software incorporates the Van Jacobson window adjustment scheme.
We use version 3.2 and are pretty happy with it. When all I can find to
complain about is CC: fields in the mailer (and thats a VMSmail problem really)
it can't be too bad a product, right?
The capability to keep up the with latest developments may become increasingly
important. The ability to respond to Usage Sensitive Charging by incorporating
a more efficient telnet may be a big win to your budget. If you use the TWG
package to connect to the wide area subnet you may appreciate their support
when BBN womps PSN 7.0 on you :-) .
Although I am not a user of the product, I have heard generally good reports
on the Multinet product. This product was (maybe still is) available from
SRI. I believe two of its developers have left SRI to persue the further
developement and enhancement of the product. You may wish to review the
recent TCP/IP archives to locate them.
Bob Enger
Contel Federal Systems
-----------[000012][next][prev][last][first]----------------------------------------------------
Date: 1 Aug 88 23:25:49 GMT
From: [email protected] (Jon Smirl)
To: [email protected]
Subject: Re: Microsoft MAC/Vector interface
| 1. You do all of your binding (setting up handlers for incoming packets)
| at CONFIG.SYS time, so you can't use many DOS (or OS/2) services while
At OS/2 config.sys time a driver can actually do an awful lot *more* than
it can after config.sys time. This is because it is running at ring 3 at
that time and can do file i/o for example. After init, all driver code is
ring 0 and can't do any os services except devhlps. If the above
remark is really about wanting to write protocol code to live at ring
3, this can actually be done within the present structure--see the
response to point 2 below.
Note that we will in the future be extending the protocol manager to add
dynamic binding and unbinding. The current bind command logically can do
that today; all that is missing is the unbind command and a way to ask the
protocol manager to issue a binds and unbinds at run time.
In fact, the version 2 protocol manager spec will allow for several
run time functions, including dynamic binding, unbinding, and query/change
module config settings. Ring 3 APIs to the protocol manager will let
applications invoke these services.
|
| 2. You cannot un-bind, ever. No transient network protocols built into
| programs, no un-loadable protocol TSRs. Instead, you have to edit a file
| & reboot if you need more memory to run your CAD program or whatever....
See note about our planned bind/unbind extensions above.
Regarding transient protocols--on OS/2 you can do this by writing a stub
protocol module that interfaces to a ring 3 protocol daemon. The daemon
would ioctl threads down to the stub to get requests and pass back
responses--or better, ioctl down the address of a shared memory area where
request queues could be managed between ring 0 and 3. A similar thing
could be done on DOS 3.
could bring in the actual protocol code as an EXE which certainly
could terminate and free its memory.
Regarding "editing a file" to reconfig: there is no requirement for a
module to take its config from protocol.ini, or to do it only at boot
time. Modules can use private means to get config, including doing it
dynamically at run time via ioctls to the driver or whatever. Modules can
be written to even resize themselves when run time reconfig happens--ie, if
they dynamically allocate their buffer space, or have an app-level daemon
do this for them. (All this is saying is that if you are creative you
can even get the effect of dynamic reconfig sooner than when we provide
a standardized way for doing it).
|
| 3. Rather than telling MAC/Vector what kind of packets you want, instead
| it goes down its list of handlers, asking them one after another "do you
| want this packet". This means that there is no possibility of
arbitration
| (or even error detection) when two applications want the same type, and
| opens the door for "badly behaved applications" to screw things up for
| the rest of us.
|
We considered providing a way to provide packet dispatch info to the
vector, but providing adequate flexibility here was far more complexity
and overhead than seemed justified by the need. What does it mean to tell
it "what kind of packet you want"--do you specify what the source address
should be, or destination SAP, or both, or some bit masked address compare,
or do you also want to include specific packet command codes, or protocol
type bytes, or other compare conditions, or what? Cases can be made for all
these and more, and that just leads to absurd complexity for a
little-needed function. In general it is a "configuration error" to have
two drivers installed that would conflict over what packets they want;
indeed, all that a complex descriptor mechanism would do is let you detect
this configuration error. That would be nicer than not detecting it, but
again, the amount of overhead to detect this rather unusual error
condition did not appear justified. The current polling scheme works just
fine for what we believe the 99% case to be--protocols sharing a mac where
the conflicts don't arise. We are interested in any concrete suggestions
on what a better solution would be, or why there is some important need
not addressed by the current solution.
microsoft!jonsm
-----------[000013][next][prev][last][first]----------------------------------------------------
Date: 2 Aug 88 00:07:46 GMT
From: [email protected] (Mark Crispin)
To: comp.protocols.tcp-ip
Subject: Proxy ARP question
It appears that my message got damaged on the way out. Anyway,
[email protected] (or %[email protected]) is trying to
get ahold of software that supports Proxy ARP and is having problems.
He isn't directly on the Internet. Can anyone help him?
-------
-----------[000014][next][prev][last][first]----------------------------------------------------
Date: 2 Aug 88 13:36:48 GMT
From: [email protected] (Roy Smith)
To: comp.protocols.tcp-ip
Subject: Re: How many people receive TCP-IP
[email protected] writes:
> An easy way to get a start at the determination is to look at the main
> distribution list at the NIC. [...] some of those direct recipients are
> mail exploders. [...] perform the above process iteratively to get some
> idea of the ultimate number of recipients.
And then, don't forget to add in all the people who read TCP-IP as
its usenet alter ego, comp.protocols.tc-ip. The most recent stats from
Brian Reid (which somehow I missed the first time around, for no reason
that I can explain) estimate that something like 9800 people see this
material in that forum. My guess is that that far outweighs the count of
people who are on the mailing list, either directly or via mail exploders.
--
Public Health Research Institute
{allegra,philabs,cmcl2,rutgers}!phri!roy -or- [email protected]
"The connector is the network"
-----------[000015][next][prev][last][first]----------------------------------------------------
Date: 2 Aug 88 14:08:48 GMT
From: [email protected] (root)
To: comp.protocols.tcp-ip
Subject: BOOTP vendor support
I am in the midst of implementing network bootstrap code for
our Amiga NFS product. I have the new Sun bootparams bootstrapper
stuff going, but it seems to fall short of what is really needed.
In particular we're a bit worried that Sun requires use of RARP
in bootstrapping and that casual perusal of vendor glossies shows
not much support for RARP by vendors other than Sun (and NFS licensees).
BOOTP seems to be a whole notch better in the sense that it is
a simpler protocol, it supplies HDW -> Internet address translation
without using RARP, and using the vendor specific field (RFC-1048)
seems to provide everything a booting machine needs eg subnet mask,
UTC time offset, name server locn, etc. Since BOOTP doesn't use
RARP we can provide portable source to our customers who do not
have it. Now, the question: who else is/will support BOOTP? The
only other vendor I've seen supporting BOOTP is SGI. Is BOOTP
a dead end in light of Sun ASI, etc?
While I've got your attention, is anyone aware of any efforts towards
automating IP address generation? It would seem a natural extentsion
to either RARP or BOOTP, modulo the usual database consistency
problems.
Rick Spanbauer
Ameristar
-----------[000016][next][prev][last][first]----------------------------------------------------
Date: 2 Aug 88 15:48:30 GMT
From: [email protected] (Dan Kegel)
To: [email protected]
Subject: TCP/IP and NFS for MacOS?
I'm asking this on behalf of a friend at a large defense contractor, who
doesn't have internet access (but does have lots of pretty missiles and guns).
He'd like to use his Unix boxes as file and CPU servers, and use a mix
of Mac SE and Mac 2 boxes as clients; Ethernet would be use to connect
everything.
We think there is an Ethernet card for the SE, so that's not a problem.
The question is software. We know about TOPS; however, it hasn't yet been
ported to his particular Unix box.
Can anybody suggest TCP/IP and (oh, please) NFS (that's Sun's Network File
System) packages that run under the Mac OS? Or any other networking
alternatives?
Thanks...
--
Dan Kegel "We had to get it passed before the columnists attacked!"
[email protected] rochester!srs!dan dan%[email protected]
-----------[000017][next][prev][last][first]----------------------------------------------------
Date: 2 Aug 88 18:56:03 GMT
From: [email protected] (Jeffrey C Honig)
To: comp.protocols.tcp-ip
Subject: Re: Again: looking for gated
Gated is available for annonymous FTP from devvax.tn.cornell.edu as
pub/gated/gated.tar.Z.
Gated is available via electronic mail by sending mail to
[email protected] with a subject line of
get gated.tar.*
Several pieces of mail will be sent to you which comprise a split,
uuencoded, compressed tar file.
Questions and experiences relating to gated may be sent to the gated
mailing list, [email protected]. Requests for addition
to the list should be sent to [email protected].
Jeff
-----------[000018][next][prev][last][first]----------------------------------------------------
Date: Tue, 2 Aug 88 21:59:26 GMT
From: [email protected] (Henry Spencer)
To: comp.protocols.tcp-ip
Subject: Re: a proposed modification to ARP
In article <[email protected]> [email protected] (David C. Plummer) writes:
>... Networks
>are a LOT LOT bigger and broadcasts are on people's mind, whether it's a
>real problem or not.
Actually, it has always seemed to me that ARP -- the mapping between physical
addresses and logical ones, so to speak -- was the one place where use of
local broadcast was proper and defensible. I personally would put ARP last
on the list of broadcast problems to be fixed, and a number of other things
much higher. I have trouble believing that ARP by itself, if it were the
only use of broadcast, would be a real problem. Is it really so?
--
MSDOS is not dead, it just | Henry Spencer at U of Toronto Zoology
smells that way. | uunet!mnetor!utzoo!henry [email protected]
-----------[000019][next][prev][last][first]----------------------------------------------------
Date: 3 Aug 88 00:43:25 GMT
From: [email protected] (Bdale Garbee)
To: comp.protocols.tcp-ip
Subject: Re: a proposed modification to ARP
>Let's also remember that ARP runs on 5 networks other than Ethernet
>(Experimental Ethernet, AX.25, ProNET, Chaosnet, and ARCNET)
Not to mention Amateur Radio AX.25 ala the KA9Q package.
-----------[000020][next][prev][last][first]----------------------------------------------------
Date: 3 Aug 88 10:57:40 GMT
From: DEDOUREK%[email protected]
To: comp.protocols.tcp-ip
Subject: Re: Re: How many people receive TCP-IP
> [email protected] writes:
> > An easy way to get a start at the determination is to look at the
> main > distribution list at the NIC. [...] some of those direct
>
> And then, don't forget to add in all the people who read TCP-IP as
> its usenet alter ego, comp.protocols.tc-ip. The most recent stats
Ditto the BITNET LISTSERV service.
John DeDourek, University of New Brunswick, Fredericton, N.B. Canada
[email protected] ([email protected])
-----------[000021][next][prev][last][first]----------------------------------------------------
Date: 3 Aug 88 13:44:39 GMT
From: [email protected] (Dennis Doubleday)
To: comp.protocols.tcp-ip
Subject: Question about TCP/IP on VMS
I currently have an application running on Ultrix which uses TCP/IP.
Each machine in the network has a server running on it. The server is
opened in passive mode and listens at a known port for traffic. Under
Ultrix this "known port" is defined by adding an entry for my server
into the file /etc/services. How is this done under VMS? How are the
well-known ports defined? Or does this depend on the TCP/IP software
you have?
-----------[000022][next][prev][last][first]----------------------------------------------------
Date: 3 Aug 88 15:22:51 GMT
From: [email protected] (James Van Bokkelen)
To: comp.protocols.tcp-ip
Subject: Re: Microsoft MAC/Vector interface
The message from microsoft!jonsm was presumably a mis-posting, since it
replied to something I had said on [email protected] (comp.protocols.tcp-ip.ibmpc).
Unless people are interested, I won't debate DOS & OS/2 arcana here.
James VanBokkelen
FTP Software Inc.
-----------[000023][next][prev][last][first]----------------------------------------------------
Date: 3 Aug 88 16:25:54 GMT
From: [email protected] (Mark Horton)
To: comp.protocols.tcp-ip
Subject: Re: ACSNET Access
In article <[email protected]> [email protected] (Dave Horsfall) writes:
>Dave Horsfall (VK2KFU), Alcatel-STC Australia, [email protected]
as [email protected], as shown in the From: line and the signature of
the referenced article. .oz is NOT an official domain, while .oz.au IS.
The UUCP map does list .oz and knows how to get to it. This puts .oz up
there with the other "semi-official" domains like .uucp, .bitnet, .cdn,
and the like. People routing via UUCP can get to them, but people using
some other incarnation of the domain system, especially TCP/IP, cannot.
Posting to a worldwide computer network with an incomplete domain name
is like giving your phone number and forgetting the country code. It
might work locally, but it doesn't necessarily work in some other country.
Please encourage other Australians to use the full name .oz.au on their
domain style addresses, unless they are really sure that the context is
specific to ACSNET.
>dave%[email protected], ...munnari!stcns3.stc.OZ.AU!dave
This stuff looks fine, although both are kludges to get around various
limitations when you're trying to say [email protected] . If this
form doesn't work, then something is broken somewhere (or maybe the
person you're sending to just doesn't answer their mail.)
Mark
-----------[000024][next][prev][last][first]----------------------------------------------------
Date: 3 Aug 88 16:44:35 GMT
From: [email protected] (Dennis.Bednar)
To: comp.protocols.tcp-ip
Subject: subnet IP mask stored in route or interface struct?
Does 4.3BSD store the IP subnet mask in the route structure
(struct rtentry) or the interface structure (struct ifnet)?
The reason I ask, is that RFC 950 suggests that it be stored
on a per interface basis. However, I have found a particular
case (described below), in which it is better to store the mask
on a per route basis. Perhaps the example I have contrived
violates an unmentioned assumption that subnets in the same
In the figure below, the ---- lines represent a single physical
ethernet cable. Gw1, and gw2 stand for gateway 1 and gateway 2.
Both gw1 and gw2 below have multi-homed IP addresses (that is two
separate home addresses, one for each network connection).
In the figure below, subnet1 and subnet2 (in the same network)
are separated apart by a different network, consisting of just
a single subnet. Subnet 1 and 2 below are class C network addresses
containing 3 bytes of <network-number>, and 4 bits for the <subnet-number>.
The network in the middle is a class B network composed of 2 bytes
of <network-number>, and 4 bits for the <subnet-number>.
gw1 gw2
-------------------- ------------ ------------------
Name subnet1 network subnet2
Number 192.7.8.0x10 128.5.0x10 192.7.8.0x20
The problem with using the IP mask for an interface is that
gw2 above will have trouble forwarding packets destined for hosts
in subnet1. Suppose there is packet destined for host
192.7.8.0x11. I will show the problem after giving some
background information.
------ Begin of some background information:
There is presumed to be 3 tables of routing table structures
containing
<destination, gateway, flags, interface-ptr>.
These 3 tables are the host routing table, the subnet routing
table, and the network routing table. Destination is the
IP address of a host (if in host routing table), of a subnet
(if in subnet routing table), or of a network (if in netowrk
routing table). The flag indicates if the route is direct (ie
through a local gateway or the home machine) or indirect thru
a remote gateway (ie the flag is used instead of the
recommended algorithm described in RFC950 to decide if the
packet should be sent directly or thru a gateway). The interface
pointed to by interface-ptr is presumed to contain (at a minimum):
The 3 tables are searched in this order: host, subnet, network, using
the dg.ip_dest as a key into the route.destination field. For a
host table search, all 4-bytes are compared. The subnet table search
is described separately below. The network table search compares
ip_network_of(dg.ip_dest) with route.destination. The search stops
when a route has been found. The subnet table search is this:
for each subnet routing table entry
if (route.dest == (dg.ip_dest & route.interface.my_ip_mask))
{
found = routing table entry;
break; /* stop table search */
}
Once the route has been found, the route.flag tells whether to send
directly or through a gateway, as opposed to the recommended algorithm
described in RFC950.
---- end of background information
Now here is the problem: the subnet table search on gw2 above will
fail to locate the route entry in its subnet table, because the ip_mask
will strip off too many bits (2.5 bytes) causing the compare of
route.destination in the subnet table to fail:
if (192.7.8.0x10 == (192.7.8.0x11 & 255.255.0xf0.0))
if (192.7.8.0x10 == (192.7.0.0))
I would like to point out that by storing an IP mask on a per route
basis, this problem would go away, since the IP mask would be correct
for the destination subnet, which is remote to this particular network.
I would appreciate any comments on this matter.
--
FullName: Dennis Bednar
UUCP: {uunet|sundc}!rlgvax!dennis
USMail: CCI; 11490 Commerce Park Dr.; Reston VA 22091
Telephone: +1 703 648 3300
-----------[000025][next][prev][last][first]----------------------------------------------------
Date: 3 Aug 88 16:58:07 GMT
From: [email protected] (Sven-Ove Westberg)
To: comp.sources.wanted,comp.protocols.tcp-ip
Subject: Whois sources.
I would be very pleased to know where I could get programs
to Unix for the tcp/whois protocol and database?
Regards,
Sven-Ove Westberg, CAD, University of Lulea, S-951 87 Lulea, Sweden.
Tel: +46-920-91677 (work) +46-920-48390 (home)
ARPA: sow%[email protected] (only dumb ARPA mailers)
-----------[000026][next][prev][last][first]----------------------------------------------------
Date: 3 Aug 88 17:25:32 GMT
From: [email protected] (Walter Underwood)
To: comp.protocols.tcp-ip
Subject: Re: HP TCP/IP Conformance
A few weeks ago, i saw something mentioned concerning problems with
HP systems with TCP/IP. ...
We are currently looking at various vendors for networkable
workstations, an HP is one of the contenders, if you or they can
show us that their workstations support TCP/IP and/or Ethernet
I think this is worth answering to the whole list. HP's Unix
machines do implement a full TCP/IP, and do work with other systems.
The networking is based on 4.2 BSD, and will be upgraded to use the
Van Jacobson algorithms at the earliest possible time.
[The Unix boxes are the HP9000 Series 300 (68000-based) and HP9000
Series 800 (RISC-based). HP's name for their Unix OS is HP-UX.]
The HP3000 minicomputers (runnning MPE) use a limited version of the
TCP/IP protocols. They do not support UDP, use real 802.3 instead
of Ethernet, and use HP Probe instead of ARP. HP is working on
Ethernet and ARP for the HP3000.
The HP3000 uses proprietary login and file transfer protocols.
Regular ARPA services (Telnet, FTP, and SMTP) are available from The
Wollongong Group.
The HP1000 runs a TCP/IP which is similar to the HP3000, but the
1000 already support Ethernet, I believe.
If you have MPE systems, you need a gateway that talks 802.3 and
Probe. The only gateways that do that are the HP9000 series 300 and
series 800 machines (HP-UX), and boxes from cisco Systems, Inc.
Walter Underwood
HP Software Engineering Systems
Palo Alto, CA
PS: HP-UX can set Precedence and Security on TCP connections.
Anybody wanna try it?
-----------[000027][next][prev][last][first]----------------------------------------------------
Date: 3 Aug 88 17:29:04 GMT
From: [email protected]
To: comp.dcom.lans,comp.protocols.tcp-ip
Subject: Status of NTP?
What is the status of NTP? I have rfc958, is this the most (and
only) relevant document?
I would like to keep 35 or so machines on my networks time-synched
*with eachother*..... having that common time be "correct" is
icing on the cake. Up till now I have tried using 4.[23]BSD timed
and /usr/ucb/rdate on UN*X machines, and they work fine, but I
certainly wouldn't mind using a more elegant method.
- Deke Kassabian
-------------------------------------------------------------------------------
\ [email protected] "Experience is something you don't /
\ or ...!rochester!ur-valhalla!deke get until just after you need it." /
\-----------------------------------------------------------------------------/
-----------[000028][next][prev][last][first]----------------------------------------------------
Date: 3 Aug 88 17:47:27 GMT
From: [email protected] (Ted Schroeder)
To: comp.protocols.tcp-ip
Subject: Re: How many people receive TCP-IP
[email protected] writes:
> An easy way to get a start at the determination is to look at the main
> distribution list at the NIC. [...] some of those direct recipients are
> mail exploders. [...] perform the above process iteratively to get some
> idea of the ultimate number of recipients.
ames!nyu.edu!phri!roy (Roy Smith) writes:
> And then, don't forget to add in all the people who read TCP-IP as
> its usenet alter ego, comp.protocols.tc-ip.
Ted Schroeder [email protected]
Ultra Network Technologies
2140 Bering drive with a domain server:
San Jose, CA 95131 [email protected]
408-922-0100
-----------[000029][next][prev][last][first]----------------------------------------------------
Date: 3 Aug 88 21:34:22 GMT
From: [email protected] (Kwang Sung)
To: comp.protocols.tcp-ip
Subject: Re: Van Jacobson's Algorithm for AT&T Stream Implementations
I hope someone on the net can answer to my question.
I am curious that whether we can apply Van Jacobson's Algorithm to
AT&T Stream TCP/IP implementations easily.
I would like to know more detail about Van Jacobson's Algorithm clearly.
-----------[000030][next][prev][last][first]----------------------------------------------------
Date: 3 Aug 88 22:13:09 GMT
From: [email protected] (Kwang Sung)
To: comp.protocols.tcp-ip
Subject: Re: Difference between 4.3 BSD and 4.4 BSD, and between V.3 and V.4
I hope someone can answer to my question.
I would like to know difference between 4.3 BSD and 4.4 BSD, and
between AT&T V.3 and AT&T V.4, in terms of networking implementations.
-----------[000031][next][prev][last][first]----------------------------------------------------
Date: 4 Aug 88 00:02:30 GMT
From: [email protected] (Chris Torek)
To: comp.protocols.tcp-ip
Subject: Re: HP TCP/IP Conformance
From: Walter Underwood <[email protected]>
I think this is worth answering to the whole list. HP's Unix
machines do implement a full TCP/IP, and do work with other systems.
The networking is based on 4.2 BSD, and will be upgraded to use the
Van Jacobson algorithms at the earliest possible time. ...
I am not sure that anything based on 4.2BSD is full TCP/IP' (unless it
has had all the 4.3BSD fixes added), but in any case, 4.3BSD is
available for the HP9000 Series 300, from the University of Utah.
Chris
-----------[000032][next][prev][last][first]----------------------------------------------------
Date: 4 Aug 88 00:14:22 GMT
From: [email protected] (Glen Wiebe)
To: [email protected]
Subject: Micom-Interlan NP100 ethernet woes
We are in the process of installing a couple of Micom-Interlan
NP100 ethernet boards in two VAX 750s. One I can get working and the
other I cannot.
The VAX 750 on which it works has disks connected to an Emulex
massbus disk controller. The VAX 750 on which I have trouble has one
RA81 disk on a DEC UDA50 disk controller. (I suspect this may be the
problem). We are running the original 4.3bsd release.
When powering up the system the NP100 goes through a series
of internal self diagnostics. It never completes these successfully
and the driver (ix0) for the NP100 cannot reset it (it times out
waiting for a response). The NP100 board is ok since it works fine
in the other VAX.
Does anyone have ideas on what the problem might be?
Thanks.
--------
Glen J. Wiebe UUCP rutgers!bungia!bthpyd!wiebe
Bethel College, St. Paul, MN ATT (612) 638-6106
-----------[000033][next][prev][last][first]----------------------------------------------------
Date: 4 Aug 88 00:52:00 GMT
From: [email protected] (Jeffrey Mogul)
To: comp.protocols.tcp-ip
Subject: Re: subnet IP mask stored in route or interface struct?
Does 4.3BSD store the IP subnet mask in the route structure
(struct rtentry) or the interface structure (struct ifnet)?
The reason I ask, is that RFC 950 suggests that it be stored
on a per interface basis. However, I have found a particular
case (described below), in which it is better to store the mask
on a per route basis. Perhaps the example I have contrived
violates an unmentioned assumption that subnets in the same
Yes, but this is not so much an "unmentioned assumption" as it is
a rule that is not stated in the most obvious place. As an author
of RFC950, I suppose I must take the blame for not repeating in
RFC950 this statement from the first page of RFC940:
The use of subnets is an optional local decision. The fact that a
network has subnets is invisible outside that network, and the change
is local and can be instituted at a site without any global Internet
perturbations. A complex of links is assigned a single IP network
number, and outside that complex it appears as a single network with
that number. Only inside does local structure appear.
[Note that the first paragraph of RFC950 says, in effect, "read RFC940."]
Following this rule, the "particular case" is in violation:
--------------------gw1----------------gw2------------------
Name subnet1 network subnet2
Number 192.7.8.0x10 128.5.0x10 192.7.8.0x20
because the distinction between subnet1 and subnet2 would have to be
visible outside network 192.7.8.0 in order for things to work.
Solutions: Use different Class C numbers for the two isolated pieces,
or tie them together with a gateway connected to both subnets. The latter
solution is less likely to fill up other people's routing tables.
-----------[000034][next][prev][last][first]----------------------------------------------------
Date: 4 Aug 88 02:29:56 GMT
From: [email protected] (Walter Underwood)
To: comp.protocols.tcp-ip
Subject: HP TCP/IP Conformance
I am not sure that anything based on 4.2BSD is full TCP/IP' (unless it
I agree, and the people that work on our TCP agree. We have fixed the
behavior, but it is still a 4.2 programming interface. That is why I
pointed out the 4.2 heritage. Geez, I'd almost forgotten how bad 4.2
was ...
wunder
-----------[000035][next][prev][last][first]----------------------------------------------------
Date: 4 Aug 1988 06:50-EDT
From: [email protected]
To: [email protected]
Cc: [email protected]
Subject: Re: TCP/IP and NFS for MacOS?
I have been given to understand that there is a Unix for the MAC.
If that is true, NFS should be available as well. The MAC Unix
is called AUX, I believe. I don't have a point of contact, but
the product is supported by Apple, I believe.
Vint Cerf
-----------[000036][next][prev][last][first]----------------------------------------------------
Date: 4 Aug 88 03:09:56 GMT
From: [email protected]
To: comp.protocols.tcp-ip
Subject: Re: Status of NTP?
Deke,
See RFC-1059. Then, you might want to talk to Mike Petry, who has a 4.3bsd
daemon which is now chiming at a few dozen systems just now. Also, a bunch
of new radio clocks have come up, making the total at least seven going
on nine. Depending on your confidence and precision required, you might
want to run NTP on only a few of your machines and timed on the rest; however,
NTP depends for robustness on having a number of peers and using a weighted
selection algorithm to cast out the falsetickers.
Dave
-----------[000037][next][prev][last][first]----------------------------------------------------
Date: 4 Aug 1988 07:19-EDT
From: [email protected]
To: [email protected]
Cc: [email protected]
Subject: Re: Status of NTP?
Deke,
NTP RFC 1059 dated July 88 just released. RFC 1059 is an elective
protocol and the RFC is in DRAFT STANDARD status.
Vint Cerf
-----------[000038][next][prev][last][first]----------------------------------------------------
Date: Thu, 4 Aug 88 12:02 EST
From: <JFISHER%[email protected]> (James R. Fisher)
To: [email protected]
Subject: tcp/ip for Amdahl UTS
Hello:
We will soon be running Amdahl's UTS (Unix) version 1.2 under VM/HPO
on an Amdahl 5890.
We want a tcp/ip implementation for it; I'd be happy to hear from
anyone out there who knows any vendors of tcp/ip for such an environment.
Thanks much.
Jim Fisher
[email protected]
-----------[000039][next][prev][last][first]----------------------------------------------------
Date: 4 Aug 88 10:50:00 GMT
From: [email protected]
To: comp.protocols.tcp-ip
Subject: Re: TCP/IP and NFS for MacOS?
I have been given to understand that there is a Unix for the MAC.
If that is true, NFS should be available as well. The MAC Unix
is called AUX, I believe. I don't have a point of contact, but
the product is supported by Apple, I believe.
Vint Cerf
-----------[000040][next][prev][last][first]----------------------------------------------------
Date: 4 Aug 88 11:19:00 GMT
From: [email protected]
To: comp.protocols.tcp-ip
Subject: Re: Status of NTP?
Deke,
NTP RFC 1059 dated July 88 just released. RFC 1059 is an elective
protocol and the RFC is in DRAFT STANDARD status.
Vint Cerf
-----------[000041][next][prev][last][first]----------------------------------------------------
Date: 4 Aug 88 13:11:48 GMT
From: [email protected] (Mike St. Johns)
To: comp.protocols.tcp-ip
Subject: TCP/IP and NFS for MacOS?
This month's BYTE has a rather scathing set of articles on A/UX - Unix
for the MAC. A/UX appears to be closest to system V than any of the
other UNIXs.
But hold on to your wallet - it costs either $5000 or$10,000
depending on your system configuration - this is *without* source code
(which does not appear to be available at this time)
Mike
-----------[000042][next][prev][last][first]----------------------------------------------------
Date: 4 Aug 88 13:25:00 GMT
From: [email protected] ("Beat the system, pull the plug.")
To: comp.protocols.tcp-ip
Subject: TCP-IP for AT&T UNIX-PC 7300's
Subject: TCP-IP for AT&T UNIX_PC 7300's
I hope someone can help me. I am a student in the Integrated
Science Program at Northwestern University and we would like to hook our
7300's to the local campus network. This requires TCP/IP software, which
we do not know where to obtain. Can anyone make any recommendations? Also
can the 7300 handle a 19200bps line for the connection? I seem to remem-
ber some discussion regarding this problem a couple of weeks ago but
skipped over it at that point as it was not relevent then. Will modifications
to the daemons help reduce the overhead so that the 7300 will be able to
keep up with the traffic it must handle? Please excuse any ignorance on my
part as I am still new to UNIX and the 7300's. Thanks.
Robert Lentz
Bitnet: Lentz@Nuacc
Internet: [email protected]
P.S. If anybody can recommend a good source for MMDF or another good mail
program this would also be appreciated.
-----------[000043][next][prev][last][first]----------------------------------------------------
Date: 4 Aug 88 13:52:09 GMT
From: [email protected] (Mikki Barry)
To: comp.newprod,comp.protocols.tcp-ip,comp.sys.mac
Subject: TCP/Connect - NCSA Telnet Plus Support
Learning Tree Software, Inc. would like to announce the formation of
a new company: InterNet Systems Corporation. ISC is modifying the
existing NCSA Telnet for the Macintosh to produce new and nifty features,
and is offering telephone support. We will begin shipping this new product
Sept. 1.
The price of $495 (with substantial discounts for multiple copies) includes an updated manual, the software, and one year of telephone support. Current NCSA Telnet users can contact us for special pricing. (703) 435-8170. Until InterNet Systems Corp. gets on the net, LTS will forward mail sent to uunet!lts!comment. InterNet Systems Corp. will be at MacWorld sharing the Kinetics booth. We will have a special show discount for this product, as well as RealTalk, a new and nifty product similar to "talk" on Unix systems. It also includes a file transfer program, and window servers. Current pricing is$79.95 for one, or $219.95 for a three pak (in a peachy keen binder that will light up your bookshelf). It has so many neato features that you really should come see it at MacWorld. Mikki Barry Grand Poohbah -----------[000044][next][prev][last][first]---------------------------------------------------- Date: 4 Aug 88 14:02:16 GMT From: [email protected] To: comp.protocols.tcp-ip Subject: Ken Olsen on TCP/IP Quoted without permission from Digital News, August 1, 1988: "Our attitude with TCP/IP is, 'Hey, we'll do it, but don't make a big system, because we can't fix it if it breaks.'" Does this reflect a lack of confidence in the Ultrix group? -----------[000045][next][prev][last][first]---------------------------------------------------- Date: 4 Aug 88 14:18:57 GMT From: [email protected] (John A. Shriver) To: comp.protocols.tcp-ip Subject: subnet IP mask stored in route or interface struct? Your configuration is illegal per RFC 1009. To quote: The interconnected LANs of an organization will be given the same network number but different subnet numbers. The distinction between the subnets of such a subnetted network must not be visible outside that network. Thus, wide-area routing in the rest of the Internet will be based only upon the <Network-number> part of the IP destination address; gateways outside the network will lump <Subnet-number> and <Host-number> together to form an uninterpreted "rest" part of the 32-bit IP address. The whole point of subnets is to provide a LAYERED, HEIRARCHICAL approach to routing. Anyone outside the subnetted network must be able to route solely on the basis of network number. Hosts on your network 128.5 cannot do this. Your configuration does not work because it is illegal. It is surely possible to envision all sorts of ways of "solving" this supposed problem. But then you will fail to solve the problem that subnetting was intended to solve. That problem was that routing at the upper (network) layer was overloading from too many networks. Subnets, by hiding a layer of the network topology, solved this. The restrctions of subnets are readily dealt with by proper (sub)network design. [The same approach was applied to DECnet in Phase IV, with areas. What you are asking for is the equivalent of allowing node 7.33 in DECnet to plopped down in the middle of area 5 and have it work.] -----------[000046][next][prev][last][first]---------------------------------------------------- Date: 4 Aug 88 14:40:03 GMT From: [email protected] (James Van Bokkelen) To: comp.protocols.tcp-ip Subject: Precedence & IP Options (was: HP TCP/IP Conformance) I can testify that HP UX doesn't have the 4.2 "crash on unknown IP option" bug (which at least a couple of other 4.2-derived Unices still have). If you (or anyone else) have Internet hosts which you would like to check out with TCP using Precedence and the IP Basic & Extended Security options, send me mail, giving the name & IP address, and any other constraints you would like to impose (I will not be able to deliver on 'a phone call before you try it'). Commercial IP routers from Proteon, and the MIT C-gateway, are known to forward packets containing these options. 4.3 Unix and cisco terminal concentrators handle them correctly at the application layer, so I have hopes that 4.3 & cisco routers will forward them as well. If you are connected to the Internet via a 4.2-based router, it may fail to forward the packets, or even crash. I will reply with e-mail declaring a time when I will do the testing (which can interrupt operations on some hosts, e.g. SunOS 3.4 and Ultrix 2.0). I will use ICMP Echo Request and TCP (usually finger, Telnet or SMTP if finger isn't supported) to test behaviour. Symptoms I have observed while testing the Basic & Extended security options include: Go deaf to the net for 5 minutes on either Ping or TCP (but not crash) Ignore Ping, crash on TCP or UDP. Ignore Ping and TCP. Ignore Ping, Reset attempted TCP connections. Ignore Ping, open TCP connections ok. Reply w/o option to Ping, open TCP connections ok. Reply w/option to Ping, ignore TCP connection attempts. Reply w/option to Ping, Reset attempted TCP connections. Reply w/option to Ping, open TCP connections ok. The current list of implementations that I have observed correctly supporting TCP with IP Precedence is: Wiscnet on IBM VM systems. KA9Q on IBM PCs. PC/TCP v2.03 (in beta test). The list of implementations which I have observed as unable to handle the RFC-1038 IP Security options will appear later this month. James VanBokkelen FTP Software Inc. (617) 868-4878 [email protected] -----------[000047][next][prev][last][first]---------------------------------------------------- Date: 4 Aug 88 15:52:28 GMT From: [email protected] (Donald Holman) To: comp.protocols.tcp-ip Subject: Re: TCP/IP and NFS for MacOS? > Mike St. Johns writes: > > But hold on to your wallet - it costs either$5000 or $10,000 > depending on your system configuration - this is *without* source code > (which does not appear to be available at this time) If this is indeed the cost, it might be less expensive to get source code from another place, and then pay a team of developers to adapt it for the new machine. Not necessarily a joke, but perhaps a semi scathing commentary on the price. these are my comments and are probably not the views of my employer. Don -----------[000048][next][prev][last][first]---------------------------------------------------- Date: 4 Aug 88 16:49:56 GMT From: [email protected] (Tom Barrett) To: comp.protocols.tcp-ip Subject: Re: TCP/IP and NFS for MacOS? In article <[email protected]> [email protected] (Mike St. Johns) writes: >This month's BYTE has a rather scathing set of articles on A/UX Scathing...hmmm...in my humble interpretation, I would say perhaps lukewarm. The summary in the review says "...[A/UX is] a good first step toward the MacII into a Unix workstation." Anyway, lest I be accused of out-of-context quoting, it's best to judge for one's self. A recent issue of UNIX World had a fairly positive review (not sure which issue, sorry), as did the June 27 issue of UNIX Today (BTW, I am a contractor, not an Apple employee). >But hold on to your wallet - it costs either$5000 or $10,000 >depending on your system configuration - this is *without* source code I'm not sure if it's clear from this posting that these prices include the fully configured MacII (monitor, floppies, 80Mb hard drive, etc.). Those interested in details about A/UX can read or post requests to comp.unix.aux. -----------[000049][next][prev][last][first]---------------------------------------------------- Date: 4 Aug 88 17:02:00 GMT From: [email protected] (James R. Fisher) To: comp.protocols.tcp-ip Subject: tcp/ip for Amdahl UTS Hello: We will soon be running Amdahl's UTS (Unix) version 1.2 under VM/HPO on an Amdahl 5890. We want a tcp/ip implementation for it; I'd be happy to hear from anyone out there who knows any vendors of tcp/ip for such an environment. Thanks much. Jim Fisher [email protected] -----------[000050][next][prev][last][first]---------------------------------------------------- Date: 4 Aug 88 17:17:27 GMT From: [email protected] (Kenneth Adelman) To: comp.protocols.tcp-ip Subject: Re: Question about TCP/IP on VMS > I currently have an application running on Ultrix which uses TCP/IP. > Each machine in the network has a server running on it. The server is > opened in passive mode and listens at a known port for traffic. Under > Ultrix this "known port" is defined by adding an entry for my server > into the file /etc/services. How is this done under VMS? How are the > well-known ports defined? Or does this depend on the TCP/IP software > you have? Depends on the TCP/IP software you have. On MultiNet you add an entry to a text file which gets compiled into a binary database and loaded into a global section for fast access. On WINS/TCP I believe that you add an entry to the etc:[000000]services file just like under Unix. Well known ports don't HAVE to be defined in these files, it just makes it convenient because your code can reference the port by name instead of number. Kenneth Adelman TGV -----------[000051][next][prev][last][first]---------------------------------------------------- Date: 4 Aug 88 20:08:55 GMT From: [email protected] (Tim Krauskopf) To: comp.protocols.tcp-ip Subject: Re: TCP/IP and NFS for MacOS The misinformation is getting a little thick. AUX for Apple's Macintosh II is a port of System V with BSD networking, (I don't know how many 4.3 enhancements are in 1.0, 1.1 should be full 4.3BSD TCP/IP) other BSD enhancements and full NFS support. It works. Right now it is plain vanilla, X is coming, black and white only for now, Mac ToolBox graphics are available. The auto-config has everyone else's UNIX beat. Running AUX doesn't prevent you from running MacOS, just takes up a whole 80MB drive. AUX does NOT cost more than$1000.
If you buy two Mac II systems with identical hardware, one with AUX and
the other with MacOS (the original Macintosh operating system), then you
will find the cost of AUX is anywhere from $200 to$500 depending on
the hardware you actually buy. Plus manuals, 6-foot set, isn't real
cheap, order separately. If you call the extra expense of the hard
disk a part of the UNIX cost, then you haven't been running many Suns.
This is a full product line, dealers and everything, contact your nearest
AUX-certified Apple dealer or a sales office.
Below this line, I am referring to MacOS, NOT AUX. For you PC users,
think of this as DOS vs. XENIX, one has the applications, the other
is UNIX.
------------------------
There is no commercial NFS for the Mac. Cayman Systems (Cambridge, MA,
(617)494-1999) is releasing "real soon now" a box which converts NFS to AFP,
the Apple Filing Protocol standard for shared disks under MacOS.
NFS for MacOS in software is doable, primarily for Ethernet-equipped
Macs, no announcements that I know of.
TCP/IP for MacOS has been announced as "in development" at Apple in
Cupertino. Target for release is before end of 1988. Demos scheduled
for the TCP/IP Interoperability Conference in September.
There are no commercial releases of TCP/IP or TCP/IP applications for MacOS
shipping that I know of at the time I am writing this. Before the end of
the year, expect 4 or more vendors to ship.
University products are available from Cornell, Brown, Illinois (NCSA),
Michigan, and Stanford, but some are restricted use.
I am biased, Anonymous FTP to 128.174.20.50 for release package and source
to NCSA Telnet for the Macintosh. What can you lose, it's public domain?
I tried to stick to facts, but if there are any opinions above, they are
my own.
Tim Krauskopf [email protected] (ARPA)
National Center for Supercomputing Applications (NCSA)
University of Illinois, Urbana-Champaign
-----------[000052][next][prev][last][first]----------------------------------------------------
Date: 4 Aug 88 20:17:27 GMT
From: [email protected] (John Caughy)
To: comp.protocols.tcp-ip,comp.os.vms
Subject: Re: TCP/IP on VMS 5.0
From article <[email protected]>, by [email protected] (Robert Noh):
>
> On a related note, does anyone have a list of TCP/IP implementations
> that run on a multiprocessor machine? This is more for a reference
> than anything else, but I still would like the information.
>
The implementation for the HP 9000 500 series from Wollongong operates
in a multiprocessor environment. The TCP/IP provides a single thread
for all users of the system and appears to be quite responsive.
-----------[000053][next][prev][last][first]----------------------------------------------------
Date: 5 Aug 88 08:16:00 PDT
From: Dave Crocker <[email protected]>
To: tcp-ip <[email protected]>
Subject: RE: Van's algorithm's in Streams
This is in response to Kwang Sung's query:
Our newest version of Streams TCP contains Van's and Nagles algorithms
for congestion control, etc. The header-predection performance code is
scheduled for addition, shortly, although we are still trying to understand
its impact under mixed traffic conditions.
Dave Crocker
VP, Engineering
The Wollongong Group
-----------[000054][next][prev][last][first]----------------------------------------------------
Date: 5 Aug 88 09:37:00 PDT
From: Leo J McLaughlin <[email protected]>
To: tcp-ip <[email protected]>
Subject: 802.3 routing
>> A few weeks ago, i saw something mentioned concerning problems with
>> HP systems with TCP/IP. ...
>> We are currently looking at various vendors for networkable
>> workstations, an HP is one of the contenders, if you or they can
>> show us that their workstations support TCP/IP and/or Ethernet
>The HP3000 uses proprietary login and file transfer protocols.
>Regular ARPA services (Telnet, FTP, and SMTP) are available from The
>Wollongong Group.
>If you have MPE systems, you need a gateway that talks 802.3 and
>Probe. The only gateways that do that are the HP9000 series 300 and
>series 800 machines (HP-UX), and boxes from cisco Systems, Inc.
>Walter Underwood
>HP Software Engineering Systems
>Palo Alto, CA
The Wollongong Group also provides a product that allows a PC to function
as a gateway for MPE systems, WIN/ROUTE2.
leo j mclaughlin iii
The Wollongong Group
-----------[000055][next][prev][last][first]----------------------------------------------------
Date: 5 Aug 88 06:09:43 GMT
From: [email protected] (Chris Torek)
To: comp.protocols.tcp-ip
Subject: Re: Difference between 4.3 BSD and 4.4 BSD, and between V.3 and V.4
4.4BSD does not exist. There is a post-4.3-BSD release of TCP; it
is available via anonymous FTP from Berkeley.edu. It implements
the Jacobsen/Karels' algorithms.
(The new TCP code is included in 4.3BSD-tahoe.)
Chris
-----------[000056][next][prev][last][first]----------------------------------------------------
Date: 5 Aug 88 08:28:00 GMT
From: [email protected] (Charles Hedrick)
To: comp.protocols.tcp-ip, [email protected]
Subject: Re: BOOTP vendor support
The only vendor that I know uses bootp is cisco. Their gateways can
use it to get IP addresses. (They can also use RARP - they send both
types of request, and believe whichever response they hear.) They
also have the code needed to pass bootp requests across gateways.
I've never understood why other vendors don't use it, since it's
clearly easier to install than RARP, and more general. I've not had
any trouble bringing up bootp on Unix systems, and it should also be
possible on Unix-based stuff like TWG's IP for VMS. I'd be inclined
to use bootp anyway for any new products.
-----------[000057][next][prev][last][first]----------------------------------------------------
Date: 5 Aug 1988 13:43-EDT
From: [email protected]
To: [email protected]
Cc: [email protected]
Subject: Re: TCP-IP for AT&T UNIX-PC 7300's
FTP Software can supply PC-based TCP/IP if you are running MS/DOS.
FTP Software is in Cambridge, MA. There are undoubtedly other sources
of supply including freeware say from MIT/LCS.
The DDN Network Information center at SRI International is another
good place to check - they have a lengthy catalog of software
which they have compiled as "DDN Protocol Implementations and
Vendors Guide" NIC 50002. It is also available on-line at
SRI-NIC.ARPA.
MMDF is available from Prof. David Farber, University of Pennsylvania,
Computer and Information Systems: [email protected]
Vint Cerf
-----------[000058][next][prev][last][first]----------------------------------------------------
Date: 5 Aug 88 16:51:00 PDT
From: Dave Crocker <[email protected]>
To: tcp-ip <[email protected]>
Subject: Re: Accidentally including the CC line
This is in reply to Bob <[email protected]> note:
Some people may have missed the trailing smile at the end of your comment
myself to use our VMS product, mostly out of masochism but partly so issues
such as the one you raise are familiar. Keith McCloghrie works on a number
of our products, but not the VMS one, so he can affort the luxury of
using a Unix interface (MH, when last I checked).
Why should I burden everyone with this clarification? Well, the problem
is that the VMS user interface to mail, with our TCP product, is standard
DEC issue, called VAXmail. While we have integrated into it as best
possible, through their foreign service interface, we do not touch the basic
vaxmail product.
We are thinking of offering a richer mail system for a number of platforms,
but that is mostly my way of trying to find an excuse to use some old
but fondly rememebered experiences.
Another alternative, shortly, will be All-In-One.
Dave Crocker
The Wollongong Group
-----------[000059][next][prev][last][first]----------------------------------------------------
Date: 5 Aug 88 10:36:55 GMT
From: [email protected] (Chris Torek)
To: comp.protocols.tcp-ip
Subject: Re: Micom-Interlan NP100 ethernet woes
The NP100 driver included in 4.3BSD (presumably written by or for
Interlan; at any rate, it was not done at Berkeley) is egregiously
buggy. A later revision of the driver (done after Berkeley got an
NP100) is available from Berkeley, either as part of 4.3BSD-tahoe or
separately. Contact Keith Bostic <[email protected]> if you
need just the driver.
Chris
-----------[000060][next][prev][last][first]----------------------------------------------------
Date: Fri, 5 Aug 88 17:01 EST
From: "Jerry Leichter ([email protected])", <[email protected]>
To: [email protected]
Subject: Moderated Newsgroup Posting
Path: venus!leichter
From: [email protected]
Newsgroups: mail.tcp-ip
Subject: Re: Ken Olsen on TCP/IP
Message-ID: <[email protected]>
Date: 5 Aug 88 17:01:31 GMT
References: <venus mail.tcp-ip:1807>
Organisation: VMS NEWS V4.0
Lines: 32
In article <venus mail.tcp-ip:1807>, [email protected] writes:
> Quoted without permission from Digital News, August 1, 1988:
>
> "Our attitude with TCP/IP is, 'Hey, we'll do it, but don't make a big
> system, because we can't fix it if it breaks.'"
>
> Does this reflect a lack of confidence in the Ultrix group?
The actual, full quote - from Ken Olsen - is:
"Our attitude with TCP/IP is, 'Hey, we'll do it, but don't make a big
system, because we can't fix it if it breaks - nobody can.'"
-------------
It's generally considered unfair to quote out of context. To CHANGE the con-
text - to deliberately mark something as a full sentence, with no indication
that you've left out part of the text, a part which changes the mean of what
came before - is bad enough. To then continue on and ask a question based on
the falsely-imputed meaning is downright dishonest.
Olsen goes on to clarify what he means even further:
"TCP/IP is OK if you've got a little informal club, and it doesn't
make any difference if it takes a while to fix it."
Now, you can disagree with this statement - probably most of the readers of
this list WILL disagree, though perhaps not all. But there's a world of
difference between disagreeing on the merits, and the intellectual dishonesty
of picking words OUT OF THE MIDDLE OF A SENTENCE and ascribing a new meaning
-- Jerry
-----------[000061][next][prev][last][first]----------------------------------------------------
Date: 5 Aug 88 13:35:04 GMT
From: [email protected] (Mike St. Johns)
To: comp.protocols.tcp-ip
Subject: TCP/IP and NFS for MacOS?
There were actually two articles - one about Apple in general, and
another about the A/UX stuff. The one about Apple in general starts
out with "... A/UX is another of Apple's software mistakes."
The other article was kinder.
Mike
(THis is the August 1988 issue of Byte we are discussing /msj/)
-----------[000062][next][prev][last][first]----------------------------------------------------
Date: 5 Aug 88 14:08:09 GMT
From: [email protected] (Alan Crosswell)
To: comp.protocols.tcp-ip
Subject: Re: BOOTP vendor support
Cisco's bootp also works on the terminal server in SLIP mode. I've
used the CMU PCIP distribution with it and it worked first time. No
more custom netdev on 8 million PC's.
/a
-----------[000063][next][prev][last][first]----------------------------------------------------
Date: 5 Aug 88 14:13:30 GMT
From: [email protected] (William C. VerSteeg)
To: comp.protocols.tcp-ip
Subject: Re: BOOTP vendor support
I agree with the opinion that BOOTP is a good way to initialize a dumb
device. We at Digital Communication Associates are designing new products
that use BOOTP and TFTP to downline load code and configurations. A
manufacturer of communications equipment has a great deal of impetous
to support these protocols. He requires them to boot. We will support
BOOTP on both our large, disk based systems and our small diskless units.
In a typical configuration, the dumb devices will boot from the disk-based
units. When a customer wants only the smaller, cheaper units, they will have
to boot from another vendor's device.
I am curious whether the minicomputer-oriented vendors will include support
for BOOTP in their standard distributions. TWG, SRI, NRC, etc would be
well served by including as much functionality as possible. However,
I wonder if the minicomputer manufacturers will be as likely to support
a protocol to load generic hardware. Would they fear selling fewer units
of there own diskless stations and terminal servers ? I also would like to
know of other BOOTP implementations to test against.
Bill VerSteeg
DCA
-----------[000064][next][prev][last][first]----------------------------------------------------
Date: 5 Aug 88 15:16:00 GMT
From: [email protected] (Dave Crocker)
To: comp.protocols.tcp-ip
Subject: RE: Van's algorithm's in Streams
This is in response to Kwang Sung's query:
Our newest version of Streams TCP contains Van's and Nagles algorithms
for congestion control, etc. The header-predection performance code is
scheduled for addition, shortly, although we are still trying to understand
its impact under mixed traffic conditions.
Dave Crocker
VP, Engineering
The Wollongong Group
-----------[000065][next][prev][last][first]----------------------------------------------------
Date: 5 Aug 88 16:18:01 GMT
From: [email protected] (Steve Alexander)
To: [email protected]
Subject: Re: Van Jacobson's Algorithm for AT&T Stream Implementations
In article <[email protected]> [email protected] (Kwang Sung) writes:
>I am curious that whether we can apply Van Jacobson's Algorithm to
>AT&T Stream TCP/IP implementations easily.
Lachman's System V STREAMS TCP has been shipping with Van's TCP (as
well as the latest UCB IP and UDP fixes) since June. Van's algorithms
were easy to integrate into our code. The fact that we run over STREAMS
At the performance seminar in May, a great deal of material was handed
out that described these enhancements. Perhaps ACE has extra copies
that you could obtain from them.
480 San Antonio Rd, Suite 100
Mountain View, CA 94040
415-941-3399
Hope this helps...
Steve Alexander, TCP/IP Development | stevea%[email protected]
Lachman Associates, Inc. | ...!{ihnp4,sun}!laidbak!stevea
-----------[000066][next][prev][last][first]----------------------------------------------------
Date: 5 Aug 88 16:37:56 GMT
From: [email protected]
To: comp.protocols.tcp-ip
Subject: Re: BOOTP vendor support
Not exactly a vendor, but the MIT uVAX C-Gateway also uses bootp, not only
to find out its IP address but also to invoke TFTP to boot the gateway
code. The gateway code also has the ability to forward bootp requests
through to appropriate bootp servers if necessary. With the one exception
that the boot code had to be specific to a subnet (because the 4.2 servers
has worked very well.
Also, CMU has been using bootp to auto-configure IBM PC's for quite a while
using the bootp vendor field to set the various other things the PC's need
to know. [Now for the vendor support part] We'll be including a bootp
client for configuring PC's using the CMU style vendor field (actually
either CMU style or RFC-1048) with our next release.
David Bridgham
FTP Software
-----------[000067][next][prev][last][first]----------------------------------------------------
Date: 5 Aug 88 17:15:36 GMT
From: cam%[email protected] (Chris Markle acc_gnsc)
To: comp.protocols.tcp-ip
Subject: Enet + TCP/IP for Honeywell
Folks,
Does anyone know of a tcp/ip implementation for Honeywell systems and the
associated enet hardware?
Chris Markle - ACC
cam%[email protected]
-----------[000068][next][prev][last][first]----------------------------------------------------
Date: 5 Aug 88 17:43:00 GMT
From: [email protected]
To: comp.protocols.tcp-ip
Subject: Re: TCP-IP for AT&T UNIX-PC 7300's
FTP Software can supply PC-based TCP/IP if you are running MS/DOS.
FTP Software is in Cambridge, MA. There are undoubtedly other sources
of supply including freeware say from MIT/LCS.
The DDN Network Information center at SRI International is another
good place to check - they have a lengthy catalog of software
which they have compiled as "DDN Protocol Implementations and
Vendors Guide" NIC 50002. It is also available on-line at
SRI-NIC.ARPA.
MMDF is available from Prof. David Farber, University of Pennsylvania,
Computer and Information Systems: [email protected]
Vint Cerf
-----------[000069][next][prev][last][first]----------------------------------------------------
Date: 5 Aug 88 18:55:34 GMT
From: [email protected] (Keith Bostic)
To: comp.protocols.tcp-ip
Subject: Re: Micom-Interlan NP100 ethernet woes
Substantial changes have been made to the Interlan np100
driver that was distributed with 4.3BSD. If anyone is
new copy.
Keith Bostic
[email protected]
uunet!keith
-----------[000070][next][prev][last][first]----------------------------------------------------
Date: 5 Aug 88 18:59:00 GMT
From: [email protected] (Dan Kegel)
To: comp.sys.mac,comp.protocols.tcp-ip
Subject: Summary: TCP/IP and NFS for the Mac
I recently asked the net for info about networking for the Mac SE, and
There seem to be only two systems that let plain old Mac programs transparantly
access files on a remote Unix fileserver:
1. TOPS, a proprietary network file system developed independantly
and later purchased by Sun; this has been available for some time.
The only Unix box that TOPS currently runs on is the Sun-3.
Either LocalTalk or Ethernet may be used to connect the Macs to the Sun.
TOPS phone number is (800) 445-8677 or (415) 769-8700.
System cost:
Software:
TOPS server on Sun ($900 for 1-4 clients,$1600 for 1-16 clients)
TOPS client on Mac ($250 per client) Hardware: using LocalTalk:$50 per client + $2000 for the Kinetics Fastpath bridge using EtherTalk:$600 per client
2. Cayman Systems' Gatorbox, an NFS (Ethernet) to AFP (LocalTalk) bridge;
the box and software sell for $3495, and takes about 6 weeks to get. The Unix box must be running NFS (and most can; many are shipped with it). It links up to 32 Macs running Apple's network (AFP on LocalTalk) to a standard Ethernet network. Cayman Systems' phone number is (617) 494-1999. System cost:$50 per client (for LocalTalk cable) + $3500 for the Gatorbox bridge Other NFS systems, rumored but not currently available, are 3. University of Michgan had a client version of NFS for the Mac at last years Sun Connectathon. Don't think they ever fielded it. 4. Peter Honeyman (one of the authors of HoneyDanBer uucp?) led a project that put tcp/ip and NFS on Macs, under contract to Apple. Apple has the software now; it's unclear when if ever they will release it. LocalTalk is Apple's 200 kilobit/sec serial networking hardware, which is quite slow compared with the 10 Megabit/sec Ethernet; one might therefore expect to be able to connect up only five or ten Macs per LocalTalk bus before seeing degradation, as opposed to fifty or so on an Ethernet bus. (I've never tried it, so I dunno.) There are also systems available that let TCP/IP aware programs communicate with other machines on an Ethernet; this isn't as nice as transparant file access, but it can be pretty darn useful. 1. Kinetics sells Ethernet boards for all versions of the Macintosh; it also sells a TCP/IP (Ethernet) to TCP/IP (Appletalk) bridge. 2. NCSA maintains a professional-looking TELNET package for the PC and the Mac which supports remote login, multiple VT102 emulation, Tek 4014 emulation, subnetting, and dynamic IP address assignment via RARP. I think this is shipped with Kinetics equipment. It is available for anonymous FTP over the Darpanet from ftp.ncsa.uiuc.edu (128.174.20.50). Contacts listed on their blurb: Tim Krauskopf [email protected] (ARPA) Gaige B. Paulsen [email protected] National Center for Supercomputing Applications (NCSA) University of Illinois, Urbana-Champaign 3. Either Stanford or Columbia maintain something called KIP and CAP which seems to be another TCP/IP package; NCSA would know more about it. 4. Phil Karn's KA9Q package is another (public-domain?) TCP/IP implementation. Thanks to everybody who replied. I'm still looking for something that supports NFS over Ethernet right to the Mac... -- Dan Kegel "We had to get it passed before the columnists attacked!" [email protected] rochester!srs!dan dan%[email protected] -----------[000071][next][prev][last][first]---------------------------------------------------- Date: 5 Aug 88 20:29:51 GMT From: [email protected] (Ozalp Babaoglu) To: comp.protocols.tcp-ip Subject: x.25 as an internet backbone suppose a country (italy, to be precise) currently has a single internet site (in pisa) and has been registered as a top-level domain (domain .IT). there are three class C type IP addresses allocated to the country. what are some reasonable ways to structure subdomains in this country domain and incorporate LANs at other sites (cities) into the internet? the physical transport medium available is x.25 (both private and PDN run by the telephone company). what is the technology of choice for ethernet-x.25 gateway hardware and the software to do the routing and encapsulation (of IP packets over x.25)? any suggestions will be appreciated. ozalp babaoglu -----------[000072][next][prev][last][first]---------------------------------------------------- Date: 6 Aug 88 02:53:00 EST From: "BARRY NEWTON" <[email protected]> To: "tcp-ip" <[email protected]> Subject: Advertising If everybody on the tcp-ip distribution list were to give the "Grand Poohbah" one telephone call on his thoughtfully provided number, he might come to a more clear understanding of the value and consideration involved in keeping crowded resources clear... But don't do it. It wouldn't be nice:-) Barry -----------[000073][next][prev][last][first]---------------------------------------------------- Date: 5 Aug 88 22:01:00 GMT From: [email protected] ("Jerry Leichter ", [email protected]) To: comp.protocols.tcp-ip Subject: Moderated Newsgroup Posting Path: venus!leichter From: [email protected] Newsgroups: mail.tcp-ip Subject: Re: Ken Olsen on TCP/IP Message-ID: <[email protected]> Date: 5 Aug 88 17:01:31 GMT References: <venus mail.tcp-ip:1807> Organisation: VMS NEWS V4.0 Lines: 32 In article <venus mail.tcp-ip:1807>, [email protected] writes: > Quoted without permission from Digital News, August 1, 1988: > > "Our attitude with TCP/IP is, 'Hey, we'll do it, but don't make a big > system, because we can't fix it if it breaks.'" > > Does this reflect a lack of confidence in the Ultrix group? The actual, full quote - from Ken Olsen - is: "Our attitude with TCP/IP is, 'Hey, we'll do it, but don't make a big system, because we can't fix it if it breaks - nobody can.'" ------------- It's generally considered unfair to quote out of context. To CHANGE the con- text - to deliberately mark something as a full sentence, with no indication that you've left out part of the text, a part which changes the mean of what came before - is bad enough. To then continue on and ask a question based on the falsely-imputed meaning is downright dishonest. Olsen goes on to clarify what he means even further: "TCP/IP is OK if you've got a little informal club, and it doesn't make any difference if it takes a while to fix it." Now, you can disagree with this statement - probably most of the readers of this list WILL disagree, though perhaps not all. But there's a world of difference between disagreeing on the merits, and the intellectual dishonesty of picking words OUT OF THE MIDDLE OF A SENTENCE and ascribing a new meaning to them that wasn't there to start with. -- Jerry -----------[000074][next][prev][last][first]---------------------------------------------------- Date: 5 Aug 88 23:23:37 GMT From: [email protected] (Patty Winter) To: comp.sys.mac,comp.protocols.tcp-ip Subject: Re: Summary: TCP/IP and NFS for the Mac In article <[email protected]> [email protected] (Dan Kegel) writes: > >4. Phil Karn's KA9Q package is another (public-domain?) TCP/IP implementation. ^^^^^^^^^^^^^^^^ For amateur radio and university research uses, yes. Otherwise, no. Patty ============================================================================= Patty Winter N6BIS DOMAIN: [email protected] AMPR.ORG: [44.4.0.44] UUCP: {decwrl,nsc,sun}!apple!winter ============================================================================= -----------[000075][next][prev][last][first]---------------------------------------------------- Date: 5 Aug 88 23:51:00 GMT From: [email protected] (Dave Crocker) To: comp.protocols.tcp-ip Subject: Re: Accidentally including the CC line This is in reply to Bob <[email protected]> note: Some people may have missed the trailing smile at the end of your comment about wishing you could accidentally replying to CC recipients. I force myself to use our VMS product, mostly out of masochism but partly so issues such as the one you raise are familiar. Keith McCloghrie works on a number of our products, but not the VMS one, so he can affort the luxury of using a Unix interface (MH, when last I checked). Why should I burden everyone with this clarification? Well, the problem is that the VMS user interface to mail, with our TCP product, is standard DEC issue, called VAXmail. While we have integrated into it as best possible, through their foreign service interface, we do not touch the basic vaxmail product. We are thinking of offering a richer mail system for a number of platforms, but that is mostly my way of trying to find an excuse to use some old but fondly rememebered experiences. Another alternative, shortly, will be All-In-One. Dave Crocker The Wollongong Group -----------[000076][next][prev][last][first]---------------------------------------------------- Date: 6 Aug 88 01:20:32 GMT From: [email protected] (root) To: comp.sys.mac,comp.protocols.tcp-ip Subject: Re: Summary: TCP/IP and NFS for the Mac This is a bit tangential an answer to the original question "Who has NFS on MacOS?". For small machines there are NFS implementations available for both the IBM PC and Amiga. Sun sells PC-NFS for the IBM PC - package price is ~$900. Ameristar Technology sells NFS
for the Amiga - package cost also $900. Since part of my time is spent at Ameristar, I'll allow myself the luxury of giving their phone number: (516) 698-0834. You probably already know how to contact Sun anyways :-). Rick Spanbauer Ameristar Technology PS. I would like to hear from anyone who has a Gator Box. -----------[000077][next][prev][last][first]---------------------------------------------------- Date: 6 Aug 88 01:48:29 GMT From: [email protected] (David R. Conrad) To: comp.protocols.tcp-ip Subject: Re: BOOTP vendor support Add the University of Maryland to the list of Universities that use bootp for PCs. Our public workstation labs use it with RFC1048 extensions to provide information for the TCP/IP for the PC that we use here. We currently use a bootp server per subnet so we don't have to worry about gateways forwarding requests although our bootp server (based on CMU's with local additions) does have forwarding capabilities. We'd also be interested in having more vendors (particularly Proteon) support bootp forwarding -drc -----------[000078][next][prev][last][first]---------------------------------------------------- Date: 6 Aug 88 07:53:00 GMT From: [email protected] ("BARRY NEWTON") To: comp.protocols.tcp-ip Subject: Advertising If everybody on the tcp-ip distribution list were to give the "Grand Poohbah" one telephone call on his thoughtfully provided number, he might come to a more clear understanding of the value and consideration involved in keeping crowded resources clear... But don't do it. It wouldn't be nice:-) Barry -----------[000079][next][prev][last][first]---------------------------------------------------- Date: 6 Aug 88 17:23:35 GMT From: [email protected] (Lars J Poulsen) To: comp.protocols.tcp-ip Subject: Re: x.25 as an internet backbone > From [email protected] Sat Aug 6 09:35:15 1988 > Date: 5 Aug 88 20:29:51 GMT > From: [email protected] (Ozalp Babaoglu) > Organization: Cornell Univ. CS Dept, Ithaca NY > Subject: x.25 as an internet backbone > To: [email protected] > > suppose a country (italy, to be precise) currently has a single > internet site (in pisa) and has been registered as a top-level domain > (domain .IT). there are three class C type IP addresses > allocated to the country. what are some reasonable ways to structure > subdomains in this country domain and incorporate LANs at other > sites (cities) into the internet? the physical transport medium > available is x.25 (both private and PDN run by the telephone company). > > what is the technology of choice for ethernet-x.25 gateway hardware > and the software to do the routing and encapsulation (of IP > packets over x.25)? any suggestions will be appreciated. > > ozalp babaoglu For each campus, assume an ethernet with its own network number. (class C may be adequate for a while). For each of these, nominate a router with an X.25 interface to be the gateway to the outside world. Suitable routers include Ultrix with ACC's ACP5250, SUN with SUNLINK, VMS with Wollongong TCP/IP and ACP5250, and many otehrs as well as standalone router boxes. The router must run EGP, ROUTE-D or similar gateway protocol to advertize reachability. If the private X.25 network has a DNIC and can communicate with the public data network, then you have one X.25 world, and all X.25 should use one network number. If not, get a network number for the X.25 network. Since X.25 has no ARP mechanism, all routers must share knowledge of IP address to X.25 address mappings. This means a centralized management of each X.25 IP network. CSNET does this on a commercial basis in the US, and it would be to your advantage to join them so that your PTT network is joined with the X.25 part of CSNET. However, I don't know if their fee schedule makes this practical. Another possibility is to declare your X.25 network to be its own IP network, and have a single gateway to the outside (via CSNET or AC.UK or via a private arrangement with a US site) but this means you have to have fairly sophisticated traffic analysis in the gateway in order to charge back the international X.25 charges to the member institutions (since they all will be charged to the gateway). I don't know of any router equipped to do this. Let me know how you arfe involved with the evangelism in Italy, and contact me if I can be of more help. / Lars Poulsen ACC Customer Service. P.S.: No slight is intended of any product not mentioned above. I have nothing against CMU TCP/IP or Hewlett-Packard. SRI MultiNet is a fine product, and so is the ACS4020... products mentioned above are for examples only. My employer does not know I'm sending this ... is that enough disclaimers ? -----------[000080][next][prev][last][first]---------------------------------------------------- Date: 7 Aug 88 04:59:14 GMT From: [email protected] (Steve DeJarnett) To: [email protected] Subject: nroff source for recent TCP/IP paper from Rutgers??? I recently read the paper posted by Charles Hedrick from Rutgers, and found it quite informative. I was wondering if the source (nroff or TeX) was available. It would be nice to have a printout that was more suitable for reading than a normal printout. I didn't save the author's email address, so sorry for the posting. Thanks in advance, ------------------------------------------------------------------------------- | Steve DeJarnett | Smart Mailers -> [email protected] | | Computer Systems Lab | Dumb Mailers -> ..!ucbvax!voder!polyslo!steve | | Cal Poly State Univ. |------------------------------------------------| | San Luis Obispo, CA 93407 | BITNET = Because Idiots Type NETwork | ------------------------------------------------------------------------------- -----------[000081][next][prev][last][first]---------------------------------------------------- Date: 7 Aug 88 05:24:30 GMT From: [email protected] (Drew Daniel Perkins) To: comp.protocols.tcp-ip Subject: Re: BOOTP vendor support > *Excerpts from ext.in.tcp-ip: 5-Aug-88 Re: BOOTP vendor support David R.* > *Conrad@terminus (517)* > We'd also be interested in having more vendors (particularly Proteon) > support bootp forwarding Hear Hear! We find BOOTP very useful. It's biggest problem though is that it requires special support in gateways to forward requests across subnets. Either that or a server for every subnet, which is a real pain since it is often cost prohibitive. As a campus support organization we can't afford to put a server machine (or two for redundancy) on each net. From my experience, it takes less than 150 lines of code or so for a fairly robust gateway forwarder implementation. In case it helps anybody, here is most of the code from our router implementation. Everyone's router is different of course, so I doubt if it will 'just slip in'. Drew /* * Bootstrap Protocol (BOOTP). RFC 951. * * 07-Oct-86 Drew D. Perkins (ddp) at Carnegie-Mellon University * Started history. * ********************************************************************** */ #include "cond/bootp.h" #if C_BOOTP > 0 /* * bp_input - process an incoming BOOTP server packet. * * dv = the device supplying the packet * p = the supplied BOOTP packet (with offset and length adjusted to * remove any encapsulating headers/trailers) * sport = the UDP source port of the sender of the datagram * saddr = the datagram's IP source address * daddr = the datagram's IP destination address * (These will typically be pointers into the encapsulating IP * header preceding the RCP packet - beware!) * * The following consistency checks are performed on the BOOTP packet: * - the physical length of the packet must be large enough to contain a * minimal BOOTP header. * If the packet is a boot request: * - the packet must not have been through too many gateways. * - the requestor must have waited a long enough time for service. * If the packet checks out, the message is counted and processed * according to the protocol. */ void bp_input(dv, p, sport, saddr, daddr) struct device *dv; struct packet *p; short sport; struct socket p_pkt saddr; struct socket p_pkt daddr; { register struct bootp p_pkt bp; register struct device *dvt; /* determined target device of pkt */ register struct ipmap *im; /* IP routing table entry */ register struct addmap *am; /* ARP routing table entry */ struct socket src, dest, tmp; /* src and dest of outgoing IP pkt */ short dport; /* destination UDP port */ int flag = 0; /* Have seen incoming device flag */ if (p->p_len < BOOTHEAD) { /* Packet large enough? */ profile(dv, bp_rmin); errorlog(p, EL_BP_RMIN); goto out; } bp = poff(bootp, p); #ifdef BOOTPDEBUG if (p->p_flag&P_TRACE) { printf("BOOTP (%d):\r\n", p->p_len); bp_prt(bp); } #endif /* BOOTPDEBUG */ switch(bp->bp_op) { /* Check opcode */ case BOOTREQUEST: /* Only forward after some amount time */ if (ntohs(bp->bp_secs) < BOOTMINSECS) { profile(dv, bp_rsecs); goto out; } /* Prevent loops */ if (bp->bp_hops++ > BOOTMAXHOPS) { profile(dv, bp_rhops); errorlog(p, EL_BP_RHOPS); goto out; } for (dvt=dv; flag == 0 || dvt != dv; dvt=dvt->dv_prnext[PR_IP]) { flag = 1; bcopy((char *)&dvt->dv_praddr[PRA_IP],(char *)&tmp, PRL_IP); if (bp->bp_giaddr.s_addr == tmp.s_addr) { profile(dv, bp_rloop); errorlog(p, EL_BP_RLOOP); goto out; } } profile(dv, bp_reqcnt); /* Fill in gateway field if empty */ if (!bp->bp_giaddr.s_addr) { copout(&dv->dv_praddr[PRA_IP], (char p_pkt) &bp->bp_giaddr, PRL_IP); } else { profile(dv, bp_rgway); } src.s_addr = bp->bp_giaddr.s_addr; dest.s_addr = daddr->s_addr; /* Check out destination address */ am = ar_map(PR_IP, (char p_pkt)daddr); if (am == 0 || !(am->am_flag&AM_BCAST)) { dest.s_addr = ipaddr(0xff, 0xff, 0xff, 0xff); profile(dv, bp_rbaddst); } dport = UD_BOOTPS; /* Send to BOOTP Server */ break; case BOOTREPLY: if (!bp->bp_yiaddr.s_addr) { profile(dv, bp_runkaddr); errorlog(p, EL_BP_RUNKADDR); goto out; } profile(dv, bp_repcnt); dest.s_addr = bp->bp_yiaddr.s_addr; /* Set up arp cache */ im = im_map(daddr, IM_ME); /* If it isn't found then we got this by mistake */ if (im == 0) { goto out; } dvt = im->im_dv; ar_remap(PR_IP,(char p_pkt)&dest,(char p_pkt)bp->bp_chaddr, dvt); src.s_addr = saddr->s_addr; dport = UD_BOOTPC; /* Send to BOOTP client */ break; default: profile(dv, bp_rbadop); errorlog(p, EL_BP_ROP); goto out; } ud_output(dv, p, sport, dport, (struct socket p_pkt) &dest, (struct socket p_pkt) &src); return; out: (*(p->p_done))(p); } void bp_prt(bp) register struct bootp p_pkt bp; { char tempa[20],tempb[20],tempc[20],tempd[20]; int i; printf(" op: %d, hops %d, id %ld, secs %d\r\n", bp->bp_op, bp->bp_hops, bp->bp_xid, bp->bp_secs); printf(" htype %d, hlen %d, chaddr ", bp->bp_htype, bp->bp_hlen); for (i = 0; i < bp->bp_hlen; i++) printf("%2x", bp->bp_chaddr[i]); printf("\r\n ciaddr = %s, yiaddr = %s, siaddr = %s, giaddr = %s\r\n", ip_fmt(&bp->bp_ciaddr, tempa), ip_fmt(&bp->bp_yiaddr, tempb), ip_fmt(&bp->bp_siaddr, tempc), ip_fmt(&bp->bp_giaddr, tempd)); } #endif /* C_BOOTP */ -----------[000082][next][prev][last][first]---------------------------------------------------- Date: 7 Aug 1988 21:06-EDT From: [email protected] To: [email protected] Cc: [email protected] Subject: Ether types per Torben Nielson's request. (that host not resolved from here.) Some Known Ethernet and IEEE802.3 "Type" Fields 6/18/88 The 13th and 14th octets of an Ethernet or IEEE802.3 packet (after the preamble) consist of the "Type" or "Length" field. These values are managed by XEROX. Some assignments are public, others private. Current information includes: Xerox Public Ethernet Packet Type documentation; IEEE802.3 Std; NIC RFC960; contributions from network managers and vendors. Hex 0000-05DC IEEE802.3 Length Field (0.:1500.) 0200 Xerox PUP (conflicts with IEEE802.3 Length Field range) (see 0A00) 0201 Xerox PUP Address Translation (conflicts ...) (see 0A01) 0600 Xerox NS IDP * 0800 DOD Internet Protocol (IP) * # 0801 X.75 Internet 0802 NBS Internet 0803 ECMA Internet 0804 CHAOSnet 0805 X.25 Level 3 0806 Address Resolution Protocol (ARP) * (for IP and for CHAOS) 0807 XNS Compatibility 081C Symbolics Private 0888 Xyplex 0900 Ungermann-Bass network debugger 0A00 Xerox IEEE802.3 PUP 0A01 Xerox IEEE802.3 PUP Address Translation 0BAD Banyan Systems 1000 Berkeley Trailer negotiation 1001-100F Berkeley Trailer encapsulation 1600 VALID-machine protocol? * 5208 BBN Simnet Private % 6000 DEC unassigned 6001 DEC Maintenance Operation Protocol (MOP) Dump/Load Assistance 6002 DEC Maintenance Operation Protocol (MOP) Remote Console 6003 DECNET Phase IV 6004 DEC Local Area Transport (LAT) 6005 DEC diagnostic protocol (at interface initialization?) 6006 DEC customer protocol 6007 DEC Local Area VAX Cluster (LAVC) 6008 DEC unassigned 6009 DEC unassigned 7000 Ungermann-Bass download 7002 Ungermann-Bass diagnostic/loopback 8003 Cronus VLN 8004 Cronus Direct 8005 HP Probe protocol 8006 Nestar 8010 Excelan 8013 Silicon Graphics diagnostic 8014 Silicon Graphics network games 8015 Silicon Graphics reserved 8016 Silicon Graphics XNS NameServer, bounce server 8019 Apollo DOMAIN 8035 Reverse Address Resolution Protocol (RARP) 8038 DEC LanBridge Management 8039 DEC unassigned 803A DEC unassigned 803B DEC unassigned 803C DEC unassigned 803D DEC Ethernet Encryption Protocol 803E DEC unassigned 803F DEC LAN Traffic Monitor Protocol 8040 DEC unassigned 8041 DEC unassigned 8042 DEC unassigned 805B Stanford V Kernel, experimental 805C Stanford V Kernel, production 807C Merit Internodal 8080 Vitalink TransLAN III Management 809B EtherTalk (AppleTalk over Ethernet) 80DE TRFS (Integrated Solutions Transparent Remote File System) 80F3 AppleTalk Address Resolution Protocol (AARP) 8107 Symbolics Private 8108 Symbolics Private 8109 Symbolics Private 8137 Novell 9000 Loopback (Configuration Test Protocol) 9001 Bridge Communications XNS Systems Management 9002 Bridge Communications TCP/IP Systems Management FF00 BBN VITAL-LanBridge cache wakeups % * These protocols use Ethernet broadcast, where multicast would be preferable. # BBN Butterfly Gateways also use 0800 for non-IP, with IP version field = 3. % BBN Private Protocols, not registered Some Known Ethernet Vendor Addresses 8/7/88 Ethernet hardware addresses are 48 bits, expressed as 12 hexadecimal digits (0-9, plus A-F, capitalized). These 12 hex digits consist of the first/left 6 digits (which should match the vendor of the Ethernet interface within the station) and the last/right 6 digits which specify the interface serial number for that interface vendor. Ethernet addresses might be written unhyphenated (e.g. 123456789ABC), or with one hyphen (e.g. 123456-789ABC), but should be written hyphenated by octets (e.g. 12-34-56-78-9A-BC). These addresses are physical station addresses, not multicast nor broadcast, so the second hex digit (reading from the left) will be even, not odd. At present, it is not clear how the IEEE assigns Ethernet block addresses. Whether in blocks of 2**24 or 2**25, and whether multicasts are assigned with that block or separately. A portion of the vendor block address is reportedly assigned serially, with the other portion intentionally assigned randomly. If there is a global algorithm for which addresses are designated to be physical (in a chipset) versus logical (assigned in software), or globally-assigned versus locally-assigned addresses, some of the known addresses do not follow the scheme. 00000C Cisco 00002A TRW 00005A S & Koch 000093 Proteon 00009F Ameristar Technology 0000AA Xerox Xerox machines 0000C0 Western Digital 0000DD Gould 000102 BBN BBN internal usage (not registered) 001700 Kabel 00DD00 Ungermann-Bass 00DD01 Ungermann-Bass 020701 Interlan UNIBUS or QBUS machines, Apollo 020406 BBN BBN internal usage (not registered) 02608C 3Com IBM PC; Imagen; Valid 02CF1F CMC Masscomp, Silicon Graphics 080002 Bridge 080005 Symbolics Symbolics LISP machines 080008 BBN 080009 Hewlett-Packard 080010 AT+T 080014 Excelan BBN Butterfly, Masscomp, Silicon Graphics 080017 NSC 08001A Data General 08001B Data General 08001E Apollo 080020 Sun Sun machines 080025 CDC 080028 TI Explorer 08002B DEC UNIBUS or QBUS machines, VAXen, LANBridges (DEUNA, DEQNA, DELUA) 080045 Xylogics??? 080047 Sequent 080049 Univation 08004C Encore 08004E BICC 080068 Ridge 080069 Silicon Graphics 08006E Excelan 08007C Vitalink TransLAN III 080089 Kinetics AppleTalk-Ethernet interface 08008B Pyramid 08008D XyVision XyVision machines AA0003 DEC Global physical address for some DEC machines AA0004 DEC Local logical address for systems running DECNET Some Known Ethernet Multicast Addresses 6/18/88 Ethernet Type Address Field Usage Multicast Addresses: 09-00-09-xx-xx-xx ???? HP multicasts 09-00-2B-01-00-00 8038 DEC LanBridge Copy packets 09-00-2B-01-00-01 8038 DEC LanBridge Hello packets 1 packet per second, sent by the designated LanBridge AB-00-00-01-00-00 6001 DEC Maintenance Operation Protocol (MOP) Dump/Load Assistance AB-00-00-02-00-00 6002 DEC Maintenance Operation Protocol (MOP) Remote Console 1 System ID packet every 8-10 minutes, by every: DEC LanBridge DEC DEUNA interface DEC DELUA interface DEC DEQNA interface (in a certain mode) AB-00-00-03-00-00 6003 DECNET Phase IV end node Hello packets 1 packet every 15 seconds, sent by each DECNET host AB-00-00-04-00-00 6003 DECNET Phase IV Router Hello packets 1 packet every 15 seconds, sent by the DECNET router AB-00-00-05-00-00 ???? Reserved DEC through AB-00-03-FF-FF-FF AB-00-04-00-00-00 ???? Reserved DEC customer private use through AB-00-04-00-FF-FF AB-00-04-01-xx-yy 6007 DEC Local Area VAX Cluster groups CF-00-00-00-00-00 9000 Ethernet Configuration Test protocol (Loopback) Broadcast Address: FF-FF-FF-FF-FF-FF 0600 XNS packets, Hello or gateway search? 6 packets every 15 seconds, per XNS station FF-FF-FF-FF-FF-FF 0800 IP (e.g. RWHOD via UDP) as needed FF-FF-FF-FF-FF-FF 0806 ARP (for IP and CHAOS) as needed FF-FF-FF-FF-FF-FF 1600 VALID packets, Hello or gateway search? 1 packets every 30 seconds, per VALID station -----------[000083][next][prev][last][first]---------------------------------------------------- Date: 7 Aug 88 21:59:16 GMT From: [email protected] To: comp.protocols.tcp-ip Subject: Re: Moderated Newsgroup Posting It was clearly wrong of me to have elided an elision symbol after my quotation. However, I rather resent being called "downright dishonest." Granted that Olsen clearly believes that the problem is TCP/IP, not any incompetence of the Ultrix group, remember that he sells a product -- Ultrix -- that includes support for networking. It would seem to me that the thrust of the quotation remains that Olsen is not serious about delivering the TCP/IP based Ultrix networking that DEC advertises. Phrased differently, I believe it fair to conclude that Olsen in fact has no confidence that his Ultrix group can deliver on DEC's marketing promises. Another quotation out of context from the same source: "VAX is VMS." This discussion is rapidly shifting away from topics of interest to the TCP-IP mailing list, and to ones more appropriate to INFO-VAX. -----------[000084][next][prev][last][first]---------------------------------------------------- Date: 7 Aug 88 23:02:44 GMT From: [email protected] ("Torben N. Nielsen") To: comp.protocols.tcp-ip Subject: Ether types... Would someone kindly mail me a copy of the current list of valid Ethernet types. I know it's out there somewhere and I've seen it fly by every so often. I'm sitting and looking at a dump of Ethernet packets and I'm seing a couple of strange things. Trying to find out what the packets are. Anyone happen to know if there're legitimate reasons for sending to yourself onan Ethernet? That is, Ethernet packets where the source and the destination address are identical? Seems pointless since as far as I know, you cannot read packets you yourself transmitted off of the wire..... Am I wrong? Torben -----------[000085][next][prev][last][first]---------------------------------------------------- Date: 8 Aug 88 01:06:00 GMT From: [email protected] To: comp.protocols.tcp-ip Subject: Ether types per Torben Nielson's request. (that host not resolved from here.) Some Known Ethernet and IEEE802.3 "Type" Fields 6/18/88 The 13th and 14th octets of an Ethernet or IEEE802.3 packet (after the preamble) consist of the "Type" or "Length" field. These values are managed by XEROX. Some assignments are public, others private. Current information includes: Xerox Public Ethernet Packet Type documentation; IEEE802.3 Std; NIC RFC960; contributions from network managers and vendors. Hex 0000-05DC IEEE802.3 Length Field (0.:1500.) 0200 Xerox PUP (conflicts with IEEE802.3 Length Field range) (see 0A00) 0201 Xerox PUP Address Translation (conflicts ...) (see 0A01) 0600 Xerox NS IDP * 0800 DOD Internet Protocol (IP) * # 0801 X.75 Internet 0802 NBS Internet 0803 ECMA Internet 0804 CHAOSnet 0805 X.25 Level 3 0806 Address Resolution Protocol (ARP) * (for IP and for CHAOS) 0807 XNS Compatibility 081C Symbolics Private 0888 Xyplex 0900 Ungermann-Bass network debugger 0A00 Xerox IEEE802.3 PUP 0A01 Xerox IEEE802.3 PUP Address Translation 0BAD Banyan Systems 1000 Berkeley Trailer negotiation 1001-100F Berkeley Trailer encapsulation 1600 VALID-machine protocol? * 5208 BBN Simnet Private % 6000 DEC unassigned 6001 DEC Maintenance Operation Protocol (MOP) Dump/Load Assistance 6002 DEC Maintenance Operation Protocol (MOP) Remote Console 6003 DECNET Phase IV 6004 DEC Local Area Transport (LAT) 6005 DEC diagnostic protocol (at interface initialization?) 6006 DEC customer protocol 6007 DEC Local Area VAX Cluster (LAVC) 6008 DEC unassigned 6009 DEC unassigned 7000 Ungermann-Bass download 7002 Ungermann-Bass diagnostic/loopback 8003 Cronus VLN 8004 Cronus Direct 8005 HP Probe protocol 8006 Nestar 8010 Excelan 8013 Silicon Graphics diagnostic 8014 Silicon Graphics network games 8015 Silicon Graphics reserved 8016 Silicon Graphics XNS NameServer, bounce server 8019 Apollo DOMAIN 8035 Reverse Address Resolution Protocol (RARP) 8038 DEC LanBridge Management 8039 DEC unassigned 803A DEC unassigned 803B DEC unassigned 803C DEC unassigned 803D DEC Ethernet Encryption Protocol 803E DEC unassigned 803F DEC LAN Traffic Monitor Protocol 8040 DEC unassigned 8041 DEC unassigned 8042 DEC unassigned 805B Stanford V Kernel, experimental 805C Stanford V Kernel, production 807C Merit Internodal 8080 Vitalink TransLAN III Management 809B EtherTalk (AppleTalk over Ethernet) 80DE TRFS (Integrated Solutions Transparent Remote File System) 80F3 AppleTalk Address Resolution Protocol (AARP) 8107 Symbolics Private 8108 Symbolics Private 8109 Symbolics Private 8137 Novell 9000 Loopback (Configuration Test Protocol) 9001 Bridge Communications XNS Systems Management 9002 Bridge Communications TCP/IP Systems Management FF00 BBN VITAL-LanBridge cache wakeups % * These protocols use Ethernet broadcast, where multicast would be preferable. # BBN Butterfly Gateways also use 0800 for non-IP, with IP version field = 3. % BBN Private Protocols, not registered Some Known Ethernet Vendor Addresses 8/7/88 Ethernet hardware addresses are 48 bits, expressed as 12 hexadecimal digits (0-9, plus A-F, capitalized). These 12 hex digits consist of the first/left 6 digits (which should match the vendor of the Ethernet interface within the station) and the last/right 6 digits which specify the interface serial number for that interface vendor. Ethernet addresses might be written unhyphenated (e.g. 123456789ABC), or with one hyphen (e.g. 123456-789ABC), but should be written hyphenated by octets (e.g. 12-34-56-78-9A-BC). These addresses are physical station addresses, not multicast nor broadcast, so the second hex digit (reading from the left) will be even, not odd. At present, it is not clear how the IEEE assigns Ethernet block addresses. Whether in blocks of 2**24 or 2**25, and whether multicasts are assigned with that block or separately. A portion of the vendor block address is reportedly assigned serially, with the other portion intentionally assigned randomly. If there is a global algorithm for which addresses are designated to be physical (in a chipset) versus logical (assigned in software), or globally-assigned versus locally-assigned addresses, some of the known addresses do not follow the scheme. 00000C Cisco 00002A TRW 00005A S & Koch 000093 Proteon 00009F Ameristar Technology 0000AA Xerox Xerox machines 0000C0 Western Digital 0000DD Gould 000102 BBN BBN internal usage (not registered) 001700 Kabel 00DD00 Ungermann-Bass 00DD01 Ungermann-Bass 020701 Interlan UNIBUS or QBUS machines, Apollo 020406 BBN BBN internal usage (not registered) 02608C 3Com IBM PC; Imagen; Valid 02CF1F CMC Masscomp, Silicon Graphics 080002 Bridge 080005 Symbolics Symbolics LISP machines 080008 BBN 080009 Hewlett-Packard 080010 AT+T 080014 Excelan BBN Butterfly, Masscomp, Silicon Graphics 080017 NSC 08001A Data General 08001B Data General 08001E Apollo 080020 Sun Sun machines 080025 CDC 080028 TI Explorer 08002B DEC UNIBUS or QBUS machines, VAXen, LANBridges (DEUNA, DEQNA, DELUA) 080045 Xylogics??? 080047 Sequent 080049 Univation 08004C Encore 08004E BICC 080068 Ridge 080069 Silicon Graphics 08006E Excelan 08007C Vitalink TransLAN III 080089 Kinetics AppleTalk-Ethernet interface 08008B Pyramid 08008D XyVision XyVision machines AA0003 DEC Global physical address for some DEC machines AA0004 DEC Local logical address for systems running DECNET Some Known Ethernet Multicast Addresses 6/18/88 Ethernet Type Address Field Usage Multicast Addresses: 09-00-09-xx-xx-xx ???? HP multicasts 09-00-2B-01-00-00 8038 DEC LanBridge Copy packets 09-00-2B-01-00-01 8038 DEC LanBridge Hello packets 1 packet per second, sent by the designated LanBridge AB-00-00-01-00-00 6001 DEC Maintenance Operation Protocol (MOP) Dump/Load Assistance AB-00-00-02-00-00 6002 DEC Maintenance Operation Protocol (MOP) Remote Console 1 System ID packet every 8-10 minutes, by every: DEC LanBridge DEC DEUNA interface DEC DELUA interface DEC DEQNA interface (in a certain mode) AB-00-00-03-00-00 6003 DECNET Phase IV end node Hello packets 1 packet every 15 seconds, sent by each DECNET host AB-00-00-04-00-00 6003 DECNET Phase IV Router Hello packets 1 packet every 15 seconds, sent by the DECNET router AB-00-00-05-00-00 ???? Reserved DEC through AB-00-03-FF-FF-FF AB-00-04-00-00-00 ???? Reserved DEC customer private use through AB-00-04-00-FF-FF AB-00-04-01-xx-yy 6007 DEC Local Area VAX Cluster groups CF-00-00-00-00-00 9000 Ethernet Configuration Test protocol (Loopback) Broadcast Address: FF-FF-FF-FF-FF-FF 0600 XNS packets, Hello or gateway search? 6 packets every 15 seconds, per XNS station FF-FF-FF-FF-FF-FF 0800 IP (e.g. RWHOD via UDP) as needed FF-FF-FF-FF-FF-FF 0806 ARP (for IP and CHAOS) as needed FF-FF-FF-FF-FF-FF 1600 VALID packets, Hello or gateway search? 1 packets every 30 seconds, per VALID station -----------[000086][next][prev][last][first]---------------------------------------------------- Date: 8 Aug 88 08:28:00 PDT From: Dave Crocker <[email protected]> To: tcp-ip <[email protected]> Subject: RE: HP TCP/IP Conformance One minor correction to Walter Underwood's note about gatewaying of packets between the 802.3-based TCP for the HP3000 MPE/V and normal Ethernet TCP/IP: In addition to the other solutions available for relaying, Wollongong offers a product called WIN/ROUTE2 for DOS. It runs as a dedication DOS application turning the PC into an IP router between HP3000s and ethernet devices. It does not talk PROBE, so that routes betweeen it and the 3000s need to be manually configured. Performance of the device scales with the speed of the PC box. Dave -----------[000087][next][prev][last][first]---------------------------------------------------- Date: 8 Aug 88 11:02:00 PDT From: Dave Crocker <[email protected]> To: tcp-ip <[email protected]> Subject: RE: Van's algorithms in Streams To answer Van's query about my previous note: We do not expect Berkeley code to port directly over to our Streams implementation. While it would be delightful if it did, the Streams architecture lends itself to a substantially different implementation style, although many of the routines can translate quite easily. In the good cases, this means that the left window on your screen shows BSD and the right show the streams code, and you do fairly straightforward translations. The other piece of my comment was simply management-speak for saying that we don't have any in-house experience with this software revolution wrought by Van, et cie, so that we ought to gain some familiarity with its dynamics before shipping it to customers (who have a fairly strong expectation that we will support the code we ship.) Given the history of Van's changes to TCP code, I suspect that my m-speak was mostly a formality. Dave -----------[000088][next][prev][last][first]---------------------------------------------------- Date: Mon 8 Aug 88 15:20:55-PDT From: William Westfield <[email protected]> To: [email protected] Subject: Some ethernet controllers can hear themselves. Some ethernet controllers are capable of hearing packets that they are transmitting as they are being transmitted. If this is true, then sending a packet to yourself is a good way to check whether the ethernet is in good shape - it checks the transceiver and the ethernet cable as well as the controller. Bill Westfield cisco Systems. ------- -----------[000089][next][prev][last][first]---------------------------------------------------- Date: Mon, 8 Aug 88 17:38:36 PDT From: [email protected] (Bill Croft) To: [email protected] Subject: BOOTP 'vendors' Although I havent been keeping close track, here is a partial list of companies and organizations using BOOTP or offering it in their products. This also includes organizations that are evaluating it or running it in-house in their R&D groups. (Let me know if your name isnt on the list). Since client and server implementations are public domain and FTPable from safe.stanford.edu, it is straightforward for a vendor to use it in their products. One of the next issues of ConneXions has an overview article on BOOTP by Jeff Mogul of DEC's Western Research Lab. Companies: Cisco, FTP Software, DEC (server in next Ultrix release), Silicon Graphics, Kinetics (CMU ROMs), DCA, BBN, Data General, HP Labs, Spider Systems Ltd., Ciba-Geigy AG, Bellcore. Universities: Stanford, CMU, MIT, Rutgers, Rice, Boston U., U. Maryland, U. Michigan, Harvard, Penn-State, Purdue, McMaster U., etc. -----------[000090][next][prev][last][first]---------------------------------------------------- Date: 8 Aug 88 12:42:36 GMT From: [email protected] (Ron Zahavi) To: comp.protocols.tcp-ip Subject: Re: Enet + TCP/IP for Honeywell >> >> Folks, >> >> Does anyone know of a tcp/ip implementation for Honeywell systems and the >> associated enet hardware? >> >> Chris Markle - ACC >> cam%[email protected] Honeywell has a tcp/ip implementation (FTP, SMTP, TELNET) for the DPS6 and DPS8 systems (I worked on the SMTP for both). For more complete information on various configurations, etc. you can contact Mr. Dana Crabil at (703) 827-3000. -- Ron -- -----------[000091][next][prev][last][first]---------------------------------------------------- Date: Mon, 8 Aug 88 16:56:17 EDT From: Root Boy Jim <[email protected]> To: [email protected] Cc: [email protected] Subject: TCP/IP _over_ TLI???? (was: TLI transport specific addresses) ? From: [email protected] (Doug McCallum) ? You would have thought that AT&T would have understood the need of ? name servers and related tools that become an absolute necessity with ? large networks. Why would you think that? Since when does TPC know anything about networks except the phone system? Their solution would more likely be a special purpose hardware box that dials 411 and communicates directly with the synthesized voice that says the number is...'. ? Doug McCallum ? Interactive Systems Corp. ? [email protected] (Root Boy) Jim Cottrell <[email protected]> National Bureau of Standards Flamer's Hotline: (301) 975-5688 The opinions expressed are solely my own and do not reflect NBS policy or agreement Careful with that VAX Eugene! -----------[000092][next][prev][last][first]---------------------------------------------------- Date: Mon 8 Aug 88 17:11:40-EDT From: Jim Stevens <[email protected]> To: [email protected] Cc: [email protected] Subject: VAX VMS 5.0 TELNET & FTP? A colleague of mine who is not currently connected to the Internet asks the following question: We are looking for a commercial version of FTP and TELNET that supports and runs within the auspices of VAX/VMS version 5.0 for our VAX 11/785 cluster. We are getting ready to convert our VAX cluster over to version 5.0, and have been advised that our EXCELAN version of FTP and TELNET are not currently supported under 5.0. EXCELAN is currently working on a 5.0 version, however it is not currently available. If anyone has any data that can help us out, it would certainly be appreciated. Please respond directly to me. Thanks, Jim Stevens ([email protected]) ------- -----------[000093][next][prev][last][first]---------------------------------------------------- Date: 8 Aug 88 15:28:00 GMT From: [email protected] (Dave Crocker) To: comp.protocols.tcp-ip Subject: RE: HP TCP/IP Conformance One minor correction to Walter Underwood's note about gatewaying of packets between the 802.3-based TCP for the HP3000 MPE/V and normal Ethernet TCP/IP: In addition to the other solutions available for relaying, Wollongong offers a product called WIN/ROUTE2 for DOS. It runs as a dedication DOS application turning the PC into an IP router between HP3000s and ethernet devices. It does not talk PROBE, so that routes betweeen it and the 3000s need to be manually configured. Performance of the device scales with the speed of the PC box. Dave -----------[000094][next][prev][last][first]---------------------------------------------------- Date: Mon, 8 Aug 88 20:35:39 cdt From: german%[email protected] (Gregory German) To: [email protected] Subject: Re: Summary: TCP/IP and NFS for the Mac >>>This is a bit tangential an answer to the original question "Who has >>>NFS on MacOS?". For small machines there are NFS implementations >>>available for both the IBM PC and Amiga. Sun sells PC-NFS for the >>>IBM PC - package price is ~$900. Ameristar Technology sells NFS
>>>for the Amiga - package cost also $900. Since part of my time >>>is spent at Ameristar, I'll allow myself the luxury of giving >>>their phone number: (516) 698-0834. You probably already know >>>how to contact Sun anyways :-). >>> >>>Rick Spanbauer >>>Ameristar Technology Here is a list of PC-NFS prices FYI. I just thought I would point out the$995 price for the PC included an ethernet card.
PC-NFS-56 Media: $325 (1-4 copies) -$175 (250+ copies)
PC-NFS-51 Media and Manual: $395 (1-4 copies) -$220 (250+ copies)
PC-NFS-3C-51 Media, Manual and Board: $995 (1-4 copies) -$645 (250+ copies)
You can get down to about $100/copy of the software with right to copy options if you are heavy (500+) use. I have not checked recently, but the board included was the 3COM 3C501 last time I checked. (Sept. 1987) Greg German ([email protected]) (217-333-8293) US Mail: Univ of Illinois, CSO, 1304 W Springfield Ave, Urbana, IL 61801 Office: 181 Digital Computer Lab. -----------[000095][next][prev][last][first]---------------------------------------------------- Date: 8 Aug 88 17:13:04 GMT From: [email protected] (Van Jacobson) To: comp.protocols.tcp-ip Subject: Re: Van's algorithm's in Streams > The header-predection performance code is scheduled for > addition, shortly, although we are still trying to understand > its impact under mixed traffic conditions. Dave - Are you working on header prediction in-house or is the above management-speak for "Berkeley hasn't given us the code yet"? (We haven't given it to anybody yet -- but "real soon now".) We've been running the header prediction tcp for 3 months now and the only "impact" I've observed is that things get faster -- under any traffic conditions. That shouldn't be too surprising: The "prediction" code adds about 6us of compares to the tcp input processing. If the prediction loses, you fall through to the old input code (about 220us of processing, on the average). If the prediction wins, you do about 25us of processing, on the average. For bidirectional dataflows (e.g., telnet, smtp, etc.) the prediction wins slightly more than half the time (there are counters in our implementation to measure this -- I was surprised the hit rate was so high). [On unidirectional flows, the prediction wins all the time.] So, the impact for, say, N packets is: old = N * 220; new = N/2 * 226 + N/2 * 31. I.e., you pick up about a factor of two on bidirectional traffic and a factor of seven on unidirectional traffic. (Times will vary -- these were on a Sun-3/60. But the new/old ratios should stay about the same on different architectures.) Of course, I should point out again that the prediction didn't make much difference in overall performance -- it just made a small part of the work smaller. Given halfway reasonable protocols (as opposed to, say, the ISO protocols) and a half decent implementation, protocol processing seems to be a small fraction of the cost of networking. So far, my data makes me suspect that people working on hardware assists for protocol processing are solving the wrong problem. - Van ps- Just to ground the above timings in reality, here's our header prediction code from the 4bsd netinet/tcp_input.c. This code goes shortly after the pcb lookup (which is cached so it usually costs 3 32-bit compares). Other than checksumming the packet & making sure the header length makes sense, this is the complete tcp input processing. /* * Header prediction: check for the two common cases * of a uni-directional data xfer. If the packet has * no control flags, is in-sequence, the window didn't * change and we're not retransmitting, it's a * candidate. If the length is zero and the ack moved * forward, we're the sender side of the xfer. Just * free the data acked & wake any higher level process * that was blocked waiting for space. If the length * is non-zero and the ack didn't move, we're the * receiver side. If we're getting packets in-order * (the reassembly queue is empty), add the data to * the socket buffer and note that we need a delayed ack. */ if (tp->t_state == TCPS_ESTABLISHED && (tiflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK && ti->ti_seq == tp->rcv_nxt && ti->ti_win == tp->snd_wnd && tp->snd_nxt == tp->snd_max) { if (ti->ti_len == 0) { if (SEQ_GT(ti->ti_ack, tp->snd_una) && SEQ_LEQ(ti->ti_ack, tp->snd_max) && tp->snd_cwnd >= tp->snd_wnd) { /* * this is a pure ack for outstanding data * and we're not in the middle of slow-start * or congestion avoidance. */ ++tcppredack; if (tp->t_rtt && SEQ_GT(ti->ti_ack,tp->t_rtseq)) tcp_xmit_timer (tp); sbdrop (&so->so_snd, ti->ti_ack - tp->snd_una); tp->snd_una = ti->ti_ack; m_freem (m); /* * If all outstanding data is acked, stop the * retransmit timer. If there's no one * waiting to output, let tcp_output decide * between more output or persist. Otherwise * give the user a crack at the new space, * assuming he'll call tcp_output when it's * filled. If there is more data to be acked, * restart retransmit timer, using current * (possibly backed-off) value. */ if (tp->snd_una == tp->snd_max) tp->t_timer[TCPT_REXMT] = 0; else if (tp->t_timer[TCPT_PERSIST] == 0) tp->t_timer[TCPT_REXMT] = tp->t_rxtcur; if ((so->so_snd.sb_flags & SB_WAIT) || so->so_snd.sb_sel) sowwakeup(so); else if (so->so_snd.sb_cc) (void) tcp_output (tp); return; } } else if (ti->ti_ack == tp->snd_una && tp->seg_next == (struct tcpiphdr *)tp && ti->ti_len <= sbspace(&so->so_rcv)) { /* * this is a pure, in-sequence data packet * with nothing on the reassembly queue and * we have enough buffer space to take it. */ ++tcppreddat; tp->rcv_nxt += ti->ti_len; /* * Drop TCP and IP headers then add data * to socket buffer */ m->m_off += sizeof(struct tcpiphdr); m->m_len -= sizeof(struct tcpiphdr); sbappend(&so->so_rcv, m); sorwakeup(so); tp->t_flags |= TF_DELACK; return; } } /* * Prediction failed: do things one step at a time. ... -----------[000096][next][prev][last][first]---------------------------------------------------- Date: 8 Aug 88 18:02:00 GMT From: [email protected] (Dave Crocker) To: comp.protocols.tcp-ip Subject: RE: Van's algorithms in Streams To answer Van's query about my previous note: We do not expect Berkeley code to port directly over to our Streams implementation. While it would be delightful if it did, the Streams architecture lends itself to a substantially different implementation style, although many of the routines can translate quite easily. In the good cases, this means that the left window on your screen shows BSD and the right show the streams code, and you do fairly straightforward translations. The other piece of my comment was simply management-speak for saying that we don't have any in-house experience with this software revolution wrought by Van, et cie, so that we ought to gain some familiarity with its dynamics before shipping it to customers (who have a fairly strong expectation that we will support the code we ship.) Given the history of Van's changes to TCP code, I suspect that my m-speak was mostly a formality. Dave -----------[000097][next][prev][last][first]---------------------------------------------------- Date: 8 Aug 88 20:09:00 GMT From: [email protected] (David R Falkenburg) To: comp.sys.mac,comp.protocols.tcp-ip Subject: Re: Summary: TCP/IP and NFS for the Mac In article <[email protected]>, [email protected] (Dan Kegel) writes: > 3. University of Michgan had a client version of NFS for the Mac at last > years Sun Connectathon. Don't think they ever fielded it. > > 4. Peter Honeyman (one of the authors of HoneyDanBer uucp?) led a project > that put tcp/ip and NFS on Macs, under contract to Apple. > Apple has the software now; it's unclear when if ever they will release it. Here at university of michigan, we had been using (testing, etc.) the CITI MacNFS. Both 3 & 4 were the same project-- Honeyman was project manager for both MacIP and MacNFS. both products are now in apple's hands. ALSO didn't anybody mention CAP (specifically AUFS)? it allows the unix box to act as an appleshare file server with the advent of System 6.0's inclusion of AppleShare Client this is a mostly free (with the exception of the kbox) alternative to systems like tops. -dave falkenburg university of michigan computer aided engineering network [email protected] umix!caen.engin.umich.edu!falken -----------[000098][next][prev][last][first]---------------------------------------------------- Date: Tue, 09 Aug 88 01:42:31 EDT From: Peter DiCamillo <CMSMAINT%[email protected]> To: [email protected] Subject: Release of Brown University's tn3270 for the Macintosh Please forgive the posting of this announcement to several relevant distribution lists. The first release of Brown University's tn3270 for the Macintosh is now available. This program consists of the NCSA TCP/IP kernel by Tim Krauskopf and Gaige B. Paulsen, Telnet 3270 option negotiation code developed by Greg Minshall at Berkeley, and 3270 emulation and Macintosh user interface code developed at Brown. It allows a Macintosh with a TCP/IP connection to access a host as a full-featured 3270 terminal. tn3270 is available via Internet anonymous FTP, over BITNET, or from Brown for a small distribution fee. Details of tn3270's features and availability are provided below. NETWORK FEATURES tn3270 includes all the features of version 2.0 of the NCSA TCP/IP kernel. These include support for both Ethernet connections and LocalTalk connections via a Kinetics gateway, a built-in FTP server, and domain nameserver support. Also, tn3270 supports dynamic IP number assignment when a Kinetics gateway is running KIP code, and allows the user to override the default Telnet terminal type and port number. EMULATION FEATURES On all Macintoshes, tn3270 emulates a 3278 with extended highlighting, APL, and the APL/Text character set. In addition, most graphics capabilities of a 3179 G or PC/GX are emulated. tn3270 also supports several 3270 enhancements, including typeahead and special blank processing. On a Macintosh II (or other Macintosh with color Quickdraw) tn3270 supports 3279 base color, four color, and eight color text, and eight color 3179 graphics. On Macintoshes with large screens, tn3270 supports either 9 or 12-point text for 24 lines, and 32 lines using 9-point text. Although primarily a 3270 emulation program, tn3270 also provides basic line mode Telnet support, and emulates a VT-52 terminal. MACINTOSH FEATURES tn3270 allows the 3270 cursor to be moved with a single mouse click, and allows the user to set the function of a double mouse click. Full MultiFinder support is provided, and on color Macintoshes the standard color picker may be used to set any screen colors. tn3270 utilizes offscreen bitmaps for fast, flicker-free screen refreshing. The speed of tn3270 can approach that of a locally-connected 3270, with updates as fast as two screens per second. SPECIAL FEATURES In addition to FTP server support, special support is provided for VM/CMS file transfer. Easy-to-use CMS RMAC and WMAC commands may be used to upload and download files during a CMS terminal session through the Telnet connection. Data transfer rates can be as high as 10K bytes/second. Brown also distributes an asynchronous terminal program, Term, which provides a user interface nearly the same as tn3270's when used with an IBM 7171. The combination of Term and tn3270 provides users with a consistent terminal interface, whether they have a high-speed network connection or a modem connection. The same CMS RMAC and WMAC commands also work with Term. HOW TO OBTAIN TN3270 Brown encourages tn3270 to be freely distributed, provided the program is not modified and the copyright notices are retained. tn3270 can be obtained in any of the following ways: Anonymous FTP from BROWNVM.BROWN.EDU (128.148.128.40): The distribution files are in the highest level directory. Begin by retrieving the file$READ-ME.FIRST which describes the other
files.
Anonymous FTP from NCSA (128.174.20.50):
The distribution files are the contents of the directory
NCSA_Telnet/tn3270.
BITNET distribution from [email protected]:
Request the distribution files by sending LISTSERV the command
"get tn3270 package". This command may be sent as a message
over BITNET, or as the first line of text in standard RFC 822
formatted mail. Other packages available are "tn3270xf" for the CMS
file transfer programs, and "term" for the Term program. Issue the
command "get local filelist" for a complete list of available
files.
Mail order from Brown:
Starting on September 1, Brown will accept mail orders for copies
of the tn3270 disk and documentation. To place an order, send a
check payable to Brown University for $20 to: tn3270 Distribution Brown University Computer Store P.O. Box 1885 Providence, RI 02912 (Orders from Rhode Island must include 6% sales tax.) KEEPING UP-TO-DATE The NCSA Telnet Digest will be used for discussing issues related to tn3270, as well as NCSA Telnet. To subscribe to the digest, send a request to [email protected]. SOURCE AVAILABILITY tn3270 source is written for Manx Aztec C, using the MPW-compatible library and include files. Brown intends to distribute the source in the near future. An announcement of source availability will be made in the NCSA Telnet Digest mentioned above. Peter DiCamillo BITNET: CMSMAINT@BROWNVM Internet: CMSMAINT%[email protected] U.S. Mail: Computing and Information Services, Brown University, P.O. Box 1885, Providence, RI 02912 Phone: (401) 863-7582 -----------[000099][next][prev][last][first]---------------------------------------------------- Date: 8 Aug 88 21:49:49 GMT From: [email protected] ("Michael F.H. Nittmann ") To: comp.protocols.tcp-ip Subject: modification to arp of course I am shure many other people thought of it, perhaps I missed it, so I shall dare to speak it out (got my asbestos overall): Why not resolve the problem of a dead hosts's ARP entries at least for orderly downed hosts by a FLUSH function code ARP packet. A host that would receive such a packet ( broadcasted for all or for local subnet) should compare the ARP contents with the originating address, and then flush the corresponding routing table entry or flag it down. This mechanism could be added to avoid timer rundowns. By the way I like that timer concept. An orderly downed host could broadcast that packet prior to it's halt, and I think most operating systems (or, challenge for interface designers, interface software could do that in a blip of last power in case of power off) even could signal their bye from the net in panic state or whatever the operating system has as last code (dump code) running prior to a real crash. Most micros sense the power line for power up and generate a power fail signal. And: if this additional packet is created, it would not rule out present implementations using ARP since they should ignore an invalid packet (which is no REQUEST or other known type). Some call that upwards compatibility. Comments, flames, shootings??? And of course, this is my personal stuff. Michael -----------[000100][next][prev][last][first]---------------------------------------------------- Date: 9 Aug 88 03:31:36 GMT From: [email protected] ("Michael F.H. Nittmann ") To: comp.protocols.tcp-ip Subject: some interim notes on the bsd network speedups Bravo! This is what I would call REAL speedups; as I understand the result, there is now a Sun 3/60 under SunOS4 with 750kB/s transfer rate and 1.25MB forwarding capacity. I do in no way discredit this work by furnishing some remarks to the mail article and I do not want anybody to do tricky quoting or implying negative contents. A good artist always merits some critics, not only thumb handclapping with the crowd. One remark to the 50% cpu load on forwarding: I guess that is the fact that the ethernet is at it's capacity limit and so the interface imposes cpu idle cycles on the transfer activities. One remark on loop unrolling: a sun is a pipelined processor machine BUT the compiler seems not to provide for memory prefetches nor for optimized loop structures. Only in this context an unrolling of scalar loops on a single processor machine can have results. One remark on "overhead" : if you have a slow scalar performing machine with some simple compiler that does not know about advantageous memory fetch instruction placing, the loop overhead seems to be small with respect to the instruction completion times within the loop. But this is not small loop overhead! A remark to the broken Cray's: it is absolutely true that on a fast machine with sophisticated instruction buffering, with compilers that take full advantage of memory "oddities" and with multiple parallel working functional units per processor the overhead of the return to the first instruction of a loop becomes prohibitive if the next instruction lies out of memory sequences and out of instruction buffers and the like. But the overhead is only big relatively to the instruction time spent within the loop which is already smaller than the sum of the executed instructions which seems not to be true in the case of the Sun. ( I intentionally left vectorization apart since this does not exist on the Sun) So Your school is perfectly right - for Your choosen combination of software (compiler, virtual memory, processor architecture ... ) and hardware. And that's it! The fact that just 1kB segments seem to be the optimum copy size seems to me more a Sun specific sort of resonance effect between memory transfers, virtual memory managing and interface readyness ON THE LOCAL MACHINE. As a physicist I learned to look very critically at experiments and their setups and I like to point out that Your performance test between two I guess equally optimized Suns certainly shows Your great competence on the field and the very true betterments Your code changes brought to the Sun OS4. But the experiment strictly only holds for Your configuration of two machines that operate at their - equal !!! - optimum configuration of packet munching parameters. This is sort of a formula I race. In a network You have to deal with what You call "broken" partners. They also work at least close to their respective optimum parameter configuration - resp. they would like to. Isn't it sort of a racism to declare that broken? And in a network You have to deal with the network medium itself. And no doubt: the bigger the chunks are, the better the network throughput is. Yes, I know that this is true for the monochromatic case of all equal packet lengths, but packet size distribution primarily causes disadvantages for the individual transfer ( small packet waiting for big one to pass). Now, if You operate a machine that's interface can deliver 100MB but the fastest channel You have will only gulp 10MB or 50MB (Ether, NSC Hyper), from the point of writing networking code on such a fast machine You have an interest to flood the net with a big packet and then continue with the honest work of letting users use the CPU until the 4MB Working station eventually may accept another packet. And even under these circumstances the networking software has to be as fast as possible to waste as little resources and cpu cycles as possible since Your CPU does not earn money by servicing 100MB interfaces with a some GB badnwidth CPU nor by pushing around small memory segments but by giving CPU cycles to users' number crunching codes. (this is a hit on the people that think " oh, the link is only xxxkB/s, why bother writing a code that could serve yyMB/s"). So on my opinion there are more viewpoints to observe than the record breaking perspective in clinical and artificial environment. disclaimers as usual (sometimes I have bad conscience because somebody pays NW costs for my private ognions) Michael. -----------[000101][next][prev][last][first]---------------------------------------------------- Date: Tue, 9 Aug 88 17:23:47 PDT From: [email protected] (Lars J Poulsen) To: [email protected] Subject: PSERV - a sample TCP/IP client/server pair PSERV - a sample piece of functional TCP/IP Berkeley socket programming. Every so often, programmers new to socket programming ask for working examples. I will give you this small example to play with. This program is a minimal remote spooling package, intended to solve a personal problem: I use every day two VMS systems and a Unix system. In my work area we have a LaserWriter connected to the Unix system, but I have to ride a sloooow elevator two floors to get to a VMS printer. I really wanted to write a small "lpd" client, but found that this would require the cooperation of system managers on both machines, since (1) LPD will only accept commands from known hosts (2) LPD will only accept connections from privileged ports (<1024) and the Wollongong VMS package enforces this also; you need system privileges to get a low-numbered port on WIN/TCP. So I decided to write my own mini protocol. This program illustrates the basic mechanism used by any server/client pair, and is small enough to dink around with fairly safely. [After all, if the system lets an unprivileged user do it, it must be safe :-) ?] The client runs un 4.3BSD or VMS/WIN/TCP; the server runs on 4.3BSD. Enjoy. / Lars Poulsen ACC Customer Service --------------------------------- Cut Here -------------------------------- In order not to clutter up TCP-IP unnecessarily (God knows I've done that enough recently) I've sent the actual source code to UNIX-SOURCES on BRL-SMOKE.ARPA. This is a relay for comp.sources; I don't know if it is two-way, so if anyone on the Usenet side needs it, I guess I can mail it. / Lars Poulsen -----------[000102][next][prev][last][first]---------------------------------------------------- Date: 9 Aug 88 15:42:24 GMT From: [email protected] (rod merry) To: [email protected] Subject: IBM VM TCP/IP? I am interested in the channel protocol which IBM uses for their VM TCP/IP to 8232 product. If you have experience with the source code or are aware of documentation from IBM please respond via email or phone. Thanks in advance. rod (612-535-8111) -----------[000103][next][prev][last][first]---------------------------------------------------- Date: 9 Aug 88 17:07:07 GMT From: [email protected] (Kwang Sung) To: [email protected] Subject: Difference between the various STREAM implementations. I hope someone on the net can answer to my interesting question. I would like know "what is the significant difference between the following various products in according to AT&T STREAMS Functional Specification ?". 1. The Wollongong STREAM implementation. 2. The Convergent STREAM implementation. ( ~ Lachman's STREAM product) 3. The Mitre STREAM implementation. ( ~ Unisoft's STREAM product) 4. CMC, EXCELAN STREAM implementation. 5. Or, any other STREAM implementation, if you can think. Kwang Sung Sr. Software Engineer, ARIX Corp. UUCP: ...!sun!aeras!smaug!kwang UUCP: ...!sun!aeras!bud!kwang -----------[000104][next][prev][last][first]---------------------------------------------------- Date: Tue, 9 Aug 88 17:44:51 GMT From: [email protected] (Henry Spencer) To: comp.protocols.tcp-ip Subject: Re: Ether types... In article <[email protected]> [email protected] ("Torben N. Nielsen") writes: >Anyone happen to know if there're legitimate reasons for sending to yourself >onan Ethernet? That is, Ethernet packets where the source and the destination >address are identical? Seems pointless since as far as I know, you cannot read >packets you yourself transmitted off of the wire..... Am I wrong? Whether you can hear yourself send is very much dependent on your Ethernet controller. Some can, some can't. -- Intel CPUs are not defective, | Henry Spencer at U of Toronto Zoology they just act that way. | uunet!attcan!utzoo!henry [email protected] -----------[000105][next][prev][last][first]---------------------------------------------------- Date: 9 Aug 88 18:12:00 GMT From: [email protected] To: [email protected] Subject: Re: Summary: TCP/IP and NFS for the Mac /* Written 11:16 pm Aug 8, 1988 by [email protected] in S39:comp.protocols.tcp-ip */ In article <[email protected]>, [email protected] (Dan Kegel) writes: > 3. University of Michgan had a client version of NFS for the Mac at last > years Sun Connectathon. Don't think they ever fielded it. > > 4. Peter Honeyman (one of the authors of HoneyDanBer uucp?) led a project > that put tcp/ip and NFS on Macs, under contract to Apple. > Apple has the software now; it's unclear when if ever they will release it. Here at university of michigan, we had been using (testing, etc.) the CITI MacNFS. Both 3 & 4 were the same project-- Honeyman was project manager for both MacIP and MacNFS. both products are now in apple's hands. ALSO didn't anybody mention CAP (specifically AUFS)? it allows the unix box to act as an appleshare file server with the advent of System 6.0's inclusion of AppleShare Client this is a mostly free (with the exception of the kbox) alternative to systems like tops. -dave falkenburg university of michigan computer aided engineering network [email protected] umix!caen.engin.umich.edu!falken /* End of text from S39:comp.protocols.tcp-ip */ -----------[000106][next][prev][last][first]---------------------------------------------------- Date: 9 Aug 88 23:46:37 GMT From: [email protected] (root) To: [email protected] Subject: Re: Summary: TCP/IP and NFS for the Mac In article <[email protected]>, [email protected] (Gregory German) writes: > Here is a list of PC-NFS prices FYI. I just thought I would point out the >$995 price for the PC included an ethernet card.
> PC-NFS-3C-51 Media, Manual and Board: $995 (1-4 copies) -$645 (250+ copies)
>
Yes, and $900 buys you NFS client, telnet, ftp and a Lance based shared memory Ethernet card for the Amiga. If you want to buy 250+ copies of AmigaNFS, I'm sure Ameristar will happily beat the$645 price too :-).
> You can get down to about 100/copy of the software with right to copy > options if you are heavy (500+) use. > > I have not checked recently, but the board included was the 3COM 3C501 > last time I checked. (Sept. 1987) > > Greg German ([email protected]) (217-333-8293) > US Mail: Univ of Illinois, CSO, 1304 W Springfield Ave, Urbana, IL 61801 > Office: 181 Digital Computer Lab. Sorry this turned somewhat commercial. This original posting was meant to be informational. Rick Spanbauer Ameristar Technology -----------[000107][next][prev][last][first]---------------------------------------------------- Date: 10 Aug 88 00:45:17 GMT From: [email protected] (Mark Boolootian) To: [email protected] Subject: info on ftp -- I am in need of some information and am hoping to obtain a few pointers from a few kindly souls. I'm a neophyte in this realm (networking) so please bare with me. We are in the process of trying to gateway a net implemented with TCP/IP to another net that is of our own design. The gateway will be provided by a VAX. I have been given the task of modifying the ftp server to speak our own homegrown protocol, thus creating what seems to me to be an "ftp gateway." I don't want to even begin to fumble around with my ideas of what is involved as my thoughts aren't very clear at this moment (nor at any other, for that matter). What I'm hoping is that some of you might steer me in a direction where I can read about ftp (and the ftp server) and get some practical knowledge about what all is involved here. Sorry if this seems open-ended and vague but that is currently where where my head resides. Please E-Mail replies and don't post to the net. I'm a long ways behind on reading this newgroup and I might never find the reply. Thanks in advance for any help. mb -- -- uucp: {gatech,ihnp4,pyramid,rutgers}!lll-lcc!booloo arpa: [email protected] -----------[000108][next][prev][last][first]---------------------------------------------------- Date: Wed, 10 Aug 88 09:46:05 -0500 From: Gurudatta Parulkar <[email protected]> To: [email protected] Cc: "Dave Clark"<[email protected]>, [email protected], [email protected] Subject: Comments on Proposed Transport Protocols We just completed a DRAFT of a technical report with the abstract enclosed. If you would like a copy to review, please send me a note. I want to mention that this report does not contain any quantitative analysis, and has only qualitative reasoning to support the claims. -guru Dr. Guru Parulkar Asst Professor [email protected] Dept of Computer Science [email protected] Washington University [email protected] St. Louis MO 63130 (314) 889-4621 ------------------------------------------------------------------------- Comments on Proposed Transport Protocols Anil Bhatia James Sterbenz Guru Parulkar [email protected] Computer and Communication Research Center Department of Computer Science Washington University St. Louis MO 63130 Abstract Over the last few years, a number of research groups have made considerable progress on the design of high speed networks -- on the order of a few hundred Mbps to a few Gbps. The emphasis of this work has been on the design of packet switches and on the design of network access protocols. However, this work has not yet addressed the internetworking and transport level issues in a high speed internet. The ARPA Internet, which has contributed a number of fundamental ideas to the field of internetworking of diverse networks, cannot be used in its current form as a model for the very high speed internetworks (VHSI) of the future.In this report, we propose a revised internet model, called the VHSI model, which among other things, argues for a number of application-oriented lightweight transport protocols (ALTPs). As part of our effort on the design of a VHSI model, we considered the appropriateness of recently proposed transport protocols, NETBLT and VMTP, as ALTP candidates. The purpose of this report is to present the results of this study, and present our thoughts on the design of ALTPs. The summary of the results of this study is that NETBLT and VMTP have contributed a number of interesting ideas to the design of transport protocols, and they do improve upon TCP within the current Internet model for the applications they were originally designed for. However, we believe that these protocols are not appropriate solutions for the VHSI model, because the underlying assumptions and trade-offs that these protocols are based on are very different in the VHSI model. For example, the VHSI model assumes a {\em quasi-reliable} connection-oriented internet protocol (as opposed to the current unreliable datagram IP), which can make performance guarantees and can ensure that the internet is congestion free (almost all the time). Also, the network speeds in the VHSI are a few order of magnitude more than what NETBLT and VMTP assume. We argue that the transport protocols in the VHSI model should avoid end-to-end flow control as much as possible, and make the end-to-end error control application specific and indepedent of the end-to-end latency. In general, the transport protocols should be simpler, designed to be mostly implemented in VLSI, well integrated with the host architecture and operating system, and targetted for a specific class of applications. The rest of this report is organized as follows: Section 2 provides an overview of the ARPA Internet model and the VHSI model. It also gives an overview of TCP and its associated problems. Section 3 provides an overview of NETBLT and VMTP and summarizes how these protocols are improvements over TCP. Section 4 describes the limitations of NETBLT and VMTP within the VHSI model. Section 5 presents our thoughts on the design of ALTP protocols for VHSI, and finally, Section 6 is the conclusion. -----------[000109][next][prev][last][first]---------------------------------------------------- Date: Wed, 10 Aug 88 09:22:01 EDT From: Barry Shein <bzs%bu-cs.bu.edu%bu-it.bu.edu%[email protected]> To: MURAKAMI%ntt-20.ntt.jp%RELAY.CS.NET%[email protected] Cc: tcp-ip%sri-nic.arpa%nuesun.ntt.jp%RELAY.CS.NET%[email protected], Crispin%sumex-aim.stanford.edu%nuesun.ntt.jp%RELAY.CS.NET%[email protected], george%iguanodon.cis.ohio-state.edu%nuesun.ntt.jp%RELAY.CS.NET%[email protected], nowicki%sun.com%nuesun.ntt.jp%RELAY.CS.NET%[email protected], celeste%coherent.com%nuesun.ntt.jp%RELAY.CS.NET%[email protected], earle%mahendo.Jpl.Nasa.Gov%nuesun.ntt.jp%RELAY.CS.NET%[email protected], he%idt.unit.no%relay.cs.net%nuesun.ntt.jp%RELAY.CS.NET%[email protected] Subject: Summary: Proxy ARP on SUN (quite a CC: list, oh well.) Here's the deal: I wrote a proxy arp based upon Sun's rarpd server which has been in production here at BU for over a year. The mainline is definitely Sun's but I call out to a bunch of routines which I wrote and put in a separate file, mainly the logic like "does this packet need a proxy rarp?" and the formatting of the reply and read-in of a table of networks to do Proxy arp for. So I've distributed it only as the .o (binary) of Sun's stuff and my added sources for relinking with a makefile and manual page. Some folks reported problems, the bit shift thing can be easily fixed but the "unaligned read" is a little mysterious (gee, works here, same machine, same OS, I'll have a look.) I don't believe any of this will work under Sun O.S. 4.0 (at least one try to recompile indicated some things had changed and 4.0 sources might be needed to make it work again.) So it's a little shaky at best, got me thru the night. Some of my tardiness in replying to people is explained by the fact that I am currently changing jobs and just haven't been around, I'm catching up (gee, these net requestors are harsh taskmasters!) The good news is this: A) I'll put what I have up for anonymous FTP soon, anyone that has a copy of my stuff should of course feel free to redistribute as stated above, binary of the mainline etc., as I distributed it. B) Haavard Eidnes claims to have completely written a new Proxyd from scratch based on my basic design (not the Sun sources) and I assume will make all sources available. He recently asked if he could just re-work the manual page I distributed and of course I said yes (Haavard: if you still haven't gotten my permission here it is again, if I didn't want people using my stuff I wouldn't give it out!) SOOOOOO... You should probably wait for B) to become available and that will solve all sorts of problems. My Proxyd kind of got out there by accident when someone mentioned I had given them a copy on one of the major lists. I knew it was a bit kinky and never really intended it for wide distribution nor thought all the problems could be worked out w/o a complete re-write due to its being based on the Sun rarpd (tho it was a good idea at the time, it was up in an hour or two.) And, of course, you might also consider Sun's product. Also, as I understand it you can get some limited amount of proxy arping by just sticking published arptab entries in with /etc/arp under SunOS or 4.3 (and probably others.) That's a limited hack as it's per-host rather than per-network so either you need large tables or small networks, but I thought I'd mention it. -Barry Shein -----------[000110][next][prev][last][first]---------------------------------------------------- Date: Wed 10 Aug 88 10:22:44 From: ken-ichiro murakami <MURAKAMI%[email protected]> To: tcp-ip%sri-nic.arpa%[email protected] Cc: Crispin%sumex-aim.stanford.edu%[email protected], george%iguanodon.cis.ohio-state.edu%[email protected], nowicki%sun.com%[email protected], celeste%coherent.com%[email protected], earle%mahendo.Jpl.Nasa.Gov%[email protected], he%idt.unit.no%relay.cs.net%[email protected] Subject: Summary: Proxy ARP on SUN I recently asked Mark<[email protected]> for info about Proxy ARP on SUN. He kindly forwarded to TCP-IP mailing-list, and I received many helpful responses. I modified and summarized these responses. Mark, George, Bill, Celeste, Greg and Haavard, thank you very much for your help. I hope this summary also helps other net people. (1) Barry Shein<[email protected]>'s proxy ARP daemon > From: "George M. Jones" <[email protected]> > I have Sun 3 (or possibly 4) binary and man page for Barry Shein's > proxy arp daemon, but you will have to contact him directly about > source. (2) "consulting special product" from Sun > From: Bill Nowicki <[email protected]> > From: "Celeste C. Stokely" <[email protected]> > From: Greg Earle <[email protected]> > Proxy ARP is available as a "consulting special product" from Sun > Software Support. If you are in the USA, you can call > 1-800-USA-4-SUN and request it. If you are not in the USA, you can > probably get it from the technical support people in your Sun sales > office. > The author, David Robinson, has made it available for anonymous FTP > from elroy.JPL.NASA.GOV as well as (I believe) the ~ftp/pub > directory on uunet.UU.NET. I should warn you that Sun's code is > basically David's, with perhaps minor modifications. Note that the > code is for SunOS 3.4 or SunOS 3.5. There is no support for SunOS > 4.0 as of yet. (3) From: Haavard Eidnes IDT <he%[email protected]> > I just happen to have written such a program. It will run on SunOS > 3.3, 3.4 and 3.5 -- the SunOS 4.0 code for using NIT is different, and > I haven't got any SunOS 4.0 machines here yet. > I tried out Barry Shein <[email protected]>'s program, proxyd, but > could not make Barry's proxyd work for me. It stopped with the > error message "badly aligned read" after a small number of packets > (when started with the '-d' option, at least). Besides, Barry's > program is only partly delivered in source form, and a comment in > there seemed to indicate that it was specific for class B subnetted > hosts. Also, there was a shift in there somewhere (>>8) that should > not be there -- I reported it to Barry, but got the usual silence... > As my program stands now, it has a couple of mis-features that I > intend to weed out before I let the net have it (I intend to > distribute it freely). I have not yet created a man page for my > program -- I thought of using Barry Shein's ,and asked him for > permission. He hasn't responded yet. > I intend also to complete the distribution with a README file before > I let it loose on the net. > Sorry, no documentation yet, but you can largely use Barry's man > page, except that you can't have comments anywhere on a line of the > /etc/proxytab file, only in the first column. > Good luck! Please report back to me if you find bugs or implement > enhancements (diff -c2 is preferred for updates/changes). Again, thank you very much for your help. --Ken Ken-ichiro Murakami NTT Laboratories Tokyo, Japan ------- -----------[000111][next][prev][last][first]---------------------------------------------------- Date: Wed, 10 Aug 88 17:58:06 PDT From: [email protected] To: [email protected] Cc: [email protected], [email protected] Subject: Re: FTP questions. I have some questions about FTP. Why is there an EOR indication in the descriptor code for block mode? If you are sending record oriented data then you are presumably using a record structure which already defines its EOR indication. Joe, Huh? If you are sending record-oriented data, then the FTP EOR indication marks the end of each record. The record structure is not assumed to be somehow encoded into the data, but is made explicit... so another system that also has record structure, but encodes it differently, can handle the data. If you are not sending record oriented data then why do you need to determine EOR? You don't. You don't have to set the EOR bit if it is inappropriate. That's the nice thing about bits, they can be on or off. Is it correct to duplicate the EOR information if you are using a record structure in block mode? No. See above. Does the EOR in block mode indicate that at most one record per block may be sent? Yes. I like the fact that you don't need to close the data connection when transfering in block or compressed mode since there is an EOF indication. When using page or record structures in stream mode, it is possible to detect EOF (since it is part of the descriptor info) even though the mode is stream. Why is it necessary to close the data connection even though EOF is indicated in the structure. It isn't necessary. Section 3.2 discusses at some length when the connection has to be closed. For block mode, it is the server's option. P.S. Does anyone know of any machine I can test block mode and record structure against? IBM VM/TCP will do block mode but only stream structure and 2.4 Ultrix does neither... Try any of the OS/MVS systems derived from the UCLA ACP. Bob Braden -----------[000112][next][prev][last][first]---------------------------------------------------- Date: Wed, 10 Aug 88 17:19:18 EDT From: [email protected] To: [email protected] Subject: FTP questions. I have some questions about FTP. Why is there an EOR indication in the descriptor code for block mode? If you are sending record oriented data then you are presumably using a record structure which already defines its EOR indication. If you are not sending record oriented data then why do you need to determine EOR? Is it correct to duplicate the EOR information if you are using a record structure in block mode? This seems to be so, but I'm seeking reassurance. Does the EOR in block mode indicate that at most one record per block may be sent? I like the fact that you don't need to close the data connection when transfering in block or compressed mode since there is an EOF indication. When using page or record structures in stream mode, it is possible to detect EOF (since it is part of the descriptor info) even though the mode is stream. Why is it necessary to close the data connection even though EOF is indicated in the structure. I have the nagging feeling that I'm missing something basic, like EOF descriptors are optional in record descriptors or EOR is optional in block descriptors. Can someone enlighten me? Please? Adthanksvance Joe Herman PC/IP @ Maryland P.S. Does anyone know of any machine I can test block mode and record structure against? IBM VM/TCP will do block mode but only stream structure and 2.4 Ultrix does neither... [email protected] -----------[000113][next][prev][last][first]---------------------------------------------------- Date: 10 Aug 88 17:04:49 GMT From: att!chinet!mcdchg!clyde!watmath!utgpu!utzoo!yunexus!maccs!beame@ucbvax.Berkeley.EDU (Carl Beame) To: [email protected] Subject: NFS for IBM PC We are currently involved in the creation of the commercial product BW-NFS, an implementation of Network File System for the PC (client version). Now that the alpha-test stage is complete, we are looking for interested parties to participate in beta-testing. The physical requirements are PCs with 3Com 3C501 ethernet cards, and DOS 3.x. Servers which implement NFS, RPC and XDR and have a C compiler are a must. - Carl Beame [email protected] ... !uunet!attcan!utzoo!utgpu!maccs!beame (416) 648-6556 -----------[000114][next][prev][last][first]---------------------------------------------------- Date: 10 Aug 88 19:23:50 GMT From: [email protected] (Phil R. Karn) To: comp.sys.mac,comp.protocols.tcp-ip Subject: Re: Summary: TCP/IP and NFS for the Mac There has apparently been some confusion regarding the status of my TCP/IP package. As it very clearly states when you bring it up, it is copyrighted by myself. Although I have granted to noncommercial users (including university and amateur radio groups) the right to use, copy and modify it for free, this does not in any way diminish my other rights under copyright, nor does it place the package into the public domain. I am well aware that my policy of openly publishing my sources makes it much harder, as a practical matter, to keep commercial users from abusing my copyright restriction. It has also probably diminished the commercial value of the software. However, very early on I decided that, despite this risk, open publication was essential to maximize the benefit to the amateur radio community for which the package is primarily intended. Although most of the code in the package is by myself, certain sections have been contributed by other amateurs with the same understanding: free for noncommercial use only. The authors of these sections are identified by comments in their respective source files. I ask others to respect the wishes of myself and the other authors in this matter. Thank you. Phil Karn, KA9Q -----------[000115][next][prev][last][first]---------------------------------------------------- Date: 10 Aug 88 20:30:18 GMT From: [email protected] (Richard Stevens) To: [email protected] Subject: IEEE 802.2, 802.3 & Ethernet questions I have a few questions regarding the use of TCP/IP on an Ethernet. From reading RFC 1042, I'm led to believe that "all communication is performed using 802.2 type 1 communication." That would seem to imply that the 8-byte LLC header and SNAP header is being used, but going through our 4.3 BSD sources, I can't find any refernces to these headers. Later in the RFC, they talk about "Interoperation with Ethernet", which makes me think that what we're using is the "Ethernet" instead of the 802.3 link level control. I can't find many references that describe 802.2 at all - I don't want to read the IEEE standard (if possible) and Stallings Volume 2 (which the local bookstore doesn't have) appears to be the only reference I've seen. (1) What are the differences between Ethernet V1.0 and V2.0 and 802.3 ? From seeing how our hardware is set up, it appears that all our interface cards are set for 802.3. (2) Do any TCP/IP implementations on an "ethernet" use the 802.2 LLC ? Looking at the RT PC AIX V2.1 manual (pp. 1-17 to 1-19) leads me to belive that this implementation does use the 802.2 LLC. (3) Why do some documents refer to the 2-byte field in the Ethernet MAC (immediately following the destination address and source address) as "length" (RFC 1042, for example) while others call it "packet type" (Comer's new book, for example) ? (4) Are there any implementations of TCP/IP on a Token-Ring (802.5) other than the RT PC ? Thanks for any light anyone can shed on this. Richard Stevens Health Systems International, New Haven, CT { uunet | yale } ! hsi ! stevens -----------[000116][next][prev][last][first]---------------------------------------------------- Date: 11 Aug 88 09:16:00 PST From: <[email protected]> To: "hsi!stevens" <[email protected]> Cc: [email protected] Subject: RE: IEEE 802.2, 802.3 & Ethernet questions Richard, >I have a few questions regarding the use of TCP/IP on an Ethernet. >From reading RFC 1042, I'm led to believe that "all communication >is performed using 802.2 type 1 communication." That would seem to >imply that the 8-byte LLC header and SNAP header is being used, >but going through our 4.3 BSD sources, I can't find any refernces >to these headers. Later in the RFC, they talk about "Interoperation >with Ethernet", which makes me think that what we're using is the >"Ethernet" instead of the 802.3 link level control. We tend to get a little lax in our use of terminology. People tend to interchange the use of the terms "Ethernet" and "802.3" even though they are not really quite the same thing. >I can't find many references that describe 802.2 at all - I don't >want to read the IEEE standard (if possible) and Stallings Volume 2 >(which the local bookstore doesn't have) appears to be the only >reference I've seen. The IEEE 802 standards are much easier reading than some of the ISO or CCITT documents. >(1) What are the differences between Ethernet V1.0 and V2.0 and 802.3 ? > From seeing how our hardware is set up, it appears that all our > interface cards are set for 802.3. First keep in mind that these specifications have mechanical, electrical and protocol components. Ethernet V1.0 is the original, derived from the 3mb/sec CSMA/CD work done at Xerox PARC. This standard was pushed by the joint efforts of DEC, INTEL, and Xerox. Ethernet V2.0 was released a few years later and mainly changed the electrical interface between the host and transceiver. The MAC headers did not change between V1.0 and V2.0 and both define the last word of the MAC header to be the protocol type. When IEEE took up standardization of LANs, 802.3 was developed for CSMA/CD (Ethernet type) LANS. 802.3 is really broader than Ethernet and covers more speeds and media types (and is still being extended). 802.3 and Ethernet V2.0 are close enough at mechanical and electrical levels to be functionally equivalent. IEEE 802 defines many MAC technologies (CSMA/CD, token bus, token ring) but attempts to provide a common link level service. To do this, 802 protocols are broken into two layers, Media Access Control (MAC) and Logical Link Control (LLC or 802.2). The MAC headers tend to differ amoung the LAN types, but each LAN type has at least one type of "Information" MAC frame. These MAC frames carry LLC packets whose length must be derived from the MAC header. For 802.3 there is only one MAC frame type. The 802.3 MAC header consists of <Dest, Src, Len>, where Dest and Src are either 2 byte or 6 byte MAC addresses and Len is the LLC packet length. For networks using 6 byte addresses, the Ethernet and 802.3 headers only differ in the last word being a protocol id or an LLC length respectively. In 802 protocols, the LLC header identifies the next layer "user" using the "Service Access Point" (SAP) fields. Unfortuneately, they only defined 6 usable bits for LLC SAPs and refused to assign standard SAP values for protocols like ARP (though IP was assigned a value). To solve this problem, the Sub-Network Access Protocol (SNAP) was defined to expand protocol identification. One variant of the SNAP header carries Ethernet protocol type codes. RFC 1042 is basically describing this situation. > >(2) Do any TCP/IP implementations on an "ethernet" use the 802.2 LLC ? > Looking at the RT PC AIX V2.1 manual (pp. 1-17 to 1-19) leads > me to belive that this implementation does use the 802.2 LLC. Most TCP/IP vendors still use Ethernet MAC headers, but there are one or two that have adopted LLC and SNAP. It is expected that when ISO protocols get established that 802.2 will be more widespread. Note that for "Etherenet" it is possible to distinguish between Ethernet and 802.3 MAC headers because the Ethernet protocol types are illegal LLC length values and vice versa. >(3) Why do some documents refer to the 2-byte field in the Ethernet > MAC (immediately following the destination address and source > address) as "length" (RFC 1042, for example) while others call > it "packet type" (Comer's new book, for example) ? As above, in Ethernet it is "type" and in 802.3 it is "length". >(4) Are there any implementations of TCP/IP on a Token-Ring (802.5) > other than the RT PC ? I believe that IBM's VM TCP/IP supports TR. I would assume Proteon does in their routers and some universities are probably running TCP/IP TRs. (Of course there is the whole TR source routing controversy :-> ). >Thanks for any light anyone can shed on this. I hope this helps. > Richard Stevens > Health Systems International, New Haven, CT > { uunet | yale } ! hsi ! stevens Art Berggreen [email protected] ------ -----------[000117][next][prev][last][first]---------------------------------------------------- Date: Thu, 11 Aug 88 09:53:43 PDT From: [email protected] To: [email protected] Cc: [email protected] Subject: Re: FTP questions. Bob, thanks for clearing up some of my misconceptions. I realize now that the EOR bit in block mode is useful for page structure. Apparently we are still not communicating. Page structure is irrelevant. Suppose you have a file that is a sequence of records; call them (C1,D1), (C2,D2), (C3,D3)..., where the Ci's are the control information that the local operating system uses to delimit records (typically a count and maybe some flag bits), and Di's are the ACTUAL DATA parts of the records. To transmit this file using FTP, you would transmit: D1, EOR, D2, EOR, D3, EOR... where the EOR flags are transmitted as specified by the FTP protocol, eg in block mode in the block headers. The local operating system control fields are NOT transmitted, only the data parts Di. Bob Braden -----------[000118][next][prev][last][first]---------------------------------------------------- Date: Thu, 11 Aug 88 09:25:05 EDT From: [email protected] To: [email protected] Cc: [email protected] Subject: Re: FTP questions. Bob, thanks for clearing up some of my misconceptions. I realize now that the EOR bit in block mode is useful for page structure. I'm still a little confused about when it is permissible to keep the data connection open. [in stream mode] >> Why is it necessary to close the data connection even though >> EOF is indicated in the structure. > It isn't necessary. Section 3.2 discusses at some length when the connection > has to be closed. For block mode, it is the server's option. My question about when to close the data connection stems from section 3.3 where it says: "When using the stream mode of data transfer, the end of file must be indicated by closing the connection." I guess that is pretty straight forward, but if EOF can be determined from the structure, it seems a shame to have to close the connection to signal EOF again. > Bob Braden Thanks for the help. Joe Herman [email protected] -----------[000119][next][prev][last][first]---------------------------------------------------- Date: Thu, 11 Aug 88 09:41:59 EDT From: [email protected] (John A. Shriver) To: [email protected] Cc: [email protected] Subject: IEEE 802.2, 802.3 & Ethernet questions IEEE 802.3 != Ethernet. There are no frame format or protocol differences between Ethernet Version 1 and 2. The only differences are subtle (but important) ones in the electrical interface over the transceiver cable between the host and transceiver. IEEE 802.3 does not have the same frame format as Ethernet. What was the type field in Ethernet becomes a length field. Thus, a new header has to be added to indicate what Network layer protocol the packet is for. This (among other things) is provided by IEEE 802.2. One backwards-compatability has been provided in 802.3 for Ethernet format frames. It turns out that almost all of the values of the type field were longer than a maximum length Ethernet packet. So, if the length is too long, it must be a type. Electrically, IEEE 802.3 is quite similar to Ethernet Version 2, mostly stricter. Again, the differences are primarily in the transceiver cable. On the coax, all three standards are fully compatible. Almost nobody runs IP over "Ethernet" using the RFC1042 encapsulation. Instead, the format defined in RFC894 "A Standard for the Transmission of IP Datagrams over Ethernet Networks" is used. (Note that RFC894 is older than those 4.3bsd sources, whereas RFC1042 is much newer.) I guess the existence of any "Ethernet" RFC1042 implmenations stems from an obsession with standards (eg. IEEE) over interoperability. Of course, the other 802 networks (802.4 and 802.5) most definitely use the RFC1042 encapsulation. -----------[000120][next][prev][last][first]---------------------------------------------------- Date: Thu, 11 Aug 88 14:58:38 MDT From: [email protected] (Chris Bogart) To: [email protected] We are going to do performance measurements of IP, both DoD and ISO versions, at NTIA, and I am looking for information concerning the two standards. Does anyone know of any documents which compare and contrast the two IP's? I'm interested in how they differ in: - interface with transport layer - functions performed Thanks in advance for any help you can give me. My UUCP mailing address is: ...ihnp4!stcvax!nbires!ntia!chris or U.S. Mail Chris Bogart NTIA/ITS.N3 325 Broadway Boulder, CO 80303 -----------[000121][next][prev][last][first]---------------------------------------------------- Date: Thu, 11 Aug 88 13:57:37 EDT From: [email protected] (Bill Barns) To: [email protected], [email protected] Cc: [email protected] Subject: Re: FTP questions. As best I recollect (someone correct me if I'm wrong), TOPS-20 transfers that use page structure and stream mode do not close the data connection after each file. I don't recall hearing anyone claim that this was the wrong thing to do, at least within the last few years. By analogy, I think it is ok to leave the connection up for record structure and stream mode. It's unfortunate that 3.3 is not quite consistent with 3.2 (and implicitly disagrees with 3.4.x also, where a point is made of saying that the close is necessary in file structure, but nothing is said about it for the other structures.) I think that 3.2 should be believed. The closing of the data connection at the end of any transfer is at the server's discretion, so you wouldn't be out of spec to do it if you are writing a server, but as you said in the first place, it seems like a useless thing to do. I believe that MIL-STD-1780 FTP is consistent with what I have just said. The relevant reference seems to be section 5.4.2, entitled "Alternate Data" (huh?) The MIL-STD has its little organizational glitches too, you see. Sigh. I have not noticed anything in the MIL-STD that replicates the troublesome wording of 3.3 of the RFC, but given the way the MIL-STD is put together, I'm not willing to make a promise even though I've got it open right in front of me. Bill Barns / MITRE / [email protected] -----------[000122][next][prev][last][first]---------------------------------------------------- Date: Thu, 11 Aug 88 17:15:28 PDT From: [email protected] To: [email protected], [email protected] Cc: [email protected] Subject: Re: FTP questions. As best I recollect (someone correct me if I'm wrong), TOPS-20 transfers that use page structure and stream mode do not close the data connection after each file. I don't recall hearing anyone claim that this was the wrong thing to do, at least within the last few years. By analogy, I think it is ok to leave the connection up for record structure and stream mode. That sounds right to me. If the receiver can unambiguously tell when the end of data has come by somehow parsing the stream, the sender does not have to close the connection to indicate EOF. The record-structure escape sequences in stream mode can carry the EOF bit, or the page structure has its own encoding that says "last page". It's unfortunate that 3.3 is not quite consistent with 3.2 (and implicitly disagrees with 3.4.x also, where a point is made of saying that the close is necessary in file structure, but nothing is said about it for the other structures.) I think that 3.2 should be believed. The closing of the data connection at the end of any transfer is at the server's discretion, so you wouldn't be out of spec to do it if you are writing a server, but as you said in the first place, it seems like a useless thing to do. Right. I believe that MIL-STD-1780 FTP is consistent with what I have just said. The relevant reference seems to be section 5.4.2, entitled "Alternate Data" (huh?) The MIL-STD has its little organizational glitches too, you see. Sigh. I have not noticed anything in the MIL-STD that replicates the troublesome wording of 3.3 of the RFC, but given the way the MIL-STD is put together, I'm not willing to make a promise even though I've got it open right in front of me. Well, I wouldn't know a MIL-STD FTP even if (especially if?) I met one coming through a dark alley on a moonless night. But people I trust tell me it is obsolete, being based on RFC-765, so I wouldn't pay attention to it anyway. Unfortunate, DoD turned its back on Internet standards some time ago. Bob Braden Bill Barns / MITRE / [email protected] -----------[000123][next][prev][last][first]---------------------------------------------------- Date: Thu, 11 Aug 88 23:20:22 -0500 From: Gurudatta Parulkar <[email protected]> To: tcp-ip%[email protected] Subject: retry > We just completed a DRAFT of a technical report with the abstract > enclosed. If you would like a copy to review, please send me a note. > I want to mention that this report does not contain any quantitative > analysis, and has only qualitative reasoning to support the claims. Comments on Proposed Transport Protocols Anil Bhatia James Sterbenz Guru Parulkar [email protected] Well, I received over 70 requests in last two days asking for copies of this report. To avoid mailing those many copies, I have decided to make it available via anonymous ftp. Could you please retrieve this via ftp to flora.wustl.edu ? In case you cannot, please send me (or to [email protected]) another note, and we'll send you a printed copy. I guess the abstract seems to have raised the expectations too much!? In any case, we'll appreciate your comments on the report. The details for anonymous ftp are Host - flora.wustl.edu (128.252.123.41) File name in pub directory - cotp.tar or cotp.tar.Z (cotp = comments on transport protocols) When you do uncompress and untar, you will get four files: cotp.tex - in LaTeX format bib.tex - bibliography to go with cotp.tex fig1.ps - figure in postscript form fig2.ps - figure in postscript form -guru Dr. Guru Parulkar Asst Professor [email protected] Dept of Computer Science [email protected] Washington University [email protected] St. Louis MO 63130 (314) 889-4621 -----------[000124][next][prev][last][first]---------------------------------------------------- Date: Thu, 11 Aug 88 14:01:28 +0200 From: [email protected] To: [email protected] Cc: [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected] Subject: Summary: Proxy ARP on SUN Barry Shein writes: Some of my tardiness in replying to people is explained by the fact that I am currently changing jobs and just haven't been around, I'm catching up (gee, these net requestors are harsh taskmasters!) Uh, I probably am guilty of some harshness, especially in my letter to Murakami that got forwarded to this list. I really am sorry for my wording, and I apologise. To follow up on Barry's good news section: I've completed my proxy arp daemon for SunOS 3.[345], with README file and man page (based on Barry's -- thanks Barry!). I'll probably get around to submitting my code to SunSpots for inclusion in their sun-source archive. However, as it usually takes some time between things get submitted to they make it to the archive, I propose that it should be FTP'able also. For those of you in a hurry, you can pick it up from loke.unit.no (IP: 128.39.5.27), in ~ftp/pub/proxyarpd.shar. It's only ~26KBytes. However, for most of you this is the other side of the Atlantic, so don't expect too god performance... Unfortunately, we'll (temporarily, but for at least 2 months) lose our internet connection this coming monday (August 15th), so I'll send a copy off to Barry and ask him to put it in their anonymous FTP area. Regards, Haavard Eidnes, Division of Computer Systems and Telematics Norwegian Institute of Technology, N-7034 Trondheim, Norway E-Mail; any of: [email protected] (will soon cease to work) he%[email protected] [email protected] h_eidnes%[email protected] -----------[000125][next][prev][last][first]---------------------------------------------------- Date: 11 Aug 88 18:25:45 GMT From: [email protected] (Dan Kegel) To: [email protected] Subject: Update on "NFS and TCP/IP for the Mac" I recently posted a summary about networking between the Mac SE and Unix machines. Enough new information has come in to make reposting worthwhile. There seem to be only two systems that let plain old Mac programs transparantly access files on a remote Unix fileserver: 1. Cayman Systems' Gatorbox This box lets Mac applications use files from any NFS file server; it is also a complete superset of the Kinetics FastPath. Not only does it allow use of TCP/IP protocols on LocalTalk, but it allows use of AppleTalk protocols on Ethernet, and translates Apple Filing Protocol requests into NFS requests regardless of whether they arrive over Ethernet or Appletalk. Either LocalTalk or Ethernet may be used to connect the Macs to the box; either thick or thin Ethernet may be specified. The number of Macs that one Gatorbox can support depends on how often the Macs need to use the network. This is a slick box! They built EXACTLY what I was looking for. Cayman Systems' phone number is (617) 494-1999. System cost: Using LocalTalk:50 per client + $3500 for the Gatorbox bridge Using EtherTalk:$600 per client + $3500 for the Gatorbox bridge 2. TOPS, a proprietary network file system developed independantly and later purchased by Sun; this has been available for some time. The only Unix box that TOPS currently runs on is the Sun-3. Either LocalTalk or Ethernet may be used to connect the Macs to the Sun. TOPS phone number is (800) 445-8677. System cost: Software: TOPS server on Sun ($900 for 1-4 clients, $1600 for 1-16 clients) TOPS client on Mac ($250 per client)
Hardware:
using LocalTalk: $50 per client +$2000 for the Kinetics Fastpath bridge
using EtherTalk: $600 per client Another NFS systems, rumored but not currently available, are 3. Peter Honeyman (one of the authors of HoneyDanBer uucp?) led a project at CITI that put tcp/ip and NFS on Macs, under contract to Apple. Apple has the software now; it's unclear when if ever they will release it. UMich was involved in testing CITI's software. Terminology: LocalTalk is Apple's 230 kilobit/sec serial networking hardware; EtherTalk is Ethernet, the standard 10 Megabite/sec networking hardware; Appletalk is Apple's set of networking protocols; TCP/IP is a standard networking protocol. (Although Appletalk is usually used with LocalTalk, and TCP/IP is usually used with Ethernet, any protocol can concievable run over any hardware.) NFS is a standard file serving protocol; Appleshare is Apple's file serving protocol. There are also systems available that let TCP/IP aware programs communicate with other machines on an Ethernet. 1. Kinetics sells Ethernet boards for all versions of the Macintosh; it also sells a TCP/IP (Ethernet) to TCP/IP (LocalTalk) bridge, called the FastPath. 2. NCSA maintains a professional-looking TELNET package for the PC and the Mac which supports remote login, multiple VT102 emulation, Tek 4014 emulation, subnetting, and dynamic IP address assignment via RARP. I think this is shipped with Kinetics equipment. 3. Either Stanford or Columbia maintain something called KIP and CAP which seems to be another TCP/IP package; this might also be used with the FastPath or Gatorbox. 4. Phil Karn's KA9Q package is another TCP/IP implementation. It is free for non-commerical use, and source is available. Thanks to everybody who sent in corrections. -- Dan Kegel "We had to get it passed before the columnists attacked!" [email protected] rochester!srs!dan dan%[email protected] -----------[000126][next][prev][last][first]---------------------------------------------------- Date: 11 Aug 88 20:16:21 GMT From: caip.rutgers.edu!aramis.rutgers.edu!athos.rutgers.edu!hedrick@rutgers.edu (Charles Hedrick) To: [email protected] Subject: Re: IEEE 802.2, 802.3 & Ethernet questions Arrgggg. There are two issues: electrical and software. Electrically, Ethernet v1, Ethernet v2, and IEEE 802.3 all put out signals that are more or less compatible on the cable. We've seen problems with Ethernet v1 talking to IEEE now and then (where we have a choice, we standardize on Ethernet v2), but by and large you can mix all three types of equipment on the same cable. However between the transceiver and the computer things are less free. Each given computer's interface board is designed with a particular type of transceiver in mind. You must use the one they had in mind. These days most equipment is designed to take either Ethernet v2 or IEEE 802.3 transceivers. The two standards are very close electrically. Some equipment can even deal with all three types of transceiver. But there is still equipment around (and probably even being sold) than can deal only with Ethernet v1 transceivers. So make sure your vendor tells you. (To make things worse, the people you can get to normally don't know the difference between the three standards, so it is sometimes hard to find out. We normally assume Ethernet v2 unless stated otherwise.) There are also differences that show up in the software rather than the hardware. 802.3, which is nominally about the hardware, does reflect this difference in its terminology, but it shows up mostly in 802.2. Ethernet uses an Ethernet type code in the Ethernet header. It does not use 802.2 By using the type codes, the device-level software is able to determine the protocol and dispatch the packet to the right protocol-handling software. IEEE did one of those wonderful political numbers on us and changed the type field to a length field. They then added 802.2 which has ways to figure out what the packet is about. Mostly TCP/IP implementors have ignored 802.2 and continued to use the Ethernet type code rather than the length code that 802.3 describes. The vendors generally claim that their systems support 802.3, but to the extent that they are putting a type code rather than a length code in the Ethernet header, one could claim that actually are supporting Ethernet v2 rather than 802.3. This is all done for compatibility. Since the original implementations were done in the days before the IEEE standards, it is natural that they used the Ethernet type code rather than 802.2. Newer implementations then continued this, in order to be able to talk to the older ones. Vendors that put out a product that insists on using 802.2 find that they can't talk to anyone. (This happened to H-P with the 3000.) Their customers tend to demand a change. However for newer networks that following the 802.x standards (e.g. token and broadband networks), it's almost certain that full 802.x, including 802.2, will be used. That's what the new 802.x RFC is about. It should probably contain a warning explaining this situation, so that people realize that it typically does not apply to Ethernet. In order to make it easier to design bridges that will connect a new network to an old one, some vendors are probably going to support both formats on Ethernet/802.3. It is possible to design software that can deal with both types of encapsulation. When you want to talk to somebody, you encode an ARP request both ways, send them both, and see which one he answers. In the ARP table, you have a flag indicating which encapsulation to use with that host. However at the moment most software for 802.3 was really designed for Ethernet, and does not use 802.2. -----------[000127][next][prev][last][first]---------------------------------------------------- Date: 11 Aug 88 23:46:18 GMT From: [email protected] (Randy D. Holmes) To: [email protected] Subject: MAC II timing on ethernet ? I was wondering if anybody could get me started in the right direction in a search for some timing stats. I'm trying to find out how fast a Mac II can transfer a large amount (1M+) of data to a second Mac II on an ethernet with various currently available configurations. Tests from RAM to RAM would be ideal, but at this point I'll settle for anything. I have contacted Kinetics, 3Com, and Apple, but nobody will admit to any bench marks. Any help at all would be greatly appreciated Randy Holmes [email protected] -----------[000128][next][prev][last][first]---------------------------------------------------- Date: 12 Aug 88 00:09:38 GMT From: [email protected] (Casey Leedom) To: [email protected] Subject: Re: IEEE 802.2, 802.3 & Ethernet questions In article <[email protected]> [email protected] (Charles Hedrick) writes: > > IEEE did one of those wonderful political numbers on us and changed the > type field to a length field. They then added 802.2 which has ways to > figure out what the packet is about. So just how complicated is this predicate that figures out what type of packet has been received. It's got to be more complicated than simply doing a case statement based on a type field. A prevoius article on this subject also mentioned the political nature of this design decision. It stated that IEEE wanted everyone to be at equal disadvantage. Does this make it right to make a bad design? > Mostly TCP/IP implementors have ignored 802.2 and continued to use the > Ethernet type code rather than the length code that 802.3 describes. Did you mean that second IEEE number (802.3 near the end of the sentence) to be 802.2? I'm still not exactly sure what the differences between 802.2 and 802.3 are, but I don't want to waste any more of your or the net's time. Thanks for the info. Casey -----------[000129][next][prev][last][first]---------------------------------------------------- Date: Fri, 12 Aug 88 08:50:49 EDT From: [email protected] (George M. Jones) To: he%[email protected] Cc: [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected] Subject: Summary: Proxy ARP on SUN I propose that it should be FTP'able also. For those of you in a hurry, you can pick it up from loke.unit.no (IP: 128.39.5.27), in ~ftp/pub/proxyarpd.shar. It's only ~26KBytes. However, for most of you this is the other side of the Atlantic, so don't expect too god performance... I managed to successfully FTP it at the blinding rate of 9.8 characters/sec. It is now available for anonymous FTP from tut.cis.ohio-state.edu (128.146.8.60) as as ~ftp/proxydarp/proxyarpd.shar ---George Jones OSU Computer & Inf. Science 2036 Neil Ave.,Columbus,Ohio 43210. 614-292-7325 [email protected] or ...!osu-cis!george Quality of life can be measured as the inverse of lawyers per thousand. -----------[000130][next][prev][last][first]---------------------------------------------------- Date: Fri, 12 Aug 88 12:48:36 EDT From: [email protected] (James Van Bokkelen) To: [email protected] Subject: TCP/IP for Token Ring As far as I know, you can get TCP/IP for 802.5 Token Ring from these vendors, for these machines: IBM PC/XT/AT/PS/2, PC/RT, 9370 & larger VM machines. Proteon PC/XT/AT, P4200 IP router FTP Software PC/XT/AT/PS/2 Some of the other VM & MVS TCP/IP vendors may also support 802.5, but I don't know for sure. James VanBokkelen FTP Software Inc. -----------[000131][next][prev][last][first]---------------------------------------------------- Date: Fri, 12 Aug 88 13:18:21 EDT From: [email protected] (Michael A. Patton) To: [email protected] Cc: [email protected] Subject: IEEE 802.2, 802.3 & Ethernet questions Date: 12 Aug 88 00:09:38 GMT From: [email protected] (Casey Leedom) [...] So just how complicated is this predicate that figures out what type of packet has been received. It's got to be more complicated than simply doing a case statement based on a type field. If you already have a case statement for Ethernet types you presumably have a default clause to discard types you don't want. You just add a simple test here that if the code is less than the max length, treat it as an IEEE802 packet. The feature of this technique is it doesn't slow down the processing of any traffic you presently deal with and can deal with IEEE802 nearly as fast as assuming that's all there is. If you want to be IEEE802 biased, you could put the max length test on the outside and do the ether-type dispatch in the "too long" clause. Again normal 802 traffic isn't slowed by the ability to handle Ethernet, and Ethernet traffic isn't much worse off. If you have a reasonable compiler, the protocol you're biased for executes an identical instruction stream as in the one protocol case and the other is charged only a few (probably 2) extra instructions. The only problem is you may get to do more processing of packets that get thrown away. Mike Patton, Network Manager Laboratory for Computer Science Massachusetts Institute of Technology Disclaimer: The opinions expressed above are a figment of the phosphor on your screen and do not represent the views of MIT, LCS, or MAP. Your mileage may vary, void where prohibited by law. :-) -----------[000132][next][prev][last][first]---------------------------------------------------- Date: Fri, 12 Aug 88 14:54:33 EST From: [email protected] To: [email protected] Subject: Help with TCP problem Hello- I am running CMU V6.2(6.3 is on order)TCP/IP on a VAX 11/785. We seem to have developed a strange problem. We can TELNET and FTP into other networks from this node but we seem to have lost connectivity with our network. All other TCP nodes on our network can connect with each other but can not connect with the 11/785. With logging enabled I get the following message: 23:59:58.26 Log event mask set to 80000000 23:59:57.84 Memory Mgmt. Fault detected., EC = 00158214 Can someone help me with this....thanks in advance Keith Heilner Heilner_k@sitvxb [email protected] ------------ -----------[000133][next][prev][last][first]---------------------------------------------------- Date: 12 Aug 88 12:58:20 GMT From: [email protected] (Celray Stalk) To: comp.sys.mac,comp.protocols.tcp-ip Subject: Re: Update on "NFS and TCP/IP for the Mac" I just received an information packet from Kinetics. Included was a paper bound book "Network Primer" published by Kinetics. Section 5, Network Software, mentions a package developed by the Center for Information Technology Integration (CITI) group of the Information Technology Division of the University of Michigan called MacNFS. According to the article, "Apple Computer has recently acquired the rights to MacNFS. For availability information, contact Apple or CITI." Anyone have information on this? -----------[000134][next][prev][last][first]---------------------------------------------------- Date: 12 Aug 88 13:16:33 GMT From: [email protected] (George M. Jones) To: [email protected] Subject: Re: Summary: Proxy ARP on SUN [email protected] writes: I propose that it should be FTP'able also. For those of you in a hurry, you can pick it up from loke.unit.no (IP: 128.39.5.27), in ~ftp/pub/proxyarpd.shar. It's only ~26KBytes. However, for most of you this is the other side of the Atlantic, so don't expect too god performance... It is now available on tut.cis.ohio-state.edu (128.146.8.60) as ~ftp/proxyarp/proxyarpd.shar. ---George Jones -=- OSU Computer & Inf. Science 2036 Neil Ave.,Columbus,Ohio 43210. 614-292-7325 [email protected] or ...!osu-cis!george Quality of life can be measured as the inverse of lawyers per thousand. -----------[000135][next][prev][last][first]---------------------------------------------------- Date: 12 Aug 88 16:21:41 GMT From: [email protected] (Dennis.Bednar) To: [email protected] Subject: Re: Summary: Proxy ARP on SUN In article <[email protected]>, bzs%bu-cs.bu.EDU%[email protected] (Barry Shein) writes: > I wrote a proxy arp based upon Sun's rarpd server ... Could someone please explain what is "proxy arp"? Thanks in advance. -- FullName: Dennis Bednar UUCP: {uunet|sundc}!rlgvax!dennis USMail: CCI; 11490 Commerce Park Dr.; Reston VA 22091 Telephone: +1 703 648 3300 -----------[000136][next][prev][last][first]---------------------------------------------------- Date: 12 Aug 88 16:39:13 GMT From: [email protected] (Ron D. Thornton) To: [email protected] Subject: Re: IEEE 802.2, 802.3 & Ethernet questions As noted, the differences between V1 ethernet, V2 ethernet, and 802.2/802.3 are both electrical and header format. On the coax, all 3 versions are fairly compatible. I don't have the specifications in front of me, but IEEE probably changed some edge specifications just to be different. On the tranceiver to controller electrical side: Version 1 used DC coupling on the tranceiver cable interface which make it totally incompatible with Version 2 or 802.3 tranceivers (some tranceivers/ controllers can be strapped for either DC or AC coupling). Version 2 changed to AC coupling on the tranceiver cable interface. V2 also specified that collision detect from the tranceiver should be forced on when a transmission is ended to provide a heartbeat or verification from the tranceiver. 803.2 took Version 2, played with some differential levels and driver/receiver specifications but remains reasonable compatible with the Version 2 tranceiver interface. It also added an optional control signal from the controller to the tranceiver and added an optional 3rd state to the collision presence signal (oscillate at 5Mhz instead of 10Mhz). On the packet header side: All 3 versions define the first 6 octets as destination address, and next 6 as source address. Version 1 and 2 ethernet use the next 2 octets as type field to define the next higher protocol level. 802.3 uses those 2 octets as a length field. Short packets may need to be padded and this field tells where data ends and padding starts. The ethernet specs leave it to the next level in the protocol to determine what is data and what is pad. 802.3 relys on the next level up, 802.2 to define more octets that are then used to determine the next level of protocol. There is an escape in the 802.3 header specification that allow 802.3 and ethernet packets to co-exist. The maximum packet length is 1500 and any 802.3 packet with a length field greater than maximum can be used in a user defined fashion. By only using ethernet type codes greater than 1500 you know at a glance if a packet is 802.3 or ethernet. All internet type codes have values greater than 1500. -Ron- [email protected] -----------[000137][next][prev][last][first]---------------------------------------------------- Date: 12 Aug 88 21:48:05 GMT From: [email protected] (Edward Bunch) To: [email protected] Subject: Re: IEEE 802.2, 802.3 & Ethernet questions I have a practical question. When dealing with tranceiver cables, how does one tell the difference between the three? I was told once that on a Ethernet tranceiver cable pin 1 (ground) was missing; ground really being on pin 7. Is this true? Need I worry about the type of tranceiver cable I use? The cables are rarely marked "For use with 802.3 etc.". -- Edward A. Bunch Fujitsu America, Inc. Computer Support and Administation. {uunet,amdahl,sun}!cerebus!edb -----------[000138][next][prev][last][first]---------------------------------------------------- Date: Sat, 13 Aug 88 09:47:41 EDT From: bzs%[email protected] To: [email protected] Cc: [email protected] Subject: Summary: Proxy ARP on SUN >In article <[email protected]>, bzs%bu-cs.bu.EDU%[email protected] (Barry Shein) writes: >> I wrote a proxy arp based upon Sun's rarpd server ... > >Could someone please explain what is "proxy arp"? >Thanks in advance. >-- >FullName: Dennis Bednar I'll be explaining it at a talk at Interop88...ok, ok, that's not what you wanted to hear. In short, a non-subnet host will broadcast an ARP for a host that's actually on another subnet and won't hear it (why?) A proxy arp daemon responds with the hardware address of the gateway the packets should be sent to (possibly, but not necessarily, itself.) The original host doesn't know better and sends subsequent traffic to that gateway which then forwards the packets appropriately. See, I believe, RFC's 925 and 1027. Doug Comer's latest text also has a section on it. -Barry Shein -----------[000139][next][prev][last][first]---------------------------------------------------- Date: 13 Aug 88 19:42:12 GMT From: [email protected] (Greg Minshall) To: comp.sys.mac,comp.protocols.tcp-ip Subject: Re: Summary: TCP/IP and NFS for the Mac Just to add a bit to the list, Kinetics has recently announced a "TCPort Toolkit", which includes TCP/IP support for the Mac (installed as drivers) and a programming library to interface to the drivers (and a "socket emulation" library). It isn't available until October or so (I haven't seen the announcement). (In addition, there is a separate product with telnet, ftp, etc.) Greg Minshall Kinetics ...ucbvax!mtxinu!kinetics!minshall (415)947-0998 -----------[000140][next][prev][last][first]---------------------------------------------------- Date: 13 Aug 88 21:13:10 GMT From: [email protected] (Henry Spencer) To: [email protected] Subject: Re: Summary: Proxy ARP on SUN In article <[email protected]> [email protected] (Dennis.Bednar) writes: >Could someone please explain what is "proxy arp"? Proxp arp is when one machine answers an ARP request aimed at another, giving its own physical address rather than the target's address. I.e., "send anything meant for him to me". The main purpose of this is to hide network partitioning: if the gateway between two physical networks does proxy ARP on network A for all machines on network B, and vice-versa, the two networks look like one on the IP level. It's sort of a poor man's subnetting. The main advantage is that it hides the topology completely and can be used with hosts that don't do subnetting properly. The main disadvantage is that it's a special-purpose hack that doesn't work well in unfavorable circumstances (e.g. complex topologies). -- Intel CPUs are not defective, | Henry Spencer at U of Toronto Zoology they just act that way. | uunet!attcan!utzoo!henry [email protected] -----------[000141][next][prev][last][first]---------------------------------------------------- Date: 14 Aug 88 05:44:19 GMT From: (Casey Leedom) To: [email protected] Subject: Re: Summary: Proxy ARP on SUN In article <[email protected]> [email protected] writes (George Jones): > > I managed to successfully FTP it at the blinding rate of 9.8 characters/sec. > It is now available for anonymous FTP from tut.cis.ohio-state.edu > (128.146.8.60) as as ~ftp/proxydarp/proxyarpd.shar I had such a difficult time getting through to Ohio State, I left copies of the shar in ~ftp/pub on lll-crg.llnl.gov (128.115.1.1) and cs.ucla.edu (128.97.28.20). Casey -----------[000142][next][prev][last][first]---------------------------------------------------- Date: Mon, 15 Aug 88 08:36:22 PDT From: DDN Reference <[email protected]> To: [email protected] Cc: [email protected], [email protected] Subject: Learning Tree Software and Internet Advertising We thought you should be made aware of the usage policies of the DDN. Read "DDN" wherever "ARPANET" is mentioned. The ARPANET was not designed for commercial gain such as product advert- isement. Learning Tree Software should pursue other means of making their products known. The following paragraphs from the DDN New User Guide, which the DDN Network Information Center produced for the Defense Communications Agency, summarize the purpose of the ARPANET. Note: ARPANET Traffic originating from other networks still needs to follow the guidelines. The purpose of the ARPANET is to provide a facility for advanced packet-switched communications technologies research and experimental communication support of government-sponsored university computer science research. Consequently, access to, and use of, ARPANET will not be authorized to support operational (as opposed to experimental) communication requirements. Such operational facilities are provided for DoD users by the DDN (such as MILNET), and for others by public and private packet-switched networks (such as TYMNET or TELENET). Users of ARPANET may only use the network to conduct the official business for which their access was authorized. They must not violate privacy or any other applicable laws, and must not use the network for private gain or for commercial purposes, such as advertising or recruiting. ------- -----------[000143][next][prev][last][first]---------------------------------------------------- Date: 15 Aug 88 10:31:00 PDT From: Dave Crocker <[email protected]> To: tcp-ip <[email protected]> Subject: Re: Van's algorithms in Streams Steve Alexander cites Lachman's Streams implementation as containing Van's performance enhancements. While the congestion control enhancements drop in relatively easily, it is my understanding that Van has not yet released his header-prediction changes. I would be interested to know the origins of the code that Lachman acquired. Steve? With respect to the ease of adding Berkeley code to Streams, the key is the degree of conformance to streams architecture. One can be formally conformant, but still have variations is certain features. Dave -----------[000144][next][prev][last][first]---------------------------------------------------- Date: Mon, 15 Aug 88 10:05:00 CDT From: [email protected] (Anil Bhatia) To: tcp-ip%[email protected] Subject: Technical report "Comments on Proposed Transport Protocols" RE: Draft of Techinal Report Comments on Proposed Transport Protocols Anil Bhatia James Sterbenz Guru Parulkar [email protected] A POSTSCRIPT version of the draft of our technical report is now available. This can be copied over the net by anonymous FTP on "flora.wustl.edu" with any password. - anil [email protected] --------------------------------------------------- Direct further enquiries to: Guru Parulkar [email protected] -----------[000145][next][prev][last][first]---------------------------------------------------- Date: Mon 15 Aug 88 09:37:57-EDT From: Del Waggoner <[email protected]> To: [email protected] Cc: [email protected] Subject: Re: TCP/IP for Token Ring thanks for the information... ------- -----------[000146][next][prev][last][first]---------------------------------------------------- Date: Mon 15 Aug 88 18:12:25-PDT From: William Westfield <[email protected]> To: [email protected] Cc: [email protected] Subject: Re: Van's algorithms in Streams Grumble. All things considered, Van's congestion control enhancments are MUCH more important than the header-prediction changes. Bill Westfield cisco Systems. ------- -----------[000147][next][prev][last][first]---------------------------------------------------- Date: 16 Aug 88 00:52:43 GMT From: [email protected] (Jerry Aguirre) To: comp.sources.wanted,comp.protocols.tcp-ip Subject: Wanted: rarp or bootp for 4.3BSD I need to be able to run either a RARP or Bootp server on a 4.3BSD Vax. Any pointers to where I can obtain either would be much appreciated. Jerry Aguirre @ Olivetti ATC -----------[000148][next][prev][last][first]---------------------------------------------------- Date: Tue, 16 Aug 88 15:40:09 PST From: [email protected] (the tty of Geoff Goodfellow) To: [email protected] Subject: BOF on SLIP at Interop 88 -- Thurs Sept 19th. There will be a birds of a feather session on SLIP at the InterOP '88 Conference Thursday Sept 29th after the formal sessions conclude. If you have SLIP hackery to share, please contact me. I'd like to schedule a few 10 minute presentations at the start of the BOF on interesting works involving SLIP, completed or in progress. Topics might be: dynamic dial-up SLIPing / SLIP header compression / SLIP security & authentication / itinerant host SLIPing / SLIP built into modems / SLIP over Value Added Networks / Etc / other suggestions welcomed... Geoff Goodfellow Anterior Technology [email protected] (415) 328-5615 ------- Interop is soliciting topics for other BOF sessions. If you feel you have a topic of interest, contact Advanced Computing Environments at (415) 941-3399 to schedule a discussion during the conference. ------- -----------[000149][next][prev][last][first]---------------------------------------------------- Date: 16 Aug 88 14:21:07 GMT From: [email protected] (A Hamilton) To: [email protected] Subject: Re: Ether loopback... In article <[email protected]> [email protected] (William Westfield) writes: : Some ethernet controllers are capable of hearing packets that they are : transmitting as they are being transmitted. If this is true, then : sending a packet to yourself is a good way to check whether the : ethernet is in good shape - it checks the transceiver and the ethernet : cable as well as the controller. : Actually not so. Many ethernet controllers have a smart processor which will check for a loopback packet and return it to the host as if it had been received from the Ethernet. But the transceivers CANNOT listen during their own transmission. In article <[email protected]> [email protected] ("Torben N. Nielsen") writes: > >Anyone happen to know if there're legitimate reasons for sending to yourself >onan Ethernet? That is, Ethernet packets where the source and the destination >address are identical? Seems pointless since as far as I know, you cannot read >packets you yourself transmitted off of the wire..... Am I wrong? > > Torben No, you are right (in terms of hardware but it has to be fixed by some form of s/w [see above]) but it is not pointless. There are 2 reasons I am aware of. 1) The IEEE 802.3 spec. says that all stations should be capable of receiving a self-addressed Ethernet packet as though it were received from the net (section 2.3.3.5). The IEEE 802.2 spec. requires a station to transmit such a packet at startup so as to perform a "duplicate address check". (The packet is an IEEE 802.2 TEST packet). It is required that exactly one reply is received in an appropriate period of time (this one packet is from the originating station itself which replies to this TEST packet as to any other). Section 6.9.2 is the relevant bit in my (out-of-date) copy. 2) Loopback tests are often required if no other station supports the relevant s/w. They can also be useful as they give very different timing effects. Under these circumstances it can be very useful if packets go out onto the real network where they can be picked up by a monitor, rather than being soft looped entirely. Adam Hamilton -----------[000150][next][prev][last][first]---------------------------------------------------- Date: 16 Aug 88 18:29:00 GMT From: [email protected] To: [email protected] Subject: Re: TFTP on PS/2 Can you make do with NCSA Telnet? I believe it supports the micro channel architecture. Mike Berger Department of Statistics Science, Technology, and Society University of Illinois [email protected] {ihnp4 | convex | pur-ee}!uiucuxc!clio!berger -----------[000151][next][prev][last][first]---------------------------------------------------- Date: 16 Aug 88 19:59:17 GMT From: [email protected] (Ragnar Sundblad) To: [email protected] Subject: Re: MAC II timing on ethernet ? In article <[email protected]> [email protected] (Randy D. Holmes) writes: > I was wondering if anybody could get me started in the right direction > in a search for some timing stats. I'm trying to find out how fast > a Mac II can transfer a large amount (1M+) of data to a second Mac II > on an ethernet with various currently available configurations. > Tests from RAM to RAM would be ideal, but at this point I'll settle > for anything. I have contacted Kinetics, 3Com, and Apple, but nobody > will admit to any bench marks. Any help at all would be greatly appreciated I made some stupid programs to benchmark ethernet bridges with MacIIs. One of them just sends ethernet packets at the highest speed possible, the other just receives and counts them. With these I got 98-99 percent, meaning ~1.24MByte/s. The NUBUS and MacII should have no troubles keeping this speed. The bottleneck is usually the ethernet driver, not the hardware. -----------[000152][next][prev][last][first]---------------------------------------------------- Date: 17 Aug 88 05:15:00 EDT From: "NRL::FARNHAM" <farnham%[email protected]> To: "tcp-ip" <[email protected]> Cc: farnham Subject: THANKS!! To all the wonderfully kind people out their in TCP/IP land who helped me gather beginners info. Thank you, I received a great deal of helpful information and have finally digested it and am moving on to the reading list I was sent. I really appreciated all of the feedback and wanted you all to know I thought it was great that so many of you responded to my queries. Emily D. Farnham code 2861.7 Naval Research Laboratory Washington, D.C. -----------[000153][next][prev][last][first]---------------------------------------------------- Date: Wed, 17 Aug 88 08:51:46 EDT From: [email protected] (T. Calkins) To: farnham%[email protected], [email protected] Cc: [email protected] Subject: Re: THANKS!! >From [email protected] Wed Aug 17 08:32:48 1988 >Received: by NADC.ARPA (5.51/1.0 ) > id AA28307; Wed, 17 Aug 88 08:32:34 EDT >Message-Id: <[email protected]> >Received: from nrl.arpa by SRI-NIC.ARPA with TCP; Wed, 17 Aug 88 02:19:20 PDT >Date: 17 Aug 88 05:15:00 EDT >From: "NRL::FARNHAM" <farnham%[email protected]> >Subject: THANKS!! >To: "tcp-ip" <[email protected]> >Cc: [email protected] >Status: R > >To all the wonderfully kind people out their in TCP/IP land who helped >me gather beginners info. >Thank you, I received a great deal of helpful information and have finally >digested it and am moving on to the reading list I was sent. I really >appreciated all of the feedback and wanted you all to know I thought it >was great that so many of you responded to my queries. > > > Emily D. Farnham > code 2861.7 > Naval Research Laboratory > Washington, D.C. > > --------------------------- Emily: Would you be interested in "sharing" the TCP/IP "beginners info" that you recieved from the net? If yes, mail it directly to me: [email protected]. If no, thanks anyway. For now, Ted Calkins ( [email protected] ) NADC = Naval Air Development Center Warminster, PA -----------[000154][next][prev][last][first]---------------------------------------------------- Date: 17 Aug 88 07:59:37 GMT From: [email protected] (David Robinson) To: [email protected] Subject: proxyarpd for SunOS 4.0 I have finished a port of proxyarpd to SunOS 4.0 using the new STREAMS NIT modules. It is available for anonymous FTP from elroy.jpl.nasa.gov [128.149.1.100] I have sent the changes back to the author also. -- David Robinson [email protected] ARPA [email protected] ARPA {cit-vax,ames}!elroy!david UUCP Disclaimer: No one listens to me anyway! -----------[000155][next][prev][last][first]---------------------------------------------------- Date: Wed, 17 Aug 88 17:09:56 EDT From: Philip Prindeville <[email protected]> To: [email protected] Cc: TCP/IP <[email protected]> Subject: Re: BOF on SLIP at Interop 88 -- Thurs Sept 19th. SLIP is currently being refined by the IETF Point-to-Point Protocol working group. Rather than have duplication of effort, you should get in contact with Dre Perkins <[email protected]> or the interest mailing list <[email protected]>... -Philip -----------[000156][next][prev][last][first]---------------------------------------------------- Date: Wed, 17 Aug 88 21:31:55 -0400 From: Craig Partridge <[email protected]> To: [email protected] Subject: Van's algorithms For people interested in Van's work, I suggest you read the paper he is giving at SIGCOMM '88 this week. It explains most of the performance improvements he has made. (SIGCOMM is probably the most important networking conference of the year -- consider this a plug to join ACM SIGCOMM). Craig -----------[000157][next][prev][last][first]---------------------------------------------------- Date: Wed, 17 Aug 88 10:12 +0300 From: Yehavi Bourvine +972-2-584279 <YEHAVI%[email protected]> To: [email protected] Subject: Tcp/Ip code for Unix V. We are looking for TcpIp sources implemented for system-V, version 5.2. Does anyone have such sources and can give them? The low-level driver is preferably EXOS, but others will be good too. Thanks in advance, __Yehavi: =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= Yehavi Bourvine, Phones: +972-2-584279, H Computation Center, +972-2-521574 H The Hebrew University of Jerusalem, H Givat-Ram, Jerusalem 91904 H H H Fax: +972-2-527349 HH H BITnet: YEHAVI@HUJIVMS H H InterNet: [email protected] H Israeli DECnet: HUJICC::YEHAVI H =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= -----------[000158][next][prev][last][first]---------------------------------------------------- Date: 17 Aug 88 18:19:22 GMT From: [email protected] (Aled Morris) To: comp.unix.wizards,comp.protocols.tcp-ip Subject: /etc/services Below, I have included a copy of my /etc/services file. I am trying to build a comprehensive table of known ports, starting from "Assigned Numbers" (the most recent version in my possession is RFC1010), and including as many operating system quirks as is feasible. Hopefully, the publication of this in Unix /etc/services format will encourage the use of standard port numbers and names, and avoid future clashes (some hope! :-) There are no doubt a large number of holes in this (my first attempt). Please mail me any corrections, and I will update my master copy. A number of services have been given protocol type "new", if you know better, please mail me. If you have already done any of this, please mail me, I don't want to duplicate anyone's effort! I assume that with the emergence of ISO networking standards, /etc/services will be updated. If anyone has implemented ISO versions of any of these services, I would be glad to include them---I expect the entry would be something like: finger 79/tp4 # ISO "Finger" server MAIL ONLY PLEASE, DON'T FOLLOWUP TO THE NET. ^^^^ ^^^^ ^^^^^^ Aled Morris systems programmer mail: [email protected] | Department of Computing uucp: ..!ukc!icdoc!awm | Imperial College talk: 01-589-5111x5085 | 180 Queens Gate, London SW7 2BZ # # /etc/services: Network services, Internet style # Aled Morris ([email protected]), 15th Aug, 1988 # # See RFC1010 "Assigned Numbers" (issued May, 1987) for details. # # Operating systems consulted were: # 4.3BSD, 4.2BSD, SunOS 4.0_Export, Gould UTX/32 2.1a, HP-UX 6.0, # Dynix 3.0.8 # # Notes: # RJE (5) all implementations used port 77 # LOGIN (49) all implementations use port 513 # MTP (57) the only private terminal access protocol I could find # PRINTER (35) all implementations use port 515 # PORTMAP (111) is the name used by HP-UX for SUNRPC # LINK (245) many 4.2 derived systems use the name for port 87 # unknown protocols are marked "new" # # NAME PORT/PROTOCOL ALIASES COMMENTS # ---- ---- -------- ------- -------- # reserved 0 # unassigned 1-4 # rje 5 # remote job entry echo 7/tcp echo 7/udp discard 9/tcp sink null discard 9/udp sink null systat 11/tcp users daytime 13/udp daytime 13/tcp netstat 15/tcp # unassigned in RFC1010 qotd 17/tcp quote # Quote of the Day chargen 19/tcp ttytst source # Character Generator chargen 19/udp ttytst source ftp-data 20/tcp ftpdata ftp 21/tcp telnet 23/tcp smtp 25/tcp mail nsw-fe 27/new # NSW User System FE msg-icp 29/new # MSG ICP msg-auth 31/new # MSG Authentication dsp 33/new # Display Support Protocol # 35/new # any private printer server time 37/tcp timserver time 37/udp timserver rlp 39/new resource # Resource Location Protocol graphics 41/new # Graphics name 42/udp nameserver whois 43/tcp nicname # usually to sri-nic mpm-flags 44/new # MPM FLAGS Protocol mpm 45/new # Message Processing Module mpm-snd 46/new # MPM [default send] ni-ftp 47/new # NI FTP #login 49/new # Login Host Protocol la-maint 51/new # IMP Logical Address Maint. domain 53/udp domain 53/tcp isi-gl 55/new # ISI Graphics Language mtp 57/tcp # any private terminal access # 59/new # any private file service ni-mail 61/new # NI MAIL via-ftp 63/new # VIA Systems - FTP tacacs-ds 65/new # TACACS-Database Service bootps 67/new # Bootstrap Protocol Server bootpc 68/new # Bootstrap Protocol Client tftp 69/udp netrjs-1 71/new # Remote Job Service netrjs-2 72/new # Remote Job Service netrjs-3 73/new # Remote Job Service netrjs-4 74/new # Remote Job Service # 75/new # any private dial out service rje 77/tcp netrjs # any private RJE service finger 79/tcp # Finger hosts2-ns 81/new # HOSTS2 Name Server mit-ml-dev 83/new # MIT ML Device mit-ml-dev 85/new # MIT ML Device link 87/tcp ttylink # any private terminal link su-mit-tg 89/new # SU/MIT Telnet Gateway mit-dov 91/new # MIT Dover Spooler dcp 93/new # Device Control Protocol supdup 95/tcp # SUPDUP hostnames 101/tcp hostname # usually to sri-nic iso-tsap 102/tcp # ISO-TSAP x400 103/tcp # ISO Mail (X.400) x400-snd 104/tcp # X.400-SND csnet-ns 105/tcp # Mailbox Name Nameserver rtelnet 107/new # Remote Telnet Service pop-2 109/tcp pop postoffice # Post Office Protocol (rev.2) sunrpc 111/udp portmap # SUN Remote Procedure Call sunrpc 111/tcp portmap auth 113/new # Authentication Service sftp 115/new # Simple File Transfer Protocol uucp-path 117/tcp # UUCP Path Service nntp 119/tcp usenet untp # Network News Transfer erpc 121/new # HYDRA Expedited RPC ntp 123/tcp # Network Time Protocol locus-map 125/new # Locus PC-Interface Net Map locus-con 127/new # Locus PC-Interface Conn Server pwdgen 129/new # Password Generator Protocol cisco-fna 130/new # CISCO FNATIVE cisco-tna 131/new # CISCO TNATIVE cisco-sys 132/new # CISCO SYSMAINT statsrv 133/new # Statistics Service ingres-net 134/new # INGRES-NET Service loc-srv 135/new # Location Service profile 136/new # PROFILE Naming System netbios-ns 137/new # NETBIOS Name Service netbios-dgm 138/new # NETBIOS Datagram Service netbios-ssn 139/new # NETBIOS Session Service emfis-data 140/new # EMFIS Data Service emfis-cntl 141/new # EMFIS Control Service bl-idm 142/new # Britton-Lee IDM NeWS 144/tcp news # Window System sur-meas 243/new # Survey Measurement #link 245/new # LINK # # unassigned 143-159 # reserved 160-223 # unassigned 224-241 # unassigned 247-255 # # KIP AppleTalk interface # official numbers as of April, 1988 # at-rmtp 201/udp # AppleTalk Routing Maintenance at-nbp 202/udp # AppleTalk Name Binding #at-3 203/udp # AppleTalk unused at-echo 204/udp # AppleTalk Echo #at-5 205/udp # AppleTalk unused at-zis 206/udp # AppleTalk Zone Information #at-7 207/udp # AppleTalk Unused #at-8 208/udp # AppleTalk Unused # # Unofficial port assignments. # exec 512/tcp biff 512/udp comsat login 513/tcp who 513/udp whod shell 514/tcp cmd # no passwords used syslog 514/udp printer 515/tcp spooler # experimental talk 517/udp # old talk (bsd4.2, utx2.0) ntalk 518/udp # new talk (bsd4.3, utx3.0) efs 520/tcp # for LucasFilm route 520/udp router routed search 525/tcp searchd # inter-machine search timed 525/udp timeserver tempo 526/tcp newdate courier 530/tcp rpc # experimental conference 531/tcp chat netnews 532/tcp readnews netwall 533/udp # -for emergency broadcasts uucp 540/tcp uucpd # uucp daemon new-rwho 550/udp new-who # experimental remotefs 556/tcp rfs_server rfs # Brunhoff remote filesystem rmonitor 560/udp rmonitord # experimental monitor 561/udp # experimental rlb 1260/tcp # HP-UX ingreslock 1524/tcp nft 1536/tcp # HP-UX nfsd 2049/udp # HP-UX NFS implementation rfa 4672/tcp # HP-UX Remote File Access man 9535/tcp # remote manual server rman 9535/udp # more of same # # the end -----------[000159][next][prev][last][first]---------------------------------------------------- Date: 17 Aug 88 20:58:59 GMT From: [email protected] (Jussi-Pekka Mantere) To: comp.sys.mac,comp.protocols.tcp-ip,comp.protocols.appletalk Subject: Re: Update on "NFS and TCP/IP for the Mac" In article <[email protected]>, dan@srs (Dan Kegel) writes: >There seem to be only two systems that let plain old Mac programs >transparantly access files on a remote Unix fileserver: > >1. Cayman Systems' Gatorbox > This box lets Mac applications use files from any NFS file server; How about using Mac files stored on the NFS file server from the Unix side? Will there be three different files for the three Macintosh file forks (info, data & resource)? If so, how will a text file be stored? Especially, is there any character set conversions from US ASCII to a "national" ASCII set (pick your favorite European character set)? > it is also a complete superset of the Kinetics FastPath. Will it be able to run KIP (Kinetics Internet Protocol) code or is it compatible with KIP style dynamic IP address assignment? How will it configure itself to the two networks? Does it "autoconfigure" itself, the way Kinetics FastPath 4 does, or does it require explicit network administration? > Not only does it allow use of TCP/IP protocols on LocalTalk, > but it allows use of AppleTalk protocols on Ethernet, and Is this "EtherTalk" ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > translates Apple Filing Protocol requests into NFS requests regardless of > whether they arrive over Ethernet or Appletalk. > Either LocalTalk or Ethernet may be used to connect the Macs to the box; > either thick or thin Ethernet may be specified. > The number of Macs that one Gatorbox can support depends on how often the > Macs need to use the network. > This is a slick box! They built EXACTLY what I was looking for. BUT: Can it be used to access both AppleTalk-in-IP speaking hosts (an Unix host running CAP (Columbia Appletalk Package)) and EtherTalk speaking hosts (a VAX/VMS host with AppleTalk for VMS, a Sun-3 with TOPS for Sun) from Macs speaking either AppleTalk or EtherTalk? To summarize: I'm impressed, but does it work for us? >Terminology: > EtherTalk is Ethernet, the standard 10 Megabite/sec networking hardware; Actually, EtherTalk is another Ethernet-protocol, and not restricted to any particular hardware. For example, a Mac can use EtherTalk over twisted pair wires, or phone lines, with the appropriate hardware. Not necessarily your "standard networking hardware" :-) > Dan Kegel "We had to get it passed before the columnists attacked!" > [email protected] rochester!srs!dan dan%[email protected] -- Jussi-Pekka Mantere [email protected] Helsinki University of Technology, Finland [email protected] Laboratory of Information Processing Science + 358 0 451 2487 -----------[000160][next][prev][last][first]---------------------------------------------------- Date: 18 Aug 88 01:41:00 EDT From: "NRL::FARNHAM" <farnham%[email protected]> To: "tcp-ip" <[email protected]> Cc: farnham Subject: Re: Status of NTP? From: NRL::MAILER 29-JUN-1988 12:38 To: NRL::FARNHAM Subj: [From: [email protected]] Charles Hedrick's tcp/ip intro Return-Path: <[email protected]> Received: from ames.arc.nasa.gov by nrl.arpa with SMTP ; Wed, 29 Jun 88 12:37:51 EDT Received: Wed, 29 Jun 88 09:33:43 PDT by ames.arc.nasa.gov (5.59/1.2) Received: from frosted.coherent.com by coherent.com (3.2/SMI-3.2) id AA26349; Wed, 29 Jun 88 09:26:40 PDT Received: by frosted.coherent.com (3.2/SMI-3.2) id AA22634; Wed, 29 Jun 88 09:26:40 PDT Date: Wed, 29 Jun 88 09:26:40 PDT From: [email protected] (Celeste C. Stokely) Message-Id: <[email protected]> To: farnham%[email protected] Subject: Charles Hedrick's tcp/ip intro I'm assuming that this is what you're looking for. If so, enjoy! ..Celeste Stokely Coherent Thought Inc. UUCP: ...!{ames,sun,uunet}!coherent!celeste Domain: [email protected] Internet: [email protected] or [email protected] or [email protected] VOX: 415-493-8805 SNAIL:3350 W. Bayshore Rd. #205, Palo Alto CA 94303 From amdcad!ames!rutgers!topaz.rutgers.edu!hedrick Mon Jun 29 15:40:52 PDT 1987 Article 451 of comp.protocols.tcp-ip: Path: sun!amdcad!ames!rutgers!topaz.rutgers.edu!hedrick >From: [email protected] (Charles Hedrick) Newsgroups: comp.protocols.tcp-ip Subject: TCP/IP introduction Message-ID: <[email protected]> Date: 28 Jun 87 07:52:42 GMT Organization: Rutgers Univ., New Brunswick, N.J. Lines: 936 I keep seeing requests on various newsgroups for an introduction to TCP/IP. I also get such requests locally. I believe that the only appropriate description of TCP/IP is the RFC's. However I also think a brief introduction is likely to be helpful before plowing right into them. The following document is an attempt to do that. It also recommends some RFC's to look at and tells you how to get them. -------------------------------- This document is a brief introduction to TCP/IP, followed by advice on what to read for more information. This is not intended to be a complete description, but merely enough of an introduction to allow you to start reading the RFC's. At the end of the document there will be a list of the RFC's that we recommend reading. TCP/IP is a set of protocols developed to allow cooperating computers to share resources across a network. It was developed by a community of researchers centered around the ARPAnet. Certainly the ARPAnet is the best-known TCP/IP network. However as of June, 87, at least 130 different vendors had products that support TCP/IP, and thousands of networks of all kinds use it. First some basic definitions. Although TCP/IP (or IP/TCP) seems to be the most common term these days, most of the documentation refers to the "Internet protocols". The Internet is a collection of networks, including the Arpanet, NSFnet, regional networks such as NYsernet, local networks at a number of University and research institutions, and a number of military networks. The term "Internet" applies to this entire set of networks. The subset of them which is managed by the Department of Defense is referred to as the "DDN" (Defense Data Network). This includes some research-oriented networks, such as the Arpanet, as well as more strictly military ones. (Because much of the funding for Internet protocol developments is done via the DDN organization, the terms Internet and DDN can sometimes seem equivalent.) All of these networks are connected to each other, and users can send messages from any of them to any other (except where security or other policy restrictions control access). Officially speaking, the Internet protocol documents are simply standards adopted by the Internet community for its own use. More recently, the Department of Defense issued a MILSPEC definition of TCP/IP. This was intended to be a more formal definition, appropriate for use in purchasing specifications. However most of the TCP/IP community continues to use the Internet standards. The MILSPEC version is intended to be consistent with it. Whatever it is called, TCP/IP is a family of protocols. A few are basic ones used for many applications. These include IP, TCP, and UDP. Others are protocols for doing specific tasks, e.g. transferring files between computers, sending mail, or finding out who is logged in on another computer. Any real application will use several of these protocols. A typical situation is sending mail. First, there is a protocol for mail. This defines a set of commands which one machine sends to another, e.g. commands to specify who the sender of the message is, who it is being sent to, and then the text of the message. However this protocol assumes that there is a way to communicate reliably between the two computers. Mail, like other application protocols, simply defines a set of commands and messages to be sent. It is designed to be used together with TCP and IP. TCP is responsible for making sure that the commands get through to the other end. It keeps track of what is sent, and retransmitts anything that did not get through. If any message is too large for one packet, e.g. the text of the mail, TCP will split it up into several packets, and make sure that they all arrive correctly. Since these functions are needed for many applications, they are put together into a separate protocol, rather than being part of the specifications for sending mail. You can think of TCP as forming a library of routines that applications can use when they need reliable network communications with another computer. Similarly, TCP calls on the services of IP. Although the services that TCP supplies are needed by many applications, there are still some kinds of applications that don't need them. However there are some services that every application needs. So these services are put together into IP. As with TCP, you can think of IP as a library of routines that TCP calls on, but which is also available to applications that don't use TCP. This strategy of building several levels of protocol is called "layering". We think of the applications programs such as mail, TCP, and IP, as being separate "layers", each of which calls on the services of the layer below it. Generally, TCP/IP applications use 4 layers: - an application protocol such as mail - a protocol such as TCP that provides services need by many applications - IP, which provides the basic service of getting packets to their destination - the protocols needed to manage a specific physical medium, such as Ethernet or a point to point line. TCP/IP is based on the "catenet model". (This is described in more detail in ien-48.txt.) This model assumes that there are a large number of independent networks connected together by gateways. The user should be able to access computers or other resources on any of these networks. Packets will often pass through a dozen different networks before getting to their final destination. The routing needed to accomplish this should be completely invisible to the user. As far as the user is concerned, all he needs to know in order to access another system is an "Internet address". This is an address that looks like 128.6.4.194. It is actually a 32-bit number. However it is normally written as 4 decimal numbers, each representing 8 bits of the address. (The term "octet" is used by Internet documentation for such 8-bit chunks. The term "byte" is not used, because TCP/IP is supported by some computers that have byte sizes other than 8 bits.) Generally the structure of the address gives you some information about how to get to the system. For example, 128.6 is a network number assigned by a central authority to Rutgers University. Rutgers uses the next octet to indicate which of the campus Ethernets is involved. 128.6.4 happens to be an Ethernet used by the Computer Science Department. The last octet allows for up to 254 systems on each Ethernet. Note that 128.6.4.194 and 128.6.5.194 would be different systems. (The structure of an Internet address is described in a bit more detail later.) Of course we normally refer to systems by name, rather than by Internet address. When we specify a name, the network software looks it up in a database, and comes up with the corresponding Internet address. Most of the network software deals strictly in terms of the address. (rfc-882.txt describes the database used to look up names.) TCP/IP is a "connectionless" protocol. Information is transfered in "packets". Each of these packets is sent through the network individually. There are provisions to open connections to systems. However at some level, information is put into packets, and those packets are treated by the network as completely separate. For example, suppose you want to transfer a 15000 octet file. Most networks can't handle a 15000 octet packet. So the protocols will break this up into something like 30 500-octet packets. Each of these packets will be sent to the other end. At that point, they will be put back together into the 15000-octet file. However while those packets are in transit, the network doesn't know that there is any connection between them. It is perfectly possible that packet 14 will actually arrive before packet 13. It is also possible that somewhere in the network, an error will occur, and a packet won't get through at all. In that case, that packet has to be sent again. In fact, there are two separate protocols involved in doing this. TCP (the "transmission control protocol") is responsible for breaking up the message into packets, reassembling them at the other end, resending anything that gets lost, and putting things back in the right order. IP (the "internet protocol") is responsible for routing individual packets. It may seem like TCP is doing all the work. And in small networks that is true. However in the Internet, simply getting a packet to its destination can be a complex job. A connection may require the packet to go through several networks at Rutgers, a serial line to the John von Neuman Supercomputer Center, a couple of Ethernets there, a series of 56Kbaud phone lines to another NSFnet site, and more Ethernets on another campus. Keeping track of the routes to all of the destinations and handling incompatibilities among different transport media turns out to be a complex job. Note that the interface between TCP and IP is fairly simple. TCP simply hands IP a packet with a destination. IP doesn't know how this packet relates to any packet before it or after it. It may have occured to you that something is missing here. We have talked about Internet addresses, but not about how you keep track of multiple connections to a given system. Clearly it isn't enough to get a packet to the right destination. TCP has to know which connection this packet is part of. This task is referred to as "demultiplexing." In fact, there are several levels of demultiplexing going on in TCP/IP. The information needed to do this demultiplexing is contained in a series of "headers". A header is simply a few extra octets tacked onto the beginning of a packet by some protocol in order to keep track of it. It's a lot like putting a letter into an envelope and putting an address on the outside of the envelope. Except with modern networks it happens several times. It's like you put the letter into a little envelope, your secretary puts that into a somewhat bigger envelope, the campus mail center puts that envelope into a still bigger one, etc. Here is an overview of the headers that get stuck on a message that passes through a typical TCP/IP network: We start with a single data stream, say a file you are trying to send to some other computer: ...................................................... TCP breaks it up into managable chunks. (In order to do this, TCP has to know how large a packet your network can handle. Actually, the TCP's at each end say how big a packet they can handle, and then they pick the smallest size.) .... .... .... .... .... .... .... .... TCP puts a header at the front of each packet. This header actually contains at least 20 octets, but the most important ones are a source and destination "port number" and a "sequence number". The port numbers are used to keep track of different conversations. Suppose 3 different people are transferring files. Your TCP might allocate port numbers 1000, 1001, and 1002 to these transfers. When you are sending a packet, this becomes the "source" port number, since you are the source of the packet. Of course the TCP at the other end has assigned a port number of its own for the conversation. Your TCP has to know the port number used by the other end as well. (It finds out when the connection starts, as we will explain below.) It puts this in the "destination" port field. Of course if the other end sends a packet back to you, the source and destination port numbers will be reversed, since then it will be the source and you will be the destination. Each packet has a sequence number. This is used so that the other end can make sure that it gets the packets in the right order, and that it hasn't missed any. (See the TCP specification for details. TCP doesn't number the packets, but the octets. So if there are 500 octets of data in each packet, the first packet might be numbered 0, the second 500, the next 1000, the next 1500, etc.) Finally, I will mention the Checksum. This is a number that is computed by adding up all the octets in the packet (more or less - see the TCP spec). The result is put in the header. TCP at the other end computes the checksum again. If they disagree, then something bad happened to the packet in transmission, and it is thrown away. So here's what the packet looks like now. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Port | Destination Port | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | various other junk | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | various other junk | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Checksum | other junk | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | your data ... next 500 octets | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ...... | If we abbreviate the TCP header as "T", the whole file now looks like this: T.... T.... T.... T.... T.... T.... T.... T.... TCP now sends each of these packets to IP. Of course it has to tell IP the Internet address of the computer at the other end. Note that this is all IP is concerned about. It doesn't care about what is in the packet, or even in the TCP header. IP's job is simply to find a route for the packet and get it to the other end. In order to allow gateways or other intermediate systems to forward the packet, it adds its own header. The main things in this header are the source and destination Internet address (32-bit addresses, like 128.6.4.194), the protocol number, and another checksum. The source Internet address is simply the address of your machine. (This is necessary so the other end knows where the packet came from.) The destination Internet address is the address of the other machine. (This is necessary so any gateways in the middle know where you want the packet to go.) The protocol number tells IP at the other end to send the packet to TCP. Although most IP traffic uses TCP, there are other protocols that can use IP, so you have to tell IP which protocol to send the packet to. Finally, the checksum allows IP at the other end to verify that the packet wasn't damaged in transit. Note that TCP and IP have separate checksums. This is because IP doesn't know anything about TCP. As far as IP is concerned, everything after its header is just a bunch of bits. So IP computes a checksum of its own header, and IP at the other end checks it to make sure that the message didn't get damaged in transit. Once IP has tacked on its header, here's what the message looks like: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | various other junk | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | various other junk | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | junk | Protocol | Header Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Destination Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TCP header, then your data ...... If we represent the IP header by an "I", your file now looks like this: IT.... IT.... IT.... IT.... IT.... IT.... IT.... IT.... At this point, it's possible that no more headers are needed. If your computer happens to have a direct phone line connecting it to the destination computer, or to a gateway, it may simply send the packets out on the line (though likely a synchronous protocol such as HDLC would be used, and it would add at least a few octets at the beginning and end). However most of our networks these days use Ethernet. So now we have to describe Ethernet's headers. Unfortunately, Ethernet has its own addresses. The people who designed Ethernet wanted to make sure that no two machines would end up with the same Ethernet address. Furthermore, they didn't want the user to have to worry about assigning addresses. So each Ethernet controller comes with an address builtin from the factory. In order to make sure that they would never have to reuse addresses, the Ethernet designers allocated 48 bits for the Ethernet address. People who make Ethernet equipment have to register with a central authority, to make sure that the numbers they assign don't overlap any other manufacturer. Ethernet is a "broadcast medium". That is, it is in effect like an old party line telephone. When you send a packet out on the Ethernet, every machine on the network sees the packet. So something is needed to make sure that the right machine gets it. As you might guess, this involves the Ethernet header. Every Ethernet packet has a 14-octet header that includes the source and destination Ethernet address, and a type code. Each machine is supposed to pay attention only to packets with its own Ethernet address in the destination field. (It's perfectly possible to cheat, which is one reason that Ethernet communications are not terribly secure.) Note that there is no connection between the Ethernet address and the Internet address. Each machine has to have a table of what Ethernet address corresponds to what Internet address. (We will describe how this table is constructed a bit later.) In addition to the addresses, the header contains a type code. The type code is to allow for several different protocol families to be used on the same network. So you can use TCP/IP, DECnet, Xerox NS, etc. at the same time. Each of them will put a different value in the type field. Finally, there is a checksum. The Ethernet controller computes a checksum of the entire packet. When the other end receives the packet, it recomputes the checksum, and throws the packet away if the answer disagrees with the original. The checksum is put on the end of the packet, not in the header. The final result is that your message looks like this: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Ethernet destination address (first 32 bits) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Ethernet dest (last 16 bits) |Ethernet source (first 16 bits)| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Ethernet source address (last 32 bits) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IP header, then TCP header, then your data | | | ... | | | end of your data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Ethernet Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ If we represent the Ethernet header with "E", and the Ethernet checksum with "C", your file now looks like this: EIT....C EIT....C EIT....C EIT....C EIT....C EIT....C When these packets are received by the other end, of course all the headers are removed. The Ethernet interface removes the Ethernet header and the checksum. It looks at the type code. Since the type code is the one assigned to IP, the Ethernet device driver passes the packet up to IP. IP removes the IP header. It looks at the IP protocol field. Since the protocol type is TCP, it passes the packet up to TCP. TCP now looks at the packet sequence number. It uses the sequence numbers and other information to combine all the packets into the original file. The ends our initial summary of TCP/IP. There are still some crucial concepts we haven't gotten to, so we'll now go back and add details in several areas. (For detailed descriptions of the items discussed here see, rfc793.txt for TCP, rfc791.txt for IP, and rfc894.txt and rfc826.txt for sending IP over Ethernet.) Well-known sockets and the applications layer ============================================= So far, we have described how a stream of data is broken up into packets, sent to another computer, and put back together. However something more is needed in order to accomplish anything useful. There has to be a way for you to open a connection to a specified computer, log into it, tell it what file you want, and control the transmission of the file. (If you have a different application in mind, e.g. computer mail, some analogous protocol is needed.) This is done by "application protocols". The application protocols run "on top" of TCP/IP. That is, when they want to send a message, they give the message to TCP. TCP makes sure it gets delivered to the other end. Because TCP and IP take care of all the networking details, the applications protocols can treat a network connection as if it were a simple byte stream, like a terminal or phone line. Before going into more details about applications programs, we have to describe how you find an application. Suppose you want to send a file to a computer whose Internet address is 128.6.4.7. To start the process, you need more than just the Internet address. You have to connect to the file transfer server at the other end. In general, network programs are specialized for a specific set of tasks. Most systems have separate programs to handle file transfers, remote terminal logins, mail, etc. When you connect to 128.6.4.7, you have to specify that you want to talk to the file transfer program. This is done by having "well-known sockets" for each program. Recall that TCP uses port numbers to keep track of individual conversations. User programs normally use more or less random port numbers. However specific port numbers are assigned to the programs that sit waiting for requests. For example, if you want to send a file, you will start a program called "ftp". It will open a connection using some random number, say 1234, for the port number on its end. However it will specify port number 21 for the other end. This is the official port number for the ftp server. Note that there are two different programs involved. You run ftp on your side. This is a program designed to accept commands from your terminal and pass them on to the other end. The program that you talk to on the other machine is the ftp server. It is designed to accept commands from the network connection, rather than an interactive terminal. There is no need for your program to use a well-known socket number for itself. Nobody is trying to find it. However the servers have to have well-known numbers, so that people can open connections to them and start sending them commands. The official port numbers for each program are given in "Assigned Numbers". Note that a connection is actually described by a set of 4 numbers: the Internet address at each end, and the TCP port number at each end. Every packet has all four of those numbers in it. (The Internet addresses are in the IP header, and the TCP port numbers are in the TCP header.) In order to keep things straight, no two connections can have the same set of numbers. However it is enough for any one number to be different. For example, it is perfectly possible for two different users on a machine to be sending files to the same other machine. This could result in connections with the following parameters: Internet addresses TCP ports connection 1 128.6.4.194, 128.6.4.7 1234, 21 connection 2 128.6.4.194, 128.6.4.7 1235, 21 Since the same machines are involved, the Internet addresses are the same. Since they are both doing file transfers, one end of the connection involves the well-known port number for file transfer. The only thing that differs is the port number for the program that the users are running. That's enough of a difference. Generally, at least one end of the connection asks the network software to assign it a port number that is guaranteed to be unique. Normally, it's the user's end, since the server has to use a well-known number. Now that we know how to open connections, let's get back to the applications programs. As mentioned above, once TCP has opened a connection, we have something that might as well be a simple wire. All the hard parts are handled by TCP and IP. However we still need some agreement as to what we send over this connection. In effect this is simply an agreement on what set of commands the application will understand, and the format in which they are to be sent. Generally, what is sent is a combination of commands and data. They use context to differentiate. For example, the mail protocol works like this: Your mail program opens a connection to the mail server at the other end. Your program gives it your machine's name, the sender of the message, and the recipients you want it sent to. It then sends a command saying that it is starting the message. At that point, the other end stops treating what it sees as commands, and starts accepting the message. Your end then starts sending the text of the message. At the end of the message, a special mark is sent (a dot in the first column). After that, both ends understand that your program is again sending commands. This is the simplest way to do things, and the one that most applications use. File transfer is somewhat more complex. The file transfer protocol involves two different connections. It starts out just like mail. The user's program sends commands like "log me in as this user", "here is my password", "send me the file with this name". However once the command to send data is sent, a second connection is opened for the data itself. It would certainly be possible to send the data on the same connection, as mail does. However file transfers often take a long time. The designers of the file transfer protocol wanted to allow the user to continue issuing commands while the transfer is going on. For example, the user might make an inquiry, or he might abort the transfer. Thus the designers felt it was best to use a separate connection for the data and leave the original command connection for commands. (It is also possible to open command connections to two different computers, and tell them to send a file from one to the other. In that case, the data couldn't go over the command connection.) Remote terminal connections use another mechanism still. For remote logins, there is just one connection. It normally sends data. When it is necessary to send a command (e.g. to set the terminal type or to change some mode), a special character is used to indicate that the next character is a command. If the user happens to type that special character as data, two of them are sent. We are not going to describe the application protocols in detail in this document. It's better to read the RFC's yourself. However there are a couple of common conventions used by applications that will be described here. First, the common network representation: TCP/IP is intended to be usable on any computer. Unfortunately, not all computers agree on how data is represented. There are differences in character codes (ASCII vs. EBCDIC), in end of line conventions (carriage return, line feed, or a representation using counts), and in whether terminals expect characters to be sent individually or a line at a time. In order to allow computers of different kinds to communicate, each applications protocol defines a standard representation. Note that TCP and IP do not care about the representation. TCP simply sends octets. However the programs at both ends have to agree on how the octets are to be interpreted. The RFC for each application specifies the standard representation for that application. Normally it is "net ASCII". This uses ASCII characters, with end of line denoted by a carriage return followed by a line feed. For remote login, there is also a definition of a "standard terminal", which turns out to be a half-duplex terminal with echoing happening on the local machine. Most applications also make provisions for the two computers to agree on other representations that they may find more convenient. For example, PDP-10's have 36-bit words. There is a way that two PDP-10's can agree to send a 36-bit binary file. Similarly, two systems that prefer full-duplex terminal conversations can agree on that. However each application has a standard representation, which every machine must support. (For more details about the protocols mentioned in this section, see rfc821.txt and rfc822.txt for mail, rfc959.txt for file transfer, and rfc854.txt and rfc855.txt for remote logins. For the well-known port numbers, see the current edition of Assigned Numbers, and possible rfc814.txt.) Protocols other than TCP: UDP and ICMP ====================================== So far, we have described only connections that use TCP. Recall that TCP is responsible for breaking up messages into packets, and reassembling them properly. However in many applications, we have messages that will always fit in a single packet. An example is name lookup. When a user attempts to make a connection to another system, he will generally specify the system by name, rather than Internet address. His system has to translate that name to an address before it can do anything. Generally, only a few systems have the database used to translate names to addresses. So the user's system will want to send a query to one of the systems that has the database. This query is going to be very short. It will certainly fit in one packet. So will the answer. Thus it seems silly to use TCP. Of course TCP does more than just break things up into packets. It also makes sure that the data arrives, resending packets where necessary. But for a question that fits in a single packet, we don't need all the complexity of TCP to do this. If we don't get an answer after a few seconds, we can just ask again. For applications like this, there are alternatives to TCP. The most common alternative is UDP ("user datagram protocol"). UDP is designed for applications where you don't need to put sequences of packets together. It fits into the system much like TCP. There is a UDP header. The network software puts the UDP header on the front of your data, just as it would put a TCP header on the front of your data. Then UDP sends the data to IP, which adds the IP header, putting UDP's protocol number in the protocol field instead of TCP's protocol number. However UDP doesn't do as much as TCP does. It doesn't split data into multiple packets. It doesn't keep track of what it has sent so it can resend if necessary. About all that UDP provides is port numbers, so that several programs can use UDP at once. UDP port numbers are used just like TCP port numbers. There are well-known port numbers for servers that use UDP. Note that the UDP header is shorter than a TCP header. It still has source and destination port numbers, and a checksum, but that's about it. No sequence number, since it is not needed. UDP is used by the protocols that handle name lookups (see ien-116.txt, rfc882.txt, and rfc883.txt), and a number of similar protocols. Another alternative protocol is ICMP ("Internet control message protocol"). ICMP is used for error messages, and other messages intended for the TCP/IP software itself, rather than any particular user program. For example, if you attempt to connect to a host, your system may get back an ICMP message saying "host unreachable". ICMP can also be used to find out some information about the network. See rfc792.txt for details of ICMP. ICMP is similar to UDP, in that it handles messages that fit in one packet. However it is even simpler than UDP. It doesn't even have port numbers in its header. Since all ICMP messages are interpreted by the network software itself, no port numbers are needed to say where a ICMP message is supposed to go. Routing ======= The description above indicated that the IP implementation is responsible for getting packets to the destination indicated by the destination address, but little was said about how this would be done. The task of finding how to get a packet to its destination is referred to as "routing". In fact many of the details depend upon the particular implementation. However some general things can be said. First, it is necessary to understand the model on which IP is based. IP assumes that a system is attached to some local network. We assume that the system can send packets to any other system on its own network. (In the case of Ethernet, it simply finds the Ethernet address of the destination system, and puts the packet out on the Ethernet.) The problem comes when a system is asked to send a packet to a system on a different network. This problem is handled by gateways. A gateway is a system that connects a network with one or more other networks. Gateways are often normal computers that happen to have more than one network interface. For example, we have a Unix machine that has two different Ethernet interfaces. Thus it is connected to networks 128.6.4 and 128.6.3. This machine can act as a gateway between those two networks. The software on that machine must be set up so that it will forward packets from one network to the other. That is, if a machine on network 128.6.4 sends a packet to the gateway, and the packet is addressed to a machine on network 128.6.3, the gateway will forward the packet to the destination. Major communications centers often have gateways that connect a number of different networks. Routing in IP is based entirely upon the network number of the destination address. Each computer has a table of network numbers. For each network number, a gateway is listed. This is the gateway to be used to get to that network. Note that the gateway doesn't have to connect directly to the network. It just has to be the best place to go to get there. For example at Rutgers, our interface to NSFnet is at the John von Neuman Supercomputer Center (JvNC). Our connection to JvNC is via a high-speed serial line connected to a gateway whose address is 128.6.3.12. Systems on net 128.6.3 will list 128.6.3.12 as the gateway for many off-campus networks. However systems on net 128.6.4 will list 128.6.4.1 as the gateway to those same off-campus networks. 128.6.4.1 is the gateway between networks 128.6.4 and 128.6.3, so it is the first step in getting to JvNC. When a computer wants to send a packet, it first checks to see if the destination address is on the system's own local network. If so, the packet can be sent directly. Otherwise, the system expects to find an entry for the network that the destination address is on. The packet is sent to the gateway listed in that entry. This table can get quite big. For example, the Internet now includes several hundred individual networks. Thus various strategies have been developed to reduce the size of the routing table. One strategy is to depend upon "default routes". Often, there is only one gateway out of a network. This gateway might connect a local Ethernet to a campus-wide backbone network. In that case, we don't need to have a separate entry for every network in the world. We simply define that gateway as a "default". When no specific route is found for a packet, the packet is sent to the default gateway. A default gateway can even be used when there are several gateways on a network. There are provisions for gateways to send a message saying "I'm not the best gateway -- use this one instead." (The message is sent via ICMP. See rfc792.txt) Most network software is designed to use these messages to add entries to their routing tables. Suppose network 128.6.4 has two gateways, 128.6.4.59 and 128.6.4.1. 128.6.4.59 leads to several other internal Rutgers networks. 128.6.4.1 leads indirectly to the NSFnet. Suppose we set 128.6.4.59 as a default gateway, and have no other routing table entries. Now what happens when we need to send a packet to MIT? MIT is network 18. Since we have no entry for network 18, the packet will be sent to the default, 128.6.4.59. As it happens, this gateway is the wrong one. So it will forward the packet to 128.6.4.1. But it will also send back an error saying in effect: "to get to network 18, use 128.6.4.1". Our software will then add an entry to the routing table. Any future packets to MIT will then go directly to 128.6.4.1. Most IP experts recommend that individual computers should not try to keep track of the entire network. Instead, they should start with default gateways, and let the gateways tell them the routes, as just described. However this doesn't say how the gateways should find out about the routes. The gateways can't depend upon this strategy. They have to have fairly complete routing tables. (It is possible to do hierarchical routing, where all of the gateways on a campus know about the campus network, but direct all off-campus traffic to a single gateway with connections off-campus.) For this, some sort of routing protocol is needed. A routing protocol is simply a technique for the gateways to find each other, and keep up to date about the best way to get to every network. rfc1009.txt contains a review of gateway design and routing. However rip.doc is probably a better introduction to the subject. It contains some tutorial material, and a detailed description of the most commonly-used routing protocol. Details about Internet addresses: subnets and broadcasting ========================================================== As indicated above, Internet addresses are 32-bit numbers, normally written as 4 octets (in decimal), e.g. 128.6.4.7. There are actually 3 different types of address. The problem is that the address has to indicate both the network and the host within the network. It was felt that eventually there would be lots of networks. Many of them would be small, but probably 24 bits would be needed to represent all the IP networks. It was also felt that some very big networks might need 24 bits to represent all of their hosts. This would seem to lead to 48 bit addresses. But the designers really wanted to use 32 bit addresses. So they adopted a kludge. The assumption is that most of the networks will be small. So they set up three different ranges of address. Addresses beginning with 1 to 126 use only the first octet for the network number. The other three octets are available for the host number. Thus 24 bits are available for hosts. These numbers are used for large networks. But there can only be 126 of these very big networks. The Arpanet is one, and there are a few large commercial networks. But few normal organizations get one of these "class A" addresses. For normal large organizations, "class B" addresses are used. Class B addresses use the first two octets for the network number. Thus network numbers are 128.1 through 191.254. (We avoid 0 and 255, for reasons that we see below. We also avoid addresses beginning with 127, because that is used by some systems for special purposes.) The last two octets are available for host addesses, giving 16 bits of host address. This allows for 64516 computers, which should be enough for most organizations. (It is possible to get more than one class B address, if you run out.) Finally, class C addresses use three octets, in the range 192.1.1 to 223.254.254. These allow only 254 hosts on each network, but there can be lots of these networks. Addresses above 223 are reserved for future use, as class D and E (which are currently not defined). Many large organizations find it convenient to divide their network number into "subnet". For example, Rutgers has been assigned a class B address, 128.6. We find it convenient to use the third octet of the address to indicate which Ethernet a host is on. This division has no significance outside of Rutgers. A computer at another institution would send any packet whose destination address began with 128.6 on the best route to Rutgers. They would not have different routes for 128.6.4 or 128.6.5. But inside Rutgers, we treat 128.6.4 and 128.6.5 as separate networks. In effect, gateways inside Rutgers have separate entries for each Rutgers subnet, whereas gateways outside Rutgers just have one entry for 128.6. Note that we could do exactly the same thing by using a separate class C address for each Ethernet. As far as Rutgers is concerned, it would be just as convenient for us to have a number of class C addresses. However using class C addresses would make things inconvenient for the rest of the world. Every institution that wanted to talk to us would have to have a separate entry for each one of our networks. If every institution did this, there would be far too many networks for any reasonable gateway to keep track of. By subdividing a class B network, we hide our internal structure from everyone else, and save them trouble. This subnet strategy requires special provisions in the network software. It is described in rfc950.txt. 0 and 255 have special meanings. 0 is reserved for machines that don't know their address. In certain circumstances it is possible for a machine not to know the number of the network it is on, or even its own host address. So 0.0.0.23 would be a machine that knew it was host number 23, but didn't know on what network. 255 is used for "broadcast". A broadcast is a message that you want every system on the network to see. Broadcasts are used in some situations where you don't know who to talk to. For example, suppose you need to look up a host name and get its Internet address. Sometimes you don't know the address of the system that has the host name data base. In that case, you might send the request as a broadcast. There are also cases where a number of systems are interested in information. It is then less expensive to send a single broadcast than to send packets individually to each host that is interested in the information. In order to send a broadcast, you use an address that is made by using your network address, with all ones in the part of the address where the host number goes. For example, if you are on network 128.6.4, you would use 128.6.4.255 for broadcasts. How this is actually implemented depends upon the medium. It is not possible to send broadcasts on the Arpanet, or on point to point lines. However it is possible on an Ethernet. If you use an Ethernet address with all its bits on (all ones), every machine on the Ethernet is supposed to look at that packet. Although the official broadcast address for network 128.6.4 is now 128.6.4.255, there are some other addresses that may be treated as broadcasts by certain implementations. For convenience, the standard also allows 255.255.255.255 to be used. This refers to all hosts on the local network. It is often simpler to use 255.255.255.255 instead of finding out the network number for the local network and forming a broadcast address such as 128.6.4.255. In addition, certain older implementations may use 0 instead of 255 to form the broadcast address, e.g. 128.6.4.0. Finally, certain older implementations may not understand about subnets. Thus they consider the network number to be 128.6. In that case, they will assume a broadcast address of 128.6.255.255 or 128.6.0.0. Until support for broadcasts is implemented properly, it can be a somewhat dangerous feature to use. Because 0 and 255 are used for unknown and broadcast addresses, normal hosts should never be given addresses containing 0 or 255. Addresses should never begin with 0, 127, or any number above 223. Addresses violating these rules are sometimes referred to as "Martians", because of rumors that the Central University of Mars is using network 225. Packet splitting and reassembly =============================== TCP/IP is designed for use with many different kinds of network. Unfortunately, network designers do not agree about how big packets can be. Ethernet packets can be 1500 octets long. Arpanet packets have a maximum of around 1000 octets. Some very fast networks have much larger packet sizes. At first, you might think that IP should simply settle on the smallest possible size. Unfortunately, this would cause serious performance problems. When transferring large files, big packets are far more efficient than small ones. So we want to be able to use the largest packet size possible. But we also want to be able to handle networks with small limits. There are two provisions for this. First, TCP has the ability to "negotiate" about packet size. When a TCP connection first opens, both ends can send the maximum packet size they can handle. The smaller of these numbers is used for the rest of the connection. This allows two implementations that can handle big packets to use them, but also lets them talk to implementations that can't handle them. However this doesn't completely solve the problem. The most serious problem is that the two ends don't necessarily know about all of the steps in between. For example, when sending data between Rutgers and Berkeley, it is likely that both computers will be on Ethernets. Thus they will both be prepared to handle 1500-octet packets. However the connection will at some point end up going over the Arpanet. It can't handle packets of that size. For this reason, there are provisions to split packets up into pieces. The IP header contains fields indicating the a packet has been split, and enough information to let the pieces be put back together. If a gateway connects an Ethernet to the Arpanet, it must be prepared to take 1500-octet Ethernet packets and split them into pieces that will fit on the Arpanet. Furthermore, every implementation of TCP/IP must be prepared to accept pieces and put them back together. This is referred to as "reassembly". TCP/IP implementations differ in the approach they take to deciding on packet size. It is fairly common for implementations to use 576-byte packets whenever they can't verify that the entire path is able to handle larger packets. The problem is that many implementations have bugs in the code to reassemble pieces. So many implementors try to avoid ever having splits occur. Different implementors take different approaches to deciding when it is safe to use large packets. Some use them only for the local network. Others will use them for any network on the same campus. 576 bytes is a "safe" size, which every implementation must support. Ethernet encapsulation: ARP =========================== There was a brief discussion above about what IP packets looked like on an Ethernet. The discussion showed the Ethernet header and checksum. However it left one hole: It didn't say how to figure out what Ethernet address to use when you want to talk to a given Internet address. In fact, there is a separate protocol for this, called ARP ("address resolution protocol"). Note by the way that ARP is not an IP protocol. That is, the ARP packets do not have IP headers. Suppose you are on system 128.6.4.194 and you want to connect to system 128.6.4.7. Your system will first verify that 128.6.4.7 is on the same network, so it can talk directly via Ethernet. Then it will look up 128.6.4.7 in its ARP table, to see if it already knows the Ethernet address. If so, it will stick on an Ethernet header, and send the packet. But suppose this system is not in the ARP table. There is no way to send the packet, because you need the Ethernet address. So it uses the ARP protocol to send an ARP request. Essentially an ARP request says "I need the Ethernet address for 128.6.4.7". Every system listens to ARP requests. When a system sees an ARP request for itself, it is required to respond. So 128.6.4.7 will see the request, and will respond with an ARP reply saying in effect "128.6.4.7 is 8:0:20:1:56:34". (Recall that Ethernet addresses are 48 bits. This is 6 octets. Ethernet addresses are conventionally shown in hex, using the punctuation shown.) Your system will save this information in its ARP table, so future packets will go directly. Most systems treat the ARP table as a cache, and clear entries in it if they have not been used in a certain period of time. Note by the way that ARP requests must be sent as "broadcasts". There is no way that an ARP request can be sent to the right system. After all, the whole reason for sending an ARP request is that you don't know the Ethernet address. So an Ethernet address of all ones is used, i.e. ff:ff:ff:ff:ff:ff. By convention, every machine on the Ethernet is required to pay attention to packets with this as an address. So every system sees every ARP requests. They all look to see whether the request is for their own address. If so, they respond. If not, they could just ignore it. (Some hosts will use ARP requests to update their knowledge about other hosts on the network, even if the request isn't for them.) Note that packets whose IP address indicates broadcast (e.g. 255.255.255.255 or 128.6.4.255) are also sent with an Ethernet address that is all ones. Getting more information ======================== This directory contains documents describing the major protocols. There are literally hundreds of documents, so we have chosen the ones that seem most important. Internet standards are called RFC's. RFC stands for Request for Comment. A proposed standard is initially issued as a proposal, and given an RFC number. When it is finally accepted, it is added to Official Internet Protocols, but it is still referred to by the RFC number. We have also included two IEN's. (IEN's are an older form of RFC.) The convention is that whenever an RFC is revised, the revised version gets a new number. This is fine for most purposes, but it causes problems with two documents: Assigned Numbers and Official Internet Protocols. These documents are being revised all the time, so the RFC number keeps changing. You will have to look in rfc-index.txt to find the number of the latest edition. Anyone who is seriously interested in TCP/IP should read the RFC describing IP (791). RFC 1009 is also useful. It is a specification for gateways to be used by NSFnet. As such, it contains an overview of a lot of the TCP/IP technology. You should probably also read the description of at least one of the application protocols, just to get a feel for the way things work. Mail is probably a good one (821/822). TCP (793) is of course a very basic specification. However the spec is fairly complex, so you should only read this when you have the time and patience to think about it carefully. Fortunately, the author of the major RFC's (Jon Postel) is a very good writer. The TCP RFC is far easier to read than you would expect, given the complexity of what it is describing. You can look at the other RFC's as you become curious about their subject matter. Here is a list of the documents you are more likely to want: rfc-index - list of all RFC's rfc1012 - somewhat fuller list of all RFC's rfc1011 - Official Protocols. It's useful to scan this to see what tasks protocols have been built for. This defines which RFC's are actual standards, as opposed to requests for comments. rfc1010 - Assigned Numbers. If you are working with TCP/IP, you will probably want a hardcopy of this as a reference. It's not very exciting to read. It lists all the offically defined well-known ports and lots of other things. rfc1009 - NSFnet gateway specifications. A good overview of IP routing and gateway technology. rfc973 - update on domains rfc959 - FTP (file transfer) rfc950 - subnets rfc894 - how IP is to be put on Ethernet, see also rfc825 rfc882/3 - domains (the database used to go from host names to Internet address and back -- also used to handle UUCP these days). See also rfc973 rfc854/5 - telnet - protocol for remote logins rfc826 - ARP - protocol for finding out Ethernet addresses rfc821/2 - mail rfc814 - names and ports - general concepts behind well-known ports rfc793 - TCP rfc792 - ICMP rfc791 - IP rfc768 - UDP rip.doc - details of the most commonly-used routing protocol ien-116 - old name server (still needed by several kinds of system) ien-48 - the Catenet model, general description of the philosophy behind TCP/IP The following documents are somewhat more specialized. rfc813 - window and acknowledgement strategies in TCP rfc815 - packet reassembly techniques rfc816 - fault isolation and resolution techniques rfc817 - modularity and efficiency in implementation rfc879 - the maximum segment size option in TCP rfc896 - congestion control rfc827,888,904,975,985 - EGP To those of you who may be reading this document remotely instead of at Rutgers: The most important RFC's have been collected into a three-volume set, the DDN Protocol Handbook. It is available from the DDN Network Information Center, SRI International, 333 Ravenswood Avenue, Menlo Park, California 94025 (telephone: 800-235-3155). You should be able to get them via anonymous FTP from sri-nic.arpa. File names are: RFC's: rfc:rfc-index.txt rfc:rfcxxx.txt IEN's: ien:ien-index.txt ien:ien-xxx.txt rip.doc is available by anonymous FTP from topaz.rutgers.edu, as /pub/tcp-ip-docs/rip.doc. Sites with access to UUCP but not FTP may be able to retreive them via UUCP from UUCP host rutgers. The file names would be RFC's: /topaz/pub/pub/tcp-ip-docs/rfc-index.txt /topaz/pub/pub/tcp-ip-docs/rfcxxx.txt IEN's: /topaz/pub/pub/tcp-ip-docs/ien-index.txt /topaz/pub/pub/tcp-ip-docs/ien-xxx.txt /topaz/pub/pub/tcp-ip-docs/rip.doc Note that SRI-NIC has the entire set of RFC's and IEN's, but rutgers and topaz have only those specifically mentioned above. -----------[000161][next][prev][last][first]---------------------------------------------------- Date: 18 Aug 88 00:52:46 GMT From: [email protected] (Charles Hedrick) To: [email protected] Subject: yes, Ethernet controllers really can hear their own output [email protected] (A Hamilton) tells us that Ethernet transceivers "CANNOT listen during their own transmission." but must use software to simulate doing so. The version 2 Ethernet spec in section 7.2.1.2 requires that "In the case of a station transmitting without collision interference, the station's own transmit transitions on the coaxial cable will also appear on the receive pair, after a delay due to propagation through the transceiver." So there is no problem with the transceiver. However most controllers can't receive at the same time as they transmit. I just took at look at the description for the Intel Ethernet chips. These are among the most common chips used in controllers (and happen to be the only ones I have details on). The 82501, which does the signal processing, is full duplex, and can handle send and receive at the same time. The controller chip, 82586, can do so only when it is in loopback mode. One gets the impression that they explicitly disallow simultaneous sending and receiving because the chip can't handle the throughput of doing both at once. (I am guessing that this is the limit because they say that in loopback mode, where they do send and receive at the same time, the size of packet must be limited in order to avoid overruning the receiver portion.) The message from Bill Westfield saying that some controllers can hear their own packets is describing an actual controller made by Bill's company (cisco). It really does hear its own output. I don't think this is the first controller with this property. (At the very least, I think Stanford's MEIS had it.) -----------[000162][next][prev][last][first]---------------------------------------------------- Date: Thu, 18 Aug 88 07:38 EST From: BEAME%[email protected] To: [email protected] Subject: RE: yes, Ethernet controllers really can hear their own output The 3C501 ethernet board for the PC can listen and receive its own output BUT ... If the packet sent is over around 512 bytes, it causes the transmitted packet to become garbled and have an incorrect CRC. -Carl -----------[000163][next][prev][last][first]---------------------------------------------------- Date: Thu, 18 Aug 88 13:46:33 -0400 From: Craig Partridge <[email protected]> To: [email protected] Subject: re: Van's algorithms I got an interesting question: > How does one go about joining SIGCOMM? There are two methods: (1) If you are already an ACM member, call the membership line and ask to be added to SIGCOMM. They will add you *free* (at least they used to). You'll only start paying SIGCOMM dues when your ACM membership is renewed. (2) If you are not an ACM member, join the ACM and while you are doing that, sign up for SIGCOMM (an extra few $$). Craig -----------[000164][next][prev][last][first]---------------------------------------------------- Date: 18 Aug 88 16:49:57 GMT From: [email protected] (Hartvig Ekner) To: [email protected] Subject: Another reason for loopback packets I have found that some ethernet chips (NIC's) simply die if they don't get to transmit a packet every now and then. This is particularly true for the early versions of the Intel 82586. Sending a loopback packet every second or so is the best solution I could come up with. Hartvig Ekner ...mcvax!diku!hartvig -----------[000165][next][prev][last][first]---------------------------------------------------- Date: 18 Aug 88 22:57:57 GMT From: [email protected] (Larry Wall) To: comp.unix.wizards,comp.protocols.tcp-ip Subject: Re: mbuf leaks In article <[email protected]> [email protected] (Michael Bloom) writes: : Can anyone suggest good techniques for tracking down mbuf leaks? I don't know if this is still valid, but in 4.2 I split up the DATA mbuf type into twenty-some-odd different types of mbufs, depending on where they were allocated. After tweaking netstat to show which DATA type, it was easy to see which allocator didn't have a matching deallocator. Generally that was sufficient to deduce the location of the leak. Sometimes a judicious printf or two helps as well, just so you don't go overboard. Generally you want to hide a printf behind a debugging variable you can turn on and off with adb. There may be better tools to diagnose this by now... Larry Wall [email protected] -----------[000166][next][prev][last][first]---------------------------------------------------- Date: 18 Aug 88 23:39:19 GMT From: [email protected] (Ron Guilmette) To: [email protected] Subject: ENOTTY running System V shl(1) with WINS/TCP-IP. Has anybody ever gotten the System V shell layers program "shl" to run on any machine which uses the Wollogong TCP-IP product (aka WINS)? I called Wollogong and they said that this is not supported and never has been. But I'm stubborn and I think it should be! (We are running WINS 2.1 on System V.3.1). The shl program works fine when used from a "real" RS-232 serial port but it (internally) gets the errno ENOTTY when it tries to do the ioctl SXTIOCLINK operation if the "controlling" "terminal" is actually an rlogin'd pty. This causes "shl" to exit with the message "not using a tty device". We tracked this into the kernel and found out that the "sxt" driver was returning the ENOTTY because of the fact that there was no "struct tty" pointer in the cdevsw[] table entry for the major device number of the /dev/ttypX devices. We were able to fix that up easily because there was already an array of "struct tty" things allocated to hold "tty" style information for the pty's. So we just forced the name of that array into the proper entry in our conf.c file and relinked the kernel. Now it doesn't get ENOTTY anymore, but "shl" gets hung up inside of the sxt driver somewhere. Does anybody have a fix? -- Ron Guilmette National SemiConductor Internet: [email protected] or [email protected] Uucp: ...{pyramid,sun,amdahl,apple}!nsc!rfg -----------[000167][next][prev][last][first]---------------------------------------------------- Date: 19 Aug 88 03:04:57 GMT From: [email protected] (Dave Horsfall) To: [email protected] Subject: Serial TCP/IP - all the same? Just a simple question - is there a single standard for TCP/IP over an RS-232 line (SLIP?), or are there many (like Ethernet1.0/2.0/802.3 etc)? We are trying to determine what is wrong with our serial link (a CCI Power 6/32 running Sys V) and our local agents have never heard of a serial TCP/IP analyser, but are willing to write a protocol module for the famous LM-1 box. If we can provide the specs, that is. As a last resort, I'll dig out the Tektronix 834, but decoding SNA frames with that was bad enough, and I won't even _consider_ looking at X.25! Hence our interest in the LM-1, if it'll do serial TCP/IP. Many thanks for any advice... -- Dave Horsfall (VK2KFU), Alcatel-STC Australia, [email protected] dave%[email protected], ...munnari!stcns3.stc.OZ.AU!dave UUCP does it with a bang! -----------[000168][next][prev][last][first]---------------------------------------------------- Date: Fri, 19 Aug 88 10:59:10 PDT From: [email protected] To: [email protected], [email protected] Cc: [email protected] Subject: Re: Van's algorithms in Streams Date: Mon 15 Aug 88 18:12:25-PDT From: William Westfield <[email protected]> Subject: Re: Van's algorithms in Streams To: [email protected] Cc: [email protected] In-Reply-To: Message from "Dave Crocker <[email protected]>" of Mon 15 Aug 88 10:31:00-PDT Message-Id: <[email protected]> Status: R Grumble. All things considered, Van's congestion control enhancments are MUCH more important than the header-prediction changes. Bill Westfield cisco Systems. ------- Bill, I strongly agree. The congestion control enhancements will improve the performance of the Internet for EVERYBODY, and will significantly improve the THROUGHPUT for the enhanced TCP's over most real Internet paths. The header-prediction changes only reduce the CPU OVERHEAD for the individual system and are mostly important for a TCP operating over a high-speed one-hop path, e.g., across a LAN. Bob Braden -----------[000169][next][prev][last][first]---------------------------------------------------- Date: 19 Aug 88 17:25:00 PDT From: John Bartas <[email protected]> To: tcp-ip <[email protected]> A Birds of a Feather session on OS/2 has been set up for 7:30pm Thursday the 29th at INTEROP 88. The discussion will include implementing TCP/IP on OS/2, supporting network hardware, porting applications, and APIs. Please contact me with any further ideas for topics. The field is wide open. Also: ACE is still looking for more BOF sessions. If you have a topic you would like to moderate a session on, contact them at (415) 941-3399 ----------------------------------------------------- John Bartas Project Leader The Wollongong Group -----------[000170][next][prev][last][first]---------------------------------------------------- Date: Fri, 19 Aug 88 14:06:36 WET DST From: Nick Felisiak <[email protected]> To: [email protected] Subject: Re: mbuf leaks In article <[email protected]> responding to <[email protected]> [email protected] (Larry Wall) writes: > > In article <[email protected]> [email protected] (Michael Bloom) writes: > : Can anyone suggest good techniques for tracking down mbuf leaks? > > I don't know if this is still valid, but in 4.2 I split up the DATA mbuf > type into twenty-some-odd different types of mbufs, depending on where they > were allocated. After tweaking netstat to show which DATA type, it was easy > to see which allocator didn't have a matching deallocator. Generally > that was sufficient to deduce the location of the leak. > [...] > > There may be better tools to diagnose this by now... > > Larry Wall > [email protected] > Working with streams buffers (rather than 4.2 mbufs), on our TCP and X.25 packages, I have used the following technique sucessfully: 1. #define allocb(size, pri) Xallocb (size, pri, __LINE__, __FILE__), and ditto for all its friends (freeb, dupb, etc). 2. Add a couple of fields to the header structures, or build parallel structures maintained by the 'X*' functions, which record the line and file info thoughtfully included by cpp as the last two parameters. 3. When a lost buffer is identified, find out exactly where it came from. Doing this *without* source is somewhat tricky - you need to put a small module between the top of tcp (or whatever), and the stream head to catch blocks coming up and down from the user. However, it is possible. Nick Felisiak [email protected] (nick%[email protected]) -----------[000171][next][prev][last][first]---------------------------------------------------- Date: 19 Aug 88 18:46:08 GMT From: [email protected] (Andy Schweig) To: [email protected] Subject: Re: Van's algorithms in Streams In article <[email protected]> [email protected] (Dave Crocker) writes: >Steve Alexander cites Lachman's Streams implementation as containing >Van's performance enhancements. While the congestion control enhancements >drop in relatively easily, it is my understanding that Van has not yet >released his header-prediction changes. I would be interested to know >the origins of the code that Lachman acquired. Steve? Steve did not mention anything about Van's header prediction code. Since it was not available at the time of our last release, it was not included. What we did include was all of the available congestion control algorithms from Van et al. >With respect to the ease of adding Berkeley code to Streams, the key is >the degree of conformance to streams architecture. One can be formally >conformant, but still have variations is certain features. It is certainly true that some of the Berkeley code requires modification before it can be incorporated into a STREAMS-based implementation. Some of it, in fact, is conceptually incompatible with the STREAMS approach. However, changes in areas such as congestion control rarely present any problems. Since our product is based on the 4.3BSD TCP/IP code, these changes pretty much just dropped right in. In areas of the code such as this that deal with the mechanics of the TCP protocol itself, there are virtually no STREAMS dependencies, so the fact that our code is STREAMS-based was not an issue. Andy Schweig - TCP/IP Development Lachman Associates, Inc. ...!laidbak!aes -----------[000172][next][prev][last][first]---------------------------------------------------- Date: 19 Aug 88 21:12:48 GMT From: [email protected] (rod merry) To: [email protected] Subject: BLAST? Can someone pass along some information on what I think is a bulk file transfer protocol called BLAST on top of TCP/IP. One of my company's salespeople has been talking about it, he says its from NCAR. thanks rod -- Rod Merry [email protected] Computer Network Technology {quest|bungia}!cnt!rod 9440 Science Center Drive Minneapolis, MN 55428 (612)535-8111 -----------[000173][next][prev][last][first]---------------------------------------------------- Date: 19 Aug 88 21:15:57 GMT From: [email protected] (Indra K. Singhal) To: comp.sys.ibm.pc,comp.protocols.tcp-ip Subject: tn3270 for the IBM PC ?? Does anyone know if tn3270 has been ported to the IBM PC ? If so, I would greatly appreciate hearing about it. Thanks. -- Indra K. Singhal | | {ucbvax,decwrl,allegra}!amdcad!indra | This space for rent ! | [email protected] | | (408) 749-5445(w) | | -----------[000174][next][prev][last][first]---------------------------------------------------- Date: Sat 20 Aug 88 03:25:05-EDT From: John Romkey <[email protected]> To: [email protected], [email protected] Subject: Packet Driver BOF at Interop '88 I'm going to be running a Birds of a Feather session at the next TCP/IP Interoperability Conference, in September. This BOF will take place on Wednesday the week of the conference, at 5PM. It won't run past 6PM because the conference reception will be then, though if there's enough interest (or need) we can continue it later on or at another time if we can find a place for it. The BOF will be about "standardizing" on a programming interface through which MS-DOS applications (yes, presumably running on IBM PC-like things) can access a network interface and send raw packets. This interface should allow multiple protocol stacks to run simultaneously in the machine, and should insulate the application as much as possible from the network media particular network interface being used. While I was at FTP Software, I designed and implemented something called the "Packet Driver" interface, which has been becoming rather popular on the PC/IP mailing list recently. The packet driver has some problems, both with ambiguities in the specification and with some important pieces of lacking functionality. I want to redesign the interface to allow it to be more efficient, more general and more powerful, and I want to make sure that it will meet the needs of protocol implementors and network itnerface manufacturers. If this is done properly, vendors of non-smart board TCP/IP implementations will not have to keep writing new drivers every time a new ethernet card comes out; they'll be able to point to this specification and have hardware vendors implement a driver which conforms to it. The hardware vendors have the advantage that as soon as they've written this driver, their hardware will be supported by whatever conforming software already uses it, with little effort on their part (no beating up on software companies to support them). I want to encourage vendors of TCP/IP and proprietary LAN protocols for the IBM PC to come to the BOF, and for IBM PC network interface vendors to attend. I hope to generate an RFC from this spec, and get several pieces of public domain software written that we can give out to people who want to support it, in order to make their task easier. - john romkey epilogue technology corp. ------- -----------[000175][next][prev][last][first]---------------------------------------------------- Date: 20 Aug 88 19:13:43 GMT From: [email protected] (Martin Holland) To: comp.protocols.tcp-ip Subject: Multiple TCP/IP servers on one Host. I have an 8 port Micom TCP/IP terminal server with all ports set to slave mode connected to a non-TCP/IP host. This setup allows TCP/IP hosts access to a non TCP/IP host over Ethernet. I now need to add more ports, and intend buying another 8 port server to add to the first. Now the problem. The first server is accessed by name and all the ports are treated as a "hunting group". How can I add a second server without giving it a different name and internet number so the user will not have to try each server in turn to find a vacant port? Is there any way, transparent to the user, that he can "TELNET server1" and if the first server is all in use automatically "TELNET server2"? Martin Holland. -----------[000176][next][prev][last][first]---------------------------------------------------- Date: 21 Aug 88 01:17:16 GMT From: [email protected] (Fletcher Mattox) To: comp.bugs.4bsd,comp.unix.wizards,comp.protocols.tcp-ip Subject: Interlan drops a byte? Has anybody else seen a 4.3BSD VAX with an Interlan Ethernet interface drop a byte of data? Well, that's what we're seeing. For example, if you % rsh remotehost cat 183_byte_file and the remotehost is a 4.3/Interlan host, the rsh will fail. If you look at a packet on the wire, say, with etherfind or tcpdump, the IP header claims there are 223 bytes (183+40 TCP/IP headers), which is correct. Yet there are really only 222 bytes of data in the packet. Hmm. Futhermore other file sizes fail. It appears that if (n%256 == 183) where n is the number of bytes in the above rsh, then TCP/IP fails because a byte is dropped from the data. If we replace the Interlan with a DEUNA, all is as it should be. Any ideas? -- Fletcher Mattox [email protected] cs.utexas.edu!fletcher -----------[000177][next][prev][last][first]---------------------------------------------------- Date: Sun, 21 Aug 88 11:23:20 EDT From: [email protected] (David M Siegel) To: [email protected] Subject: SGMP Our Proteon Gateways support SGMP (simple gateway monitoring protocol). Does anyone have pointers to Unix software that can frob the gateway using this protocol? Proteon claims there is some software floating around, but couldn't point me to it. Thanks, -Dave -----------[000178][next][prev][last][first]---------------------------------------------------- Date: Sun, 21 Aug 88 22:24:42 EDT From: "Robert J. Reschly Jr." <[email protected]> To: Fletcher Mattox <[email protected]> Cc: [email protected] Subject: Re: Interlan drops a byte? Fletcher, I just tried two tests against vgr.brl.mil, a vax running 4.3 (plus some tahoe code, I believe), and did not see the problem you mention. Vgr is a Perdue implementation dual 780 and is running an Interlan NI1010 Ethernet card. I ran the tests from a Gould 6081 connected to the same Ethernet. The first test was against a file containing 90 'a's, a newline, 91 'b's, and another newline, and the second was against a file containing 183 'a's. I piped the output of the "rsh" to 'wc', and got 183 bytes both times. Two questions, a) which Interlan interface are you using, and b) do you have any other Interlan boards you can test against? Our experience has been that, though the board is not the fastest, it has been reliable. Later, Bob -------- Phone: (301)278-6678 AV: 298-6678 FTS: 939-6678 Arpa: [email protected] (or BRL.ARPA) UUCP: ...!brl-smoke!reschly Postal: Robert J. Reschly Jr. Advanced Computer Systems Team Systems Engineering and Concepts Analysis Division U.S. Army Ballistic Research Laboratory ATTN: SLCBR-SE (Reschly) APG, MD 21005-5066 (Hey, *I* don't make 'em up!) **** For a good time, call: (303) 499-7111. Seriously! **** -----------[000179][next][prev][last][first]---------------------------------------------------- Date: 21 Aug 88 20:12:43 GMT From: [email protected] (Charles Hedrick) To: [email protected] Subject: Re: SGMP The usual recommendation for SGMP is to talk to the folks at Nysernet. An initial implementation was done at RPI. It's more or less public (not public domain, but freely distributable). Nysernet cleaned it up a good deal, and is selling it for a minimal cost (not enough to make money -- just enough to cause everybody maximal administrative overhead). They have also produced an SNMP version. cisco and Rutgers have been playing with the original RPI code. As long as you don't want anything sophiscated (e.g. I haven't gotten the X window-based stuff to work), it's fine. I'm not sure how happy cisco would be about doing free software distribution to Proteon's customers, but you could take our copy. (However you should probably consider Nyser's first. It's likely to be better in the long run.) There is also a project at Berkeley that's rewriting SGMP. So far they seem to have a subroutine library but almost no applications. (By the way, I don't know who to contact at these Nysernet or Berkeley, so please don't ask. At cisco, you might contact [email protected].) -----------[000180][next][prev][last][first]---------------------------------------------------- Date: 21 Aug 88 20:38:43 GMT From: [email protected] (Edward Vielmetti) To: [email protected] Subject: Re: SGMP Merit is using an sgmp monitor to watch the NSFnet machines. I believe I saw an "IBM Internal Use Only" banner on it, but to be quite honest I have no idea what its availability is. It runs under X and is quite colorful. I suspect that [email protected] would be able to give you more information if they are willing. The file nis.nsf.net: [NSFNET] MONITOR.MTG-6-88 has some interesting information on sgmp and snmp strategies for the NSFnet backbone. (nis.nsf.net is 35.1.1.48). --Ed Edward Vielmetti, U of Michigan mail group -----------[000181][next][prev][last][first]---------------------------------------------------- Date: Mon, 22 Aug 88 10:19:09 PDT From: [email protected] To: [email protected] (Charles Hedrick) Cc: [email protected] Subject: Re: SGMP The RPI SGMP tools are available for anonymous ftp from clash.cisco.com (192.31.7.24). The file you want is sgmp.tar.Z. It is a compressed tar file containing the most recent working sources with bug fixes made at cisco and Rutgers. Please note that this software is being provided as is without any assertion as to its quality, usefulness or correctness. This code will make core files for you if you push it too hard. However it is quite useful as an introduction to ASN.1 and SGMP if you are persistant enough. Any bug reports sent to me will be politely ignored. However, if you fix a bug, please send it back for inclusion in the distribution. Greg Satz cisco Systems PS. requests for sending this through the mail cannot be honoured so please do not ask. -----------[000182][next][prev][last][first]---------------------------------------------------- Date: 22 Aug 88 12:49:00 PDT From: Dave Crocker <[email protected]> To: tcp-ip <[email protected]> Subject: Re: Van's algorithms in Streams Another religious issue... Network friendliness vs. throughput? Clearly, any host participating in an internet needs to be a good neighbor. Van, et cie's, combined efforts seem to provide enough mechanism to settle the questions of "how?" The question of whether it is more or less important that performance is, mostly, deciding on the number of checksums that can fit on the head of a PIN. Nonetheless, I am curious to see the dominant point of view assuming that internet friendliness must be the answer. It presupposes a certain kind of market. If 90% of the marketplace is on small lans, then performance is likely to be foremost in the customers' minds. They do little or no internetting and therefore do not care about congestion control. No, the current number probably is not 90%, but there is a threshold, somewhere, that says performance needs to dominate. Dave -----------[000183][next][prev][last][first]---------------------------------------------------- Date: Mon, 22 Aug 88 13:36:43 -0400 From: Atul Khanna BBNCC 20/670 873-2531 <[email protected]> To: Craig Partridge <[email protected]> Cc: [email protected], [email protected] Subject: Re: Van's algorithms >> (2) If you are not an ACM member, join the ACM and while you are >> doing that, sign up for SIGCOMM (an extra few$$). You can also join SIGCOMM without becoming an ACM member (annual dues =$37).
-----------[000184][next][prev][last][first]----------------------------------------------------
Date: 22 Aug 88 15:27:53 GMT
From: [email protected] (James Van Bokkelen)
To: comp.protocols.tcp-ip
Subject: Re: tn3270 for the IBM PC??
Greg Minshall's spring 1987 Unix tn3270 distribution included a TN3270 for
the PC, but it was built around U-B's socket library (for their NIU card),
and used a curses package that Berkeley had done (which may not have been
generally available). This may have changed in newer releases.
FTP Software's PC/TCP has included a TN3270 since July 1987 (based on Greg's
3270 emulator). It emulates a 3278-2, and does screen redisplays quite
rapidly (1/4 sec or less). The version that will ship with v2.03 of PC/TCP
has a re-mappable keyboard, simple 4-color support, and will emulate a 3278-4
on an EGA or VGA.
IBM's TCP/IP for DOS also includes a TN3270, but I haven't seen it or
its manual. It was done at UMD under contract (based on Greg's code, I
think).
James VanBokkelen
FTP Software Inc.
(617) 868-4878
-----------[000185][next][prev][last][first]----------------------------------------------------
Date: 22 Aug 88 16:29:08 GMT
To: comp.protocols.appletalk,comp.protocols.tcp-ip
Subject: Re: Broadcast IP on Apple LocalTalk
From article <[email protected]>, by [email protected] (Greg Minshall):
> From article <[email protected]>, by pugs%[email protected] (Tom Lyon):
> There are a few points here. First off, there is no relation between
> AppleTalk zones and IP subnetworks specified "anywhere". The fact is
> that quite often there is such a relation, but no one can count on it.
I disagree. The MacIP implementations I know of do a lookup for the gateway
with the zone name "*". This implies that the "domain" (if you will)
for the MacIP forwarding is the current zone. The MacIP forwarding is
generally specified as an IP subnet or a subrange thereof. So, a relationship
excists between AppleTalk zones and IP subnet forwarding by the gateway.
I've taken this to further imply that an IP broadcast should be sent by
a gateway to all nets in the current zone, just and an NBP Bridge request
would be.
Certainly I haven't seen any of this on paper. One could argue that it's
not part of any formal spec, but that the implementations seem to enforce the
relationship described above.
ps: I have a terrible cold and all of this might be jibberish; but at least
it's an interesting thought ;-)
--
"What will you do when you wake up one morning to find that God's made you
blind in a beautiful person's world and all those great recepies have let you
down, and you're twenty and a half and you're not getting age where you go look
for the boys 'says I love you lets get married and have kids." -Billy Bragg.
-----------[000186][next][prev][last][first]----------------------------------------------------
Date: 22 Aug 88 17:19:09 GMT
From: [email protected]
To: comp.protocols.tcp-ip
Subject: Re: SGMP
The RPI SGMP tools are available for anonymous ftp from clash.cisco.com
(192.31.7.24). The file you want is sgmp.tar.Z. It is a compressed tar file
containing the most recent working sources with bug fixes made at cisco and
Rutgers. Please note that this software is being provided as is without any
assertion as to its quality, usefulness or correctness. This code will make
core files for you if you push it too hard. However it is quite useful as
an introduction to ASN.1 and SGMP if you are persistant enough. Any bug
reports sent to me will be politely ignored. However, if you fix a bug,
please send it back for inclusion in the distribution.
Greg Satz
cisco Systems
PS. requests for sending this through the mail cannot be honoured so please
-----------[000187][next][prev][last][first]----------------------------------------------------
Date: 22 Aug 88 17:36:43 GMT
From: [email protected] (Atul Khanna BBNCC 20/670 873-2531)
To: comp.protocols.tcp-ip
Subject: Re: Van's algorithms
>> (2) If you are not an ACM member, join the ACM and while you are
>> doing that, sign up for SIGCOMM (an extra few $$). You can also join SIGCOMM without becoming an ACM member (annual dues = 37). -----------[000188][next][prev][last][first]---------------------------------------------------- Date: 22 Aug 88 19:49:00 GMT From: [email protected] (Dave Crocker) To: comp.protocols.tcp-ip Subject: Re: Van's algorithms in Streams Another religious issue... Network friendliness vs. throughput? Clearly, any host participating in an internet needs to be a good neighbor. Van, et cie's, combined efforts seem to provide enough mechanism to settle the questions of "how?" The question of whether it is more or less important that performance is, mostly, deciding on the number of checksums that can fit on the head of a PIN. Nonetheless, I am curious to see the dominant point of view assuming that internet friendliness must be the answer. It presupposes a certain kind of market. If 90% of the marketplace is on small lans, then performance is likely to be foremost in the customers' minds. They do little or no internetting and therefore do not care about congestion control. No, the current number probably is not 90%, but there is a threshold, somewhere, that says performance needs to dominate. Dave -----------[000189][next][prev][last][first]---------------------------------------------------- Date: 22 Aug 88 20:29:06 GMT From: [email protected] (William Westfield) To: comp.protocols.tcp-ip Subject: Re: Serial TCP/IP - all the same? There are many different serial encapsulations used by TCP/IP over serial lines. To start with, it depends on whether the line is synchronous or asynchronous. The protocol used on async lines (SLIP) is pretty standard, and has its own RFC (RFC1055). On synchronous lines, things are more complicated - for example, our (cisco Systems) products support about 5 different encapsulations. Two of these are X.25 and DDN X.25, which are pretty much standardized. An ordinary X.25 protocol analyzer is useful for debugging these. We also support LAPB (level 2 of X.25) with and without a "packet type" field, and a sort of bare HDLC protocol (which is not any sort of standard, but can be documented). Other vendors are rumored to use DEC's DDCMP protocols, and/or various non-standard protocols, some of which are considered proprietary. There is currently an Internet Engineering Task Force who is investigating the specification of a standard for Point-to-Point serial links, but this is likely to take a while, and it is still likely that a vendor would like to talk their own protocol to their own boxes. I don't know of any serial analyzers that support ANY of the TCP/IP formats used on serial lines - even the standard ones... Bill Westfield cisco Systems. ------- -----------[000190][next][prev][last][first]---------------------------------------------------- Date: 22 Aug 88 22:32:53 GMT From: [email protected] (Dennis.Bednar) To: [email protected] Subject: Re: Serial TCP/IP - all the same? In article <[email protected]>, [email protected] (Dave Horsfall) writes: > Just a simple question - is there a single standard for TCP/IP over an > RS-232 line (SLIP?), or are there many (like Ethernet1.0/2.0/802.3 etc)? > > We are trying to determine what is wrong with our serial link (a CCI > Power 6/32 running Sys V) and our local agents have never heard of a > serial TCP/IP analyser, but are willing to write a protocol module for > the famous LM-1 box. If we can provide the specs, that is. Yes, there is a single standard for SLIP. It basically is a protocol that describes the format and manner when sending IP packets over a serial (RS-232 asynchronous) line. SLIP is not that complicated. Basically SLIP describes the characters used to surround an IP packet, and describes how such characters may be sent as data within the IP packet by using data escaping conventions. There are several sources of information: The recent RFC written by John Romkey (I believe) that describes SLIP, A mail message that I once posted that describes SLIP (below). You can also use a line monitor (aka datascope) to look at the packets on the RS-232 asynch line. From my own experience, when things don't work, it is usually a network configuration or routing problem. Make sure that your gateways file is correct. Netstat or nstat may be helpful. Also check that your hosts file is correct. Usually one of the gateways doesn't know how to properly forward an IP packet, and the packet sometimes loops until the TTL (time to live) field in the IP header hits zero, and the packet disintegrates. Finally, it would be rather easy to write a SLIP RS-232 line analyzer. Simply dedicate two RS-232 ports for "passing thru" information, while capturing it. That is, read from port 1, and write the same to port 2, and vice-versa. Place the two ports between the sending and receiving machines, and you then passively intercept the traffic between the two active machines. Then you can use your computer to analyze the packets at a leisurely basis. I once wrote such a tool. Below is the text of an old message that describes the SLIP packet format, and justifies the rules for the escape conventions used: How IP Packets are Sent over an Asynchronous Line +------------+--------------------------------------------+-------------+ | LNI header | LNI (Local Network Interface) data | LNI Trailer | +------------+-----------+------------+-------------------+-------------+ | IP header | TCP header | optional TCP data | +-----------+------------+-------------------+ |<------------ Data Encoding Rules --------->| Special Octets Used For Data Encoding Name Hex Octal Decimal Description FRMEND 0xc0 0300 192 Frame End Character FRMESC 0xdb 0333 219 Frame Escape Character M_FRMEND 0xdc 0334 220 Meta Frame End Character M_FRMESC 0xdd 0335 221 Meta Frame Escape Character There is no LNI header for an asynchronous serial line. That is, there is no special character to introduce a sent frame. In the LNI data field, the sender applies the following rules: A data FRMEND octet is sent as FRMESC, M_FRMEND sequence. A data FRMESC octet is sent as FRMESC, M_FRMESC sequence. All other octets are sent without any translation. The receiving IP decodes by stripping and translating the extra octets. The LNI trailer contains only the FRMEND octet. That is, a frame is sent ending with the FRMEND character. Example: Want to send ('a', FRMESC, 'b', FRMEND, 'c'). Sent as ('a', FRMESC, M_FRMESC, 'b', FRMESC, M_FRMEND, 'c', FRMEND). Note the last sent octet is not part of the LNI data field. Data Octet To Send Data Sequence Actually Sent Hex Octal Decimal Hex Octal Decimal 0xdb 0333 219 (0xdb, 0xdd) (0333, 0335) (219, 221) 0xc0 0300 192 (0xdb, 0xdc) (0333, 0334) (219, 220) Justification of the Rules: 1. Sending the FRMEND data octet as a FRMESC, M_FRMEND sequence: We must be able to send the FRMEND as a data character, so the FRMEND has to be escaped, otherwise the receiver would misinterpret it as a premature end of packet. 2. Sending the FRMESC data octet as a FRMESC, M_FRMESC sequence: Because the FRMESC is used as an escape, there has to be a way of treating a FRMESC as data. For example, if this rule weren't defined, then there would be an ambiguous packet. Suppose the sender wanted to send the (data_char, FRMESC, M_FRMEND, data_char) sequence. According to rule 1 only, there would be no translation of octets. Therefore the receiver would receive it as (data_char, FRMEND_data_char, data_char), which is not what is intended. -- FullName: Dennis Bednar UUCP: {uunet|sundc}!rlgvax!dennis USMail: CCI; 11490 Commerce Park Dr.; Reston VA 22091 Telephone: +1 703 648 3300 -----------[000191][next][prev][last][first]---------------------------------------------------- Date: 22 Aug 88 22:42:08 GMT From: [email protected] (Dennis.Bednar) To: [email protected] Subject: Re: Interlan drops a byte? In article <[email protected]>, [email protected] (Fletcher Mattox) writes: > > If you look at a packet on the wire, say, with etherfind or tcpdump, > ... Say, these "ethernet sniffer" tools sound like very useful tools. Do these tools run on the UNIX machine, or on a PC? Is source available? Tell me more about them. Thanks. -- FullName: Dennis Bednar UUCP: {uunet|sundc}!rlgvax!dennis USMail: CCI; 11490 Commerce Park Dr.; Reston VA 22091 Telephone: +1 703 648 3300 -----------[000192][next][prev][last][first]---------------------------------------------------- Date: 23 Aug 88 02:29:10 GMT From: [email protected] (David R. Conrad) To: comp.protocols.tcp-ip Subject: Re: tn3270 for the IBM PC?? >IBM's TCP/IP for DOS also includes a TN3270, but I haven't seen it or >its manual. It was done at UMD under contract (based on Greg's code, I >think). Nope. IBM's tn3270 is based originally on work done by Jacob Rehkter at IBM's TJ Watson Research Center, modified by Drew Perkins of CMU, then modified by us. -drc ------------------------------------------------------------------------------- David R. Conrad The University of Maryland arpa: [email protected] (301) 454-2946 PC/IP Group bitnet: [email protected] -----------[000193][next][prev][last][first]---------------------------------------------------- Date: Tue, 23 Aug 88 08:56:45 EDT From: Frank KAstenholz <[email protected]> To: <[email protected]> Cc: Dave Crocker <[email protected]> Subject: Re: Van's algorithms in Streams Speaking as a commercial developer who is trying to make extensive use of TCP/IP in a product that will eventually be required to move large images through a network very quickly and highly reliably I would say that the more important of the two choices (friendliness vs speed) is that one be a good neighbor. Our products perform newspaper composition - editing articles, pictures, ads, graphics, etc, designing pages, and sending full page images to a photo typesetter. All of this requires a fairly large bandwidth (worst case - a newspaper page could be over 20 Megabytes and the requirement is to ship one of these pages to the phototypesetter every minute). However, while the speed requirement is high, that can allways be alleviated by throwing more money at the system (buying more/bigger CPU's, etc, etc). What is important to us (and maybe many other commercial developers/users of TCP) is that the network be reliable. If the newspaper does not get printed then the publisher looses his/her ad revenue for the day, etc, etc and that is millions. So, a reliable network is more important than a fast one - even on a single local lan. This is only one data point but I guess that it represents a large portion of the people who wish to integrate TCP into their products. Frank Kastenholz Atex/EPPS/Eastman Kodak All opinions are mine and mine alone (etc etc etc). -----------[000194][next][prev][last][first]---------------------------------------------------- Date: 23 Aug 88 05:32:10 GMT From: [email protected] (Barry Margolin) To: comp.protocols.tcp-ip Subject: Re: Serial TCP/IP - all the same? In article <[email protected]> [email protected] (Dennis.Bednar) writes: > Justification of the Rules: The justifications you gave explain why there must be SOME escape convention (which should go without saying), but not why that particular one was chosen. Why is this particular escape convention better than the old "double the special characters" convention or preceding a special character by the escape character? I don't think the doubled-character convention would actually work in SLIP because of the lack of a header (if a packet begins with FRMEND_data_char there would be three FRMEND characters in a row, and it would look like the FRMEND_data_char is actually the last character of the previous packet). But it would work to precede a FRMEND_data_char or FRMESC_data_char with a FRMESC: when forming a packet, you search for a FRMEND or FRMESC; if you find a FRMESC first you remove it from the stream, read the next character into the packet buffer, and then search again. The only advantage I see of the chosen scheme is that packetization and escape processing can occur as separate steps; was this the issue that resulted in this more complex scheme? Barry Margolin Thinking Machines Corp. [email protected] {uunet,harvard}!think!barmar -----------[000195][next][prev][last][first]---------------------------------------------------- Date: 23 Aug 88 07:16:49 GMT From: [email protected] (Rob Hulsebos) To: comp.protocols.tcp-ip Subject: Re: Difference between the various STREAM implementations. In article <[email protected]> [email protected] (Kwang Sung) writes: >I would like know "what is the significant difference between the following >various products in according to AT&T STREAMS Functional Specification ?". > >1. The Wollongong STREAM implementation. >2. The Convergent STREAM implementation. ( ~ Lachman's STREAM product) >3. The Mitre STREAM implementation. ( ~ Unisoft's STREAM product) >4. CMC, EXCELAN STREAM implementation. >5. Or, any other STREAM implementation, if you can think. Me too! Me too! Especially anything to do with Unisoft! ------------------------------------------------------------------------------ R.A. Hulsebos ...!mcvax!philmds!hulsebos Philips I&E Automation Modules phone: +31-40-785723 Building TQ-III-1, room 11 Eindhoven, The Netherlands # cc -O disclaimer.c ------------------------------------------------------------------------------ -----------[000196][next][prev][last][first]---------------------------------------------------- Date: Tue, 23 Aug 88 11:26:55 edt From: [email protected] To: [email protected], [email protected] Subject: Re: BLAST? BLAST stands for Blocked Asynch protocol (I think) it is usually done over serial lines. It is proprietary, but the company does have implementations for a bunch of HW. BLAST gives something on the order of ZMODEM file xfer rates, 2 - 3 times Kermits. The only way I can see to run BLAST over TCP/IP would be to establish [Da Telnet session and run it over that session. No matter what the problem, it wuld seem there is a better solution. Hope this helps Stephen Northcutt ([email protected]) Standard disclaimer applies -----------[000197][next][prev][last][first]---------------------------------------------------- Date: 23 Aug 88 12:05:03 GMT From: [email protected] (Scott Brim) To: comp.protocols.tcp-ip Subject: Re: Serial TCP/IP - all the same? >I don't know of any serial analyzers that support ANY of the TCP/IP >formats used on serial lines - even the standard ones... > >Bill Westfield For a project we almost did last year, both Tekelec and LP-COM were interested in writing a TCP/IP formatting module for us to watch T1 lines (taking into account the encapsulation schemes of several vendors), and for a reasonable price to boot. One of them was even willing to talk with us during the development process to make sure it suited our needs(!) I don't know if they went ahead without us or not. Scott -----------[000198][next][prev][last][first]---------------------------------------------------- Date: 23 Aug 88 12:56:45 GMT From: [email protected] (Frank KAstenholz) To: comp.protocols.tcp-ip Subject: Re: Van's algorithms in Streams Speaking as a commercial developer who is trying to make extensive use of TCP/IP in a product that will eventually be required to move large images through a network very quickly and highly reliably I would say that the more important of the two choices (friendliness vs speed) is that one be a good neighbor. Our products perform newspaper composition - editing articles, pictures, ads, graphics, etc, designing pages, and sending full page images to a photo typesetter. All of this requires a fairly large bandwidth (worst case - a newspaper page could be over 20 Megabytes and the requirement is to ship one of these pages to the phototypesetter every minute). However, while the speed requirement is high, that can allways be alleviated by throwing more money at the system (buying more/bigger CPU's, etc, etc). What is important to us (and maybe many other commercial developers/users of TCP) is that the network be reliable. If the newspaper does not get printed then the publisher looses his/her ad revenue for the day, etc, etc and that is millions. So, a reliable network is more important than a fast one - even on a single local lan. This is only one data point but I guess that it represents a large portion of the people who wish to integrate TCP into their products. Frank Kastenholz Atex/EPPS/Eastman Kodak All opinions are mine and mine alone (etc etc etc). -----------[000199][next][prev][last][first]---------------------------------------------------- Date: 23 Aug 88 15:24:27 GMT From: [email protected] (Pierre LAFORGUE) To: comp.bugs.4bsd,comp.unix.wizards,comp.protocols.tcp-ip Subject: Re: Interlan drops a byte? In article <[email protected]> [email protected] (Fletcher Mattox) writes: >Has anybody else seen a 4.3BSD VAX with an Interlan Ethernet interface >drop a byte of data? Well, that's what we're seeing. >For example, if you > % rsh remotehost cat 183_byte_file >and the remotehost is a 4.3/Interlan host, the rsh will fail. Your report is not very accurate; I think it depends of the Interlan interface. Here, we are using the both types: NI1010A and NP100. Both work well (I tried your test, of course). May be your problem comes from your software driver. For instance, the original BSD4.3 NP100 driver was bugged. You may ask Un. of Berkeley for the updated driver. -- Pierre LAFORGUE [email protected] [email protected] uunet.uu.net!imag!pierre -----------[000200][next][prev][last][first]---------------------------------------------------- Date: 23 Aug 88 15:26:55 GMT From: [email protected] To: comp.protocols.tcp-ip Subject: Re: BLAST? BLAST stands for Blocked Asynch protocol (I think) it is usually done over serial lines. It is proprietary, but the company does have implementations for a bunch of HW. BLAST gives something on the order of ZMODEM file xfer rates, 2 - 3 times Kermits. The only way I can see to run BLAST over TCP/IP would be to establish [Da Telnet session and run it over that session. No matter what the problem, it wuld seem there is a better solution. Hope this helps Stephen Northcutt ([email protected]) Standard disclaimer applies -----------[000201][next][prev][last][first]---------------------------------------------------- Date: 23 Aug 88 17:35:16 GMT From: [email protected] (Paul Pomes) To: comp.protocols.tcp-ip Subject: Interlan drops a byte? I've also run into the problem using a Interlan 1010A card in a 4.3 BSD VAX 11/780 with Van's TCP fixes. Transfers kept coming up one byte short in transferring the X.V11R2 split files from expo.lcs.mit.edu to uxc.cso.uiuc.edu. It was not a constant problem. Retrying the transfer would usually get the complete file. One file did require six attempts before a 512,000 copy was obtained rather than 511,999. A cmp of the two files showed the difference to be at the very end of the file. Paul Pomes Univ of Ill, CSO -----------[000202][next][prev][last][first]---------------------------------------------------- Date: 23 Aug 88 18:38:06 GMT From: [email protected] (Steve Pope) To: comp.protocols.tcp-ip Subject: Re: Serial TCP/IP - all the same? >The justifications you gave explain why there must be SOME escape >convention (which should go without saying), but not why that >particular one was chosen. Why is this particular escape convention >better than the old "double the special characters" convention or >preceding a special character by the escape character? > >Barry Margolin Let me attempt an answer -- the SLIP frame-escape method has the property that the only place a FRAME_END character appears in the SLIP-encoded data is between packets, i.e. FRAME_END doesn't occur within a packet even in escaped form. Thus, transmitting SLIP's use one or more FRAME_ENDs to clear an idle channel, and a receiving slip always knows to reset itself if it gets a FRAME_END. This approach might have a slight robustness advantage. Other escape conventions might not provide the transmitting SLIP with a definite way of resetting the receiver if the receiver is in an unknown state. steve pope ([email protected]) -----------[000203][next][prev][last][first]---------------------------------------------------- Date: 23 Aug 88 18:49:58 GMT From: [email protected] (Mike St. Johns) To: comp.protocols.tcp-ip Subject: wanted - Nameserver binaries for an ULTRIX 2.0 The subject says it all - I've got the named/domaind stuff from Berkeley, but since I've got a binary only system - I've got some trouble even getting the libraries built! Is there anyone out there with a source-license Ultrix 2.0 who has built the nameserver libraries and is willing to give me a copy - binary? Umm - this is for a uVax II. Thanks, Mike -----------[000204][next][prev][last][first]---------------------------------------------------- Date: 23 Aug 88 20:13:14 GMT From: [email protected] (Thomas Eric Brunner) To: comp.protocols.tcp-ip Subject: Re: Interlan drops a byte? Dennis Bednar wrote asking for "ethernet sniffer" info, whether they (etherfind, tcpdump) ran on Unix boxes, PCs, was source available, etc. I've just gone through using two reasonable tools, the Network General "Sniffer", and the Exelan "LANalyser", both PC based for ethernet analysis, as well as using Van's Tcpdump (daily) and SMI's Etherfind (only where tcpdump is not available) for the purpose of determining why a diskless Sun fails under some conditions to boot when running the 4.0 release of the Sun OS. So I'll share what little I know. The "Sniffer" is a menu-driven package that runs on a PC, either lap-top or the usual notion of a PC. It only uses 2 bytes of a packet for filtering, so one's ability to form a reasonably complex "from/to/size/type" boolean is limited, though I personally didn't find this limitation a problem at all - having lived with "noisier" tools. Price, 19,000, 15,000 for the single-board PC. The "LANalyser" is less menu-oriented, also runs on a PC, either flavor, and uses more bytes for filtering. Price, 15,000. The LANalyser was the choice of SRI's link-level folks whos interest is mostly in connectivity diagnosis. The Sniffer was the choice of my own staff, whos interest is both connectivity and network-level and above diagnosis. With it we found that the diskless boot problem resulted from interactions between VMS hosts running TWG/SRI ip software and the Sun's broadcast boot request. Details available upon request. Tcpdump is not available in source form, one can either ftp it from any of the usual places, or if one is not able to ftp from say, lbl or ucbarpa, via tape from someone who is. It comes as an executable binary (Sun 3.x), with awk scripts for digestion of its output, in tar format. On a lan with a lot of hosts, getting a Sun just to run tcpdump seems very reasonable to me -- I've seen a quote for a 3/50 (used) for 850... I use it to catch the initiation of "hostile" and "questionable" events here - we've several scripts to wrap it which may be in our ftp area (spam) if either I or Tim remember to keep those versions current, and to diagnosis some really bad vendor cruft (line-at-a-time smtp, with a seperate cr/lf packet!), etc. Etherfind is available from SMI as part of their operating system release. It supports fewer of the boolean constructions than tcpdump, and I really avoid using it since Van's first release of tcpdump. Another possibility is SMI's traffic routine, which is visual, a nice intro to the activities on the wire, but little beyond that. Almost no filtering is possible. Each of these use the NIT interface, particular to SMI, which has bugs. For those sourced, putting metering into the device driver(s) is an equivalent approach. Others on this last can easily improve on this little note, in particular someone from Network General and Exelan on pricing, "protocol suite" software extra pricing, and capabilities. Happy lan-ing Dennis! Eric -----------[000205][next][prev][last][first]---------------------------------------------------- Date: 23 Aug 88 20:18:44 GMT From: [email protected] (Brian Ruptash) To: comp.protocols.tcp-ip Subject: Test Specifications According to USAF DDN PMO people, the NBS is working on a full suite DDN (DDN X.25, TCP/IP et al, FTP, TELNET, SMTP) reference test system, under contract for DCA. Apparently this system necessitates active responders in the host under test. Does anyone know of this system, and whether its specifications, and more importantly those for the responders, are available yet? -- Brian -----------[000206][next][prev][last][first]---------------------------------------------------- Date: 23 Aug 88 20:56:45 GMT From: [email protected] ("Marty Schoffstall") To: comp.protocols.tcp-ip Subject: Re: SGMP The usual recommendation for SGMP is to talk to the folks at Nysernet. An initial implementation was done at RPI. It's more or less public (not public domain, but freely distributable). Nysernet cleaned it up a good deal, and is selling it for a minimal cost (not enough to make money -- just enough to cause everybody maximal administrative overhead). Actually we rewrote it from scratch and saved the "look and feel" of the applications. Additionally we added about 10 more applications including a BSD/UNIX agent/server. We followed the CMU model for Tektronix/VMS/TCP administratively, becaue we heard it worked, time will tell though. However we have distributed a LOT of university/ non-profit licenses (source) so far, and we release a new version about every quarter so its not an orphan. These are important due to the growing network management needs in terms of more complex and useful tools. (By the way, I don't know who to contact at these Nysernet or Berkeley, so please don't ask. At cisco, you might contact [email protected].) [email protected] does work for people who are interested. Marty -----------[000207][next][prev][last][first]---------------------------------------------------- Date: 23 Aug 88 21:26:44 GMT From: [email protected] To: comp.protocols.tcp-ip Subject: Re: SGMP For information on NYSERNet's SGMP distribution, please contact Edward Nadeau, NYSERNet Inc., 165 Jordan Road, Troy, NY 12180 [email protected] (518) 283-8860 Our SNMP (IDEA0011-02) distribution is not available for public distribution yet. Wengyik -----------[000208][next][prev][last][first]---------------------------------------------------- Date: 23 Aug 88 21:49:39 GMT From: [email protected] (Philip Prindeville) To: comp.protocols.tcp-ip Subject: Re: BOF on SLIP at Interop 88 -- Thurs Sept 19th. Well, having seen a plethora of "please add me" messages to [email protected] following my posting on this list about how one can (passively) follow developments on the SLIP working group, and feeling immensely guilty about it, I should restate that (as per age-old tradition), requests to be added to the list should be sent to: [email protected] asking to be added to the "interest" list. Please do NOT send requests directly to ietf-ppp-interest, or the whole readership will get a copy of your message. Thanks for your cooperation, -Philip -----------[000209][next][prev][last][first]---------------------------------------------------- Date: 24 Aug 88 02:54:54 GMT From: [email protected] (Paul Vixie) To: comp.protocols.tcp-ip Subject: Re: Serial TCP/IP - all the same? # Let me attempt an answer -- the SLIP frame-escape method has the # property that the only place a FRAME_END character appears in the # SLIP-encoded data is between packets, i.e. FRAME_END doesn't occur # within a packet even in escaped form. Now let _me_ list another reason why this is a Good Thing. There are quite a few smart serial devices in the world these days. Most of the time they don't use any of their smarts -- getting UNIX line editing into the serial board is something one can be quite proud of, if one can make it work at all. If you can help do SLIP by adding some logic to your serial card, you can get a nice performance bang for a small amount of effort: tell your serial card to collect bytes until a timeout, buffer overflow, or terminating character in the input. If you use a large enough timeout and buffer, your main CPU only has to deal with SLIP when a whole packet has arrived. If you don't have a smart serial card, you can still get a little bit of benefit from this down in the lowest levels of your input driver. But if you have a protocol that makes you keep track of state between input characters, it gets harder no matter where you are trying to optimize it, and you will probably end up not optimizing it. Yours for fewer interrupts, -- Paul Vixie Digital Equipment Corporation Work: [email protected] Play: [email protected] Western Research Laboratory uunet!decwrl!vixie uunet!vixie!paul Palo Alto, California, USA +1 415 853 6600 +1 415 864 7013 -----------[000210][next][prev][last][first]---------------------------------------------------- Date: 24 Aug 88 04:58:40 GMT From: [email protected] (Merton Campbell Crockett) To: comp.protocols.tcp-ip Subject: Re: BLAST? I remember getting a number of brochures (sp) several years ago on BLAST. My memory may be faulty; however, as I recall they were offering an ISO 1745 based protocol package using options A, B, and C. Option C being the transparent mode with a CRC for longitudinal integrity using either CRC-16 or CRC-CCITT (ISO 2145?). Basically, a souped up IBM Bisynchronous Serial Communications (BSC) protocol with a generic nameplate. It would be a good replacement for SLIP over a long haul, multi-drop, and/or store and foreward link--uses standard well-formed packets which can be supported by chips such as the 68521 rather than a roll your own home-brew protocol. Merton Campbell Crockett EATON Information Management Systems System Software Manager 31717 La Tienda Drive, Box 5009 AN/GYQ-21(V) Program Westlake Village, CA 91359 Internet: [email protected] Easynet: DECWRL::[email protected] -----------[000211][next][prev][last][first]---------------------------------------------------- Date: 24 Aug 88 11:23:31 GMT From: [email protected] (Steven D. Miller) To: comp.protocols.tcp-ip Subject: Re: Interlan drops a byte? The problem here is not in your Interlan card; I've had the same problem with my Sun-3/60. I did a packet spy once, and it seems that under certain circumstances, expo seems to send the FIN with a sequence number that is one too low. The spy I made of the problem is enclosed below, so that others more knowledgeable in the ways of TCP may check my reasoning. I think expo is running vanilla SunOS 3.4 TCP, but I'm by no means certain of that... -Steve Spoken: Steve Miller Domain: [email protected] UUCP: uunet!mimsy!steve Phone: +1-301-454-1808 USPS: UMIACS, Univ. of Maryland, College Park, MD 20742 pktnum 2483, timestamp 577459160 sec 410000 usec, len 54 Ethernet level: dst host 08:00:20:00:6f:74, src host 02:07:01:00:8a:17, type 800 IP header: version 4, header len 5, service 0, len 228, id 95c5, off 0, ttl 18, protocol 6, sum e, src 121e00d4, dst 80087803 TCP header: source port 14, dst port 477, <seq,ack> 1d52972,108d4e01 data off 5, flags=10<ACK> window 1000, sum 45a2, urgent 0 TCP data length 512 (0x200) bytes pktnum 2484, timestamp 577459160 sec 410000 usec, len 54 Ethernet level: dst host 02:07:01:00:8a:17, src host 08:00:20:00:6f:74, type 800 IP header: version 4, header len 5, service 0, len 28, id b6f9, off 0, ttl 1e, protocol 6, sum dad9, src 80087803, dst 121e00d4 TCP header: source port 477, dst port 14, <seq,ack> 108d4e01,1d52f72 data off 5, flags=10<ACK> window 2000, sum f076, urgent 0 TCP data length 0 (0x0) bytes pktnum 2485, timestamp 577459160 sec 530000 usec, len 54 Ethernet level: dst host 08:00:20:00:6f:74, src host 02:07:01:00:8a:17, type 800 IP header: version 4, header len 5, service 0, len 228, id 95c6, off 0, ttl 18, protocol 6, sum d, src 121e00d4, dst 80087803 TCP header: source port 14, dst port 477, <seq,ack> 1d52b72,108d4e01 data off 5, flags=10<ACK> window 1000, sum 81b0, urgent 0 TCP data length 512 (0x200) bytes pktnum 2486, timestamp 577459160 sec 530000 usec, len 54 Ethernet level: dst host 02:07:01:00:8a:17, src host 08:00:20:00:6f:74, type 800 IP header: version 4, header len 5, service 0, len 28, id b6fa, off 0, ttl 1e, protocol 6, sum dad8, src 80087803, dst 121e00d4 TCP header: source port 477, dst port 14, <seq,ack> 108d4e01,1d52f72 data off 5, flags=10<ACK> window 2000, sum f076, urgent 0 TCP data length 0 (0x0) bytes pktnum 2487, timestamp 577459160 sec 810000 usec, len 54 Ethernet level: dst host 08:00:20:00:6f:74, src host 02:07:01:00:8a:17, type 800 IP header: version 4, header len 5, service 0, len 228, id 95c7, off 0, ttl 18, protocol 6, sum c, src 121e00d4, dst 80087803 TCP header: source port 14, dst port 477, <seq,ack> 1d52d72,108d4e01 data off 5, flags=10<ACK> window 1000, sum 96d3, urgent 0 TCP data length 512 (0x200) bytes [expo sent 512 bytes after seq 1d52d72 ] pktnum 2488, timestamp 577459160 sec 810000 usec, len 54 Ethernet level: dst host 02:07:01:00:8a:17, src host 08:00:20:00:6f:74, type 800 IP header: version 4, header len 5, service 0, len 28, id b6fb, off 0, ttl 1e, protocol 6, sum dad7, src 80087803, dst 121e00d4 TCP header: source port 477, dst port 14, <seq,ack> 108d4e01,1d52f72 data off 5, flags=10<ACK> window 2000, sum f076, urgent 0 TCP data length 0 (0x0) bytes [fnord acks that] pktnum 2489, timestamp 577459160 sec 930000 usec, len 54 Ethernet level: dst host 08:00:20:00:6f:74, src host 02:07:01:00:8a:17, type 800 IP header: version 4, header len 5, service 0, len 1b8, id 95c8, off 0, ttl 18, protocol 6, sum 7b, src 121e00d4, dst 80087803 TCP header: source port 14, dst port 477, <seq,ack> 1d52f71,108d4e01 data off 5, flags=19<FIN,PUSH,ACK> window 1000, sum 2a8, urgent 0 TCP data length 400 (0x190) bytes [expo, whose sequence number was 1d52f72, now sends a FIN with the sequence number one too low.] pktnum 2490, timestamp 577459160 sec 930000 usec, len 54 Ethernet level: dst host 02:07:01:00:8a:17, src host 08:00:20:00:6f:74, type 800 IP header: version 4, header len 5, service 0, len 28, id b6fc, off 0, ttl 1e, protocol 6, sum dad6, src 80087803, dst 121e00d4 TCP header: source port 477, dst port 14, <seq,ack> 108d4e01,1d53102 data off 5, flags=10<ACK> window 1e71, sum f075, urgent 0 TCP data length 0 (0x0) bytes [fnord acks that] pktnum 2491, timestamp 577459161 sec 70000 usec, len 54 Ethernet level: dst host 02:07:01:00:8a:17, src host 08:00:20:00:6f:74, type 800 IP header: version 4, header len 5, service 0, len 28, id b6fe, off 0, ttl 1e, protocol 6, sum dad4, src 80087803, dst 121e00d4 TCP header: source port 477, dst port 14, <seq,ack> 108d4e01,1d53102 data off 5, flags=11<FIN,ACK> window 2000, sum eee5, urgent 0 TCP data length 0 (0x0) bytes [fnord sends its fin, with seq # 108d4e02] pktnum 2492, timestamp 577459161 sec 230000 usec, len 54 Ethernet level: dst host 08:00:20:00:6f:74, src host 02:07:01:00:8a:17, type 800 IP header: version 4, header len 5, service 0, len 28, id 95cb, off 0, ttl 18, protocol 6, sum 208, src 121e00d4, dst 80087803 TCP header: source port 14, dst port 477, <seq,ack> 1d53102,108d4e01 data off 5, flags=11<FIN,ACK> window 1000, sum fee5, urgent 0 TCP data length 0 (0x0) bytes pktnum 2493, timestamp 577459161 sec 250000 usec, len 54 Ethernet level: dst host 02:07:01:00:8a:17, src host 08:00:20:00:6f:74, type 800 IP header: version 4, header len 5, service 0, len 28, id b6ff, off 0, ttl 1e, protocol 6, sum dad3, src 80087803, dst 121e00d4 TCP header: source port 477, dst port 14, <seq,ack> 108d4e01,1d53103 data off 5, flags=11<FIN,ACK> window 2000, sum eee4, urgent 0 TCP data length 0 (0x0) bytes pktnum 2494, timestamp 577459161 sec 270000 usec, len 54 Ethernet level: dst host 08:00:20:00:6f:74, src host 02:07:01:00:8a:17, type 800 IP header: version 4, header len 5, service 0, len 28, id 95cc, off 0, ttl 18, protocol 6, sum 207, src 121e00d4, dst 80087803 TCP header: source port 14, dst port 477, <seq,ack> 1d53102,108d4e02 data off 5, flags=11<FIN,ACK> window 1000, sum fee4, urgent 0 TCP data length 0 (0x0) bytes pktnum 2495, timestamp 577459161 sec 410000 usec, len 54 Ethernet level: dst host 08:00:20:00:6f:74, src host 02:07:01:00:8a:17, type 800 IP header: version 4, header len 5, service 0, len 28, id 95cd, off 0, ttl 18, protocol 6, sum 206, src 121e00d4, dst 80087803 TCP header: source port 14, dst port 477, <seq,ack> 1d53103,108d4e02 data off 5, flags=10<ACK> window 1000, sum fee4, urgent 0 TCP data length 0 (0x0) bytes pktnum 2496, timestamp 577459161 sec 410000 usec, len 54 Ethernet level: dst host 02:07:01:00:8a:17, src host 08:00:20:00:6f:74, type 800 IP header: version 4, header len 5, service 0, len 28, id b700, off 0, ttl 1e, protocol 6, sum dad2, src 80087803, dst 121e00d4 TCP header: source port 477, dst port 14, <seq,ack> 108d4e02,0 data off 5, flags=4<RST> window 0, sum 41c9, urgent 0 TCP data length 0 (0x0) bytes -----------[000212][next][prev][last][first]---------------------------------------------------- Date: 24 Aug 88 14:01:27 GMT From: [email protected] (Ronald G Minnich) To: comp.protocols.tcp-ip Subject: Re: Serial TCP/IP - all the same? In article <[email protected]> [email protected] (Paul Vixie) writes: >Now let _me_ list another reason why this is a Good Thing. There are quite >a few smart serial devices in the world these days. Most of the time they >don't use any of their smarts -- getting UNIX line editing into the serial Second the motion. Actually there have been quite a few systems over the years that support 'break sets' or 'tell me when you get this character or an overflow'. A few that come to mind: HP3000-supported 'tell me when you get a buffer terminated by x'- with timeout DG Eclipse with their smart ALM- supported programmable break sets. Commodore Amiga- supports 'tell me when you get a buffer terminated by x' Louie Mammakos' port of the Karn code uses the amiga's ability to suck up a bunch of characters 'til you get FRAME_END. This is a Good Thing. Saves the amiga OS a lot of work, and opens the possibility of letting a smart chip do the job. The 'two escape chars. in a row' seems like a good idea till you have to handle all the weird exception conditions... i had never really thought about why the way SLIP does it is such a good idea till now, but it sure is a good idea. ron -----------[000213][next][prev][last][first]---------------------------------------------------- Date: 24 Aug 88 14:45:09 GMT From: [email protected] (James Van Bokkelen) To: comp.protocols.tcp-ip Subject: Less expensive network monitors If you have less than 15K to spend, and already own a sufficiently IBM- compatible PC or AT, both the Lanalyzer and the Sniffer are available in do-it-yourself versions, where you get a card and software and install it in your machine. I believe the price range is 5K - 9K. Performance is comparable to the complete versions (which is necessarily lower than the HP monitor, because the Sniffer uses an existing PC Ethernet interface (3C505 in some versions, NP600 or other cards in others) to capture packets, and Excelan uses a specialized relative of their EXOS205 card, with a conventional LAN controller chip). If you don't have 5K, but do have a PC (or AT or PS/2), and particularly if you already own an Ethernet (or ProNET-10) card, you can either buy LANWatch (from us, 1200 quantity 1), or get the MIT/CMU PC-IP distribution, and use Netwatch (which is free). Both packages put the Ethernet interface in promiscuous mode, and capture as many of the passing packets as they can. Netwatch only runs on the interfaces supported by PC-IP (NI5010, 3C500 and P1300) which are all single-buffered, so you won't do too well on loaded networks. LANWatch supports lots of cards (including Proteon's P1340/1344 for monitoring 802.5 token rings), and many of these can do pretty well, particularly in a fast AT or PS/2. However, you are never going to capture all the traffic on a heavily-loaded network. LANWatch also has lots of neat features that Netwatch doesn't have, and you get enough source to change/enhance the packet parsing and filtering routines, as well as support. James VanBokkelen FTP Software Inc. (617) 868-4878 PS: LANWatch has a help hot key instead of menus, for those in a hurry... -----------[000214][next][prev][last][first]---------------------------------------------------- Date: 24 Aug 88 20:29:09 GMT From: [email protected] (Ron Guilmette) To: comp.protocols.tcp-ip Subject: Does TCP/IP "comform" to ISO/OSI? I'm sitting here looking at a document that says that "The XYZ implementation of TCP/IP comforms to the ISO/OSI reference model." I'm not really a networking kinda guy so I don't know if that's a lie or not. Is it? I seem to recall having heard once that TCP/IP is NOT COMFORMANT with ISO/OSI. -- Ron Guilmette National SemiConductor Internet: [email protected] or [email protected] Uucp: ...{pyramid,sun,amdahl,apple}!nsc!rfg -----------[000215][next][prev][last][first]---------------------------------------------------- Date: 24 Aug 88 21:28:23 GMT From: [email protected] (William C. VerSteeg) To: comp.protocols.tcp-ip Subject: Test suite for IP based systems Is there an application program written to test IP based systems ? Public domain code would be best, but I would consider paying for a good test suite. I recall that somebody was trying to start a firm for this purpose, but I never heard any hard facts about a test suite. What I am looking for is something that I can put on a private ethernet cable, do some minimal configuration (i.e give it some IP addresses and the applications that I want tested), and walk away from. I would like to come back and have a printout saying "Yes the target knows about redirects", "The target responds to the following Telnet negotiations properly", "The target can FTP a file at xxxxx Bytes/Sec",etc. I need this suite for regression testing of systems that I am modifying. It is so time consuming to make sure nothing breaks as I add new features to my code. If such a system doesn't exist, would anybody like to work with me to put one together? Bill VerSteeg Digital Communications Associates -----------[000216][next][prev][last][first]---------------------------------------------------- Date: 24 Aug 88 22:52:35 GMT From: [email protected] (Tait Kirkham) To: comp.dcom.lans,comp.protocols.tcp-ip Subject: RUNNING FTP IN BATCH MODE Does anyone out there know if it is possible to run ftp in a "batch" mode? Specifically, I wish to be able to connect to a remote system and execute FTP commands from a batch file, rather than having to log in and type the commands in at the terminal. Does anyone know if this is possible? Currently I am running on a 286 PC, DOS, and Excelan software. I would appreciate any information you may have to offer. Thanks in advance Tait Kirkham -- {pyramid,uunet}!versatc!tait Tait Kirkham Versatec, 2805 Bowers Avenue, Santa Clara, Ca. 95051 (408)988-2800x5070 -----------[000217][next][prev][last][first]---------------------------------------------------- Date: 24 Aug 88 23:58:58 GMT From: [email protected] (Kwang Sung) To: comp.protocols.tcp-ip Subject: Layer 7 Protocol Converters, "Type of Service" Routing Thanks everyone on the net for answering to my questions on STREAMS. I wish you can go and see my country KOREA for 1988 summer Olympics. As a matter of fact, Korea is the safest country like Israel. So, don't worry, and please go and see. I have another questions to someone on the network. 1. In order to migrate to OSI from DoD, I think, we need Layer 7 Protocol Converters to provide interoperability for coexistence. Is anybody working on, or has anybody worked on those Protocol Converters before ? Please give me the name of the product. 2. I would like to know which product has already included "Type of Service" routing. Thanks again, please reply to me. Kwang Sung Sr. Software Engineer ARIX Corp. UUCP: ...!sun!aeras!smaug!kwang -----------[000218][next][prev][last][first]---------------------------------------------------- Date: 25 Aug 88 00:27:57 GMT From: [email protected] (Gregory R. Simpson @ The North Coast) To: comp.os.vms,comp.protocols.tcp-ip Subject: Interfacing HP Workstations to VMS (alternative methods/comments) Hello, I'm interested in any first hand experience people might have with interfacing Unix Based Workstations with a VMS Decnet network. My specific situation is this: My employer is considering the purchase of several HP Workstations. However, for the purchase to be approved, they must interface cleanly with our large installed base of VMS machines. My approaches toward achieving this goal are: 1) TCP/IP interface... Probably the public domain CMU version. 2) NFS ... A commercial product 3) NS ... Hp's proprietary networking 4) NFS'ing the HP's to an Ultrix uVax and then running decnet between the uVax and the Vax Clusters... How good are the above solutions? Would someone on an HP be able to easily spool jobs to a printer on a VMS machine using one of the above approaches? Do you know of a better approach to achieving a high level of connectivity? Any and all comments are appreciated. Please mail results to me, and I will summarize if interest warrants it. I prefer mail to the address shown below, although other addresses are acceptable. Thanks for any insight, Greg (Prefered e-mail address: simpsong%[email protected]) -- --- Gregory R. Simpson Prefered Internet: SIMPSONG%[email protected] or Alternate Internet: [email protected] UUCP: <BACKBONE>!cbosgd!ncoast!simpsong UUCP: {ames,mit-eddie,harvard,talcott}!necntc!ncoast!simpsong -----------[000219][next][prev][last][first]---------------------------------------------------- Date: 25 Aug 88 00:58:46 GMT From: [email protected] (Rex A. Buddenberg) To: comp.protocols.tcp-ip Subject: Friendliness vs performance For Dave Crocker. I would recast the question more in terms of capacity/throughput traded off against robustness/fault tolerance/survivability. Fair? Most users tend to underestimate the real fault tolerance needs. Once a network is put in place, it attracts applications like ants to a picnic. Before you can spell TCP/IP, the network has become so critical that it's failure becomes intolerable. I'm familiar with a few horror stories like one about a bank that lost its funds transfer net for several hours. The interest charges on the cash it had to borrow to keep afloat ranged into 8 figures. I have three very clear requirements where workstations and sensors on a LAN is clearly the best way to go. In all three cases, network loading is very modest -- one ridiculously so: in terms of dozens of bytes per day [!!]. But fault tolerance -- immunity against either damage or component failure -- is vital to all three. The curious technological development is that in the LAN world, this isn't a trade off. The only fault tolerant LAN architecture out there readily available is doubly linked rings. Discounting Proteon's proprietary products, this leaves FDDI -- somewhat higher performance than ether... Fault tolerance is a lot like paychecks -- most of us rather take them for granted. They come every couple weeks -- especially for us folks whose paychecks are provided by the taxpayers. And like LAN service -- expected to be there when we want to use it. Watch the fracas when your taken for granted paycheck or LAN fails. I'd suggest a caveat for a vendor: fault tolerance may not gain you lots of customers, but lack of it can lose a bunch. Rex Buddenberg -----------[000220][next][prev][last][first]---------------------------------------------------- Date: 25 Aug 88 10:39:00 PDT From: Dave Crocker <[email protected]> To: tcp-ip <[email protected]> Subject: Re: Friendliness vs. Performance It is quite heartening to have honest-to-goodness customers demanding robustness features. In a perhaps-overly-cautious attempt to avoid getting commercial in the discussion, I did not mention in my previous note that our VMS product was one of the -- maybe even THE -- first to be shipped to customers with Van & Co.'s congestion/slow-line features and the next releases of our Streams and DOS products will contain them. In other words, folks, please don't take my previous comments as suggesting that the robustness features should not be included. My concern was that the absolute assumption of its requirement be tempered somewhat by looking at actual customer requirements; in some percentage of cases, reasonable robustness and superb performance are more important than superb robustness and reasonable performance. Please note that standard implementations of TCP, using old-style congestion and retransmission algorithms, are significantly robust. In fact, we probably are missing the boat by using the term to refer to the recent improvements... The new capabilities do not alter data-loss with respect to the user. They alter packet-loss on the net, thereby reducing retransmission requirements. With or without the new features, users will get equivalent data transfer integrity at the receiving application. With the new code, however, successful COMPLETION of the transfer may be different. (I.e., if you get the bits, they will be correct.) In effect, I was going creating an artificial constraint, much like asking a person who they would save, if a parent and a spouse were drowning and they could save only one. On the other hand, there are limited development resources and prioritizing customer requirements is essential. Just because all you knowledgeable, demanding networkers have the priorities set one way -- which I agree with as someone who has suffered with Internet performance -- does not mean that it is correct for the masses. Long-term, it IS correct, since they will all be part of a global internet and will be subject to the phenomena that the new algorithms address. However, short-term, many of those networkers are isolated. Dave -----------[000221][next][prev][last][first]---------------------------------------------------- Date: 25 Aug 88 06:07:28 GMT From: [email protected] (Charles Hedrick) To: comp.protocols.tcp-ip Subject: Re: Does TCP/IP "comform" to ISO/OSI? Saying that something conforms to the OSI reference model is essentially meaningless, so yes, TCP/IP does conform. The reference model is the basic conceptual layering. You can use those layers to analyze just about any protocol suite. What you're thinking of is the ISO protocol suite. That's a specific set of protocols, and TCP/IP doesn't follow it. As far as I can tell, vendor statements that their (non-ISO) protocol follows the OSI reference model is almost entirely hype. At best it means that the design is close enough to ISO that eventual migration to the ISO protocols will be easier than with a protocol suite that is very different in philosophy. -----------[000222][next][prev][last][first]---------------------------------------------------- Date: Thu, 25 Aug 88 11:57:06 CDT From: Mike Rackley <RACKLEY%[email protected]> To: <[email protected]> Subject: named vs. bind SunOS4.0 documents the named daemon as providing internet domain name server capability. I have seen references on the net to porting bind to SunOS4.0 to provide the same capability. What are the differences in named and bind? Mike Rackley Mississippi State University -----------[000223][next][prev][last][first]---------------------------------------------------- Date: 25 Aug 1988 11:59-EDT From: [email protected] To: [email protected] Cc: [email protected], [email protected] Subject: Re: Interlan drops a byte? Steve, It looks like another instance of the "have to retransmit a FIN, so better subtract one from the sequence #" bug. Note that the response (maybe to pktnum 2483, but possibly to an earlier packet since the timestamps on 2483 and 2484 are identical) in pktnum 2484 was to ack 1d52f72. Thus the receiver has already received the data being retransmitted in pktnums 2485, 2487 and 2489. [Clearly useless retransmissions -- maybe (the timestamps are all very close) an instance of the "retransmit all unacked data on a retransmission timeout" algorithm, or (the timestamps are not exactly equal) a "retransmit on ack before updating/processing send-left & processing the retransmit queue" design deficiency]. It would have been nice if the trace began earlier, say on the first transmission of the packet containing sequence number 1d53100; was a FIN sent at the "same" time? [Note [fnord sends its fin, with seq # 108d4e02] you mean 108d4e01. Also, notice that in pktnum 2492, a FIN is being (re)transmitted at a different sequence number, 1d53102, than it was in pktnum 2489, 1d53101 = 1d52f71+190.] Charlie -----------[000224][next][prev][last][first]---------------------------------------------------- Date: 25 Aug 88 10:22:44 GMT From: [email protected] (Guus van der Wal) To: comp.protocols.tcp-ip Subject: KA9Q with MOCOM NI5010 This must have been asked many times before, but I began to use Ethernet only recently. I have a MICOM interlan NI5010 ethernet adapter in my IBM pc/at. I also have Phil Karn's KA9Q TCP-IP software. The KA9Q docs only talk about the 3COM 3C500 ethernet card. Is there anybody out ther who has (made) KA9Q working with MICOM ?? Thanks in advance Guus -- Guus van der Wal Computing Centre Technical University Delft USEnet: rcdswal@dutrun BITnet: rcdswal@hdetud1 -----------[000225][next][prev][last][first]---------------------------------------------------- Date: 25 Aug 88 12:51:00 GMT From: [email protected] To: comp.protocols.tcp-ip Subject: Re: BLAST? There is a product called BLAST (and BLAST II) sold by Communications Research Group (800-242-5278 or 504-923-0888). It is an asynchronous file transfer package akin to XMODEM and Kermit. Their literature claims it is far more robust ("error-free" read error correction) and higher performance than either of the above. It is full duplex and uses a sliding window protocol and one spot in their literature says it is X.25 and ISO compatible so maybe the sliding window stuff is borrowed from X.25. I don't think it has anything to do with TCP/IP at all although you could probably run it over a Telnet or Rlogin connection. Our company sells it on our Un*x boxes, I personally have never used it so cannot verify or deny its functionality or performance. Hope this helps. Monty. -----------[000226][next][prev][last][first]---------------------------------------------------- Date: Thu, 25 Aug 88 17:22:52 EDT From: Alex McKenzie <[email protected]> To: Ron Guilmette <[email protected]> Cc: [email protected] Subject: Re: Does TCP/IP "comform" to ISO/OSI? It is my personal understanding (as an active participant in some of the ISO groups) that the Reference Model was developed by ISO as a guide to how ISO should think about the functional decomposition of service/protocol standardization. This is something of concern to ISO internally; not something of external concern. Thus there is no Conformance Statement clause in the Reference Model standard, and (consequently) no objective way to evaluate the claim that something does or doesn't "conform to the reference model". Rather, the Reference Model was made an International Standard so the world outside ISO could see and understand (perhaps not agree with) the rules which were to govern the development of standards for particular services and protocols by ISO. Regards, Alex McKenzie -----------[000227][next][prev][last][first]---------------------------------------------------- Date: 25 Aug 88 15:59:00 GMT From: [email protected] To: comp.protocols.tcp-ip Subject: Re: Interlan drops a byte? Steve, It looks like another instance of the "have to retransmit a FIN, so better subtract one from the sequence #" bug. Note that the response (maybe to pktnum 2483, but possibly to an earlier packet since the timestamps on 2483 and 2484 are identical) in pktnum 2484 was to ack 1d52f72. Thus the receiver has already received the data being retransmitted in pktnums 2485, 2487 and 2489. [Clearly useless retransmissions -- maybe (the timestamps are all very close) an instance of the "retransmit all unacked data on a retransmission timeout" algorithm, or (the timestamps are not exactly equal) a "retransmit on ack before updating/processing send-left & processing the retransmit queue" design deficiency]. It would have been nice if the trace began earlier, say on the first transmission of the packet containing sequence number 1d53100; was a FIN sent at the "same" time? [Note [fnord sends its fin, with seq # 108d4e02] you mean 108d4e01. Also, notice that in pktnum 2492, a FIN is being (re)transmitted at a different sequence number, 1d53102, than it was in pktnum 2489, 1d53101 = 1d52f71+190.] Charlie -----------[000228][next][prev][last][first]---------------------------------------------------- Date: 25 Aug 88 16:10:01 GMT From: [email protected] (Jeremy G Harris) To: comp.protocols.tcp-ip Subject: Call queueing The BSD listen(2) syscall (on a socket) provides for the specification of a queue of pending connection requests. So does the TLI T_LISTEN function. What are the pros and cons of this functionality? Is it merely a matter of the cost of copying a protocol control block versus the cost of opening and initialising one? Or is there also a functional benefit? Jeremy. -- Jeremy Harris [email protected] -----------[000229][next][prev][last][first]---------------------------------------------------- Date: 25 Aug 88 20:17:00 EDT From: <[email protected]> To: "dcrocker" <[email protected]> Cc: <[email protected]> Subject: Friendliness vs. Performance: Performance can provide two WINS I do not mean to diminish the importance of the Friendliness aspects of Van's work. Indeed, I am a user of WIN/TCP 3.2 and thus enjoy the benefits. Van's header-prediction / code-streamlining work can however provide two improvements for the user. First, given the proper underlying network(s), the user can see improvements in transfer speed. More importantly, regardless of the underlying network(s), the user will enjoy a REDUCTION in the amount of CPU utilization. Thus, Van's work could be thought of as efficiency improvements. Everyone wants faster computers; Van has done something to help. Van Jacobson for President! Cheers, Bob Enger -----------[000230][next][prev][last][first]---------------------------------------------------- Date: 25 Aug 88 16:46:41 GMT From: [email protected] (John Sambrook) To: comp.protocols.tcp-ip Subject: Hanging FTP sessions I've run into a problem with ftp(1) and would appreciate some advice. I would like to move some files via anonymous FTP from one system to another. The systems in questions are Data General MV/10000 systems running DG/UX 3.11 and DG/UX TCP/IP 2.02. I am, of course, able to login to the remote system as user "anonymous", password "guest". If I then do an "ls" command I get a listing of the three directories (bin, etc, pub) in ~ftp, as I expect. So far, nothing unusual. Now, if I try to get a long list, with "ls -l", the connection seems to hang. Believe me, I have waited for periods of thirty minutes but have never gotten past this hang condition. I have the same problem if I try to copy the files I want from ~ftp/pub. The connection is established as expected, with the "PORT" and "Opening data connection" messages printed on our end, but no data ever flows. I have hash mark printing on. I have tried several different systems locally (including VMS, AOS/VS, 4.3BSD) to fetch the files but I still have the hang condition. I don't know if it is related, but when I do "stat" on our local ftp(1) system it prints the page size of both "ftp-user" and "ftp-daemon" as 2048 bytes. Is it possible that this is too long and that some type of fragmentation is occuring? Sorry I can't be more concrete; I don't have a lot of experience debugging TCP/IP problems, and even fewer tools for doing so. Please feel free to send mail; I'll post a summary of responses. If you would rather post a response that's fine too, though I doubt many other people have this problem. Thank you very much, John Sambrook Internet: [email protected] University of Washington RC-05 UUCP: uw-nsr!john Seattle, Washington 98195 Dial: (206) 548-4386 -- John Sambrook Internet: [email protected] University of Washington RC-05 UUCP: uw-nsr!john Seattle, Washington 98195 Dial: (206) 548-4386 -----------[000231][next][prev][last][first]---------------------------------------------------- Date: 25 Aug 88 16:57:06 GMT From: [email protected] (Mike Rackley) To: comp.protocols.tcp-ip Subject: named vs. bind SunOS4.0 documents the named daemon as providing internet domain name server capability. I have seen references on the net to porting bind to SunOS4.0 to provide the same capability. What are the differences in named and bind? Mike Rackley Mississippi State University -----------[000232][next][prev][last][first]---------------------------------------------------- Date: 25 Aug 88 17:14:17 GMT From: [email protected] (James Van Bokkelen) To: comp.protocols.tcp-ip Subject: 4.3 networking bugs The "FIN bit with incorrect sequence number" problem appeared in some early 4.3 tapes. There is a fix for it, which I think has been circulated on comp.bugs.4bsd, and may be available for FTP from ucbarpa. If not, I have a copy (pub/fin_bug.43) on vax.ftp.com. If you don't have source, bitch at your vendor (the fix first circulated last summer). Depending on the vintage of your 4.3, there are a number of other bugs which appear in TCP output, or cause network-related crashes. I know of 9 of these, there may be more. There is another bug, which I just saw: The Van Jacobsen 4.3 code which was made public domain a few months ago sends ICMP Source Quench messages with random values in the "code" field. I asked a friend with source, and he says that the field is not initialized (it should always be 0). James VanBokkelen FTP Software Inc. -----------[000233][next][prev][last][first]---------------------------------------------------- Date: 25 Aug 88 17:39:00 GMT From: [email protected] (Dave Crocker) To: comp.protocols.tcp-ip Subject: Re: Friendliness vs. Performance It is quite heartening to have honest-to-goodness customers demanding robustness features. In a perhaps-overly-cautious attempt to avoid getting commercial in the discussion, I did not mention in my previous note that our VMS product was one of the -- maybe even THE -- first to be shipped to customers with Van & Co.'s congestion/slow-line features and the next releases of our Streams and DOS products will contain them. In other words, folks, please don't take my previous comments as suggesting that the robustness features should not be included. My concern was that the absolute assumption of its requirement be tempered somewhat by looking at actual customer requirements; in some percentage of cases, reasonable robustness and superb performance are more important than superb robustness and reasonable performance. Please note that standard implementations of TCP, using old-style congestion and retransmission algorithms, are significantly robust. In fact, we probably are missing the boat by using the term to refer to the recent improvements... The new capabilities do not alter data-loss with respect to the user. They alter packet-loss on the net, thereby reducing retransmission requirements. With or without the new features, users will get equivalent data transfer integrity at the receiving application. With the new code, however, successful COMPLETION of the transfer may be different. (I.e., if you get the bits, they will be correct.) In effect, I was going creating an artificial constraint, much like asking a person who they would save, if a parent and a spouse were drowning and they could save only one. On the other hand, there are limited development resources and prioritizing customer requirements is essential. Just because all you knowledgeable, demanding networkers have the priorities set one way -- which I agree with as someone who has suffered with Internet performance -- does not mean that it is correct for the masses. Long-term, it IS correct, since they will all be part of a global internet and will be subject to the phenomena that the new algorithms address. However, short-term, many of those networkers are isolated. Dave -----------[000234][next][prev][last][first]---------------------------------------------------- Date: 25 Aug 88 17:49:28 GMT From: [email protected] (Edward Wilkinson) To: comp.bugs.4bsd,comp.unix.wizards,comp.protocols.tcp-ip Subject: Re: Interlan drops a byte? -- NOW: ethernet sniffer tools In article <[email protected]> [email protected] (Dennis.Bednar) writes: )In article <[email protected]>, [email protected] (Fletcher Mattox) writes: )) )) If you look at a packet on the wire, say, with etherfind or tcpdump, )) ... ) )Say, these "ethernet sniffer" tools sound like very useful tools. )Do these tools run on the UNIX machine, or on a PC? Is source )available? Tell me more about them. Thanks. Same here, please! These sound very useful, especially for those debugging ethernet programs. Post the info as it would probably be of use to many. Thanks in advance, Ed -- Ed Wilkinson @ Computer Centre, Massey University, Palmerston North, NZ uucp: {uunet,watmath!cantuar}!vuwcomp!csvaxa!edward DTE: 530163000005 Janet/Greybook: [email protected] Phone: +64 63 69099 x8587 CSnet/ACSnet/Internet: [email protected] New Zealand = GMT+12 -----------[000235][next][prev][last][first]---------------------------------------------------- Date: 25 Aug 88 18:46:15 GMT From: [email protected] (Ken Koster N7IPB) To: comp.sys.ibm.pc,comp.protocols.tcp-ip,comp.protocols.tcp-ip.ibmpc Subject: Networking PC's with VMS , UNIX and Mac's running TOPS Sundstrand is in the process of choosing a network package that is capable of handling our diverse collection of systems. We currently have a large number of MSDOS pc's (AT,XT,PS-2's,etc.) and 1 AT running uPort UNIX (My machine) that are not networked. We also have a number of VAX running VMS that are networked with DECNET and 30-40 MAC's that are networked with TOPS. I have been asked to submit a list outlining the networking requirements for the engineering department. I would appreciate comments from anyone who has experience either setting up or using various products in this kind of environment. All comments and suggestions would be greatly appreciated. PLEASE - PLEASE - Email direct to me I WILL summerize for the net. Thanks in advance.-- Ken Koster Work: uport SYSV uunet!pilchuck!algedi!kenk A lone Unix-pc Home: Amiga uunet!pilchuck!algedi!kkamie!kenk in the MSDOS swamp Packet Radio: N7IPB@KE7OM -----------[000236][next][prev][last][first]---------------------------------------------------- Date: 25 Aug 88 21:22:52 GMT From: [email protected] (Alex McKenzie) To: comp.protocols.tcp-ip Subject: Re: Does TCP/IP "comform" to ISO/OSI? It is my personal understanding (as an active participant in some of the ISO groups) that the Reference Model was developed by ISO as a guide to how ISO should think about the functional decomposition of service/protocol standardization. This is something of concern to ISO internally; not something of external concern. Thus there is no Conformance Statement clause in the Reference Model standard, and (consequently) no objective way to evaluate the claim that something does or doesn't "conform to the reference model". Rather, the Reference Model was made an International Standard so the world outside ISO could see and understand (perhaps not agree with) the rules which were to govern the development of standards for particular services and protocols by ISO. Regards, Alex McKenzie -----------[000237][next][prev][last][first]---------------------------------------------------- Date: 25 Aug 88 22:25:46 GMT From: [email protected] (Dan Lynch) To: comp.protocols.tcp-ip Subject: Re: Does TCP/IP "comform" to ISO/OSI? Ron, The OSI model is intended to be a reference model for discussing and describing computer to computer communications. It is an idealization of how that communications should take place. It was developed in the late 70's. It has a sevenlayer description that rather clearly describers what should happen on each computer and with their communications devices. TCP/IP when looked at from that model perspective has 4 or 5 layers distinctly differentiated. (Of ocurse, TCP/IP does all of the work, it just does it with a different number of layers -- if you like cake, who cares if it is 5 or 7 layers?) But, TCP/IP does not interoperate with the ISO implementations of OSI. Saying that would be very "confusing". I have seen IBM and DEC and Apple documents that all compare their proprietary protocols to the OSI model They all essentially say they conform to the OSI model. They do, as does TCP/IP. It just does not mean much. What matters is "can the two computers send meaningful traffic back and forth?" Dan ------- -----------[000238][next][prev][last][first]---------------------------------------------------- Date: 25 Aug 88 22:39:11 GMT From: cpw%[email protected] (C. Philip Wood) To: comp.protocols.tcp-ip Subject: Re: Does TCP/IP "comform" to ISO/OSI? The question is: Does OSI conform to ARM? The answer is: No. Phil Wood, [email protected] -----------[000239][next][prev][last][first]---------------------------------------------------- Date: 26 Aug 88 00:17:00 GMT From: [email protected] To: comp.protocols.tcp-ip Subject: Friendliness vs. Performance: Performance can provide two WINS I do not mean to diminish the importance of the Friendliness aspects of Van's work. Indeed, I am a user of WIN/TCP 3.2 and thus enjoy the benefits. Van's header-prediction / code-streamlining work can however provide two improvements for the user. First, given the proper underlying network(s), the user can see improvements in transfer speed. More importantly, regardless of the underlying network(s), the user will enjoy a REDUCTION in the amount of CPU utilization. Thus, Van's work could be thought of as efficiency improvements. Everyone wants faster computers; Van has done something to help. Van Jacobson for President! Cheers, Bob Enger -----------[000240][next][prev][last][first]---------------------------------------------------- Date: 26 Aug 88 00:49:52 GMT From: [email protected] (Charles Hedrick) To: comp.protocols.tcp-ip Subject: Re: Friendliness vs. Performance It's hard to make guesses as to what will sell. But aside from occasional tests in the PC-compatible area, there isn't a lot of benchmarking hysteria in the TCP/IP world. So I'd think vendors would not be under the sort of pressure to get performance at all costs that they are in some other markets. From the point of view of a manager I can tell you that I get lots of calls about inability to get mail through to distant sites, and broken telnet connections. By and large our users do not carefully time their FTP's and call me when their throughput is only 100 kbits/sec. I have conducted various reviews of Internet performance at the IETF meetings, where we asked an assemblage of network managers what problems they were seeing. Again, it's clear that everytime somebody gets a "connection broken" message, their network manager gets an irate call, but I don't see signs of irate users demanding 20% more speed. (Gross slowdowns are another thing, of course.) So if there were really a speed/robustness tradeoff, I'd strongly recommend that vendors favor robustness. But I'm not even convinced that there is. The only case I know of where using Van's recommendations would slow you down is where by not using them you manage to get more than your fair share of a gateway. It's clear that this isn't a stable situation: only one person can do this at a time, and you can't guarantee that he will be able to do it consistently. Furthermore, you're going to start seeing gateways that defend themselves against this sort of thing. This is not just a concern of us wierdos on the Internet either. There are lots of big corporate networks being built, and they typically have lots of serial lines carefully spec'ed to have no more bandwidth than necessary. -----------[000241][next][prev][last][first]---------------------------------------------------- Date: Fri, 26 Aug 88 09:37:06 PDT From: [email protected] To: [email protected] Cc: [email protected] Subject: RUNNING FTP IN BATCH MODE See RFC-1068. --jon. -----------[000242][next][prev][last][first]---------------------------------------------------- Date: Fri, 26 Aug 88 07:03:22 edt From: [email protected] To: [email protected], [email protected] Subject: Re: RUNNING FTP IN BATCH MODE FTP SW has a script facility for their FTP that will allow you to automate login/send/receives. They also have drivers of the excelan card. Now the only question is, did I beat JVB to the punch. :-) Stephen Northcutt ([email protected]) My only relationship with FTP SW is as a user of their products! -----------[000243][next][prev][last][first]---------------------------------------------------- Date: Fri, 26 Aug 88 18:39:29 -0700 From: Keith McCloghrie <[email protected]> To: [email protected] Cc: [email protected] Subject: Re: SGMP There is some question about how long SGMP will be around. It is being replaced by SNMP, the specification for which has just been published as RFC 1067. Yesterday's official annoucement (from Jon Postel/Joyce Reynolds) stated : "This memo specifies a draft standard for the Internet community. TCP/IP implementations in the Internet which are network manageable are expected to adopt and implement this specification." The concept of a "draft" standard is new to the Internet community, but the latter sentence leaves no room for doubt about what conformant TCP/IP vendors must do. Note that whereas SGMP (as its name implies) was aimed at managing IP gateways, SNMP uses the set of variables (called the MIB - the Management Information Base) specified by RFC-1065/1066. This set not only includes just about all the gateway-specific and common variables of SGMP, but also adds an initial set of host-specific variables (e.g. TCP and UDP objects). As a result, many more vendors are already implementing SNMP for gateways and for hosts, than ever implemented SGMP. Keith. -----------[000244][next][prev][last][first]---------------------------------------------------- Date: 26 Aug 88 11:03:22 GMT From: [email protected] To: comp.protocols.tcp-ip Subject: Re: RUNNING FTP IN BATCH MODE FTP SW has a script facility for their FTP that will allow you to automate login/send/receives. They also have drivers of the excelan card. Now the only question is, did I beat JVB to the punch. :-) Stephen Northcutt ([email protected]) My only relationship with FTP SW is as a user of their products! -----------[000245][next][prev][last][first]---------------------------------------------------- Date: 26 Aug 88 13:13:23 GMT From: [email protected] (Merton Campbell Crockett) To: comp.protocols.tcp-ip Subject: Re: Does TCP/IP "comform" to ISO/OSI? Dan: You were absolutely right when you stated, "...TCP/IP does not interoperate with the ISO implementations of OSI. Saying that would be very "confusing"." It is confusing! What *is* an ISO implementation of OSI. OSI is merely a architectural reference model. It is not a protocol nor is it a protocol suite. I have written networking software ten (10) years ago that is con- formant to the OSI model. I doubt that you can find any software suite that allows two (2) or more computer systems to exchange information that is not conformant to the OSI model. The model is a formalized statement of the logical process to establish a communication link and exchange information. Now if you had said that IP/TCP is not interoperable with the ISO IP/T4 protocols or the Internet protocol suite is not interoperable with the DECNet protocol suite. That would be less "confusing". Merton -----------[000246][next][prev][last][first]---------------------------------------------------- Date: 26 Aug 88 14:00:31 GMT From: [email protected] To: comp.protocols.tcp-ip Subject: Re: 4.3 networking bugs The unitialized code field for ICMP source quench goes back to the original 4.3, Van's code just inherited it. -----------[000247][next][prev][last][first]---------------------------------------------------- Date: 26 Aug 88 14:32:58 GMT From: [email protected] (Nancy Connor) To: comp.dcom.lans,comp.protocols.tcp-ip Subject: Re: RUNNING FTP IN BATCH MODE You can execute FTP commands from a batch file on some systems. I don't know if Excelan's version of TCP/IP on the PC does this, but some do. In particular, FTP Software's PC/TCP product does this via "take files". Our FTP client will allow you to specify your login name, password and the name of a file on the command line and will then execute commands from the batch file you've specified. If you want more information on PC/TCP, send me mail, but I can't help with Excelan's product. -Nancy Connor FTP Software ...!harvard!ftp!nancy [email protected] -----------[000248][next][prev][last][first]---------------------------------------------------- Date: 26 Aug 88 17:11:52 GMT From: [email protected] (Karl Auerbach) To: comp.protocols.tcp-ip Subject: Re: SGMP My company, Epilogue Technology, is developing a set of tools for SNMP (the sucessor to SGMP). These include a complete SNMP agent which is both highly portable and small. The same tools could support an SNMP management station. Target date for completion is September 15. These tools have been updated to conform to RFC1065/1066/1067. For further information, please contact Epilogue Technology at 415/594-1141. --karl-- -----------[000249][next][prev][last][first]---------------------------------------------------- Date: 26 Aug 88 18:01:27 GMT From: [email protected] (Gurudatta Parulkar) To: comp.protocols.tcp-ip Subject: References Dear Sir/Madam: I am looking for discussions/references that happened approximately 1 - 3 years ago that debated the pros and cons of using a fixed Vs variable packet length in high speed packet switches. In particular I am interested in their effect on switch to switch synchronization and also the implications on queue/buffer sizes. References or text including those debates would be greatly appreciated. Neil Barrett Washington University in Saint Louis Computer and Communication Research Center St. Louis, Mo 63130 Net Address: [email protected] neil%[email protected] neil%[email protected] -----------[000250][next][prev][last][first]---------------------------------------------------- Date: 26 Aug 88 18:24:48 GMT From: [email protected] (Andy Liwen) To: comp.protocols.tcp-ip Subject: TCP/IP for big, big Blue We are looking for _high speed_ connections to an IBM, big iron, type main frame, via TCP/IP / EtherNet, from a SUN or like processor. The data we need to transfer must move faster than the 56Kb rate available to the majority of "line" type connections we have found. Either vanilla ethernet or token-ring seem to be the fastest connections viable for the big blue beast. What we are seeking help on is software TCP/IP access from the big blue iron and hardware alternatives. We have only confirmed IBM (gag) token ring availability on the blue end. We would like to consider ethernet alternatives for blue also. If any one has leads, connections, or products in this area, e-mail replys would really be appreciated. //Andy Liwen ______________________________________________________________________________ uucp : ..uunet!ocsmd!andy bitnet : andy%[email protected] snail : Online Computer Systems internet : [email protected] 20251 Century Blvd. -----------[000251][next][prev][last][first]---------------------------------------------------- Date: 26 Aug 88 20:06:49 GMT From: [email protected] (Michael Padlipsky) To: comp.protocols.tcp-ip Subject: Re: Does TCP/IP "comform" to ISO/OSI? If there were a Supreme Court of Science (and if it hadn't been packed), I'd be delighted to accept a case which held that the protocol sub-suite consisting of TCP-or-UDP-over-IP is a more appropriate realization of stated "OSI" "Reference Model" principles than is the protocol sub-suite consisting of X.25-and-X.75, on a contingency fee basis. However, since as Charles Hedrick rightly observes, "TCP/IP" isn't in the set of International Standards Organization-sanctioned protocols, and since "conform to OSI" really ought to connote "interoperate with other protocols/ protocol interpeters in the ISO-sanctioned set", if there were a Supreme Court of Semantics, I daresay I'd only be willing to attempt to defend your XYZ Corp.'s blurb on a win-lose-or-draw flat fee basis-- and that a large enough one to be able to retire comfortably on. (And if I won, I'd be sure that that court was packed.) Or, if legal metaphors are not to your taste, a fair way of answering your question is, "Not in any practical sense, even though a sufficiently subtle protocol theologian could probably have a lot of fun with it." cheers, map P.S. In case the reference to the "ARM" in Phil Wood's message was not familiar, it stands for the ARPANET Reference Model, which preexists the ISO/OSI RM in fact, though not on paper (i.e., the ARM didn't get written up [or down] until some years after it had been "invented" ... and used). ------- -----------[000252][next][prev][last][first]---------------------------------------------------- Date: 26 Aug 88 20:07:34 GMT From: [email protected] (Markku Savela) To: comp.protocols.tcp-ip Subject: CMU TCP/IP and APOLLO ACCESS package Apollo have a package (ACCESS?), which makes the files on the VMS visible on the Apollo work station (kind of NFS). I guess there is no hope of getting it work under CMU TCP/IP? (Officially it seems to function only with Wollongong and Excelan TCP/IP packages on the VMS). I was brave enough to try starting ACCESS on VAX/VMS running CMU TCP/IP and was revarded by a nice "FATAL BUG CHECK ..." :-) Never expected it to work, but some people win in lotteries, too... -- Markku Savela, [email protected] -----------[000253][next][prev][last][first]---------------------------------------------------- Date: 26 Aug 88 20:27:00 GMT From: [email protected] (Markku Savela) To: comp.protocols.tcp-ip Subject: CMU TCP/IP problem? This question would belong to some CMU TCP/IP mailing list, but I cannot subscribe (I have to pay for received private mail). We have a CMU TCP/IP version 6.2 on VMS (micro VAX). There seems to be something wrong in closing FTP file transfer connections. They seem seem hang around in some WAIT-state for several seconds after the transfer is completed. This causes problems with MSEND/MPUT -commands, if there are several short files. IP ACP runs out of connections after 20 or 30 files... Perhaps I should order the next version 6.3? Or is this a serious case of RTFM?. Being no wizard on TCP/IP, I installed the package almost with all defaults... Another minor inconvenience is, that it looks like I couldn't FTP files from VMS, unless user has directly access rights to the files. If access rights are given through ACL's, CMU TCP/IP does not seem to notice and refuses the transfer (specifically: user has been granted an "access identifier" and files have a specific ACL entry for this identifier giving access to the owners). Another case of RTFM? :-) --- Markku Savela, [email protected] -----------[000254][next][prev][last][first]---------------------------------------------------- Date: 26 Aug 88 21:32:34 GMT From: [email protected] (Dan Lynch) To: comp.protocols.tcp-ip Subject: Re: Test suite for IP based systems Bill, I know of no such wonderful regression test suite. DCA has developed (via a contractor) a whole set of tests for TCP/IP and the three applications that does what you want, but it requires putting a lot of probe points in the tested system. The software is available from NBS now. Dan ------- -----------[000255][next][prev][last][first]---------------------------------------------------- Date: 27 Aug 88 01:39:29 GMT From: [email protected] (Keith McCloghrie) To: comp.protocols.tcp-ip Subject: Re: SGMP There is some question about how long SGMP will be around. It is being replaced by SNMP, the specification for which has just been published as RFC 1067. Yesterday's official annoucement (from Jon Postel/Joyce Reynolds) stated : "This memo specifies a draft standard for the Internet community. TCP/IP implementations in the Internet which are network manageable are expected to adopt and implement this specification." The concept of a "draft" standard is new to the Internet community, but the latter sentence leaves no room for doubt about what conformant TCP/IP vendors must do. Note that whereas SGMP (as its name implies) was aimed at managing IP gateways, SNMP uses the set of variables (called the MIB - the Management Information Base) specified by RFC-1065/1066. This set not only includes just about all the gateway-specific and common variables of SGMP, but also adds an initial set of host-specific variables (e.g. TCP and UDP objects). As a result, many more vendors are already implementing SNMP for gateways and for hosts, than ever implemented SGMP. Keith. -----------[000256][next][prev][last][first]---------------------------------------------------- Date: Sat, 27 Aug 88 19:35:37 -0400 From: Mike Brescia <[email protected]> To: Martin Holland <[email protected]> Cc: [email protected] Subject: Re: Multiple TCP/IP servers on one Host. How can I add a second server without giving it a different name and internet number so the user will not have to try each server in turn to find a vacant port? I could imagine designing a solution based on the fact that the MICOMs are connected on an ethernet, and they could cooperate, using the same IP address (and, by the way, the same ethernet address, preferably a 'multicast' one). Address recognition in a particular one of the boxes would have to include the IP protocol (TCP), and the TCP port (corresponding to the terminal port.) I know of no such design being implemented, nor how you would invent one that would work on a non-promiscuous net. Perhaps you can trade your box in for one with more ports. Good hunting, Mike -----------[000257][next][prev][last][first]---------------------------------------------------- Date: 27 Aug 88 16:42:06 GMT From: [email protected] (John L Grzesiak) To: [email protected] Subject: Net Help Hello: I have an implementation I'd like to try and have little idea about how to go about it. I have a few UNIX boxes , two of which are CADMUS 9000's . I have Network cards and drivers for these systems. The cards I have are: 3com ethernet and Excelan EXOS 203 (a pair of each). What I'd like to know is: A) Which of these is a better install? (Ease of install , reliable , versatile ,etc) B) Can these cards be cheated and how? ( Can they be used point to point without tranceivers because all I need from them is remote disk mount capability) C) If these cards can't be cheated , where can I get thin ethernet tranceivers and equipment for these? Any help is appreciated - Thank you in advance..... John Grzesiak Omega Dynamics 47 Spring Street Wallingford Ct 06492. (203) 284-8530 voice (203) 289-9300 work (9-5 Eastern) (203) 284-3776 guest:guest (computer) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -----------[000258][next][prev][last][first]---------------------------------------------------- Date: 27 Aug 88 21:55:22 GMT From: [email protected] (Charles Hedrick) To: comp.protocols.tcp-ip Subject: Re: named vs. bind Named and bind are sort of the same thing. Named is the name of the name daemon program. Bind seems to be the name of the package as a whole, which includes named and the resolver. However people sometimes say they are bringing up bind when they mean named and visa versa. Sun includes bind as part of 4.0. However there are reasons why somebody might want to start with the current Berkeley source and reinstall it: - they might want the very latest version of named - they might want to build the resolver into libc Let me explain. In case you're not familiar with the terms: the name daemon is a program that keeps a database of all hosts known to your machine. When other programs want to look up a name, they send a message to your name daemon. If it doesn't already know, the name daemon asks other servers around the net, and eventually comes up with an answer, which it sends back to your program. The reason for sending all requests through a single name daemon rather than having each program talk to the network for itself is that this allows the name daemon to build up a cache of known names, so that it normally doesn't have to go out to the network. Individual application programs typically don't last very long, so any cache they built up wouldn't do much good. You need not run the name daemon on each machine. You can put it just on a few servers and point the other systems to them. The resolver is simply a set of subroutines used to send questions to the name daemon, and get back the responses. The most commonly used subroutine is a replacement for gethostbyname. It looks to the caller like the gethostbyname supplied by Sun, but instead of looking things up in the host table or YP, it asks the name daemon. Now, for why somebody might want to port bind to Sun 4.0. Sun supplies named (possibly called in.named). It's slightly out of date, though there's an update package you can get from Sun with the newest one. Sun also supplies the resolver routines in a library libresolv.a. However that only helps you if you have source, since you have to load your programs with -lresolv. Sun's version of telnet, ftp, etc., is not loaded with the resolver, so they will not talk to named. Their idea is that programs should use YP, and YP should talk to named if the name isn't in the YP database. Unfortunately, the interface from YP to named doesn't work. There's an update package you can get from Sun to fix that. However even if it worked, some of us don't like having to go through two different daemons to look up names. Also, the Berkeley resolver lets users define their own abbreviations for host names, and if you put the requests through YP, that mechanism doesn't work. So some of us want to rebuild the sharable library, /usr/lib/libc.so.1.x, so that it has the resolver instead of the YP-based gethostbyname and gethostbyaddr. Because of the way sharable libraries work, this will instantly fix telnet, ftp, etc. If you don't do much Arpanet traffic, it's probably good enough to get the bind update package from Sun, which has the newest named and the fixed version of ypserv that knows how to talk to named. However if you do a lot of network traffic, you'll want to talk to your Sun representative and ask them to create a version of libc with the resolver in it. -----------[000259][next][prev][last][first]---------------------------------------------------- Date: 27 Aug 88 22:32:15 GMT From: [email protected] (Fletcher Mattox) To: comp.bugs.4bsd,comp.unix.wizards,comp.protocols.tcp-ip Subject: Re: Interlan drops a byte? In article <[email protected]> [email protected] (Pierre LAFORGUE) writes: >In article <[email protected]> [email protected] (Fletcher Mattox) writes: >>Has anybody else seen a 4.3BSD VAX with an Interlan Ethernet interface >>drop a byte of data? Well, that's what we're seeing. >>For example, if you >> % rsh remotehost cat 183_byte_file >>and the remotehost is a 4.3/Interlan host, the rsh will fail. > >Your report is not very accurate; Well, no. The report is quite accurate. Maybe it's not as complete as it could have been, though. :-) card: Interlan BD-N11010, rev C, assy rev A, S.N A-103. transceiver: Interlan NA1010 driver: @(#)if_de.c 7.1 (Berkeley) 6/5/86 It does appear that nobody else has seen this, so I'm still a little puzzled. Someone did mention that Interlan shipped some bad cards about five years ago which had a similar problem. Our card is at least that old. Anyway, I've quite worrying about it and just replaced it with a DEUNA, since we have plenty of those. Thanks to all who responded. Fletcher -----------[000260][next][prev][last][first]---------------------------------------------------- Date: 27 Aug 88 23:35:37 GMT From: [email protected] (Mike Brescia) To: comp.protocols.tcp-ip Subject: Re: Multiple TCP/IP servers on one Host. How can I add a second server without giving it a different name and internet number so the user will not have to try each server in turn to find a vacant port? I could imagine designing a solution based on the fact that the MICOMs are connected on an ethernet, and they could cooperate, using the same IP address (and, by the way, the same ethernet address, preferably a 'multicast' one). Address recognition in a particular one of the boxes would have to include the IP protocol (TCP), and the TCP port (corresponding to the terminal port.) I know of no such design being implemented, nor how you would invent one that would work on a non-promiscuous net. Perhaps you can trade your box in for one with more ports. Good hunting, Mike -----------[000261][next][prev][last][first]---------------------------------------------------- Date: 28 Aug 88 03:45:59 GMT From: [email protected] (John Romkey) To: comp.protocols.tcp-ip Subject: Re: Call queueing [email protected] asked about why listen(2) allows a queue of pending connection requests. Under the BSD networking model, when you want to listen() for a connection, you first get a socket and then listen() on it. When a connection is opened, you do an accept() (which gets you a new socket) to actually get ahold of the connection. A server which wants to be able to handle more than one connection at a time normally fork()s, and the child process does the actual work while the parent goes back to listen()ing. If you don't allow a queue of pending requests, then from the time when the listen() completes to the time when the server issues a new listen(), there is no one listening. Any incoming requests will then get a reset. The window of time is probably pretty small, on the order of milliseconds, but you want it to be 0. So you need listen() to be able to handle more than one incoming request. And you have to tell listen() how many to handle so that the kernel can allocate appropriate resources. - john romkey -----------[000262][next][prev][last][first]---------------------------------------------------- Date: 28 Aug 88 03:48:54 GMT From: aglew%[email protected] (Andy-Krazy-Glew) To: comp.protocols.tcp-ip Subject: SGMP ..> Software for SGMP monitoring My wife wrote some stuff to collect statistics from SGMP gateways working for the University of Illinois' CSO. I'm forwarding your note to her, and you can send her email at [email protected]. Andy "Krazy" Glew. Gould CSD-Urbana. 1101 E. University, Urbana, IL 61801 [email protected] - preferred, if you have nameserver [email protected] - if you don't [email protected] - if you use DoD hosttable aglew%[email protected] - domains are supposed to make things easier? My opinions are my own, and are not the opinions of my employer, or any other organisation. I indicate my company only so that the reader may account for any possible bias I may have towards our products. -----------[000263][next][prev][last][first]---------------------------------------------------- Date: 28 Aug 88 03:50:38 GMT From: [email protected] (Casey Leedom) To: comp.bugs.4bsd,comp.unix.wizards,comp.protocols.tcp-ip Subject: Re: Interlan drops a byte? In article <[email protected]> [email protected] (Fletcher Mattox) writes: > card: Interlan BD-N11010, rev C, assy rev A, S.N A-103. > transceiver: Interlan NA1010 > driver: @(#)if_de.c 7.1 (Berkeley) 6/5/86 Well, I think you're going to have an enormous amount of difficulty trying to use if_de.c with your Interlan. Why don't you try if_il.c? And as someone mentioned earlier, you should grab the latest copy of that driver since there were some significant bugs in the copy distributed with 4.3BSD. Casey -----------[000264][next][prev][last][first]---------------------------------------------------- Date: 28 Aug 88 06:48:11 GMT From: [email protected] (Sung Kwon Chung) To: comp.dcom.lans,comp.protocols.tcp-ip Subject: Re: RUNNING FTP IN BATCH MODE Here are two quick solutions to do batch-mode ftp. They are written in shell script, that means they are of no use for some of you who don't have the shell, sorry. The first one (ftp1.sh) is for simple ftp'ing. It works fine for small number of files. The limit depends on the command buffer size of mget' and some other factors unknow to me :-) Is is used like, % ftp1.sh host pub a b c d e f g to get file a, b, ..., g on host:pub. The second one (doftp) is a bit more complicated, but versatile (and extensible if you want). doftp uses other two shell scripts (ftp.sh and waitfor). It requires a file which contains the names of the files to be ftp'ed. Each line in the file contains one file name. If files.list' contains wanted file names on host:pub, % doftp host pub files.list will transfer all of them (of course, if everything goes right). I used it to bring over 70 odd (irregularly selected) files from an archive site. To use them, extract the scripts to their names and do "chmod +x" them. Please see the notes at the end of this message before trying them. ========================= ftp1.sh ========================= #!/bin/sh # # simple ftp # Usage: ftp1.sh host direcrory file1 file2 file3 ..... # host=1; directory=2; shift; shift; ftp -n -i host << ___EOF___ user anonymous guest cd directory mget * bye ___EOF___ exit ? ------------------------------------------------------------ The following three files are for the doftp'. ========================= doftp ========================= #!/bin/sh # Usage: doftp host directory namelistfile # needs ftp.sh and waitfor # Set up the pipes and temp files, and invoke ftp and its command feeder # ftp-out$$ : conversation during the job, feed-back to ftp.sh
# ftp-log$$: just for logging the commands # [email protected], 8/22/88 if test "#" != "3" then echo "doftp host directory namelistfile" 1>&2 exit 1 fi oldmask=umask # umask 077 # if we need to make the conversation unreadable cat >ftp-out$$ </dev/null
cat >ftp-log$$</dev/null umask oldmask ( ftp.sh 2 3 <ftp-out$$) |
tee ftp-log$$| ( ftp -v -n 1 >ftp-out$$ 2>&1 )
------------------------------------------------------------
========================= ftp.sh =========================
#!/bin/sh
# ftp.sh: ftp command feeder
#
# Uage: (sleep 1; ftp.sh dir namelistfile <ftp-out) |
# (ftp -v -n host-name >ftp-out)
# See doftp' and waitfor'
# [email protected], 8/22/88
if test "$#" != "2" then echo " Uage: (sleep 1; ftp.sh dir namelistfile <ftp-out) | (ftp -v -n host-name >ftp-out)" 1>&2 exit 2 fi echo "user anonymous guest" # login result=waitfor "230" # okay? if test "$result" = "ERROR"
then exit 1
fi
echo "cd $1" result=waitfor "250" # 250 CWD successful if test "$result" = "ERROR"
then exit 1
fi
# other FTP commands here, if needed
for f in cat $2 # main loop do destName=$f # file name change may be used here. a:b.c --> a-b.c
if test ! -f $destName # get it, only when it is not there then echo "get$f $destName" result=waitfor "226" # 226 Transfer complete case "$result" in
"OK") echo "got $f" 1>&2 ;; "ERROR") echo "failed getting$f, abort the job" 1>&2;
exit 1;;
# other cases may need to be considered here
esac
fi
done
exit 0
------------------------------------------------------------
========================= waitfor ==========================
#!/bin/sh
# Usage: result=waitfor string
# wait for given string from std input while monitoring error messages
# Usually, string' is an expected message number (e.g., 250). It
# detects 5xx error messages.
# [email protected], 8/22/88
while true
do
if test "$aLine" != "" then case "$aLine" in
"$1"*) echo "OK"; exit 0 ;; *'timed out'*) echo "ERROR"; exit 1 ;; # timeed out message 5*) echo "ERROR"; exit 1 ;; # 5XX error msg *) ; esac else sleep 3 fi done ------------------------------------------------------------ The scripts are for anonymous login. For non-anonymous login, you can change the user' command line. (Be sure to set proper file protection in this case.) Or you can use .netrc file and auto-login feature. In this case, '-n' option is in doftp' should be removed. There is much room for improvement especially for error message handling, and retrial in the case of partial fairlure. So please feel free to make further extensions or modifications as needed. Hope this helps some of you. Sung K. Chung | [email protected] Dept. of Computer Science, FR-35 | {decvax,ucbvax}!uw-beaver!uw-june!sung University of Washington | Seattle, WA 98195 | -----------[000265][next][prev][last][first]---------------------------------------------------- Date: 28 Aug 1988 18:59-EDT From: [email protected] To: [email protected] Cc: [email protected] Subject: SIGCOMM Membership SIGCOMM also allows affiliate membership. If you are a member of any of the AFIPS organizations, IEEE, etc., you can become an affiliate member of SIGCOMM without necessarily being a member of ACM. I don't have the dues information at hand, but it costs more that way than if you are already a member of ACM, but possibly less if you don't plan to become a member of ACM because you are already a member of, say, IEEE Computer or Communication Societies. I'll check the$ figures and post to TCP/IP.
Vint
-----------[000266][next][prev][last][first]----------------------------------------------------
Date: 28 Aug 88 15:14:41 GMT
From: [email protected] (Fletcher Mattox)
To: comp.bugs.4bsd,comp.unix.wizards,comp.protocols.tcp-ip
Subject: Re: Interlan drops a byte?
>> driver: @(#)if_de.c 7.1 (Berkeley) 6/5/86
Um, make that:
driver: @(#)if_il.c 7.1 (Berkeley) 6/5/86
-----------[000267][next][prev][last][first]----------------------------------------------------
Date: 28 Aug 1988 22:55-EDT
From: [email protected]
To: [email protected]
Cc: [email protected]
Subject: Re: Does TCP/IP "comform" to ISO/OSI?
Just about anything that is layered can be claimed to be conformant.
The TCP/IP protocols don't necessarily include all layers of OSI
(e.g., there isn't a distinct session or presentation layer, for
instance).
I don't think there is much advantage in conformance to the
reference model - the great advantages come from having a
set of compatible and interoperable protocols supported by
many vendors. This is certainly the case for the bulk of the
TCP/IP implementations and will presumably be the case, some day,
for many of the OSI implementations also.
Vint Cerf
-----------[000268][next][prev][last][first]----------------------------------------------------
Date: 28 Aug 88 22:59:00 GMT
From: [email protected]
To: comp.protocols.tcp-ip
Subject: SIGCOMM Membership
SIGCOMM also allows affiliate membership. If you are a member of
any of the AFIPS organizations, IEEE, etc., you can become an
affiliate member of SIGCOMM without necessarily being a member of ACM.
I don't have the dues information at hand, but it costs more that
way than if you are already a member of ACM, but possibly less if
you don't plan to become a member of ACM because you are already a
member of, say, IEEE Computer or Communication Societies.
I'll check the \$ figures and post to TCP/IP.
Vint
-----------[000269][next][prev][last][first]----------------------------------------------------
Date: 28 Aug 88 23:00:52 GMT
To: comp.bugs.4bsd,comp.unix.wizards,comp.protocols.tcp-ip
Subject: Re: Interlan drops a byte?
In article <[email protected]> ([email protected]) I write:
> Well, I think you're going to have an enormous amount of difficulty
> trying to use if_de.c with your Interlan. Why don't you try if_il.c?
> And as someone mentioned earlier, you should grab the latest copy of that
> driver since there were some significant bugs in the copy distributed
> with 4.3BSD.
> From: Chris Torek <[email protected]>
> Apparently Interlan makes a DEUNA-style board. Also, the major bugs
> were in if_np.c, not if_il.c ...
Opps! I should know better too. Thanks for the correction.
Casey
-----------[000270][next][prev][last][first]----------------------------------------------------
Date: 29 Aug 88 02:55:00 GMT
From: [email protected]
To: comp.protocols.tcp-ip
Subject: Re: Does TCP/IP "comform" to ISO/OSI?
Just about anything that is layered can be claimed to be conformant.
The TCP/IP protocols don't necessarily include all layers of OSI
(e.g., there isn't a distinct session or presentation layer, for
instance).
I don't think there is much advantage in conformance to the
reference model - the great advantages come from having a
set of compatible and interoperable protocols supported by
many vendors. This is certainly the case for the bulk of the
TCP/IP implementations and will presumably be the case, some day,
for many of the OSI implementations also.
Vint Cerf
-----------[000271][next][prev][last][first]----------------------------------------------------
Date: Mon, 29 Aug 88 10:58:42 EDT
To: [email protected]
Subject: TDR function of Micom NI5210 card
Has anyone ever gotten the TDR function of the Micom NI5210 card to work?
I've tried it using both thinwire and transceiver connections, opens, shorts
and good connections (plus disconnected xcver cable) and the TDR status
returned is always 87FF
which is , ethernet OK.
Anyone have any ideas?
[email protected]
-----------[000272][next][prev][last][first]----------------------------------------------------
Date: 29 Aug 1988 11:18-EDT
From: [email protected]
To: [email protected]
Cc: [email protected]
Subject: Re: Call queueing
Jeremy,
As John pointed out, the call queueing is used to reduce the
probability that a SYN arrives during a window where there is no listening
connection to bind it to, thus causing a RESET to be returned. Queueing
can only reduce it, since it is always possible for there to be more
arriving SYNs than there are remaining free queue slots. However, I reguard
specifying the size to the kernel to be more for the purpose of "limiting"
resources (such as processes [from the forks] and cpu cycles) than for
"allocating" them.
one of the "minuses" with the BSD implementation is that not only does the
listen cause the arriving SYN to be accepted and bound to a new TCP connection
block, but that the protocol machine is also started. Thus a connection may
proceed to the ESTABLISHED state and accept/ACKnowledge (usually 4K bytes of)
data before the application-level peer (process) is even created. This
prevents the process from:
1) examining the IP-address identity of the caller before deciding
ACKnowledge the SYN vs. send a RESET,
What if X were to place a "collect" call to such an implementation
and send 4K data; then the receiver process start up and decides
it doesn't want to accept the call. Who pays for the 4K bytes?
(The receiver COULD make the 4K available to the appliaction.)
2) checking its routing tables and applying administratively specified
3) selecting initialization parters based on IP-level parameters such as
TOS and options, or
Maybe local system has a method for setting the TCP MSS (which
the spec says has to be in the SYN packet).
4) specifying initial TCP-level options, etc.
Charlie
-----------[000273][next][prev][last][first]----------------------------------------------------
Date: 29 Aug 88 08:35:20 GMT
From: [email protected] (Rob Hulsebos)
To: comp.protocols.tcp-ip,comp.unix.questions
Subject: ftp/rcp can't copy devices
When I use the 'ftp' or 'rcp' command, and want to copy a disk-partition
(accessed via /dev/rdsk/*) to the other end, both utilities
complain: "not a plain file".
Of course, the manual doesn't mention that only plain files can be
transferred. Does anybody know why ftp and rcp behave this way?
Suprisingly, copying _to_ a device is allowed. An ftp-command like
"put /unix /dev/null" works fine, and is a nice trick to test the overhead
incurred by the filesystem on the receiving end.
------------------------------------------------------------------------------
R.A. Hulsebos ...!mcvax!philmds!hulsebos
Philips I&E Automation Modules phone: +31-40-785723
Building TQ-III-1, room 11
Eindhoven, The Netherlands # cc -O disclaimer.c
------------------------------------------------------------------------------
-----------[000274][next][prev][last][first]----------------------------------------------------
Date: Mon, 29 Aug 88 14:28:19 EDT
From: "Roger Fajman" <RAF%[email protected]>
To: [email protected]
Cc: [email protected]
Subject: Re: TCP/IP for big, big Blue
Check out ACC, Advintech, Fibronics, and Network Solutions for TCP/IP
for IBM mainframes running the MVS and MVS/XA operating systems. For
VM, your best bet is probably the IBM TCP/IP for VM package. They all
should be listed in the SRI-NIC vendors guide.
-----------[000275][next][prev][last][first]----------------------------------------------------
Date: 29 Aug 88 14:11:50 GMT
From: [email protected] (Kurt D. Baumann)
To: comp.protocols.tcp-ip
Subject: TCP/IP under RTX on a PDP-11
Does anyone have any information where I might obtain a copy of
TCP/IP running under RTX on a pdp-11? I have someone who is
interested getting a copy running on his pdp-11. Thanks...
Please send mail to me concerning the above if you have any leads as
to where I might be able to find a RTX version of TCP/IP.
By the way, we did not know, that posting to what we thought
(wrongly it seems) was a usenet only group, that our message would
get put onto the arpanet. Sorry about that, we had no intention of
Thanks!
Kurt Baumann
uunet!lts!kdb
-----------[000276][next][prev][last][first]----------------------------------------------------
Date: 29 Aug 88 14:58:42 GMT
To: comp.protocols.tcp-ip
Subject: TDR function of Micom NI5210 card
Has anyone ever gotten the TDR function of the Micom NI5210 card to work?
I've tried it using both thinwire and transceiver connections, opens, shorts
and good connections (plus disconnected xcver cable) and the TDR status
returned is always 87FF
which is , ethernet OK.
Anyone have any ideas?
[email protected]
-----------[000277][next][prev][last][first]----------------------------------------------------
Date: 29 Aug 88 15:18:00 GMT
From: [email protected]
To: comp.protocols.tcp-ip
Subject: Re: Call queueing
Jeremy,
As John pointed out, the call queueing is used to reduce the
probability that a SYN arrives during a window where there is no listening
connection to bind it to, thus causing a RESET to be returned. Queueing
can only reduce it, since it is always possible for there to be more
arriving SYNs than there are remaining free queue slots. However, I reguard
specifying the size to the kernel to be more for the purpose of "limiting"
resources (such as processes [from the forks] and cpu cycles) than for
"allocating" them.
one of the "minuses" with the BSD implementation is that not only does the
listen cause the arriving SYN to be accepted and bound to a new TCP connection
block, but that the protocol machine is also started. Thus a connection may
proceed to the ESTABLISHED state and accept/ACKnowledge (usually 4K bytes of)
data before the application-level peer (process) is even created. This
prevents the process from:
1) examining the IP-address identity of the caller before deciding
ACKnowledge the SYN vs. send a RESET,
What if X were to place a "collect" call to such an implementation
and send 4K data; then the receiver process start up and decides
it doesn't want to accept the call. Who pays for the 4K bytes?
(The receiver COULD make the 4K available to the appliaction.)
2) checking its routing tables and applying administratively specified
3) selecting initialization parters based on IP-level parameters such as
TOS and options, or
Maybe local system has a method for setting the TCP MSS (which
the spec says has to be in the SYN packet).
4) specifying initial TCP-level options, etc.
Charlie
-----------[000278][next][prev][last][first]----------------------------------------------------
Date: 29 Aug 88 15:48:02 GMT
From: [email protected] ("Doug McCallum")
To: comp.protocols.tcp-ip
Subject: Re: Call queueing
-------
> The BSD listen(2) syscall (on a socket) provides for the specification
> of a queue of pending connection requests. So does the TLI T_LISTEN function.
> What are the pros and cons of this functionality? Is it merely a matter
> of the cost of copying a protocol control block versus the cost of opening
> and initialising one? Or is there also a functional benefit?
The reason you want to allow for queueing of incoming connection requests is
that you want to buffer them while an application is processing a previous
one. The alternative is to reject the connections until the application is
there will be cases where multiple connection requests arrive back-to-back
from the network. You don't want to reject these so you queue them until
there is time to properly respond.
In the BSD systems, the queued connection requests get accepted
automatically. In the TLI mechanism, it is possible that the connection
request has not been responded to giving the application final say on
whether to accept or reject the request.
One minor clarification, the TLI indication to queue connection requests is
in the t_bind call and not the t_listen. T_listen is not the same as the
socket listen. t_listen waits for an incoming connection request and
returns that to the application. The information in the connection request
is then given to the t_accept call if the connection is to be accepted or
the t_snddis call if the connection is to be rejected.
-----------[000279][next][prev][last][first]----------------------------------------------------
Date: 29 Aug 88 17:57:35 GMT
From: [email protected] (Ahola Jari)
To: comp.dcom.lans,comp.sys.hp,misc.wanted,comp.protocols.tcp-ip
Subject: TCP/IP for HP 3000/935 and associated questions
Hello there,
I'd like to hear comments from those of you who are familiar
with the software (hardware?) from the Wollongong Group for
the HP 3000 series, if such a thing even exists. The problem
is that we should connect tens of HP's Vectra series PCs, a Sun
workstation to serve the PCs and then the problem: we should also
get the 3000/935 from HP connected to this mess (preferably via Sun).
Question: Has the Wollongong group anything to offer (or some other
party) to provide the following services between Sun/HP 3000 ?
Regular TCP/IP services
Other Goodies
Any information would be greatly appreciated.
-jja
--
Jari 'jja' Ahola | Tampere University of Technology, CS dept.
Opiskelijankatu 16 A 12 | P.O. Box 527, 33101 Tampere, Finland
33720 Tampere | Tel (intl) 358 31 162708 (work)/358 31 174009 (home)
Finland. Puh. 931-174009| Net address: jja@tut (UUCP) AHOLA@FINTUTA (BITNET)
-----------[000280][next][prev][last][first]----------------------------------------------------
Date: 29 Aug 88 18:24:23 GMT
From: [email protected] (Brian Lloyd)
To: comp.protocols.tcp-ip
Subject: Looking for more complete FTP implementations
Here at Sirius Systems we have just about completed our new FTP server and
are looking for others with whom we might exchange files at the upcoming
Interop-88 show. At the show we expect to have the following features:
Modes: Stream, Block, and Compressed
Structure: File and Record
Type: ASCII and Image
Format: Noprint, TELNET, and Control (ASA)
We are not going to do structure page since we do not run on
DECSystem-20's. Neither are we going to support type EBCDIC since the
hosts speak ASCII. We are also not going to implement the following FTP
commands since they would serve no function on our hosts:
ALLO, ACCT, CDUP, SMNT
In addition to the above we plan to implement the ability to restart a
failed transfer from a checkpoint. For those of you who care, we use
5120 octets (bytes) as our checkpoint interval (unless someone else can
give us a good reason to use some other value or formula).
If you have an FTP that can do more than the minimum defined
implementation we would like to hear from you. Thanks.
Brian Lloyd
Sirius Systems, Inc.
P.O. Box 2202
Petersburg, VA 23804
(804) 733-7944
[email protected]
Share and enjoy!
-----------[000281][next][prev][last][first]----------------------------------------------------
Date: 29 Aug 88 18:28:19 GMT
From: [email protected] ("Roger Fajman")
To: comp.protocols.tcp-ip
Subject: Re: TCP/IP for big, big Blue
Check out ACC, Advintech, Fibronics, and Network Solutions for TCP/IP
for IBM mainframes running the MVS and MVS/XA operating systems. For
VM, your best bet is probably the IBM TCP/IP for VM package. They all
should be listed in the SRI-NIC vendors guide.
-----------[000282][next][prev][last][first]----------------------------------------------------
Date: Tue, 30 Aug 88 00:30 EDT
From: PMDF Mail Server <Postmaster%[email protected]>
To: [email protected]
Subject: Undeliverable mail
Your message could not be delivered to:
WARD
Your message has been enqueued and undeliverable for 3 days.
The mail system will continue to try to deliver your message
The beginning of your message follows:
-----------[000283][next][prev][last][first]----------------------------------------------------
Date: 29 Aug 88 23:45:54 GMT
From: [email protected] (James Van Bokkelen)
To: comp.protocols.tcp-ip
Subject: Re: TDR function of MICOM NI5210 card
PC/TCP's NI5210 driver implements the TDR function, and I've tested it,
so the hardware is there. Check your code carefully against the Intel
handbook for the 82586. I don't think it has anything to do with
jumpers on the card.
James VanBokkelen
FTP Software Inc.
-----------[000284][next][prev][last][first]----------------------------------------------------
Date: 30 Aug 88 00:05:08 GMT
From: [email protected] (Chris Torek)
To: comp.protocols.tcp-ip,comp.unix.questions
Subject: Re: ftp/rcp can't copy devices
In article <[email protected]> [email protected] (Rob Hulsebos) writes:
>When I use the 'ftp' or 'rcp' command, and want to copy a disk-partition
>(accessed via /dev/rdsk/*) to the other end, both utilities
>complain: "not a plain file".
>
>Of course, the manual doesn't mention that only plain files can be
>transferred. Does anybody know why ftp and rcp behave this way?
Both attempt to determine the size of the file before sending it.
(Only rcp's protocol actually requires this.) There is no way to
find the size of a special file without reading it, and in the process
the data may vanish (e.g., reading /dev/tty or a socket).
--
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain: [email protected] Path: uunet!mimsy!chris
-----------[000285][next][prev][last][first]----------------------------------------------------
Date: 30 Aug 88 02:25:29 GMT
From: [email protected] (Scott W. Rogers)
To: comp.protocols.tcp-ip
Subject: In search of resolver for EXCELAN under XENIX and/or DOS...
In search of a Domain Name Resolver for EXCELAN TCP/IP 8/29/88
I am in search of a domain name resolver (source preferred, binary ok)
for the Excelan TCP/IP under XENIX (8011-04) and/or for Excelan TCP/IP
for DOS (8051 or something like that). A name Server would also be
necessary, but not required as we have a SUN and a VAX running named.
Excelan TCP/IP (for DOS and XENIX) is based on 4.1BSD sockets (yeach).
If anyone has or knows of any ports for Excelan TCP/IP, please let me
know directly via E-MAIL at "[email protected]". I WILL summarize
to the net.
------------------------------------------------------------------------
Scott W. Rogers Computer Sciences Corporation - Systems Division
AT&T: (703) 876-1363 3160 Fairview Park Dr. - Falls Church, VA 22152
Fax: (703) 876-4072 Internet: [email protected]
------------------------------------------------------------------------
-----------[000286][next][prev][last][first]----------------------------------------------------
Date: 30 Aug 88 04:03:28 GMT
From: [email protected] (Alexander Dupuy)
To: comp.protocols.tcp-ip,comp.unix.questions
Subject: Re: ftp/rcp can't copy devices
Actually, it is possible to copy from a device, using a somewhat obscurely
documented feature of ftp. You can specify a shell command as the source or
destination of a tranfer - the command runs on the local machine in either
case. An example which I used just a few weeks ago:
% ftp another_machine
ftp> send "|dd if=/dev/rst8" somefile.tar
# silly messages from dd and ftp deleted
ftp> bye
%
You don't need the quotes if the command is one word. This can be quite useful
for spooling dumps to a remote machine which doesn't support /etc/rmt - a big
IBM mainframe with _lots_ of disk space is ideal. By creating a ~/.netrc file,
you can even have ftp batch jobs to spool your dumps.
As Chris Torek noted, the rcp protocol requires that the size of the file be
known, which is not possible in general for devices. There is no equivalent
feature (that I know of) in rcp to allow sending from programs.
@alex
--
inet: [email protected]
uucp: ...!rutgers!columbia!dupuy
-----------[000287][next][prev][last][first]----------------------------------------------------
Date: 30 Aug 88 14:27:03 GMT
From: [email protected] (Russ Nelson)
To: comp.protocols.tcp-ip
Subject: Re: KA9Q with MOCOM NI5010
In article <[email protected]> [email protected] (Guus van der Wal) writes:
I have a MICOM interlan NI5010 ethernet adapter in my IBM pc/at.
I also have Phil Karn's KA9Q TCP-IP software. The KA9Q docs
only talk about the 3COM 3C500 ethernet card.
Is there anybody out ther who has (made) KA9Q working with MICOM ??
Ha! Interesting that you should ask that question, since I have recently
ported Bill Doster's NI5010 driver from C (to be compiled in) to a packet
driver. This is not tested, however. You (and in fact, anyone who is
interested) can either debug it yourself or wait until I get a NI5010
loaned to me from another department, which may take as long as two weeks.
I'll mail a copy to anyone who's really hot to get a copy...
--
--russ (nelson@clutx [.bitnet | .clarkson.edu])
Shuzan held out his short staff and said, "If you call this a short staff,
you oppose its reality. If you do not call it a short staff, you ignore the
facts. Now, what do you wish to call it?"
-----------[000288][next][prev][last][first]----------------------------------------------------
Date: 30 Aug 88 16:15:44 GMT
From: [email protected] ([email protected] (Kent W. England))
To: comp.protocols.tcp-ip
Subject: Re: Does TCP/IP "comform" to ISO/OSI?
>I'd be delighted to accept a case which held that the protocol sub-suite
>consisting of TCP-or-UDP-over-IP is a more appropriate realization of
>stated "OSI" "Reference Model" principles than is the protocol sub-suite
>consisting of X.25-and-X.75
Seems to me this argument of "OSI implies X.25 and X.75" is a little
obsolete. In the US, I don't expect to have to run OSI protocols over
virtual circuit networks, but rather that future OSI-IP internetworks
will be "equivalent" to the Internet, that is, a connectionless,
datagram network. In fact, I am looking forward to running OSI
applications, like directory service, on top of tcp/ip protocols.
Of course, in Europe (except UK) the situation is different.
Kent England, Boston University
-----------[000289][next][prev][last][first]----------------------------------------------------
Date: 30 Aug 88 17:41:21 GMT
From: [email protected] (Keith Mitchell)
To: comp.protocols.tcp-ip
Subject: Re: Multiple TCP/IP servers on one Host.
In <[email protected]>, Martin Holland raises the issue of how
to get several terminal servers acting in "milking machine" mode to the same
host, to appear as one to other nodes on the network. I could suggest
upgrading to a SpiderPort, which has 10 lines to the NTS100's 8, but I don't
think this is really a terribly helpful solution.
This is an interesting problem, and while there are a number of possible
approaches to solving which fit in with the TCP/IP archectiture, none are
completely satisfactory, particularly if the requirement is for a scheme
which is transparent to the incoming (Telnet client) caller.
One approach could be to use the Telnet Reconnection option (NIC 15391). Here
the connection would be established to a Telnet server which knows when
all the ports on one server were full, and could then tell the client
to try connecting to a different server on another Internet address. However,
this requires the Reconnection option to be implemented on all possible
clients. Since I have never heard of any implementations of this with TCP, I
suspect this approach is a non-starter. Has anyone used the Telnet
Reconnection option over TCP for this sort of thing anywhere ?
There is also an issue here of who does the redirect - should there be a
central server which everybody connects to intially, and which keeps track
of everyone's resources so it knows where to redirect to, or should one
server simply redirect to another when it knows it is full ? The issue
of who knows what ports are free is something which generally needs to be
addressed for various schemes like this. For example, the ARP-based scheme
proposed by Mike Brescia <[email protected]>.
Another way is to fudge name lookup in some way. If a name server could be
got at, it could return a different address in response to the same user
string depending on how loaded the telnet servers are. This is not very nice
as it blurs functional boundaries between name servers, and what one could
call "resource location servers". This suggests another approach, where the
client sends a request out to find out what server(s) have free ports, and
uses the information returned to decide who to actually connect to (cf
BOOTP). Resource Location Protocol (RFC 887) might be a possibility here.
A cleaner scheme for exploiting the name lookup mechanism as a solution is
to have an alias-on-fail arrangement. For example if a given hostname fails,
prepend a "&" and try again. The host table would then look something like:
spport1 192.35.138.1
&spport1 192.35.138.2
spport2 192.35.138.3
The disadvantages with this are again it requires non-standard client
software, and the cumulative time-out delay could get quite large towards
the end of the list (eg. &&&spport1 ).
Clearly with all these schemes there is a trade-off between cleanness of
approach, and how transparent it is to existing hosts. If one approach could
be standardised on as best, then I think some progress towards solving
Keith Mitchell
Spider Systems Ltd. [email protected]
Edinburgh, Scotland keith%[email protected]
+44 31-554 9424 ...!uunet!ukc!spider!keith
-----------[000290][next][prev][last][first]----------------------------------------------------
Date: 30 Aug 88 20:03:21 GMT
From: [email protected] (Tom Cunningham)
To: comp.os.vms,comp.protocols.tcp-ip
Subject: CMU TCP/IP and Micom NI1010A
From what I gather, CMU TCP/IP does not support the Micom NI1010A Ethernet
interface. Has anyone modified the code so that it does?
Tom Cunningham Motorola Inc. Austin TX
uunet!mnetor!oakhill!tomc
cs.utexas.edu!oakhill!tomc
--
Tom Cunningham Motorola Inc. Austin TX
uunet!mnetor!oakhill!tomc
cs.utexas.edu!oakhill!tomc
-----------[000291][next][prev][last][first]----------------------------------------------------
Date: 30 Aug 88 20:12:35 GMT
From: [email protected] (Ole J. Jacobsen)
To: comp.protocols.tcp-ip
Subject: NVLAP information
For informationon NVLAP, contact
John L. Donaldson
Manager, Laboratory Accreditation
National Institute of Standards and Technology (formerly NBS)
Gaithersburg, MD 20899
(301) 975-4016
Ole
-------
-----------[000292][next][prev][last][first]----------------------------------------------------
Date: 30 Aug 88 20:52:34 GMT
From: [email protected] (Phil R. Karn)
To: comp.protocols.tcp-ip
Subject: Re: KA9Q with MOCOM NI5010
> Is there anybody out ther who has (made) KA9Q working with MICOM ??
I have recently added support for FTP Software's Packet Driver
interface. This allows the code to use any packet driver that follows
the spec. Several people have so far contributed drivers for the following
boards:
TRW PC-2000
NI5010
WD8003
and others are on the way (SLIP, 3C501). A major revision of the package
should be out in a month or so; watch for it.
Phil
-----------[000293][next][prev][last][first]----------------------------------------------------
Date: 30 Aug 88 21:16:56 GMT
From: [email protected] (Phil R. Karn)
To: comp.protocols.tcp-ip
Subject: Re: Does TCP/IP "comform" to ISO/OSI?
> Does OSI conform to ARM?
>
> No.
And, of course, one might ask the question: "Do the 'OSI Protocols'
But even if you limit the discussion to reference models, the "OSI
Model" is hopelessly out of date. By the time you delete the unnecessary
layers (e.g., Session), combine distinct layers that really shouldn't be
separate (e.g., Application and Presentation), create the sublayers
required by modern concepts like internetworking (the Internet and
Subnet Layer) and multiple access networks (e.g., the Media Access
Layer), about the only morsel you'd still have left from the original
OSI model is that "Layering is often a useful tool in building
networks".
Then when you add Postel and Cohen's paper showing how a fixed number of
layers is simply unworkable in the real world, what you finally end up
with looks remarkably like the ARPANET Reference Model (ARM).
But does ISO ever revise its preconceived ideas and admit its mistakes?
Of course not. It just covers them over with even more paper and ad
hype.
"No Need for XYZ, Just TCP!" --Seen on a British billboard
Phil
-----------[000294][next][prev][last][first]----------------------------------------------------
Date: 30 Aug 88 22:36:03 GMT
From: [email protected] ([email protected] (Kent W. England))
To: [email protected]
Subject: Telnet Options Commonly Supported
I am trying to find a list of the most commonly supported
Telnet options that would be useful for a terminal server or other
implementation to support on the Internet. I am not interested in
MILnet specific options, unless they are likely to be adopted in the
Internet.
Is this list reasonably complete and well defined?
Original rfc854 characters supported:
interrupt (^C)
abort (^C, ^X?)
hello (Are You There?)
erase character (<BS> or <DEL>)
erase line (^U)
new line character(s) (<CR><LF> or <CR>)
bell (^G)
tab, vt, lf, ff
Commonly supported options:
binary mode
echo control (remote and local, mostly remote)
suppress Go Ahead (not needed for ansi-style terminals)
status (confirm status of telnet options)
terminal type character string
telnet 3270 data streams (tn3270)
I have glanced over rfc1053 and the X.3 terminal handling and
transmission control parameters look quite interesting, but I suspect
it's too early to expect anyone to have any implementations of this.
Have I omitted any widely supported options or included any
widely unsupported options in the above list?
Is there a document that goes into more detail summarizing the
state of telnet options as of a recent date?
Kent England, Boston University
-----------[000295][next][prev][last][first]----------------------------------------------------
Date: 30 Aug 88 23:08:37 GMT
From: [email protected] ("Billy Brackenridge")
To: comp.protocols.tcp-ip
Subject: Microsoft 3Comm MAC Spec available via FTP
I now have an on-line copy of the Microsoft / 3Comm Media ACcess
(MAC) protocol specification.
This specification is the Microsoft 3Comm proposed standard for low
level networking under MS-DOS and OS/2. If you make any kind of
network hardware for IBM-PC or AT machines or write transport layer
protocols, you should look at this specification.
This file can be obtained via FTP from VENERA.ISI.EDU with the
password GUEST. cd to the directory pub and retrieve the file.
The file is 225K bytes long. No I won't mail it to you unless
exceptional conditions warrant exceptional behavior.
This version is dated 5/14/88. There are minor changes since the last
version I distributed.
Feel free to copy this document. Microsoft has assured me they are
interested in the widest possible distribution.
In the past networking code for the PC has been incompatible. The
various TCP/IP packages have been unable to operate resident in a PC
with the commercial proprietary network packages. If this standard is
adopted by the industry, users should have a wider choice of
interoperating protocol stacks and network hardware.
I would like to assume that part of Microsoft's and 3Comm's
motivation for publishing this specification is to get feedback from
the network community. Unfortunately the specification has leaked out
slowly and in a form that appears to be "take it of leave it". There
have been many objections to portions of this specification. Like
"The Last Temptation of Christ" many of those who cry the loudest
haven't read or comprehended the specification. I have corresponded
with others actually attempting to implement this specification who
have serious reservations and suggestions for improvement.
John Romkey will be running a PC special interest group session at
Interop '88. Many people have expressed an interest in discussing
this specification at that session. Everyone with whom I have
corresponded has expressed an interest in seeing a Microsoft and/or
3Comm representative at Interop '88 who can answer technical
-------
-----------[000296][next][prev][last][first]----------------------------------------------------
Date: 30 Aug 88 23:32:51 GMT
From: [email protected] (Karl Auerbach)
To: comp.protocols.tcp-ip
Subject: Re: TDR function of MICOM NI5210 card
Recently I put together a driver for an Ether-board that uses the Intel
82586 controller. As part of the software initialization I had it do
a TDR check. It was useful for testing the cable, and more importantly,
the drop cable and connectors.
However, there were circumstances where the TDR check failed -- mainly
on broadband networks and over-extended Ethernets.
If you do the TDR it would probably be useful to add an option to bypass
the test for those nets on which it fails but not as a result of an error.
--karl--
-----------[000297][next][prev][last][first]----------------------------------------------------
Date: 31 Aug 88 08:35:00 PDT
From: Dave Crocker <[email protected]>
To: tcp-ip <[email protected]>
Subject: Re: Multiple TCP/IP servers on one host
You have a basic question to ask: Is the solution to your problem constrained
to use existing mechanisms or do you have freedom to implement additional
capabilities? If you must use only existing products, then you are unlikely
to find a solution.
In general, Keith Mitchell's set of alternative is reasonable, if you
can build your own mechanisms. (There are some interesting problems
involved with having the different milking machines know about each other
and each other's availability, but most of this is surmountable.)
Probably the minimum amount of effort -- even having a minute chance of
working without any development -- is to use the ability of the Domain
Name Service to list multiple addresses for a host. Here's how it goes:
1. For management purposes, list each milking machine by a unique name.
Then, you can access specific ones, when you need to.
2. Choose a generic name, under which you list all of the milking machines'
3. When you need to do an access, use the generic name to do a DNS lookup
and get the list of addresses.
4. Choose an address from the list. If you want to attemp load-leveling,
throw a random number, to select the first address.
(Sorry, but true, empirically-derived load-leveling does not work
without all of the inter-milking machine communication mentioned above.)
5. Pray that the milking machine product sends a reasonable rejection when
all of its lines are full.
6. When receiving such an error, try the next address.
The reason that you may be able to use this scheme without software development
is that there may be some telnet implementations out there that do step 6
Dave Crocker
The Wollongong Group
-----------[000298][next][prev][last][first]----------------------------------------------------
Date: 31 Aug 88 02:22:20 GMT
From: [email protected] (Everett F. Batey II)
To: comp.protocols.tcp-ip
Subject: Sun netstat traffic for DECNet
Is there any experience using Sun network tools, traffic, netstat, etc to
monitor and diagnose DECNET or DEC LAT, DEC PCSA? Do any of the Sun
services know how to identify the DEC protos?
--
[email protected] sun!tsunami!suned1!efb [email protected]
Any statements / opinions made here are mine, alone, not those of the
United States, the DoD, the Navy, the Congress, the Judiciary, nor ...
-----------[000299][next][prev][last][first]----------------------------------------------------
Date: 31 Aug 88 14:14:05 GMT
From: [email protected] (Judy Messing)
To: comp.protocols.tcp-ip
Subject: Re: Test suite for IP based systems
Bill,
The DCA Upper Level Test System, the DCA system referred to by Dan Lynch, is
available through NTIS (National Technical Information Service). It does not
require any tuning of your protocol implementation. It does however
require simple application programs (specifications for which are also
available from NTIS) which act as the upper level user of your protocol.
The Test System refers to this programs as remote drivers. Currently,
the Test System runs using Ultrix 1.1. I believe DCA has plans to port
the system to other operating systems.
We developed this system for DCA and often used the test suites in regression
testing as we tried to ensure that adding new capabilities did not break
things that formerly worked. If you have further questions, I'll be glad
Judy Messing
Unisys
-----------[000300][next][prev][last][first]----------------------------------------------------
Date: 31 Aug 88 14:31:47 GMT
From: hlg%[email protected] (Howard Goodman acc_gnsc)
To: comp.protocols.tcp-ip
Subject: PING w/source route option
I am looking for a version of PING which supports the source-route option.
If anyone has such an animal, would they please respond to me directly.
The versions I am looking for run on a Vax 750/Unix and a 3B System V.
Thank you.
---------
Howard Goodman
hlg%[email protected]
-----------[000301][next][prev][last][first]----------------------------------------------------
Date: 31 Aug 88 14:46:00 GMT
From: [email protected]
To: comp.protocols.tcp-ip
Subject: ANNEX II Terminal Server Experiences?
From: "Alan S. Watt" <watt-alan>
I just received a technical blurb on the "ANNEX II" terminal server
by Encore Computer Corp. What is especially interesting about it
is you can configure any number of the ports for SL/IP. The blurb
doesn't mention whether it does proxy ARP, but does say it has
"Full support of 4.3 bsd TCP/IP including Subnets", and "Complete
implementaiton of IP routing".
Question:
Does anyone out there have any experience using this machine
with SL/IP, and if so would they share them, either by
follow-up or E-mail?
- Alan S. Watt
High Speed Networking, Science and Engineering Computing Facility
Dunham 232; (203) 432-4243,4007
[email protected]
-----------[000302][next][prev][last][first]----------------------------------------------------
Date: 31 Aug 88 15:00:21 GMT
From: [email protected] (scott)
To: comp.bugs.4bsd,comp.unix.wizards,comp.protocols.tcp-ip
Subject: Re: Interlan drops a byte?
In article <[email protected]> [email protected] (Fletcher Mattox) writes:
>Has anybody else seen a 4.3BSD VAX with an Interlan Ethernet interface
>drop a byte of data? Well, that's what we're seeing.
I've seen Micom/Interlan Ethernet controllers drop bytes. I've seen
them loose a bit, left shifting subsequent data by a bit. Somehow, these
errors were not caught by any of their protocol error checking.
Micom/Interlan claims that fixes are/were in the works. BTW, this was
observed on a Multibus I board.
--
Scott H. Crenshaw scott%[email protected]
h-three Systems Corporation uunet!h-three!scott
POB 12557 100 Park Drive Suite 204
Research Triangle Park, NC 27607 (919) 549-8334
-----------[000303][next][prev][last][first]----------------------------------------------------
Date: 31 Aug 88 15:35:00 GMT
From: [email protected] (Dave Crocker)
To: comp.protocols.tcp-ip
Subject: Re: Multiple TCP/IP servers on one host
You have a basic question to ask: Is the solution to your problem constrained
to use existing mechanisms or do you have freedom to implement additional
capabilities? If you must use only existing products, then you are unlikely
to find a solution.
In general, Keith Mitchell's set of alternative is reasonable, if you
can build your own mechanisms. (There are some interesting problems
involved with having the different milking machines know about each other
and each other's availability, but most of this is surmountable.)
Probably the minimum amount of effort -- even having a minute chance of
working without any development -- is to use the ability of the Domain
Name Service to list multiple addresses for a host. Here's how it goes:
1. For management purposes, list each milking machine by a unique name.
Then, you can access specific ones, when you need to.
2. Choose a generic name, under which you list all of the milking machines'
3. When you need to do an access, use the generic name to do a DNS lookup
and get the list of addresses.
4. Choose an address from the list. If you want to attemp load-leveling,
throw a random number, to select the first address.
(Sorry, but true, empirically-derived load-leveling does not work
without all of the inter-milking machine communication mentioned above.)
5. Pray that the milking machine product sends a reasonable rejection when
all of its lines are full.
6. When receiving such an error, try the next address.
The reason that you may be able to use this scheme without software development
is that there may be some telnet implementations out there that do step 6
Dave Crocker
The Wollongong Group
-----------[000304][next][prev][last][first]----------------------------------------------------
Date: 31 Aug 88 16:55:26 GMT
From: [email protected] ([email protected] (Kent W. England))
To: comp.protocols.tcp-ip
Subject: Re: Multiple TCP/IP servers on one Host.
In article <[email protected]>
> [email protected] (Keith Mitchell) writes:
>
>In <[email protected]>, Martin Holland raises the issue of how
>to get several terminal servers acting in "milking machine" mode to the same
>host, to appear as one to other nodes on the network.
>
There are actually two problems: How to assign multiple
rotaries (telco terminology) to one box and how to assign multiple
boxes to one rotary. It seems to me the solutions to both problems are
related and require particular capabilities of both client and host
server telnet implementations.
>This is an interesting problem, and while there are a number of possible
>approaches to solving which fit in with the TCP/IP archectiture, none are
>completely satisfactory, particularly if the requirement is for a scheme
>which is transparent to the incoming (Telnet client) caller.
>
Seems to me that name server lookup can handle this
transparently, so long as the resolver in the client telnet takes
reasonable actions on the response received.
>
>Another way is to fudge name lookup in some way. If a name server could be
>got at, it could return a different address in response to the same user
>string depending on how loaded the telnet servers are.
This is the same situation as a multi-homed host and I believe
the name server is set up to handle this with multiple records for a
single host. Just substitute the concept of "multi-box rotary" for
"multi-homed host". Name servers return all addresses listed for a
given name. The resolver on the telnet client would need to be smart
enough to try all returned names before giving up on the connection
request. So the problem becomes one for the client (ie terminal)
server and not the host (ie, milking machine) server. If the client
server simply tries the first address returned and drops others, then
this approach fails.
The other situation is different. The host server must be
able to associate a subset of its ports to one IP address, possibly
down to one IP address per port. Then the client telnet requests
service by name and receives either the single IP address that the
host server will associate to, say, three serial ports, or it receives
three separate responses corresponding to the three separate ports of
that rotary. In the first case, the client only has to try one
connection and the host server handles port contention itself. The
second case is the same as the multi-box rotary problem above and the
client server must be able to try multiple addresses in sequence
before aborting the attempt and reporting back to the user.
So it seems to me that the solution is partly in client telnet
(try all addresses in sequence) and partly in the host telnet
(associate one or more ports to one IP address for efficiency).
Kent England, Boston University
-----------[000305][next][prev][last][first]----------------------------------------------------
Date: 31 Aug 88 18:24:24 GMT
To: comp.protocols.tcp-ip
Subject: Re: Does TCP/IP "comform" to ISO/OSI?
Kent England:
Just for the record, it seems to ME that there's no connection whatsoever
between my observation that TCP/UDP-IP is philosophically closer to the
"Reference Model" than X.25-X.75 and "this argument of 'OSI implies X.25
and X.75'" you mention. If anything, the observation is more reasonably
misconstruable as a suggestion that OSI precludes X.25-X.75 than that it
implies 'em, although it doesn't say that either.
Of more interest, however, is whether you'll actually be able to satisfy
your stated expectation that you won't "have to run OSI protocols over
virtual circuit networks " "[i]n the US": As long as DDN and GOSIP mandate
X.25, neither ARPA nor ISO IP users will be able to avoid paying (in one or
more senses) for unasked-for subnet functionality, in the long haul, as it
were. Are you, perhaps, counting on ISDN to save the day? (For that
matter, does anybody out there know for sure whether ISDN, unlike X.25, WILL
offer datagram service, and, unlike X.75, dynamic/"real" alternate routing?)
If so, you'd be better advised to argue with the proprietors of DDN and
the propounders of GOSIP about the non-OSIness of X.25, not with me, since
the bold-face line in the middle of p.154 of _The Elements of Networking
Style_ (Prentice-Hall, 1985) proves that I haven't lumped OSI and X.25 for
several years--even if I'll never forgive the panacea pedlars who had
tricked me into lumping them previously.
cheers, map
-------
-----------[000306][next][prev][last][first]----------------------------------------------------
Date: 31 Aug 88 22:55:50 GMT
From: [email protected] (Marshall Rose)
To: comp.protocols.tcp-ip
Subject: Re: Does TCP/IP "comform" to ISO/OSI?
Phil, you make me sad. But now I will make you angry!
Neither you nor I are unbiased observers. In as much as you have given
your slanted view (i.e., no need for session, presentation should be
application-specific, etc.), I might as well give my slanted views.
The problem with you TCP/IP extremists is that you only have one tool, a
hammer. It's a nice stainless steel hammer which gets the job done
quite handily. But it is still a hammer. As such, every problem to you
guys looks like a nail. (In fairness, OSI extremists are the same way).
Although at the lower layers, OSI (levels 3&4) is still quite silly at times;
at the upper layers, I think the TCP/IP community could learn quite a
few things. Some of which you might even find useful.
I won't bother launching into an assault on TCP/IP at this point, for
two reasons: 1) you wouldn't appreciate it, and 2) I'm using it to get
things done today.
The problem is that you snipe at the parts you don't like, rather than
trying to appreciate the entire picture. On the whole, OSI has a lot of
good points going for it, even though some of the actual parts are
pretty lousy.
/mtr
END OF DOCUMENT |
# A manufacturer ships its product in boxes with edges of 4 inches. If 12 boxes are put in a carton and completely fill the carton, what is the volume of the carton?
Jun 3, 2016
Volume of carton would be $768$ cubic inches
The volume of one box is $4 \times 4 \times 4 = 64$ cubic inches.
As he puts $12$ boxes in a carton, the volume of carton would be
$12 \times 64 = 768$ cubic inches |
# Sort already sorted array - after changing several elements
Problem:
Given $S$ — a sorted array where some of the elements were randomly changed, assuming that you're provided with an $S_1$ — an array of indexes of changed elements. Design an algorithm that will sort the array in $O(n)$ time.
Additionally, we know that $\text{length of }S_1\le\log_2(\text{length of }S)$.
Example:
$S$ — [3, 5, 7, (20), 15 ,(0) ,16]
$S_1$ — [3, 5]
() - Changed elements
Question:
I have some troubles designing the algorithm. My first idea was to just use Count or Radix sort algorithm, but as the values which are changed can be random I've ruled out count sort as potential candidate.
The second idea is to:
1. Load the values based on indexes of $S_1$ into new array $S_x$.
2. Rewrite $S$ without the elements of indexes provided in $S_1$.
3. Sort $S_x$.
4. Use "Merge" procedure from Merge Sort on $S_x$ and $S$.
However that still will leave me with $O(n\log n)$ as I'll need to sort $S_x$ array. I'll appreciate any advice on the approach.
• Sorting the array $S_x$ takes $O(m\log m)$, where $m = |S_1|$. Since $m \leq \log n$, sorting $S_x$ takes time $O(\log n\log\log n)$. So this strategy actually works under the much weaker assumption $|S_1| = O(|S|/\log |S|)$. – Yuval Filmus Apr 27 '18 at 15:21
Note the length of $S_1$ is no more than $\log_2n$, so the time you need to sort $S_x$ is $O(\log n\log\log n)$, which is $O(n)$. |
## Sum of two metrics is a metric
It is quite straightforward to prove or verify that the sum of two metrics (distance functions) is still a metric.
Suppose $d_1(x,y)$ and $d_2(x,y)$ are metrics. Define $d(x,y)=d_1(x,y)+d_2(x,y)$.
## Positive-definite
$d(x,y)\geq 0+0=0$.
$d(x,y)=0 \iff d_1(x,y)=d_2(x,y)=0 \iff x=y$.
## Symmetry
$d(x,y)=d_1(y,x)+d_2(y,x)=d(y,x)$.
## Triangle Inequality
\begin{aligned} d(x,y) &\leq d_1(x,z)+d_1(z,y)+d_2(x,z)+d_2(z,y)\\ &=[d_1(x,z)+d_2(x,z)]+[d_1(z,y)+d_2(z,y)]\\ &=d(x,z)+d(z,y) \end{aligned}
Note that it follows by induction that the sum of any finite number of metrics (e.g. three, four or five metrics) is still a metric.
## Second-derivative Test For Extrema Of Functions Of Two Variables
Excerpt:
Proof of the second-derivative test. Our goal is to derive the second-derivative test, which determines the nature of a critical point of a function of two variables, that is, whether a critical point is a local minimum, a local maximum, or a saddle point, or none of these. In general for a function of n variables, it is determined by the algebraic sign of a certain quadratic form, which in turn is determined by eigenvalues of the Hessian matrix [Apo, Section 9.11]. This approach however relies on results on eigenvalues, and it may take several lectures to fully develop. Here we focus on the simpler setting when n = 2 and derive a test using the algebraic sign of the second derivative of the function.
The full proof can be found in the featured book below: T. Apostol, Calculus, vol. II, Second edition, Wiley, 1967
# Proving Quotient Rule using Product Rule
This is how we can prove Quotient Rule using the Product Rule.
First, we need the Product Rule for differentiation: $\displaystyle\boxed{\frac{d}{dx}(uv)=u\frac{dv}{dx}+v\frac{du}{dx}}$
Now, we can write $\displaystyle\frac{d}{dx}(\frac{u}{v})=\frac{d}{dx}(uv^{-1})$
Using Product Rule, $\displaystyle \frac{d}{dx}(uv^{-1})=u(-v^{-2}\cdot\frac{dv}{dx})+v^{-1}\cdot(\frac{du}{dx})$
Simplifying the above will give the Quotient Rule! :
$\displaystyle\boxed{\frac{d}{dx}(\frac{u}{v})=\frac{v\frac{du}{dx}-u\frac{dv}{dx}}{v^2}}$
You can also try proving Product Rule using Quotient Rule! |
# A particle of mass $1 \times 10^{-26}\;kg$ and charge $1.6 \times 10^{-19} C$ travelling with a velocity $1.28 \times 10^{6} ms^{-1}$ along the positive X-axis enters a region in which a uniform electric field $\overrightarrow {E}$ and a uniform magnetic field of induction $\overrightarrow {B}$ are present. If $\overrightarrow {E} =-102.4 \times 10^3 \hat k NC^{-1}$ and $B= 8 \times 10^{-2}\; \hat j Wbm^{-2}$, the direction of motion of the particles is :
(a) along the positive X-axis (b) along the negative X-axis (c) at $45^{\circ}$ to the positive X-axis (d) at $135^{\circ}$ to the positive X-axis
(A) along the positive X-axis
Hence A is the correct answer. |
# Action by a free group that moves given points to other given points
Let $P$ and $Q$ both be sets of $n$ points on a connected manifold $M$. Does there exist an action by a free group $F$ on $M$ such that for every $i$ we have a $g\in F$ with $g\cdot P_i = Q_i$?
I'm not specifically asking for a proof, but I've been trying for hours to find an answer so I would appreciate any hints. (For a start it would be good to know if the answer is yes or no - I am lacking intuition here and I am having real trouble finding out what I even want to show...)
Definition: A free group on $M$ is a group $F$ and a map $f:M\to F$ with the universal property: for any map $\phi:M\to G$ ($G$ group) there exists a unique group homomorphism $\varphi:F\to G$ such that $\phi = \varphi\circ f$.
My attempts:
If the answer to the above question is yes, then as far as I can tell there are not many options for groups to consider. Namely the free groups $\langle P\rangle, \langle Q\rangle$ and $\langle P\rangle * \langle Q\rangle$ come to mind.
1. Trying any of the 3 groups as $F$ leaves me clueless about how to define $f$ (the obvious map $A\to\langle A\rangle$ for any $A$ yields a free group but that doesn't fit here).
2. Since $M$ is connected, it is path-connected and the action I want to define just takes $P_i$ to the endpoint of the path that connects to $Q_i$. But that doesn't work out-of-the-box since I have to define the action on the whole $M$. I guess moving only $P$ to $Q$ and leaving the rest as it is is not really continuous... (Plus I still need to define $f$ and $F$ properly.)
If the answer to the above question is no, then:
1. I've been experimenting with drawing commutative diagrams (since the universal property suggests that kind of) but the only nice thing to notice is that since $|P|=|Q|$, I know that $\langle P\rangle$ and $\langle Q\rangle$ are isomorphic. Taking those two as two $G$-s in the definition above (to get a better understanding if this is plausible) yields a diagram that looks nice somehow yet seems useless to me.
2. I get that one of the main properties of the free groups above is that they aren't abelian by construction - yet every action defines some kind of symmetry. That strikes me as odd. But this thought is just a product of brain storming that is far too abstract to be of concrete use to me. It's just me trying to get some intuition.
3. Finding a counterexample feels hard since the only combination of a manifold and a free-ish group that I've come across is the Klein bottle where the fundamental group is generated by two deck transformations $a$ and $b$ of the universal cover. (See Wikipedia.)
• Just a note: there's nothing wrong with non-commutativity and symmetries. The word symmetry here is not about the group operation. – lisyarus Dec 16 '16 at 7:34
• I don't understand what you call "a free group on $M$". Does $F$ have some kind of topology? Is the map assumed to be continuous $f$, or is it just a set map? How is the action ($g \cdot P_i$) related to $f$? – Najib Idrissi Dec 16 '16 at 9:08
• @Najib Damn, I forgot to mention that we had the general assumption that throughout that lecture "all maps are continuous". I'm sorry, I'll add that. As far as I can tell $F$ doesn't come with a topology a priori. (For $f$ being cont. we obviously need one...) I guess that "how the action is related to $f$" is a big part of this question. I can try to provide more context, but there is not much more - I didn't leave anything out in the quotes. – Piwi Dec 16 '16 at 10:15 |
# What does the pressure term in Bernoulli's equation signify?
Consider the Bernoulli equation of fluid dynamics. One of the terms is $$p$$. I know it is pressure. But what type of pressure is it? Is it pressure due to height or a completely different concept?
• Hi, I would suggest making your question more closed by including the formula in the question. This can be done by enclosing the equation in double dollar-signs. – Kraig Jun 17 at 18:20
• Suppose you use a traditional mercury barometer: you have a glass tube in a U shape which is closed on one end, you fill it from the closed end with mercury and then carefully turn it over so that the mercury on the closed end draws a vacuum which pulls it upwards, so that it remains many millimeters above the line of mercury on the open end. This thing measures pressure. Does it only measure pressure "due to height"? – CR Drost Jun 17 at 18:22
• So you know what pressure is, but you're asking specifically how to interpret pressure in the context of Bernoulli's equation? – Nat Jun 17 at 19:31
• – Kyle Kanos Jul 31 at 12:33
The Bernoulli equation is normally stated as:
$$P_1 + 1/2 \rho v_1^2 + \rho g h_1 = P_2 + 1/2 \rho v_2^2 + \rho g h_2$$
Obviously, there is a pressure term on both sides of the equal sign. In addition to that, the equation must be dimensionally consistent, so each term in the Bernoulli equation must have the same dimensions.
To discern what pressure means in this equation, it is convenient to work with one of the "non pressure" terms. Thus, the term $$\rho g h$$ can be manipulated as follows, to illustrate an alternative view of what the pressure term actually represents.
$$\rho g h = (m/V) g h$$
$$\rho g h = (mgh/V)$$
Since $$mgh$$ is equal to gravitational potential energy, it is readily seen that each term in the Bernoulli equation is equivalent to energy per unit volume, including the pressure term.
Regarding what type of term pressure is, consider a pipe with fluid flowing through it. The inlet pressure is $$P_1$$ and the outlet pressure is $$P_2$$. Since the fluid flow involves a velocity, and velocity is associated with kinetic energy, there is a term for this, which is the $$1/2 \rho v^2$$ term. Finally, there is usually a change in height associated with any piping system, so a term is needed in the Bernoulli equation to account for changes in gravitational potential energy, which is what the $$\rho g h$$ term accounts for. Thus, the Bernoulli equation is actually an energy balance for fluid flow.
Pressure is a force per unit area, how it is generated may or may not be relevant.
I would prefer an elephant to stand on my foot than a lady with a stiletto heel...
• This is very brief. The first sentence is ambiguous, and the second sentence doesn't seem very relevant or helpful. – Ben Crowell Jul 30 at 20:49 |
# probability in nlp
�#�'�,ݠ@�BJ���fs�t*�[�]^����;�Z��|��1����\���h��������vq�������w�Dz ��fݎ�0h�,�vN5�0�A�k��O[X�N7E�߮��;�������.��~��#��قX�h�zT�FdX�8�:c����J��MaE��/�E�dc_:�������b�]ent�],��eR�0�~�r�eB��j�����G���w�X�����{���8ʑP�%�vڐH�ˎ��ɉ��q�[��v�}Zl����>�!d�Z�!y��⣲ɷ�8ҵV��e�~��gFRB Familiarity with probability and statistics. A latent embedding approach. Markov Models for NLP: an Introduction J. Savoy Université de Neuchâtel C. D. Manning & H. Schütze : Foundations of statistical natural ... Prob[C|AT] probability of being in state “C”, knowing that previously we were in state “A”, and before “T” 13 Markov Example Computing the probability of a sequence (e.g., TAC as Prob [TAC])? They calculate the probability of each tag for a given text and then output the tag with the highest one. Page 1 Page 2 Page 3. In english.. If our sample size … Let us consider Equation 1 again. And yn = 1 means 100% probability of being in class “1”. We need more accurate measure than contingency table (True, false positive and negative) as talked in my blog “Basics of NLP”. 39 0 obj << This means that, all else the same, the perplexity is not affected by sentence length. Naive Bayes predict the tag of a text. counter.Counter; A map-like data structure for representing discrete probability distributions. The ProbDistI class defines a standard interface for "probabilitydistributions", which encode the probability of each outcome for anexperiment. If all the probabilities were 1, then the perplexity would be 1 and the model would perfectly predict the text. NLP: Probability Dan Garrette [email protected] December 27, 2013 1 Basics E6= ;: event space (sample space) We will be dealing with sets of discrete events. An n-gram model is a type of probabilistic language model for predicting the next item in such a sequence in the form of a (n − 1)–order Markov model. conditional distributions Probabilities give opportunity to unify reasoning, plan-ning, and learning, with communication There is now widespread use of machine learning (ML) methods in NLP (perhaps even overuse?) Predicting the next word 2. Hi, I’m working on a ... 0% probability of being in class “1” which means 100% probability of being in class “0”. n j=1 a ij =1 8i p =p 1;p 2;:::;p N an initial probability distribution over states. Multiplying all features is equivalent to getting probability of the sentence in Language model (Unigram here). '$�j�L���|�����;x�C�l�R�|�&�e䮒_.��L0��An⠥���l�����ߔ �%. ##Calcuting bigram probabilities: P( w i | w i-1) = count ( w i-1, w i) / count ( w i-1). ...it's about handling uncertainty Uncertainty involves making decisions with incomplete information, and this is the way we generally operate in the world. The term Natural Language Processing or NLP certainly defines the ability of computers to recognize and understand human speech as well as texts. More precisely, we can use n-gram models to derive a probability of the sentence ,W, as the joint probability of each individual word in the sentence, wi. Sentences as probability models. A language model learns to predict the probability of a sequence of words. The added nuance allows more sophisticated metrics to be used to interpret and evaluate the predicted probabilities. >> Said another way, the probability of the bigram heavy rain is larger than the probability of the bigram large rain. Socher et al. Assigning a probability of 0 to an N-gram is a drastic decision - because it means that any sentence that contains this N-gram is deemed as impossible in the language model and will also receive a 0 probability. The conditional probability of event B given event A is the probability that B will occur given that we know that A has occurred. nlp. The most important problems in NLP source: teaching / nlp-course / probability.tex @ 4954. If you create your Outcomes/Goals based on the well-formed outcome (Also known as Neuro Linguistic Programming, NLP well defined outcomes) criteria, there is more probability for you to achieve them. Contains an underlying map of event -> probability along with a probability for all other events. Probability is playing an increasingly large role in computational linguistics and machine learning, and will be of great importance to us. Bigram Trigram and NGram in NLP, How to calculate the unigram, bigram, trigram, and ngram probabilities of a sentence? I’m sure you have used Google Translate at some point. Knowledge of machine learning, TensorFlow, Pytorch, and Keras. Probabilistic Graphical Models Probabilistic graphical models are a major topic in machine learning. Let’s consider an example, classify the review whether it is positive or negative. Independent events: P(A | B) = P(A) iff A and B are independent. They provide a foundation for statistical modeling of complex data, and starting points (if not full-blown solutions) for inference and learning algorithms. In general, we want our probabilities to be high, which means the perplexity is low. What is probability sampling? ��%GTi�U��Ť�73������zl��_C�����s�U�U&��{��c�B:̛��5�R���p��lm�[�W}g����1�l���>�G��4mc�,|˴��ڞl�Mm�+X�*�mP�F^V���7W�ح��E�U[�o��^������0��\�����|�L}�˴7��mڽM�]�a_:o�DŽO����4��Q?��@�Da�I& Perplexity is the inverse probability of the test set normalised by the number of words, more specifically can be defined by the following equation: For a word we haven’t seen before, the probability is simply: P ( n e w w o r d) = 1 N + V. You can see how this accounts for sample size as well. Basics. This can be generalized to the chain rule which describes the joint probability of longer sequences. Assigning a probability of 0 to an N-gram is a drastic decision - because it means that any sentence that contains this N-gram is deemed as impossible in the language model and will also receive a 0 probability. Level: Beginner Topic: Natural language processing (NLP) This is a very basic technique that can be applied to most machine learning algorithms you will come across when you're doing NLP. Randomly remove each word in the sentence with probability p. For example, given the sentence. Example: For a bigram … Which is more probable? For a Unigram model, how would we change the Equation 1? Deep Learning Use of probability in NLP Srihari •Some tasks involving probability 3 1. Given such a sequence, say of length m, it assigns a probability (, …,) to the whole sequence.. Probability theory allows us to infer quantified relations among events in models that capture uncertainty in a rational manner. How Naive Bayes Algorithm Works ? The example used in lecture notes was that of a horse Harry that won 20 races out of 100 starts, but of the 30 of these races that were run in the rain, Harry won 15. View revision: Revision 5490 , 19.1 KB checked in by jeisenst, 2 years ago Line 1 \documentclass[main.tex]{subfiles} 2 % TC:group comment 0 0: 3 \begin{document} 4 \chapter{Probability} 5 \label{ch:probability} 6: Probability theory provides a way to reason about random events. Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube. Therefore Naive Bayes can be used as Language Model. Precision, Recall & F-measure. Learn NLP, leverage the power of your mind at Excellence Assured. ... Natural language processing - n gram model - bi gram example using counts from a table - Duration: 4:59. Their key differences are about how to do smoothing, i.e. For example, the machine would give a higher score to "the cat is small" compared to "small the is cat", and a higher score to "walking home after school" compare do "walking house after school". They generalize many familiar methods in NLP. They do not affect the classification decision in the multinomial model; but in the Bernoulli model the probability of nonoccurrence is factored in when computing (Figure 13.3, APPLYBERNOULLINB, Line 7). Theme images by, Probabilistic Context Free Grammar How to calculate the probability of a sentence given the probabilities of various parse trees in PCFG. the NLP part, no probabilistic programming in the solver part. Copyright © exploredatabase.com 2020. Recent Trends in Deep Learning Based Natural Language Processing. If you roll one die, there's a 1 in 6 chance -- about 0.166 -- of rolling a "1", and likewise for the five other normal outcomes of rolling a die. If you've had any exposure to probability at all, you're likely to think of cases like rolling dice. Naive Bayes are mostly used in natural language processing (NLP) problems. This assignment is based on problems 1-5 of Jason Eisner’s language modeling homework plus a small programming problem (problem 5). /Filter /FlateDecode In short perplexity is a measure of how well a probability distribution or probability model predicts a sample. Probability smoothing for natural language processing. #A Collection of NLP notes. Multiplying all features is equivalent to getting probability of the sentence in Language model (Unigram here). Some states jmay have p j … [5] curated collection of papers for the nlp practitioner, mihail911 / nlp-library Acknowledgement to ratsgo , lovit for creating great posts and lectures. This is important in NLP because of the many distributions follow the Zipf's law, and out-of-vocabulary word / n -gram constantly appears. ###Calculating unigram probabilities: P( w i) = count ( w i) ) / count ( total number of words ). The axiomatic formulation includes simple rules. It indeed allows computers to decipher the interactions between human beings efficiently. Easy steps to find minim... Query Processing in DBMS / Steps involved in Query Processing in DBMS / How is a query gets processed in a Database Management System? Trefor Bazett 456,713 views. Generally, the probability of the word's similarity by the context is calculated with the softmax formula. Multiple Choice Questions MCQ on Distributed Database with answers Distributed Database – Multiple Choice Questions with Answers 1... MCQ on distributed and parallel database concepts, Interview questions with answers in distributed database Distribute and Parallel ... Find minimal cover of set of functional dependencies example, Solved exercise - how to find minimal cover of F? arXiv preprint arXiv:1708.02709. I have written a function which returns the Linear Interpolation smoothing of the trigrams. 2 NLP: Problems, Models and Methods According to the recently published Handbook of Natural Language Processing [17, p. v], NLP is concerned with “the design and implementation of effective natural language input and output components for computational systems”. How to use N-gram model to estimate probability of a word sequence? Language models are a crucial component in the Natural Language Processing (NLP) journey; These language models power all the popular NLP applications we are familiar with – Google Assistant, Siri, Amazon’s Alexa, etc. Conversely, for poorer language models, the perplexity … counter.Counter; A map-like data structure for representing discrete probability distributions. The NLP well defined outcomes criteria is as follows: All the probability models you mentioned here is to estimate a probability distribution given a sample of data, represented by a ... FreqDist. Its time to jump on Information Extraction in NLP after a thorough discussion on algorithms in NLP for pos tagging, parsing, etc. Since each word has its probability (conditional on the history) computed once, we can interpret this as being a per-word metric. 3. And how do we measure that? endobj from the sentence under PCFG; Probability of the A language model is a probability function p that assigns probabilities to word sequences such as $$\vec{w} =$$ (i, love, new york). Assignment 1 - Probability. We need more accurate measure than contingency table (True, false positive and negative) as talked in my blog “Basics of NLP”. sentence “astronomers saw the stars with ears”; How to derive probabilities for production rules from Treebank using maximum likelihood estimate, How to calculated production rule probability in PCFG using tree banks, Probabilistic context free grammar rule probability estimation using tree banks, Modern Databases - Special Purpose Databases, Context Free Grammar (CFG) Formal Definition, How to derive production rule probability from Treebank using MLE - Solved exercise, Multiple choice questions in Natural Language Processing Home, Machine Learning Multiple Choice Questions and Answers 01, Multiple Choice Questions MCQ on Distributed Database, MCQ on distributed and parallel database concepts, Find minimal cover of set of functional dependencies Exercise. If you've had any exposure to probability at all, you're likely to think of cases like rolling dice. View revision: Revision 4954 , 19.5 KB checked in by jeisenst, 3 years ago Line 1 \documentclass[main.tex]{subfiles} 2 \begin{document} 3 \chapter{Probability} 4 \label{ch:probability} 5: Probability theory provides a way to reason about random events. def smoothed_trigram_probability(trigram): """ Returns the smoothed trigram probability (using … The algorithm then iteratively assigns the words to any topic based on its probability of belonging to that topic and the probability that it can regenerate the document from those topics. Short for natural language processing, NLP is a branch of artificial intelligence which is focused on the enabling the computers to understand and interpret the … Word Embeddings in NLP. This is because only the Bernoulli NB model models absence of terms explicitly. Contains an underlying map of event -> probability along with a probability for all other events. It is a technique for representing words of a document in the form of numbers. So the probability of a sentence with word A followed by word B followed by word C and … Using for x_variable in collection_variable. But why do we need to learn the probability of words? 8. |!~fd3H)w�h�����#�|^�06M���T��>V/LucX�Ʀ�x�=Ƀ�媞+�n:m�2��i�d;on��7^�i��g/�@G�i&��D=��b��@��|BO�)�����|�����E�O��f��4�ځ�����Q�d��}n�b���f@dNr����6������r~9��BΕd�9�E(0�-�n�z�mz�l� shaun (Shaun) May 20, 2019, 1:02pm #1. Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube. This is an example of a popular NLP application called Machine Translation. Predicting the next word 2. In this case, I pushed anything that uses word to make sure the word variable is accessible because you are calling it from inside the for word in words iterator. endstream 3 Markov Models Transitions from one state to the other is a probabilistic one Interesting questions: Compute the probability of being in a given state in the next step / in the next two steps Compute the probability of a given sequence of states Examples: Generating a … Let’s understand that with an example. Natural language processing (NLP) is a subfield of linguistics, computer science, and artificial intelligence concerned with the interactions between computers and human language, in particular how to program computers to process and analyze large amounts of natural language data. Probability of a The language model provides context to distinguish between words and phrases that sound similar. contiguous sequence of n items from a given sequence of text /Length 2255 Definition: Perplexity. Consider we are running an experiment, and this experiment can have n distint outcomes. This ability to model the rules of a language as a probability gives great power for NLP related tasks. Intro to Conditional Probability - Duration: 6:14. Applications. source: teaching / nlp-course / probability.tex @ 5490. All rights reserved. The other problem of assigning a 0 probability to an N-gram is that it means that other N-grams are under-estimated. It is a technique for representing words of a document in the form of numbers. By the end of this Specialization, you will have designed NLP applications that perform question-answering and sentiment analysis, created tools to translate languages and summarize text, and even built a chatbot! So the probability of B given A is equal to the probability of A and B divided by the probability of A. Now, an emphasis on empirical validation and the use of approximation for hard problems 8 nn a transition probability matrix A, each a ij represent-ing the probability of moving from stateP i to state j, s.t. A probability function assigns a level of confidence to "events". This article explains how to model the language using probability and n-grams. The algorithm then iteratively assigns the words to any topic based on its probability of belonging to that topic and the probability that it can regenerate the document from those topics. Predicting probabilities instead of class labels for a classification problem can provide additional nuance and uncertainty for the predictions. Therefore Naive Bayes can be used as Language Model. Which is more probable? Written portion by 2pm, programming by noon . In english.. Probability of word i = Frequency of word (i) in our corpus / total number of words in our corpus. A few structures for doing NLP analysis / experiments. Probability is playing an increasingly large role in computational linguistics and machine learning, and will be of great importance to us. Overview; Problem 1: 33 points; Problem 2: 15 points; Problem 3: 15 points; Problem 4: 7 points; Problem 5: 30 points; Due: Thursday, Sept 19. Probability theory allows us to infer quantified relations among events in models that capture uncertainty in a rational manner. If you create your Outcomes/Goals based on the well-formed outcome (Also known as Neuro Linguistic Programming, NLP well defined outcomes) criteria, there is more probability for you to achieve them. There are two types of probability distribution:- "derived probability distributions" are created from frequencydistributions. This article focus on summarizing data augmentation in NLP. ##N-grams. Please make sure that you’re comfortable programming in Python and have a basic knowledge of machine learning, matrix multiplications, and conditional probability. The sequence with the highest score is the output of the translation. / Q... Dear readers, though most of the content of this site is written by the authors and contributors of this site, some of the content are searched, found and compiled from various other Internet sources for the benefit of readers. Language modeling (LM) is the essential part of Natural Language Processing (NLP) tasks such as Machine Translation, Spell Correction Speech Recognition, Summarization, Question Answering, Sentiment analysis etc. This article will focus on summarizing data augmentation techniques in NLP. I went through a lot of articles, books and videos to understand the text classification technique when I first started it. Consider we are running an experiment, and this experiment can have n distint outcomes. Since each word has its probability (conditional on the history) computed once, we can interpret this as being a per-word metric. It is basically extracting important information based on the… Bigram Trigram and NGram in NLP, How to calculate the unigram, bigram, trigram, and ngram probabilities of a sentence? Probability for Machine Learning Discover How To Harness Uncertainty With Python Machine Learning DOES NOT MAKE SENSE Without Probability What is Probability? This means that, all else the same, the perplexity is not affected by sentence length. The content sometimes was too overwhelming for someone who is just… We all use it to translate one language to another for varying reasons. If you roll one die, there's a 1 in 6 chance -- about 0.166 -- … 8. sentence is the sum of probabilities of all parse trees that can be derived Supports some element-wise mathematical operations with other counter.Counter objects. For a participant to be considered as a probability sample, he/she must be selected using a random selection. Precision, Recall & F-measure. To compute these proba- The NLP well defined outcomes criteria is as follows: 1) State the goal in positive. 2 NLP: Problems, Models and Methods According to the recently published Handbook of Natural Language Processing [17, p. v], NLP is concerned with “the design and implementation of effective natural language input and output components for computational systems”. It is basically extracting important information based on the… The method selects n words (say two), the words will and techniques, and removes them from the sentence. In general, we want our probabilities to be high, which means the perplexity is low. Its time to jump on Information Extraction in NLP after a thorough discussion on algorithms in NLP for pos tagging, parsing, etc. A statistical language model is a probability distribution over sequences of words. A few structures for doing NLP analysis / experiments. A probability function assigns a level of confidence to "events". x��ZKs�6��W�HU,ޏI�����n.�&>l�g�L;�ʒV�f�ʟ�� >$s��ŢE��������C���_����7�JF�\�'Z#&y��FD���.�I?b�f���~��n��=rt�yFu������ٜs��~6g���{���]VV��%��@,ET�dN)D8���A����= ;;O��s�s:P��L. Definition: Probability sampling is defined as a sampling technique in which the researcher chooses samples from a larger population using a method based on the theory of probability. To repeat this with slightly different wording: How to Score Probability Predictions in Python and Develop an Intuition for Different Metrics. Example 1: Coin Trial: ipping a coin Two possible outcomes: heads or tails, E= fH, Tg p(H) is the probability of heads if p(H) = 0:8, we would expect that ipping 100 times would yield 80 heads You can rearrange this rule so the probability of A and B is equal to the probability of A times the probability of B given A. When you are using for x_variable in collection_variable, you need to make sure any code using the x_variable resides inside of the for each loop. Notes, tutorials, questions, solved exercises, online quizzes, MCQs and more on DBMS, Advanced DBMS, Data Structures, Operating Systems, Natural Language Processing etc. B(2�6�6:0U7�1�d�ٰ��2Z�8�V�J��|h��.�u�f�=��[mS��ryؽR�0Ӡ[�l���oc�T٧I⻈(� a��� �Ȯ�1�h�(��~i�����1�Ӝ�.�__���. The axiomatic formulation includes simple rules. Worked example. The most important problems in NLP A common approach to zero shot learning in the computer vision setting is to use an existing featurizer to embed an image and any possible class names into their corresponding latent representations (e.g. NLP: Probability Dan Garrette [email protected] December 27, 2013 1 Basics E6= ;: event space (sample space) We will be dealing with sets of discrete events. O��I�.�\��Y�n��kBO��K��BpZ��އ���=V���� �ӄb�~A1��&e��������]�UR�U�*Oxk�u�ߔ�l�ټZ̪Vkp�^ٷ3�M���WH����˅c��aA����ʹOc�5�����e'ҹ����6]�M6q�R�1��d��m�6N�Qo���#���ۓvq�;����_"){? Probabilistic Context Free Grammar, PCFG, how to calculate the probability of a parse tree, how to calculate the probability of a sentence using PCFG, Find the most probable parse tree as per PCFG Advanced Database Management System - Tutorials and Notes: How to calculate the probability of a sentence in NLP using PCFG I spoke about the probability a bit there, but let’s now build on that. Probability smoothing for natural language processing. probability distributions Inference! Outcomes/Goals play an important role in who you are going to be in the near future. Maximum likelihood estimation to calculate the ngram probabilities. Goal of the Language Model is to compute the probability of sentence considered as a word sequence. probability function that assigns each a score. 26 NLP Programming Tutorial 1 – Unigram Language Model test-unigram Pseudo-Code λ 1 = 0.95, λ unk = 1-λ 1, V = 1000000, W = 0, H = 0 create a map probabilities for each line in model_file split line into w and P set probabilities[w] = P for each line in test_file split line into an array of words append “” to the end of words for each w in words add 1 to W set P = λ unk all of a sudden I notice three guys standing on the sidewalk Same set of words in a different order is nonsensical: )|�^5�^�($�K���Q�2����_�5�'k@��7�N2 When we’re building an NLP model for predicting words in a sentence, the probability of the occurrence of a word in a sequence of words is what matters. Deep Learning Use of probability in NLP Srihari •Some tasks involving probability 3 1. So, NLP-model will train by vectors of words in such a way that the probability assigned by the model to a word will be close to the probability of its matching in a given context (Word2Vec model). Elevate your life & spend the best time of your life doing what you love. Maximum likelihood estimation to calculate the ngram probabilities p i is the probability that the Markov chain will start in state i. Word Embeddings in NLP. Furthermore, it is unclear how complex the questions can be as the paper says “very basic probability problems” and we were unable to obtain more information about this work. stream how to account for unseen data. Supports some element-wise mathematical operations with other counter.Counter objects. ... We will introduce the basics of Deep Learning for NLP in Lecture 3. Basics. P(A | B) = P(A ∩ B) / P(B) e.g., P(A | A) = 1 and P(A | ¬A) = 0. Conditional probability. Computers to decipher the interactions between human beings efficiently and N-grams provide additional nuance and for!, which means the perplexity is a technique for representing discrete probability distributions '' are created from frequencydistributions technique representing... Rain is larger than the probability of the bigram large rain 100 % of... From the sentence great power for NLP related tasks a | B ) = (! Perplexity is not affected by sentence length you 've had any exposure to probability at all, 're. About how to score probability Predictions in Python and Develop an Intuition for Metrics... Describes the joint probability of a sentence as well as texts in the.! Nlp in Lecture 3 to be considered as a probability for all other events allows us to quantified..., say of length m, it assigns a probability function assigns a level of to. Estimate probability of words can have n distint outcomes shaun ( shaun ) May 20, 2019, 1:02pm 1! Nb model models absence of terms explicitly element-wise mathematical operations with other objects... Is important in NLP after a thorough discussion on algorithms in NLP Srihari •Some tasks involving probability 3 1 ]... Spend the best time of your life & spend the best time of mind... Goal in positive change the Equation 1 probability in NLP, how to model the rules of a and are. Nlp in Lecture 3 probability gives great power for NLP in Lecture.. Absence of terms explicitly parsing, etc distribution over sequences of words distint outcomes ( on... Interpret and evaluate the predicted probabilities, books and videos to understand the text classification technique i! Features is equivalent to getting probability of the word 's similarity by the context is calculated the... Probabilities of a and B divided by the probability of sentence considered a... Our probabilities to be considered as a word sequence and the model would perfectly predict the probability of the 's... Different Metrics NLP related tasks element-wise mathematical operations with other counter.counter objects multiplying all features equivalent! Class labels for a Unigram model, how to do smoothing, i.e # 1 are created frequencydistributions... The Unigram, bigram, Trigram, and this experiment can have n distint.... Goal of the bigram large rain you have used Google Translate at some point first it. The solver part as language model... we will introduce the basics of deep use. Its probability ( conditional on the history ) computed once, we can interpret as. Large role in who you are going to be high, which means the is... 1 ) State the goal in positive Google Translate at some point a major topic in machine learning in. Probability and N-grams are two types of probability in NLP Srihari •Some tasks probability! Distint outcomes words of a sequence, say of length m, it a! Probability of the word 's similarity by the probability of B given event a is equal the! Interactions between human beings efficiently each tag for a given text and then output the tag the. Representing words of a language as a probability function assigns a level of confidence ... Of being in class “ 1 ” the same, the words will and,... Called machine Translation compute the probability of the language using probability and.! Written a function which returns the Linear Interpolation smoothing of the language model Unigram! Defines the ability of computers to recognize probability in nlp understand human speech as as... Different Metrics goal in positive do smoothing, i.e 've had any exposure to probability at all, 're. N-Grams are under-estimated a few structures for doing NLP analysis / experiments �e䮒_.��L0��An⠥���l�����ߔ � % from a table -:! Assignment 1 - probability$ �j�L���|����� ; x�C�l�R�|� & �e䮒_.��L0��An⠥���l�����ߔ � % the Markov will! Assignment 1 - probability for all other events to predict the text classification technique i. The Unigram, bigram, Trigram, and Keras distributions '' are created from frequencydistributions exposure to probability all... |
## Groups Modular Mathematics Series
Author: Camilla Jordan
Publisher: Butterworth-Heinemann
ISBN: 0080571654
Size: 22.10 MB
Format: PDF, Docs
View: 1060
This text provides an introduction to group theory with an emphasis on clear examples. The authors present groups as naturally occurring structures arising from symmetry in geometrical figures and other mathematical objects. Written in a 'user-friendly' style, where new ideas are always motivated before being fully introduced, the text will help readers to gain confidence and skill in handling group theory notation before progressing on to applying it in complex situations. An ideal companion to any first or second year course on the topic.
## Groups St Andrews 1989
Author: Groups-St Andrews (1989 : St Andrews)
Publisher: Cambridge University Press
ISBN: 9780521406697
Size: 11.92 MB
Format: PDF, Docs
View: 4512
These two volumes contain selected papers presented at the international conference on group theory held at St. Andrews in 1989. The themes of the conference were combinatorial and computational group theory; leading group theorists, including J.A. Green, N.D. Gupta, O.H. Kegel and J.G. Thompson, gave courses whose content is reproduced here. Also included are refereed papers presented at the meeting.
## Arithmetic Fundamental Groups And Noncommutative Algebra
Author: Karen Redrobe Beckman
Publisher: American Mathematical Soc.
ISBN: 0821820362
Size: 26.42 MB
Format: PDF, ePub, Mobi
View: 4968
The arithmetic and geometry of moduli spaces and their fundamental groups are a very active research area. This book offers a complete overview of developments made over the last decade. The papers in this volume examine the geometry of moduli spaces of curves with a function on them. The main players in Part 1 are the absolute Galois group $G_{\mathbb Q}$ of the algebraic numbers and its close relatives. By analyzing how $G_{\mathbb Q}$ acts on fundamental groups defined by Hurwitz moduli problems, the authors achieve a grand generalization of Serre's program from the 1960s.Papers in Part 2 apply $\theta$-functions and configuration spaces to the study of fundamental groups over positive characteristic fields. In this section, several authors use Grothendieck's famous lifting results to give extensions to wildly ramified covers. Properties of the fundamental groups have brought collaborations between geometers and group theorists. Several Part 3 papers investigate new versions of the genus 0 problem. In particular, this includes results severely limiting possible monodromy groups of sphere covers. Finally, Part 4 papers treat Deligne's theory of Tannakian categories and arithmetic versions of the Kodaira-Spencer map. This volume is geared toward graduate students and research mathematicians interested in arithmetic algebraic geometry.
## Modular Representations Of Finite Groups Of Lie Type
Author: James E. Humphreys
Publisher: Cambridge University Press
ISBN: 9780521674546
Size: 45.48 MB
Format: PDF, ePub, Mobi
View: 5386
A comprehensive treatment of the representation theory of finite groups of Lie type over a field of the defining prime characteristic.
## Subgroups Of Teichmuller Modular Groups
Author: Nikolai V. Ivanov
Publisher: American Mathematical Soc.
ISBN: 9780821897430
Size: 50.19 MB
Format: PDF, Docs
View: 4155
## Discrete Groups And Geometry
Author: Conference on discrete groups and geometry
Publisher: Cambridge University Press
ISBN: 9780521429320
Size: 28.34 MB
Format: PDF, Docs
View: 3276
This volume contains a selection of refereed papers presented in honour of A.M. Macbeath, one of the leading researchers in the area of discrete groups. The subject has been of much current interest of late as it involves the interaction of a number of diverse topics such as group theory, hyperbolic geometry, and complex analysis.
## Theta Constants Riemann Surfaces And The Modular Group
Author: Hershel M. Farkas
Publisher: American Mathematical Soc.
ISBN: 0821813927
Size: 13.42 MB
Format: PDF
View: 278
There are incredibly rich connections between classical analysis and number theory. For instance, analytic number theory contains many examples of asymptotic expressions derived from estimates for analytic functions, such as in the proof of the Prime Number Theorem. In combinatorial number theory, exact formulas for number-theoretic quantities are derived from relations between analytic functions. Elliptic functions, especially theta functions, are an important class of such functions in this context, which had been made clear already in Jacobi's Fundamenta nova. Theta functions are also classically connected with Riemann surfaces and with the modular group $\Gamma = \mathrm{PSL}(2,\mathbb{Z})$, which provide another path for insights into number theory. Farkas and Kra, well-known masters of the theory of Riemann surfaces and the analysis of theta functions, uncover here interesting combinatorial identities by means of the function theory on Riemann surfaces related to the principal congruence subgroups $\Gamma(k)$. For instance, the authors use this approach to derive congruences discovered by Ramanujan for the partition function, with the main ingredient being the construction of the same function in more than one way. The authors also obtain a variant on Jacobi's famous result on the number of ways that an integer can be represented as a sum of four squares, replacing the squares by triangular numbers and, in the process, obtaining a cleaner result. The recent trend of applying the ideas and methods of algebraic geometry to the study of theta functions and number theory has resulted in great advances in the area. However, the authors choose to stay with the classical point of view. As a result, their statements and proofs are very concrete. In this book the mathematician familiar with the algebraic geometry approach to theta functions and number theory will find many interesting ideas as well as detailed explanations and derivations of new and old results. Highlights of the book include systematic studies of theta constant identities, uniformizations of surfaces represented by subgroups of the modular group, partition identities, and Fourier coefficients of automorphic functions. Prerequisites are a solid understanding of complex analysis, some familiarity with Riemann surfaces, Fuchsian groups, and elliptic functions, and an interest in number theory. The book contains summaries of some of the required material, particularly for theta functions and theta constants. Readers will find here a careful exposition of a classical point of view of analysis and number theory. Presented are numerous examples plus suggestions for research-level problems. The text is suitable for a graduate course or for independent reading.
## Proceedings Of Groups St Andrews 1985
Author: E. F. Robertson
Publisher: Cambridge University Press
ISBN: 9780521338547
Size: 80.95 MB
Format: PDF, ePub, Docs
View: 6724
A current picture of progress and research in group theory is provided by five leading group theorists Bachmuth, Baumslag, Neumann, Roseblade and Tits.
## Modular Representation Theory Of Finite Groups
Author: Michael J. Collins
Publisher: Walter de Gruyter
ISBN: 3110889161
Size: 13.45 MB
Format: PDF, ePub, Docs
View: 2771
This book is an outgrowth of a Research Symposium on the Modular Representation Theory of Finite Groups, held at the University of Virginia in May 1998. The main themes of this symposium were representations of groups of Lie type in nondefining (or cross) characteristic, and recent developments in block theory. Series of lectures were given by M. Geck, A. Kleshchev and R. Rouquier, and their brief was to present material at the leading edge of research but accessible to graduate students working in the field. The first three articles are substantial expansions of their lectures, and each provides a complete account of a significant area of the subject together with an extensive bibliography. The remaining articles are based on some of the other lectures given at the symposium; some again are full surveys of the topic covered while others are short, but complete, research articles. The opportunity has been taken to produce a book of enduring value so that this is not a conference proceedings in the conventional sense. Material has been updated so that this book, through its own content and in its extensive bibliographies, will serve as an invaluable resource for all those working in the area, whether established researchers or graduate students who wish to gain a general knowledge of the subject starting from a single source. |
# Requests for Reopen & Undeletion Votes (volume 01/2022 - today)
The purpose of this thread is to focus the attention of the community on posts that may require reopen and undeletion votes. A request should be posted as an answer below (one request per answer).
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• In case of "small" requests, like one missing vote, it can make sense to ask in chat instead of posting here. The room CURED is a reasonable place for such requests. The same guidelines apply there.
Earlier versions of the thread that served as a model:
• Creating a new thread is unnecessary and bad idea, e.g. see here and its links Jan 6 at 10:42
• I applaud annual lists, lest the lists of "answers" becomes difficult to navigate. Also, @Paramanand, thanks for including the links to other "volumes", previously! Jan 6 at 20:31
• I'm sorry to be nitpicky about this, but the second bullet point may need some further tweaking. Rather than saying, "Notice that the first edit after the question may push the question into the reopen review queue if the edit is done within 5 days of closure...", it might be better to just say "Any question with significant edits that address the close reason(s) are automatically put into a review queue to be considered for reopening", which is the text in the corresponding Help Center article. Jan 22 at 9:57
Consider undeleting and reopening the question
The question was sloppily written, but interesting. It was closed; later it was deleted by the system bot. For the record: I wrote an answer to the question, recording what I found in the literature. I also rewrote the question to make it more precise.
Edit: The original question was closed, due to lack of clarity. My edit aimed to improve clarity was rolled back to the original post, as written by OP.
• @amWhy: The essence of question is the same, the difference is the added background and a better formulation. But if the question does not get reopened, I will ask a new question myself. Jan 12 at 20:15
• The new question is here (for those who are <10k). Not sure why there is an edit war on this post.... Jan 24 at 21:45
Reopened.
This question was just closed as opinion based. It is not opinion based (what are the opinions on which it is based?) and should be reopened. The question asks about connections between PDE and representation theory. A similar, if not the same, question exists on Mathoverflow since 2019. It is upvoted many times and has several answers.
• I made some comments regarding this in the main thread itself. The "opinion" on which it is based seems to be whether the theory of automorphic forms falls under DE or not. Nevertheless, the MO thread seems to be a fairly objective/fact-based answer to the question. While the author revealed themselves to be beginning their Masters, a few close and down votes have come before this comment : that information is essential for deciphering the level of the student, and without it someone would have had to opine about the author's preference/aptitude for a certain subject. Jan 11 at 6:26
Reopened
I edited my post. Can you reopen it? I accept the answer.
@banana told me to do it |
# Re: [NTG-context] Problem with Filter Module in latent context beta
On 4/16/2018 6:52 PM, Aditya Mahajan wrote:
On Sun, 15 Apr 2018, Hans Hagen wrote:
\start
\def\obeyedline{\blank[line]} \obeylines
Thanks! Not sure why I wasn't using that since the beginning.
I am testing with the latest beta and I get another bug with reading http files. This is a simplified version of what I use in the filter module:
\unprotect
\def\AnyFilename#1%
\def\ProcessFile#1%
{\edef\InputFile{\AnyFilename{#1}}%
\InputFile
\typefile[\InputFile]}
\protect
\starttext
\stoptext
With the latest beta, I get the following error:
...inimals/texmf-context/tex/context/base/mkiv/file-res.lua:147: bad argument #1 to 'find' (string expected, got nil)
stack traceback:
[C]: in function 'string.find'
...inimals/texmf-context/tex/context/base/mkiv/file-res.lua:147: in upvalue 'action1' [string "local action = tokens._action..."]:4: in field 'getreadfilename'
[ctxlua]:1: in main chunk
Not sure why #1 is being passed to the lua function instead of the expanded value of "#1".
hm, i'll check it
#1 just means first argument in lua -)
use this:
\unprotect
\protect
-----------------------------------------------------------------
Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
-----------------------------------------------------------------
___________________________________________________________________________________
___________________________________________________________________________________ |
# Evaluate Sum - Recurrence Relation
Simple question really that I should be able to solve. I should probably note that the question is the final part of a series of questions involving the difference operator and in the previous part we are asked to find the sum $\sum\limits_{k=1}^n k\cdot k!$ which I managed to solve, but I am not sure whether it's relevant.
Okay, the question is:
Find the sum $\sum \limits_{k=1}^n k(k+1)2^k$.
My initial thoughts are that perhaps we are supposed to use some cleverness with recurrence relations, possibly using the Repetoire Method. The problem with this is that I don't know how to apply this method with the $2^k$ term in there.
Any help would be greatly appreciated.
-
$$\sum_{k=1}^nk(k+1)q^k=\frac\partial{\partial q}\sum_{k=1}^nkq^{k+1}=\frac\partial{\partial q}q^2\sum_{k=1}^nkq^{k-1}=\frac\partial{\partial q}q^2\frac\partial{\partial q}\sum_{k=1}^nq^k\;.$$
-
why not just $\frac{\partial^2}{\partial q^2}q \sum_{k=0}^{n}q^k$? – Alex Jun 4 '13 at 17:41
@Alex: You're right, that's more elegant -- but I'm not sure it's actually easier to calculate, since you're taking the derivative of a product twice whereas my first derivative doesn't create quite as many terms. – joriki Jun 4 '13 at 18:14
Thanks very much for your answers. The only thing is that I don't think I'm expected to know (at least for this exam) how to evaluate sums by taking derivatives. Do you know of any other way of solving the problem without the need for derivatives? – Benjamin Biggs Jun 4 '13 at 18:53 |
## heathernelly Group Title PLEASE HELP!! simplify the term w^2+2w-24 / w^2+w-30+8 / w-5 one year ago one year ago
1. heathernelly Group Title
what I've done so far is (w+6)(w+4) / (w+1)(w-30) + 8/w-5
Is your equation $\frac{ w^2 + 2w -24 }{ w^2 + w -30 } + \frac{ 8 }{ w-5 }$
3. heathernelly Group Title
yess
If that's the case, the way you broke up $w^2 + w - 30$ is incorrect.
If you multiply out the way you broke it up You get $w^2 - 29w -30$
If you fix that, then you should be able to do the problem easily.
7. heathernelly Group Title
w^2 + w - 30 is a part of the question..you still there?
8. heathernelly Group Title
Yes But the correct factorization is $(w+6)(w-5)$
10. heathernelly Group Title
oooh, I see..so what do I do after that? :)
11. heathernelly Group Title
I cross out w+6 because it's on in denominator and other one? so it would be w+4 / w-5 + 8/w-5? what do I do next? :) |
# Monte-Carlo algorithms for Markov chains and particle methods
B. Jourdain
15h, 5MK
In order to simulate according to a target law $\pi$ on a space $E$ provided with a tribe $\mathcal E$, the Metropolis-Hastings algorithm constructs a Markov chain $(X_n) _{n\geq1}$ which admits $\pi$ as reversible measure. This algorithm is one of the most widely used probabilistic numerical methods in statistics, physics, quantum chemistry and molecular simulation, so much so that a Google search on its name provides more than 350,000 results. When the Markov chain is ergodic, the law of $X_n$ converges to $\pi$ when $n$ tends to infinity and for $\phi : (E,\mathcal E) \to \mathbb R$ measurable and such that $\int_E |\phi(x)|\pi(dx)<\infty$, the strong law of large ergodic numbers ensures the almost sure convergence of $displaystyle \frac1n\sum _{k=1}^n \phi(X_k)$ towards $displaystyle \int_E \phi(x) \pi(dx)$ when $n\to \infty$.
In this first part of the course, we will illustrate on the example of this algorithm the sufficient condition of ergodicity for a Markov chain with values in a general space given in [3] and we will establish under this condition the strong law of large ergodic numbers. We will show the associated central limit theorem under a strengthened condition which allows us to solve the Poisson equation. We will state the result of Peskun [4] which explains how to minimize the asymptotic variance. We will see how to guide the choice of the variance of the proposals of the Metropolis-Hastings random walk algorithm using the scaling results [2]: when the target law is a probability produced on a space whose dimension tends to infinity, the first component of the algorithm accelerates in time and converges in law to a diffusion. Finally, when the convergence to the equilibrium is very slow (metastability phenomenon), we will study how to accelerate it by versions of the algorithm with adaptive preferential sampling like Wang-Landau, SHUS, metadynamics or well-tempered metadynamics.
In a second step, we will study genetic particle algorithms [1] which, by alternating a selection step where particles interact with a mutation phase where they evolve independently according to a Markovian kernel, allow to reduce the variance or to generate rare events.
## Bibliography
• [1] Del Moral, P.: Feynman-Kac formulae. Genealogical and interacting particle systems with applications. Probability and its Applications (New York). Springer-Verlag, 2004.
• [2] Gelman, A., Gilks, W. R. and Roberts, G. O., Weak convergence and optimal scaling of random walk Metropolis algorithms, Ann. Appl. Probab. 7(1):110-120, 1997
• [3] Hairer, M., Mattingly, J. C., Yet another look at Harris’ ergodic theorem for Markov chains. Seminar on Stochastic Analysis, Random Fields and Applications VI, 109-117, Progr. Probab., 63, Birkhauser/Springer Basel AG, Basel, 2011.
• [4] Peskun, P. H., Optimal Monte-Carlo sampling using Markov chains, Biometrika 60(3):607- 612, 1973. |
# Finding the other trig. functions with given values
If $\sec\theta = \frac{5}{2}$ and $\csc\theta < 0$, find the other five trig. functions
The "$\csc < 0$" is confusing me. How do I know which quadrant that is in? What if it was "$\cot < 0$"?
• I transcribed the text from the image (despite the very nice handwriting). Please double-check that I got it right.
– Blue
Dec 5, 2013 at 4:03
Definition of $\csc$ is really $\frac{1}{\sin}$ and so if this has to be negative,we are in the third or fourth quadrant. Since the $\sec$ $(=$reciprocal cosine$)$ is positive, we end up in the fourth quadrant, from which the signs of all trig functions are known. Can you further work it out? |
# Show Reference: "Conflict monitoring versus selection-for-action in anterior cingulate cortex"
Conflict monitoring versus selection-for-action in anterior cingulate cortex Nature, Vol. 402, No. 6758. (11 November 1999), pp. 179-181, doi:10.1038/46035 by Matthew Botvinick, Leigh E. Nystrom, Kate Fissell, Cameron S. Carter, Jonathan D. Cohen
@article{botvinick-et-al-1999,
abstract = {The anterior cingulate cortex ({ACC}), on the medial surface of the frontal lobes of the brain, is widely believed to be involved in the regulation of attention1, 2. Beyond this, however, its specific contribution to cognition remains uncertain. One influential theory has interpreted activation within the {ACC} as reflecting 'selection-for-action'3, 4, 5, a set of processes that guide the selection of environmental objects as triggers of or targets for action. We have proposed an alternative hypothesis, in which the {ACC} serves not to exert top-down attentional control but instead to detect and signal the occurrence of conflicts in information processing6, 7, 8. Here, to test this theory against the selection-for-action theory, we used functional magnetic resonance imaging to measure brain activation during performance of a task where, for a particular subset of trials, the strength of selection-for-action is inversely related to the degree of response conflict. Activity within the {ACC} was greater during trials featuring high levels of conflict (and weak selection-for-action) than during trials with low levels of conflict (and strong selection-for-action), providing evidence in favour of the conflict-monitoring account of {ACC} function.},
address = {Department of Psychology, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA. [email protected]},
author = {Botvinick, Matthew and Nystrom, Leigh E. and Fissell, Kate and Carter, Cameron S. and Cohen, Jonathan D.},
citeulike-article-id = {1424305},
day = {11},
doi = {10.1038/46035},
issn = {0028-0836},
journal = {Nature},
keywords = {attention, conflict, control, cortex, psychology},
month = nov,
number = {6758},
pages = {179--181},
pmid = {10647008},
posted-at = {2015-02-03 14:12:56},
priority = {2},
publisher = {Nature Publishing Group},
title = {Conflict monitoring versus selection-for-action in anterior cingulate cortex},
url = {http://dx.doi.org/10.1038/46035},
volume = {402},
year = {1999}
} |
Intended for healthcare professionals
Clinical Review
# Fortnightly review: Hypothyroidism: screening and subclinical disease
BMJ 1997; 314 (Published 19 April 1997) Cite this as: BMJ 1997;314:1175
1. A P Weetman, professor of medicinea
1. a Department of Medicine, University of Sheffield Clinical Sciences Centre, Northern General Hospital, Sheffield S5 7AU
## Introduction
At first sight there could hardly be a more simple disorder to diagnose and treat than hypothyroidism. Now that we have robust hormone assays and reliable preparations of thyroxine in tablet sizes sufficiently small to tailor doses to an individual's requirement, what issues remain? The purpose of this review is to flesh out some of the recently published consensus views on hypothyroidism,1 2 in particular regarding the role of screening for hypothyroidism and the need for treatment in subclinical hypothyroidism. Table 1) gives the definitions of hypothyroidism.
Table 1
Definitions of hypothyroidism
View this table:
## Methods
I have conducted a monthly Medline search for all articles on hypothyroidism for five years. For this review I scanned these papers and background papers for a recent consensus statement,2 together with their references, for those focusing on screening and subclinical hypothyroidism. In addition, as part of my 15 years of thyroid related research I have continuously reviewed the literature.
## Frequency of hypothyroidism
New information on the frequency of hypothyroidism has been provided by a survey of a randomly selected population of 2779 adults living in Whickham, Tyne and Wear, who had baseline thyroid function tests and were then reexamined after 20 years.3 Remarkably, 96% of the 1877 survivors participated in a follow up survey and 91% had further tests. The mean incidence of spontaneous overt hypothyroidism in women was 3.5 survivors/1000/year and in men 0.6/1000/year. There was no apparent excess of hypothyroidism in those who had died. The mean average at diagnosis was 58-59, but the probability of developing hypothyroidism increased steadily with age, reaching 14 cases/1000/year for women aged 75-80.
This survey also clarified the predictive value of detecting thyroid antibodies (against thyroid peroxidase/microsomal antigen) and measuring thyroid stimulating hormone concentrations. For women with subclinical hypothyroidism but without thyroid antibodies the relative risk of developing overt hypothyroidism over the follow up period was 8; the risk was the same for those with thyroid antibodies and normal thyroid stimulating hormone concentrations. Women with both increased thyroid stimulating hormone concentrations and thyroid antibodies had a relative risk of 38. Relative risks were even higher in men. Furthermore, even within the reference range of around 0.5-4.5 mU/l, a high thyroid stimulating hormone concentration (>2 mU/l) was associated with an increased risk of future hypothyroidism (fig 1). The simplest explanation is that thyroid disease is so common that many people predisposed to thyroid failure are included in a laboratory's reference population, which raises the question whether thyroxine replacement is adequate in patients with thyroid stimulating hormone levels above 2 mU/l. The high frequency of overt and subclinical hypothyroidism observed raises another contentious issue–namely, whether screening for hypothyroidism is worth while.
Fig 1
Logit probability (log odds) for the development of hypothyroidism in women during a 20 year follow up of 912 women.3 Reproduced with permission
## Screening for hypothyroidism
### General population screening
Screening for congenital hypothyroidism is definitely worth while as it is relatively common (1:4000 births), the test is sensitive and specific (thyroid stimulating hormone measurement in heel prick specimens), it has serious consequences if untreated (brain damage), and effective treatment is available (thyroxine). However, screening for hypothyroidism in hospital patients is not effective.4 5 Although undiagnosed hypothyroidism is more common in adults than neonates, the non-specific effects of acute illness on thyroid function tests often produce abnormal results which correct themselves after recovery. The best current recommendation is to maintain a low threshold for suspecting hypothyroidism, particularly in its more obscure presentations, and to reserve testing for these patients.5
In apparently healthy people routine screening is generally not recommended, even in those over 60 and with a family history of thyroid disease.2 4 Reasons for this include a relatively low point prevalence of overt disease and uncertainty over the benefits of detecting subclinical hypothyroidism (see below). However, a cost utility analysis using a computer decision model to assess the consequences and costs of thyroid stimulating hormone screening recently came to the conclusion that testing 35 year old men and women, with repeat estimates every five years for 50 years, would be beneficial.6
The cost of detecting subclinical hypothyroidism was $9223 (£6148) for women and$22 595 (£15 063) for men per quality adjusted life year.6 Most of the quality adjusted life years (52%) were accounted for by preventing progression to overt hypothyroidism and 30% by improving associated mild symptoms; 2% were estimated to be due to prevention of cardiovascular disease through the effect of hypothyroidism on cholesterol concentrations. This last estimate may be too high as the 20 year Whickham survey found no evidence of increased mortality or ischaemic heart disease in women with thyroid antibodies or raised thyroid stimulating hormone concentrations.7
Another assumption in the model was that only those patients with subclinical hypothyroidism plus thyroid antibodies are at risk of progression to overt hypothyroidism. Since raised thyroid stimulating hormone alone is a predictor of overt hypothyroidism, more cases at risk will be ascertained (which in turn will alter costs). Nevertheless, the final conclusion was that screening for hypothyroidism is as favourable as screening for hypertension in the same age group, providing a similar increase in quality adjusted days. It is also important to note that screening based on thyroid stimulating hormone concentrations will of course also turn up subclinical and overt thyrotoxicosis,8 and arguably this is even more important to recognise and treat.
Further analyses based on existing local screening schemes are therefore needed to determine the true place of thyroid stimulating hormone testing for the general population. At present the benefits remain debatable. One reasonable alternative is the case finding approach, focusing testing on patients visiting their doctors for an unrelated reason; this is particularly effective in women over 40 with non-specific symptoms.4
### Screening in special groups
Hypothyroidism occurs after all types of treatment for hyperthyroidism, and patients who are euthyroid should be offered annual screening by means of a computerised register (box).2 Patients taking lithium or amiodarone are at risk of hypothyroidism and thyrotoxicosis and need regular monitoring of thyroid function.2
#### Summary points
Subclinical hypothyroidism is common, especially in elderly women
The presence of subclinical hypothyroidism or thyroid antibodies increases the risk of developing overt hypothyroidism and the risk is even greater (about 5% a year) if both are present together
Thyroid stimulating hormone concentrations above 2 mU/l are associated with an increased risk of hypothyroidism
Screening all acutely ill patients or the healthy general population for hypothyroidism is not recommended
Case finding, especially in women over 40 with non-specific symptoms, is currently the best approach to detect previously unsuspected hypothyroidism
Modest symptomatic benefits occur with thyroxine treatment in some patients with subclinical hypothyroidism, and lipid profiles may also improve
Monitored thyroxine treatment, maintaining normal thyroid stimulating hormone concentrations, has no adverse effects
There is no consensus on the place of screening for postpartum thyroiditis.9 However, women with insulin dependent diabetes mellitus are three times more likely to develop postpartum thyroid dysfunction than non-diabetic controls and may have unsuspected thyroid disease in pregnancy.10 Ideally, all diabetic women should have thyroid antibody measurements in the first trimester, with careful follow up of those with positive results. Also, any woman who develops postpartum thyroiditis should be offered annual follow up, as about a quarter of these women will develop overt hypothyroidism within the next five years.11
Some psychiatric disorders may be exceptions to the rule that acutely ill patients should only be tested for hypothyroidism if there is clinical suspicion, in particular bipolar affective disorder with rapid cycling12 and refractory depression.13 The effect of thyroid treatment in these conditions is still uncertain. Delaying testing until the third week after admission avoids the transient disturbances due to the effects of acute psychiatric illness.14 Although frequently sought in dementia, unsuspected hypothyroidism is rare.4 There is an unexplained association between breast cancer and autoimmune (Hashimoto's) thyroiditis, with a threefold increase in the prevalence of thyroid antibodies, and it may be worth screening such patients for thyroid dysfunction.15
## Treatment of subclinical hypothyroidism
A big argument in favour of screening is that recognition and treatment of subclinical hypothyroidism is beneficial.6 At first sight this seems paradoxical because free thyroxine concentrations are normal and some regard the exclusion of symptoms as a criterion for diagnosis (table 1).2 8 However, many patients do have non-specific symptoms, such as tiredness and weight gain, which could be due to hypothyroidism. After all, the thyroid function tests needed to establish the biochemical diagnosis have usually been performed because of this suspicion. Also, after treatment with thyroxine the patient may notice an improvement in symptoms previously unrecognised because of the slow progression of thyroid failure and its variable manifestations. As thyroid stimulating hormone concentrations above 2 mU/l reflect a disturbance of the thyroid-pituitary axis (fig 1), values above the upper level of the typical reference range (4.5 mU/l) are highly significant departures from normal rather than one tail of the normal distribution. Is there any hard evidence that these patients benefit from early treatment?
### Effect on neuropsychiatric and other symptoms
One small crossover trial has indicated that thyroxine improves symptom scores (including mental lethargy) and psychometric performance compared with a placebo.16 This trial is supported by a study which included patients previously treated for hyperthyroidism17 and by a prospective, unblinded trial of thyroxine in patients with subclinical hypo- thyroidism.18 More tenuous is the evidence that subclinical hypothyroidism is common in affective disorders, as such observations have been uncontrolled or the effects of thyroxine replacement have not been assessed.19 20 21
Postpartum symptoms of depression are more common in women who have thyroid antibodies than in those without irrespective of biochemical thyroid dysfunction.22 Also, in patients with rapid cycles of a bipolar affective disorder the most significantly associated thyroid disorder was thyroid antibody positivity and not raised thyroid stimulating hormone concentration.12 Whatever the reason, the implication is that some mood disturbance in subclinical hypothyroidism has an immunological rather than an endocrinological basis, in which case thyroxine treatment would not help.
### Effect on lipids
The adverse effects of subclinical hypothyroidism on cholesterol concentrations have been promoted as a reason for screening and treatment.6 23 A recent study found an association of subclinical hypothyroidism not only with raised low density lipoprotein cholesterol and low high density lipoprotein cholesterol concentrations but also with raised lipoprotein(a).24 Although hypothyroidism theoretically increases the risk of cardiovascular disease, there is no evidence that thyroxine will reverse this potential and, indeed, any such risk must be small, given the results from the Whickham survey.7 The effects of thyroxine replacement on cholesterol lowering alone are modest. A re-analysis of intervention studies between 1976 and 1995 led to the following conclusions25:
• Subclinical hypothyroidism is two to three times more common than expected in people with increased total plasma cholesterol concentrations
• Total cholesterol is only slightly raised (0-30% above normal) in subclinical hypothyroidism.
#### Indications for screening for hypothyroidismEstablished
Congenital hypothyroidism
Treatment of hyperthyroidism
Neck irradiation
Pituitary surgery or irradiation
Patients taking amiodarone or lithium
#### Probably worth while
Type 1 diabetes antepartum*
Previous episode of postpartum thyroiditis
Unexplained infertility
Women over 40 with non-specific complaints
Refractory depression; bipolar affective disorder with rapid cycling
Turner's syndrome; Down's syndrome
Autoimmune Addison's disease
#### Uncertain
Breast cancer
Dementia
Patients with a family history of autoimmune thyroid disease
Pregnancy, looking for postpartum thyroiditis*
Obesity
Idiopathic oedema
#### Not indicated
Acutely ill patients with no clinical reason to suspect thyroid disease
*Check thyroid antibodies; screen positive patients post partum using thyroid stimulating hormone.
### Other effects
Minor alterations in heart muscle contractility, determined by systolic time intervals, occur in around half of patients, although not all studies agree.8 Only a subgroup with the most serious abnormalities improves with thyroxine replacement.17 An asymptomatic polyneuropathy can be identified in subclinical hypo- thyroidism,26 but the response to treatment has not been analysed and the clinical impact of this is even less clear than for alterations in myocardial function. One potentially important adverse effect of subclinical hypothyroidism is to alter the dynamics of prolactin release, with unknown consequences for gonadal function and fertility.27 Testing for thyroid disease seems warranted in all women and men with unexplained infertility.
Another argument in favour of instituting thyroxine replacement is that it prevents the onset of overt hypothyroidism. This is particularly persuasive for people with raised thyroid stimulating hormone concentrations plus thyroid antibodies, who have an annual risk of developing overt hypothyroidism of around 5%.3 Practically, however, the patient is probably not spared many follow up visits in return for starting thyroxine early. This is because thyroxine dose requirements are less in subclinical hypothyroidism than in overt disease, and so careful monitoring is needed until the normal replacement dose is reached (100-150 μg daily). At this time checks every one to three years can be instituted, provided that thyroid stimulating hormone concentrations are normal and stable.
## Disadvantages of treatment
Are there risks from taking thyroxine which argue against treating subclinical hypothyroidism? Providing thyroid stimulating hormone concentrations are restored to the reference range, the answer is no, and even if too much is given, the risks of osteoporosis are more theoretical than real. A meta-analysis of studies of excessive thyroxine treatment found no reduction in bone mass in premenopausal women, although postmenopausal women had a significant excess annual bone loss of 0.9%/year after 10 years.28 However, no increased rate of fractures occurs, despite this loss, and it is also important to distinguish those who are taking thyroxine for iatrogenic hypothyroidism from those with spontaneous hypothyroidism: in the first group there has usually been a period of hyperthyroidism which contributes to the bone loss.29
The other main concern is the action of excessive thyroxine on the heart. Subclinical hyperthyroidism in people aged 60 or older is associated with a trebling of the risk of atrial fibrillation over 10 years.30 It is not clear whether the risk applies equally to patients taking thyroxine for iatrogenic hypothyroidism and those with spontaneous hypothyroidism. This study is the most persuasive reason to maintain normal thyroid stimulating hormone concentrations in all patients receiving thyroxine, whether for subclinical or overt hypothyroidism. On balance, the risks of properly monitored thyroxine treatment are almost non-existent.
## Conclusions
Clinical and subclinical hypothyroidism are common. The presence of either a raised thyroid stimulating hormone concentration or thyroid antibodies indicates an increased risk of future hypothyroidism and this is greater when both occur together. Screening for hypothyroidism may be more cost effective than usually presumed and certain subgroups at risk can be identified, but further work is needed to establish the optimum strategy. On the other hand, the high frequency of abnormal thyroid function test results in acutely ill patients means that any testing should be reserved for those in whom there is clinical suspicion of thyroid dysfunction. There are modest benefits from treating subclinical hypothyroidism, and figure 2) suggests a management strategy.
Fig 2
Algorithm for managing non-iatrogenic subclinical hypothyroidism. Thyroid peroxidase antibodies alone are recommended for screening as thyroglobulin antibodies rarely occur in the absence of these antibodies2
1. 1.
2. 2.
3. 3.
4. 4.
5. 5.
6. 6.
7. 7.
8. 8.
9. 9.
10. 10.
11. 11.
12. 12.
13. 13.
14. 14.
15. 15.
16. 16.
17. 17.
18. 18.
19. 19.
20. 20.
21. 21.
22. 22.
23. 23.
24. 24.
25. 25.
26. 26.
27. 27.
28. 28.
29. 29.
30. 30. |
# Review of Roger Mathew Grant, Beating Time & Measuring Music in the Early Modern Era (Oxford University Press, 2014)
## Rowland Moseley
KEYWORDS: history of music theory, meter, tempo, metronome, tempo giusto
PDF text
Volume 22, Number 4, December 2016
[1] In this addition to the Oxford Studies in Music Theory series, Roger Mathew Grant presents a history of temporal regulation in European music from the sixteenth to the early nineteenth centuries.(1) Written and argued with unfailing finesse, Beating Time & Measuring Music pairs sophisticated readings of music-theoretical texts with lucid summations of historical trends. It offers music theorists valuable information and insight about meter studies, the history of music theory, and the wider history of ideas.(2) At the same time, the whole book stands to interest a broad academic audience, and performers will appreciate its lessons concerning analysis and performance practice.
[2] In each of the monograph’s three parts, addressing the sixteenth and seventeenth, eighteenth, and early nineteenth centuries respectively, Grant examines three facets of meter: its description and conceptualization in theoretical writings, its mediation by techniques and technologies (of human or mechanical action), and its manifestation in notated musical compositions. That three-fold investigation is skewed neither to historically informed analysis nor to history with analytical illustration. Instead, the strands combine to tell of broad changes in how meter was imagined and realized in European music-making over three and a half centuries.
[3] “Meter” bears unpacking here. At its core, Grant’s subject is meter and its mensural equivalents as construed by American music theorists since 1980.(3) Beat, pulse, accent, measure, time signature, and hypermeter are integral concepts, whereas more complex and irregular aspects of rhythm are excluded (5). But the subject extends to elements of character, affect, and movement that were once wedded to meter. Grouping intervenes, too. The most important inclusion is tempo, which came to be notated and evaluated separately from the signatured meter only late in Grant’s historical purview.
#### Changing Times: The Eighteenth Century
[4] Two epochal upheavals fascinate Grant, and explicit, eloquent reminders of these large themes recur throughout the book. The first concerns notions of time and motion (that is, physical motion and, more generally, any kind of change). Once the Scholastic tradition had been substantially dispersed by “natural philosophy,” the category of motus lost its superior claim as that which conditioned tempus and gave it reality, and time came to be regarded as a universal dimension that extended irrespective of mobile or immobile things (15, 24, 93, 96–99). Insofar as people who made and thought about music saw tactus as a matter of both time and motion, the redrawing of philosophical categories swept music with it. The second upheaval concerns the transmission of knowledge about tempo and is more particular to music, though it has direct parallels in contemporaneous efforts at standardization and measurement in manufacture, trade, and mapping. The 1815 invention and widespread adoption of Maelzel’s metronome is the main event, situated in a large patchwork of mechanical innovation, theory, opinion, and notational practice that all marked the messy divorce of tempo from meter. Change came in the form not of philosophical revolution, but of an initiative to communicate music’s proper speed precisely in an age when musicians could no longer be expected to infer a suitable tempo from a piece’s metrical signature and written rhythmic values (125–27).
[5] Pivotal to both these changes, in Grant’s estimation, was the demise of tempo giusto after its heyday in the early eighteenth century.(4) Even by mid-century, tempo giusto was on the wane;(5) in response, some concerned citizens mounted preservation efforts while others turned their minds to new, rational methods of transmitting tempo. Chapter 5, at the heart of Grant’s book, analyzes these twin responses: the impulse to document the early century’s myriad meter–character–tempo types, and the impulse to make musical chronometers. Revealed in these responses are “the anxieties of an age newly aware of the possibilities for temporal exactitude” (127). Grant reaches back to the seventeenth century (Bononcini and Mersenne) but focuses on the mid-to-late eighteenth century. Entrusting some of his own cataloging to the second of two extremely useful appendices, Grant takes stock of the eighteenth century’s “huge expansion of discourse on meter signatures” (106) and its “explosion of lists” (109).(6) His account of the chronometric impulse is equally succinct and rich in detail.(7) The device of the pendulum, which was essential to chronometers, might have been better separated from the outgoing paradigm of motus in this chapter, but only to save readers from confusion on a historical point that is really beyond doubt.(8)
[6] Within part II, which bears witness to the momentous changes of the eighteenth century, chapter 5’s tale of preservationism and rationalism speaks to meter’s mediating “techniques.” Concepts, meanwhile, are the stuff of chapter 4, which unpacks the shift lurking in the book’s title: no longer beating time, but measuring music. Treading a new path through familiar ground, Grant discerns three stages as metric theory navigates from a beat-based to a measure-based system: some theorists busy themselves with itemizing the many kinds of measure (notably Marpurg, who counted 56); others set out to slim and simplify the metrical signatures (Rameau, Montéclair, Lacassagne); then Kirnberger synthesizes an accent theory whereby meter becomes a matter of attentive listening.(9) Overall, meter undergoes a “shared and significant change” with natural philosophy’s new vision of time as separate from motus (122).
[7] Chapter 6, “The Eighteenth-Century Alla Breve,” is the analytical chapter of part II, and it concerns the metric type that Grant sees as tempo giusto’s last hurrah. Unpicking historic definitions more complicated than just duple-metered, stile antico music under a ₵ signature, Grant reveals the alla breve as a site of obstinate connections between meter, tempo, rhythmic style, and character, and as a phenomenon that elicited eighteenth-century voices on the general severance of meter and tempo.(10) In barely twenty pages of text, this engrossing chapter explores the issue from many angles. It includes observations of the ₵ signature’s prevalence in counterpoint texts; an eye-opening study of notational choices in eighteenth-century manuscript copies and printed editions of Palestrina and other sixteenth-century masters; and a compact review of the alla breve’s theorization by Scheibe, Kirnberger, Marpurg, and Koch.(11)
[8] Some arguments in Grant’s alla breve analyses struck me as provisional and contestable, such as the idea that pieces by Handel and Quantz combined distinctly modern and archaic music in playful commentaries on the ₵ signature as a metric umbrella for different styles. Take the trio sonata by Quantz (QV 2.anh 3), from the second quarter of the century. During its alla-breve second movement, the continuo first supplies a walking bass to the upper-voice entries of a contrapuntal theme, then drops out in the codetta, before furnishing the bass entry that completes the imitative exposition; at this point, an episode begins with far-from-antico features, namely, arpeggiation, modular repetition, and coordinated downbeat rests in two of the parts. Grant ascribes some importance to the bass part’s negotiation of counterpoint and continuo, and makes more of the stile antico’s collision with galant figuration.(12) But are old and new styles really in “dialogue,” and specifically at Quantz’s bidding?
[9] Imitative trio movements by German contemporaries of Quantz, and by Corelli before them, frequently deploy the bass as harmonic support for the initial entry. Even conceding Grant’s finer points about thematic content and melodic style, Quantz’s exposition seems broadly in line with similar movements stretching back a generation. Regarding the galant episode, is this a marked incursion of a different style or, I wonder, a modest update to longstanding sequential devices? Interior episodes, in fugues no less, often explored the spectrum between antico decorum and instrumental exhibition. Grant’s ear for stylistic depth is superb. But using music as evidence in the history of ideas sets a high bar. History of this sort cannot be written on the back of pieces that harness an untold mix of styles for their own ends, but needs clear, knowing examples. Questioning the oppositions of polyphony to homophony and “countermelody” to continuo bass, I saw less significance than Grant did, for instance, in the third-species texture that begins symphony finales by Michael Haydn and Joseph Haydn. All the same, the beauty of Grant’s engaging and always intelligent interpretations is that they invite the reader to think deeply, and highly, of music’s compositional record. Music analysis plays a rewarding role in this book and proves itself as an instrument of historical insight on music theory and Western thought more broadly.
#### Early “Early Modern” Meter
[10] If part II chronicles meter’s eighteenth-century upheavals, part I furnishes the backstory: its ultimate message is of stasis in metrical conceptions during the sixteenth and seventeenth centuries. As mensural signs fell from use and bar lines were adopted, beat-centered ideas and practices endured. Lippius’s Synopsis musicae of 1612 epitomizes the breezy changes of the period with its disregard for perfect division and a table that applies the terms bis, semel, demidiam, quartam, etc. to the various rhythmic values as factors of the semibreve (whence “whole note”). But chapter 1, on meter’s theorization and conceptualization in this early period, shows the continued centrality of the beat, defined by motion, across the generational divides of Ornithoparchus, Zarlino, Lippius, and Loulié.(13) The first of Grant’s excellent appendices charts the theorization of the beat and citations of Aristotle in more than 60 sources.
[11] Chapters 2 and 3, completing part I, address pre-eighteenth-century meter in terms of mediating techniques and compositional practice. Chapter 2 examines the beat as performed, imagined, and philosophized, and presents an important addition to the academic literature on the science of time in relation to music. Accessible to a wider audience including non-academic musicians, chapter 3 offers a study of triple meter and its lopsided deployment of tactus.(14) Its case for a historical reappraisal of triple-metered music draws cleverly upon the tradition of paired, duple- then triple-metered dances and upon the lingering notational practice of blackening. Through this practice, filled noteheads of usually open shape alerted the reader to any short–long partitions of the thesis–arsis pair (usually long–short) in tempus perfectum or triple meter. Chapter 3 demonstrates the tactus-wise inequality of triple meter in music by Susato, Schein, and Purcell—first, as a fact of compositional derivation (when after-dances are based on their fore-dances); second, as a matter of musical content (when motive and harmonic rhythm meld two thirds of the triple measure). The credentials of chapter 3 as a work of analysis and a probable springboard for future work are worth underscoring: the mainly analytical half of the chapter (71–90) can be appreciated without digesting the theoretical half (63–71). That said, the theoretical half is of vital interest to metric theorists; here, Grant situates early modern theory against more recent scholarship (Lerdahl and Jackendoff, Hasty, London), with triple meter as the gauge of their divergence. One element of chapter 3 that merits general attention is Grant’s take on hemiola, a prime example of history renewing us with old ways of thinking about and moving to music:
What was different about hemiolas in unequal triple meter—which was neither in place when the hemiola practice originated [i.e. in late-medieval music], nor is recalled in analytical literature today—was that the first part of many cadential hemiolas was actually the normative division of the measure. . . . It is both a way of organizing duple groupings within a triple context and also a way in which two unequal duple groupings (one trochaic, one iambic) join each other to create a composite, symmetrical phenomenon that is made of four unequal—rather than three equal—parts. (89–90, emphasis mine)
[12] Altogether, the book’s opening chapters add superbly to the scholarship of musical meter and metrical theory for a period that is underserved.(15) Part I stands on its own as an important contribution quite apart from its preparatory role in the broadest narrative of changing paradigms. Yet to the extent that part I is meant as a prequel to part II, it is light in some areas. Chapter 1 misses the direct account of modern meter’s emergence from mensural practice that would introduce Renaissance and early Baroque metric theory to a non-specialist and fully prepare chapter 4. Part I also leaves the reader somewhat adrift regarding the emergence of tempo giusto, the demise of which is a major theme of subsequent chapters. In the early eighteenth-century notion of tempo giusto, an association between written rhythmic denominations and performed durations can be traced to late medieval practice, but specific couplings of tempo to character are not so easy to delineate historically.
#### Later Measures
[13] Part III extends the narrative of meter’s eighteenth-century upheavals as far as the 1830s. And, in many respects, the early nineteenth century stands for today, with metronome marks, time signatures emptied of connotations of character or speed, and meter viewed as an activity of the mind. Part III, then, includes the bid for history’s relevance, connecting remote ideas to the common fare of present music education and notational practice. But Grant is, happily, less invested in styling the book’s intangible lessons for analysis or performance today than in recounting the vivid events of the period when musical meter became comprehensively modern.
[14] Anyone with an interest in the history of the metronome, or issues of music and quantification, should read chapter 7, “The Reinvention of Tempo,” which tells how Maelzel’s metronome capitalized on the promise of previous chronometers under new conditions. While this chapter examines the invention and reception of Maelzel’s famous device (alongside previous or rival designs), its primary aim is to illuminate contemporaneous critical discourse by Türk, Gottfried Weber, Rousseau, Schiller, Fétis, and others. As before, Grant exhibits deep proficiency with a wide range of sources, and writes history that is sophisticated and compelling. Some of Grant’s loftier statements invite skepticism, but the same statements are spun with a kind of transparent exuberance that helps the reader absorb the big ideas and lean on them to learn the nuance of the argument. And while I admit wishing for more authorial arbitration of the relevant science—“how long is a seconds pendulum . . . at sea level, 45°N, then?”—Grant was wise not to weigh in. Ultimately, Beating Time & Measuring Music is not about the logistics of either beating or measuring, but rather the interaction with shifting concepts and musical sensibilities. Grant charts a shrewd course between big ideas and the copious minutiae of nineteenth-century efforts to quantify tempo and much else.
[15] An ensemble cast of composers and writers attest to the new century’s flexible and savvy attitude to meter in chapter 8, “The Persistent Question of Meter.”(16) This chapter relates innovations in theory and composition that reveal a conclusive rift between tempo (as pace) and meter (as accentual structure). In what Grant dubs “integrated metric shifts,” composers change meter without implication for character or affect, and theorists, more attuned to listening than before, describe effects of meter and hypermeter that float free of notation. Meanwhile, Beethoven becomes prolific in “paratextual expression markings” that speak to thoroughly post-tempo-giusto aesthetics. On one level, Grant’s arguments are simple and easy to accept. For instance, there can be no doubt that meter changes start to happen more and mean less, and this supports a large point about the growing absence of ties between meter and character. (Chapter 7 has peeled off the issue of tempo already.) Yet interpretation occasionally sits heavy in this chapter. Thus, Grant recalls eighteenth-century German theorists’ injunctions against over-barring (as they saw it) so he can show liberalizing attitudes to hypermeter in the following century: earlier theorists were uncomfortable with measures behaving as beats. However, it can be hard to see through the mixed registers of a source that shares deep musical insight and unglamorous instruction at the same time. It can be even harder to line up suitable comparisons between multiple sources from a panoply of different cultures. An injunction from Koch may betray an eighteenth-century mistrust of hypermeter (221), or perhaps it simply warns novice composers of a mistake that would remain a mistake forty years later.(17) Still, Grant’s overarching conclusions would not be overturned by localized re-readings of this evidence. In fact, the book equips its readers to analyze eighteenth- and nineteenth-century music for themselves along the lines that Grant reveals as important, and that added to my enjoyment and appreciation of the book’s plenty-convincing arguments.
#### Conclusion
[16] In summary, Beating Time & Measuring Music in the Early Modern Era is an excellent book. Read cover to cover, it offers an astute, detailed, and impressively concise history of major upheavals in music’s temporal regulation. Chapter by chapter, the book is also a trove of readings for graduate courses in theory, history, analysis, and even performance practice. Grant brings European music into dialogue with the history of Western ideas about time and quantification, and shows that musical thought and musical practice were not merely auxiliaries to revolutions in science and philosophy. Big ideas are seldom far from view, and much persuasive evidence is amassed to them despite a general circumvention, on a medium scale, of historical narration or reports on theoretical debates. To be sure, the author speaks outside of professional music theory circles when he promises “trouble” for his readers’ “casual assumptions about meter”: few followers of Music Theory Online will have a blasé attitude to meter’s theorization, and an assault on their remaining beliefs might not sound appealing (7). But with tact and agility, Grant opens his readers’ eyes to an abundance of historical evidence and to new, old ideas about the ordering of musical time. Scholars across a wide range of historical and musical expertise will be richly rewarded by this book, and it will help to shape the academic agenda of theorists, analysts, and historians of theory, perhaps as much with metrical matters in the sixteenth and seventeenth centuries as with the subsequent upheavals at the core of Grant’s narrative.
Rowland Moseley
New York, NY
[email protected]
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Boone, Graeme M. 2000. “Marking Mensural Time.” Music Theory Spectrum 22 (1): 1–43.
Boone, Graeme M. 2000. “Marking Mensural Time.” Music Theory Spectrum 22 (1): 1–43.
Brown, Clive. 1999. Classical and Romantic Performing Practice 1750–1900. Oxford University Press.
Brown, Clive. 1999. Classical and Romantic Performing Practice 1750–1900. Oxford University Press.
DeFord, Ruth I. 2015. Tactus, Mensuration, and Rhythm in Renaissance Music. Cambridge University Press.
DeFord, Ruth I. 2015. Tactus, Mensuration, and Rhythm in Renaissance Music. Cambridge University Press.
Grant, Roger Mathew. 2009. “Epistemologies of Time and Metre in the Long Eighteenth Century.” Eighteenth-Century Music 6 (1): 59–75.
Grant, Roger Mathew. 2009. “Epistemologies of Time and Metre in the Long Eighteenth Century.” Eighteenth-Century Music 6 (1): 59–75.
Malin, Yonatan. 2010. Songs in Motion: Rhythm and Meter in the German Lied. Oxford University Press.
Malin, Yonatan. 2010. Songs in Motion: Rhythm and Meter in the German Lied. Oxford University Press.
Maurer Zenck, Claudia. 2000. Vom Takt: Untersuchungen zur Theorie und kompositorischen Praxis im ausgehenden 18. und beginnenden 19. Jahrhundert. Böhlau.
Maurer Zenck, Claudia. 2000. Vom Takt: Untersuchungen zur Theorie und kompositorischen Praxis im ausgehenden 18. und beginnenden 19. Jahrhundert. Böhlau.
McAuley, Tomas. 2013. “Rhythmic Accent and the Absolute: Sulzer, Schelling, and the Akzenttheorie.” Eighteenth-Century Music 10 (2): 277–86.
McAuley, Tomas. 2013. “Rhythmic Accent and the Absolute: Sulzer, Schelling, and the Akzenttheorie.” Eighteenth-Century Music 10 (2): 277–86.
Mirka, Danuta. 2009. Metric Manipulations in Haydn and Mozart: Chamber Music for Strings, 1787–1791. Oxford University Press.
Mirka, Danuta. 2009. Metric Manipulations in Haydn and Mozart: Chamber Music for Strings, 1787–1791. Oxford University Press.
Rothstein, William. 2008. “National Metrical Types in Music of the Eighteenth and Early Nineteenth Centuries.” In Communication in Eighteenth-Century Music, ed. Danuta Mirka and Kofi Agawu, 112–59. Cambridge University Press.
Rothstein, William. 2008. “National Metrical Types in Music of the Eighteenth and Early Nineteenth Centuries.” In Communication in Eighteenth-Century Music, ed. Danuta Mirka and Kofi Agawu, 112–59. Cambridge University Press.
Rothstein, William. 2011. “Metrical Theory and Verdi’s Midcentury Operas.” Dutch Journal of Music Theory 16 (2): 93–111.
—————. 2011. “Metrical Theory and Verdi’s Midcentury Operas.” Dutch Journal of Music Theory 16 (2): 93–111.
### Footnotes
1. Grant’s monograph adds to the already strong representation of meter studies in the current series (Mirka 2009, Malin 2010). Chapters 4 and 6 address some of the same history as Mirka, but from a different angle.
2. This book stands alongside several important historical studies of meter to have appeared this century, including Boone 2000, Maurer Zenck 2000, Rothstein 2008 and 2011, Mirka 2009, McAuley 2013, and DeFord 2015. Grant’s own 2009 article is an earlier iteration of parts of chapters 4 and 5.
3. Grant himself refers to “twenty-first century understandings” (5); the suggestion that contemporary metric theory dates from ca. 1980 is mine.
4. Grant defines tempo giusto as “the idea that the meter signature, note values, and character of any piece can indicate its natural or ‘just’ tempo” (125).
5. More information on tempo giusto is available in David Fallows’s dictionary articles on “tempo giusto” and “Tempo and Expression Marks” in New Grove II and at Oxford Music Online (Grant cites these on 111n63 and 125n1).
6. In Grant’s account of this documentary or taxonomic impulse, Vion, Marpurg, Kirnberger, and Galeazzi receive top billing. The spotlight falls in part on their choices of musical illustration, whether Vion’s citation of contemporary musical excerpts, or Marpurg’s and Galeazzi’s custom-composed examples.
7. Details of this history include William Tans’ur’s idea for multiple pendulums to mark plural levels of subdivision, Diderot’s testimony that his contemporaries regretted not knowing at what speed Lully’s music should go, and the concern of Loulié for an earlier generation of Lully interpreters isolated in the French provinces.
8. Otherwise, I saw only minor alternatives to Grant’s reading or characterization of his sources. A translation from Johann Forkel cites the “hour hand” of a clock where “hour marks” seems more correct in a comparison to bar lines (“den Taktstrichen, gleichsam als Stundenweiser anzusehen,” 126n2), and a quotation from Rousseau is introduced so as to portray musicians’ anticipated neglect of the chronometer as Rousseau’s own dissatisfaction (133).
9. According to Grant, “Kirnberger’s theory found a way to accommodate the period’s multiple meters with the French simplification schemes” (117).
10. Grant writes that it “indexed both the stylistic connotations of sixteenth-century counterpoint and the doubling of speed that would have been required to bring this long-note music into accord with the shorter notes of the eighteenth century” (148). Grant and other scholars of the alla breve seem to agree that it called for speeds that were objectively a little slower than double speed. Agreeing with Clive Brown (1999) on this point, Grant nonetheless has a subtly different notion of how this was (159n32). For a perhaps contentious statement on tempo, consider Grant’s assessment that diminution of tempo was not needed, in spite of a ₵ signature, in the final movements of four symphonies from Michael Haydn, Joseph Haydn, and Mozart (his “Jupiter”): “Their long-note music had already been reconciled with contemporary practice through mixing of styles” (179). This implies quite slow speeds for the three movements besides Mozart’s.
11. See 148–59 (“Long-Note Music in the Eighteenth Century”) and 164–69. These latter pages introduce—somewhat late in the text—the use of breve-length bars under the so-called “large” alla breve, as distinct from the prevailing “small” kind (which Praetorius sensibly termed the alla semibreve). Grant then spells out the options for understanding the big-boned version as either a simple or a “compounded” duple meter (effectively 2/1 or 4/2, corresponding to Scheibe’s and Marpurg’s interpretations). A Graun composition is seen to treat the large alla breve as a compounded meter by aligning subject entries and cadences interchangeably with the downbeat or midpoint of its measures.
12. By way of introducing the Quantz movement, Grant characterizes the bass as sidestepping contrapuntal rigor: “Another way of using basso continuo in an imitative movement is to remove it from the structure of imitation altogether” (163). And then: “the bass participates briefly in the imitation” (163, emphasis mine). However, the bass is not uninvolved in the imitative structure as the movement proceeds: it states the subject head in the relative minor at m. 61, and states the full subject in the tonic at m. 110 for what is the final entry.
13. Other theorists of special focus in this chapter are Agricola, Pisa, and Banchieri, with further significant mentions of Vicentino, Fludd, Mersenne, and Kircher.
14. The meter signatures of compositions and theorists’ examples that appear in this chapter include 3/1, 3, C3, ${\text{}}_{2}^{3}$, and ₵3.
15. As Grant puts it: “While a recent growth of scholarship on mensuration and proportion signs has helped to elucidate long-standing problems in the history of notation and questions of performance practice—particularly with regard to tempo—little scholarship exists that addresses the theories of meter and conceptions of the beat that were in place during the sixteenth and seventeenth centuries” (17; see 17n4 for the sizeable literature that Grant credits in this statement).
16. The composers are Haydn, Mozart, Beethoven, Rossini, Méhul, Boieldieu, and Spohr; the writers are Momigny, Weber, E. T. A. Hoffmann, and Fétis.
17. Consider, in another example of possible over-interpretation, Mozart’s second-act finale to Die Entführung aus dem Serail and the moment Blonde takes up ${\text{}}_{8}^{12}$ against the prevailing ₵ for a tirade against Pedrillo. Mozart may have shown, as Grant claims, that meter signatures were becoming notational conveniences to be mixed and matched (225), but, equally, he may have shown that meter’s inherent characterfulness persisted: different meters suited characters in (comic) dispute.
Grant’s monograph adds to the already strong representation of meter studies in the current series (Mirka 2009, Malin 2010). Chapters 4 and 6 address some of the same history as Mirka, but from a different angle.
This book stands alongside several important historical studies of meter to have appeared this century, including Boone 2000, Maurer Zenck 2000, Rothstein 2008 and 2011, Mirka 2009, McAuley 2013, and DeFord 2015. Grant’s own 2009 article is an earlier iteration of parts of chapters 4 and 5.
Grant himself refers to “twenty-first century understandings” (5); the suggestion that contemporary metric theory dates from ca. 1980 is mine.
Grant defines tempo giusto as “the idea that the meter signature, note values, and character of any piece can indicate its natural or ‘just’ tempo” (125).
More information on tempo giusto is available in David Fallows’s dictionary articles on “tempo giusto” and “Tempo and Expression Marks” in New Grove II and at Oxford Music Online (Grant cites these on 111n63 and 125n1).
In Grant’s account of this documentary or taxonomic impulse, Vion, Marpurg, Kirnberger, and Galeazzi receive top billing. The spotlight falls in part on their choices of musical illustration, whether Vion’s citation of contemporary musical excerpts, or Marpurg’s and Galeazzi’s custom-composed examples.
Details of this history include William Tans’ur’s idea for multiple pendulums to mark plural levels of subdivision, Diderot’s testimony that his contemporaries regretted not knowing at what speed Lully’s music should go, and the concern of Loulié for an earlier generation of Lully interpreters isolated in the French provinces.
Otherwise, I saw only minor alternatives to Grant’s reading or characterization of his sources. A translation from Johann Forkel cites the “hour hand” of a clock where “hour marks” seems more correct in a comparison to bar lines (“den Taktstrichen, gleichsam als Stundenweiser anzusehen,” 126n2), and a quotation from Rousseau is introduced so as to portray musicians’ anticipated neglect of the chronometer as Rousseau’s own dissatisfaction (133).
According to Grant, “Kirnberger’s theory found a way to accommodate the period’s multiple meters with the French simplification schemes” (117).
Grant writes that it “indexed both the stylistic connotations of sixteenth-century counterpoint and the doubling of speed that would have been required to bring this long-note music into accord with the shorter notes of the eighteenth century” (148). Grant and other scholars of the alla breve seem to agree that it called for speeds that were objectively a little slower than double speed. Agreeing with Clive Brown (1999) on this point, Grant nonetheless has a subtly different notion of how this was (159n32). For a perhaps contentious statement on tempo, consider Grant’s assessment that diminution of tempo was not needed, in spite of a ₵ signature, in the final movements of four symphonies from Michael Haydn, Joseph Haydn, and Mozart (his “Jupiter”): “Their long-note music had already been reconciled with contemporary practice through mixing of styles” (179). This implies quite slow speeds for the three movements besides Mozart’s.
See 148–59 (“Long-Note Music in the Eighteenth Century”) and 164–69. These latter pages introduce—somewhat late in the text—the use of breve-length bars under the so-called “large” alla breve, as distinct from the prevailing “small” kind (which Praetorius sensibly termed the alla semibreve). Grant then spells out the options for understanding the big-boned version as either a simple or a “compounded” duple meter (effectively 2/1 or 4/2, corresponding to Scheibe’s and Marpurg’s interpretations). A Graun composition is seen to treat the large alla breve as a compounded meter by aligning subject entries and cadences interchangeably with the downbeat or midpoint of its measures.
By way of introducing the Quantz movement, Grant characterizes the bass as sidestepping contrapuntal rigor: “Another way of using basso continuo in an imitative movement is to remove it from the structure of imitation altogether” (163). And then: “the bass participates briefly in the imitation” (163, emphasis mine). However, the bass is not uninvolved in the imitative structure as the movement proceeds: it states the subject head in the relative minor at m. 61, and states the full subject in the tonic at m. 110 for what is the final entry.
Other theorists of special focus in this chapter are Agricola, Pisa, and Banchieri, with further significant mentions of Vicentino, Fludd, Mersenne, and Kircher.
The meter signatures of compositions and theorists’ examples that appear in this chapter include 3/1, 3, C3, ${\text{}}_{2}^{3}$, and ₵3.
As Grant puts it: “While a recent growth of scholarship on mensuration and proportion signs has helped to elucidate long-standing problems in the history of notation and questions of performance practice—particularly with regard to tempo—little scholarship exists that addresses the theories of meter and conceptions of the beat that were in place during the sixteenth and seventeenth centuries” (17; see 17n4 for the sizeable literature that Grant credits in this statement).
The composers are Haydn, Mozart, Beethoven, Rossini, Méhul, Boieldieu, and Spohr; the writers are Momigny, Weber, E. T. A. Hoffmann, and Fétis.
Consider, in another example of possible over-interpretation, Mozart’s second-act finale to Die Entführung aus dem Serail and the moment Blonde takes up ${\text{}}_{8}^{12}$ against the prevailing ₵ for a tirade against Pedrillo. Mozart may have shown, as Grant claims, that meter signatures were becoming notational conveniences to be mixed and matched (225), but, equally, he may have shown that meter’s inherent characterfulness persisted: different meters suited characters in (comic) dispute.
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# g -factor of electrons in gate-defined quantum dots in a strong in-plane magnetic field
@article{Stano2018gO,
title={g
-factor of electrons in gate-defined quantum dots in a strong in-plane magnetic field},
author={Peter Stano and Chen-Hsuan Hsu and Marcel Serina and Leon C. Camenzind and Dominik M. Zumbuhl and Daniel Loss},
journal={Physical Review B},
year={2018}
}
• P. Stano, +3 authors D. Loss
• Published 12 August 2018
• Physics
• Physical Review B
We analyze orbital effects of an in-plane magnetic field on the spin structure of states of a gated quantum dot based in a two-dimensional electron gas. Starting with a $k\ifmmode\cdot\else\textperiodcentered\fi{}p$ Hamiltonian, we perturbatively calculate these effects for the conduction band of GaAs, up to the third power of the magnetic field. We quantify several corrections to the $g$-tensor and reveal their relative importance. We find that for typical parameters, the Rashba spin-orbit…
6 Citations
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We investigate theoretically the Zeeman effect on the lowest confined electron in quantum wires and quantum dots. A general relation is established between the symmetry of a low-dimensional system
Possible Spin Polarization in a One-Dimensional Electron Gas.
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Physical review letters
• 1996
The measured enhancement of the $g$ factor as the subbands are depopulated suggests that the 0.7 structure'' is induced by electron-electron interactions.
Spin and cyclotron energies of electrons in GaAs ∕ Ga 1 − x Al x As quantum wells
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A five-level $\mathbf{P}∙\mathbf{p}$ model of the band structure for $\mathrm{GaAs}$-type semiconductors is used to describe the spin ${g}^{*}$ factor and the cyclotron mass ${m}_{c}^{*}$ of
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Five-level $\mathbf{k}∙\mathbf{p}$ band model is used to describe the spin $g$ factor of conduction electrons in undoped $\mathrm{Ga}\mathrm{As}∕{\mathrm{Ga}}_{0.65}{\mathrm{Al}}_{0.35}\mathrm{As}$
Electron g -factor of valley states in realistic silicon quantum dots
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Physical Review B
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We theoretically model the spin-orbit interaction in silicon quantum dot devices, relevant for quantum computation and spintronics. Our model is based on a modified effective mass approach which
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The spin-splitting factor of the electrons at the very bottom of the conduction band in strained As/InP type-I quantum wells is reported and experimental proof of quantum confinement-dependent anisotropy of g is given.
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A silicon metal-oxide-semiconductor electron spin-orbit qubit
This work exploits spin-orbit coupling to demonstrate full, all-electrical control of a metal-oxide-semiconductor electron spin qubit, demonstrating that the MOS interface inherently provides properties for two-axis qubit control, while not increasing noise relative to other material choices. |
# How Many Nines
Time Limit: 1 Second
Memory Limit: 65536 KB
## Description
If we represent a date in the format YYYY-MM-DD (for example, 2017-04-09), do you know how many 9s will appear in all the dates between Y1-M1-D1 and Y2-M2-D2 (both inclusive)?
Note that you should take leap years into consideration. A leap year is a year which can be divided by 400 or can be divided by 4 but can't be divided by 100.
## Input
The first line of the input is an integer T (1 ≤ T ≤ 105), indicating the number of test cases. Then T test cases follow. For each test case:
The first and only line contains six integers Y1, M1, D1, Y2, M2, D2, their meanings are described above.
It's guaranteed that Y1-M1-D1 is not larger than Y2-M2-D2. Both Y1-M1-D1 and Y2-M2-D2 are between 2000-01-01 and 9999-12-31, and both dates are valid.
We kindly remind you that this problem contains large I/O file, so it's recommended to use a faster I/O method. For example, you can use scanf/printf instead of cin/cout in C++.
## Output
For each test case, you should output one line containing one integer, indicating the answer of this test case.
## Sample Input
4
2017 04 09 2017 05 09
2100 02 01 2100 03 01
9996 02 01 9996 03 01
2000 01 01 9999 12 31
## Sample Output
4
2
93
1763534
## Hint
For the first test case, four 9s appear in all the dates between 2017-04-09 and 2017-05-09. They are: 2017-04-09 (one 9), 2017-04-19 (one 9), 2017-04-29 (one 9), and 2017-05-09 (one 9).
For the second test case, as year 2100 is not a leap year, only two 9s appear in all the dates between 2100-02-01 and 2100-03-01. They are: 2017-02-09 (one 9) and 2017-02-19 (one 9).
For the third test case, at least three 9s appear in each date between 9996-02-01 and 9996-03-01. Also, there are three additional nines, namely 9996-02-09 (one 9), 9996-02-19 (one 9) and 9996-02-29 (one 9). So the answer is 3 × 30 + 3 = 93.
None |
Research
# Blow-up criterion for 3D compressible viscous magneto-micropolar fluids with initial vacuum
Peixin Zhang
Author Affiliations
School of Mathematical Sciences, Huaqiao University, Quanzhou, 362021, P.R. China
Boundary Value Problems 2013, 2013:160 doi:10.1186/1687-2770-2013-160
Received: 18 February 2013 Accepted: 16 June 2013 Published: 1 July 2013
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
### Abstract
In this paper, the author establishes a blow-up criterion of strong solutions to 3D compressible viscous magneto-micropolar fluids. It is shown that if the density and the velocity satisfy ρ L ( 0 , T ; L ) + u L s ( 0 , T ; L r ) < , where 2 s + 3 r 1 and 3 < r , then the strong solutions to the Cauchy problem can exist globally over R 3 × [ 0 , T ] . The initial density may vanish on open sets, that is, the initial vacuum is allowed.
MSC: 76N10, 35B44, 35B45.
##### Keywords:
compressible magneto-micropolar fluids; blow-up criterion; strong solution; vacuum
### 1 Introduction
In this paper, we consider the following 3D compressible viscous magneto-micropolar fluids:
{ ρ t + div ( ρ u ) = 0 , ( ρ u ) t + div ( ρ u u ) ( μ + ξ ) u ( μ + λ ξ ) div u + P = 2 ξ × w + ( × H ) × H , ( ρ w ) t + div ( ρ u w ) μ w ( μ + λ ) div w + 4 ξ w = 2 ξ × u , H t × ( u × H ) = × ( σ × H ) , div H = 0 , (1.1)
where x = ( x 1 , x 2 , x 3 ) R 3 is the spacial coordinate and t 0 is the time. The unknown functions ρ = ρ ( t , x ) , u = u ( t , x ) = ( u 1 , u 2 , u 3 ) ( t , x ) , w = w ( t , x ) = ( w 1 , w 2 , w 3 ) ( t , x ) , H = H ( t , x ) = ( H 1 , H 2 , H 3 ) ( t , x ) and P ( ρ ) = A ρ γ ( A > 0 , γ > 1 ) are the fluid density, velocity, micro-rotational velocity, magnetic field and pressure, respectively. The constants μ, λ, ξ, μ , λ and σ are the viscosity coefficients of the fluid satisfying
μ , μ , ξ , σ > 0 , 2 μ + 3 λ 4 ξ 0 , and 2 μ + 3 λ 0 . (1.2)
System (1.1)-(1.2) describing the motion of aggregates of small solid ferromagnetic particles relative to viscous magnetic fluids, such as water, hydrocarbon, ester, fluorocarbon, etc., in which they are immersed, covers a wide range of heat and mass transfer phenomena, under the action of magnetic fields, and is of great importance in practical and mathematics applications (see [1]). Indeed, (1.1) is composed of the balance laws of mass, momentum, moment of momentum and magnetohydrodynamic, respectively. Due to its importance in mathematics and physics, there is a lot of literature devoted to the mathematical theory of the compressible viscous magneto-micropolar system (see [2-4]).
For the incompressible magneto-micropolar fluid models where ρ = C o n s t . , Rojas-Medar [5] established local existence and uniqueness of strong solutions by the Galerkin method. Ortega-Torres and Rojas-Medar [6] proved global existence of strong solutions for small initial data. A BKM type blow-up criterion for smooth solution that relies on the vorticity of velocity only was obtained by Yuan [7]. For regularity results, refer to Yuan [8] and Gala [9].
In particular, if the effect of angular velocity field of the particle’s rotation is omitted, i.e., w = 0 , then (1.1) reduces to compressible magnetohydrodynamic equations (MHD). There are numerous important progress on compressible MHD (see [10-12] and the references therein). The local strong solutions to the compressible MHD with large initial data were respectively obtained by Vol’pert-Khudiaev [10] and Fan-Yu [11] in cases that the initial density is strictly positive and the initial density may vanish. Xu-Zhang [12] proved a blow-up criterion that if T < is the maximal time of existence of a strong solution, then
sup T T ( ρ L ( 0 , T ; L ) + u L s ( 0 , T ; L w r ) ) = ,
where L w r is the weak L r space and r, s satisfy
2 s + 3 r 1 , 3 < r . (1.3)
If H = 0 , (1.1) reduces to compressible micropolar fluid equations. Mujakovic [13,14] considered the one-dimensional motion of compressible viscous micropolar fluids and studied the local/global existence. The global existence of strong solutions to the 1D model with initial vacuum was also obtained in [15]. For multi-dimensional compressible magneto-micropolar equations, Amirat and Hamdache [16] proved the global existence of weak solutions with finite energy and the adiabatic constant for γ > 3 / 2 , which generalized Lions’ pioneering work [17] and the work by Feireisl et al.[18]. Chen [19] established the local existence and uniqueness of strong solutions under the assumption that the initial density may vanish, and in [20] Chen et al. proved a blow-up criterion that
sup T T ( ρ L ( 0 , T ; L ) + ρ u L s ( 0 , T ; L r ) ) = ,
where r, s satisfy (1.3).
If H = 0 and w = 0 , (1.1) reduces to isentropic compressible Navier-Stokes equations. In [21], the authors established a Serrin-type blow-up criterion that
sup T T ( div u L 1 ( 0 , T ; L ) + ρ u L s ( 0 , T ; L r ) ) = ,
or
sup T T ( ρ L ( 0 , T ; L ) + ρ u L s ( 0 , T ; L r ) ) = ,
where r, s satisfy (1.3).
In this paper, our main purpose is to establish a blow-up criterion of strong solutions for system (1.1) with the following conditions:
{ ( ρ , u , w , H ) ( x , 0 ) = ( ρ 0 , u 0 , w 0 , H 0 ) ( x ) in R 3 , ( ρ , u , w , H ) ( x , t ) 0 as | x | . (1.4)
To proceed, we introduce the following notations. For 1 r , we denote the standard homogeneous and inhomogeneous Sobolev spaces as follows:
{ L r = L r ( R 3 ) , D k , r = { u L loc 1 ( R 3 ) | k u L r < } , u D k , r : = k u L r , W k , r = L r D k , r , H k = W k , 2 , D k = D k , 2 , D 1 = { u L 6 | u L 2 < } .
To present the main result, we first give the following local existence and uniqueness of strong solutions to the Cauchy problem (1.1), (1.2) and (1.4) with initial vacuum (without proof), which can be obtained by the same method developed by Choe-Kim in [22] (see also Fan-Yu [11] and Chen [19] for MHD and compressible micropolar fluids, respectively).
Theorem 1.1Assume that for some q ( 3 , 6 ] , the initial data ( ρ 0 , u 0 , w 0 , H 0 ) satisfy
0 ρ 0 L 1 H 1 W 1 , q , u 0 D 1 D 2 , w 0 H 2 , H 0 H 2 , div H 0 = 0 , (1.5)
and the compatibility conditions
( μ + ξ ) u 0 ( μ + λ ξ ) div u 0 + P 0 2 ξ × w 0 ( × H 0 ) × H 0 = ρ 0 1 / 2 g 1 , (1.6)
μ w 0 ( μ + λ ) div w 0 2 ξ × u 0 + 4 ξ w 0 = ρ 0 1 / 2 g 2 , (1.7)
with some ( g 1 , g 2 ) L 2 . Then there exists a positive time T ( 0 , ) such that the problem (1.1), (1.2) and (1.4) has a unique strong solution ( ρ , u , w , H ) in R 3 × [ 0 , T ] satisfying, for some q 0 ( 3 , 6 ] ,
{ ρ C ( [ 0 , T ] ; L 1 H 1 W 1 , q 0 ) , ρ t L ( 0 , T ; L 2 L q 0 ) , ρ 0 , ( u , w , H ) C ( [ 0 , T ] ; D 1 D 2 ) L 2 ( 0 , T ; D 2 , q 0 ) , w C ( [ 0 , T ] ; L 2 ) , H C ( [ 0 , T ] ; H 2 ) , ( ρ u t , ρ w t , H t ) L ( 0 , T ; L 2 ) , ( u t , w t , H t ) L 2 ( 0 , T ; D 1 ) . (1.8)
Motivated by [20,21] and [12], we have the main purpose in this paper to prove a blow-up criterion for the problem (1.1), (1.2) and (1.4). More precisely, the main result in this paper reads as follows.
Theorem 1.2Assume that the initial data ( ρ 0 , u 0 , w 0 , H 0 ) satisfies (1.5)-(1.7). Let ( ρ , u , w , H ) be a strong solution of the Cauchy problem (1.1), (1.2) and (1.4) with the regularities (1.8). If T ( 0 , + ) is the maximal time of existence, then
lim T T ( ρ L ( 0 , T ; L ) + u L s ( 0 , T ; L r ) ) = , (1.9)
for anyrandssatisfying (1.3).
Remark 1.3 Theorem 1.1 proves that the strong solutions of (1.1), (1.2) and (1.4) can exist only in a small time T , which means that if T is the maximal time of existence, then there must be some component of the fluid mechanics blow-ups. Theorem 1.2 points out one kind of blow-up mechanics.
Remark 1.4 There is no any additional growth condition on the micro-rotational velocity w and magnetic field H. This reveals that the density and the linear velocity play a more important role compared to the angular velocity of rotation of particles and the magnetic field in the regularity theory of solutions to 3D compressible magneto-micropolar fluid flows.
The rest of the paper is devoted to completing the proof of Theorem 1.2.
### 2 Proof of Theorem 1.2
First, we give the following well-known Gagliardo-Nirenberg inequality that will be used frequently.
Lemma 2.1For p [ 2 , 6 ] , q ( 1 , ) and r ( 3 , ) , there exists some generic constant C > 0 , which may depend onp, qandr, such that for any f H 1 and g L q D 1 , r , we have
f L p C f L 2 ( 6 p ) / 2 p f L 2 ( 3 p 6 ) / 2 p , (2.1)
g L C g L q q ( r 3 ) / ( 3 r + q ( r 3 ) ) g L r 3 r / ( 3 r + q ( r 3 ) ) . (2.2)
The following BKM’s type inequality which will be used to estimate u L and ρ L q with q ( 3 , 6 ] can be found in [12].
Lemma 2.2For 3 < q < , there is a constant C = C ( q ) , depending only onq, such that the following estimate holds for all u L 2 D 1 , q :
u L C ( div u L + × u L ) log ( e + 2 u L q ) + C u L 2 + C . (2.3)
The proof of Theorem 1.2 is based on the contradiction arguments. Let ( ρ , u , w , H ) be a strong solution of the problem (1.1), (1.2) and (1.4) as described in Theorem 1.1. Suppose that (1.9) is false, that is,
lim T T ( ρ L ( 0 , T ; L ) + u L s ( 0 , T ; L r ) ) M 0 < , (2.4)
where r, s satisfy (1.3) and M 0 is a constant.
One can easily deduce from the following energy estimate (1.1), (1.2) and (1.4).
Lemma 2.3It holds that
sup 0 t T ( ρ L 1 L γ + ρ u L 2 2 + ρ w L 2 2 + H L 2 2 ) + 0 T ( u L 2 2 + w H 1 2 + H L 2 2 ) d t C . (2.5)
Here and hereafter, C denotes a generic positive constant which may depend onμ, μ , λ, λ , ξ, σ, A, γ, ρ 0 , u 0 , w 0 , H 0 , g 1 , g 2 , Tand M 0 .
We denote the material derivative of f by f ˙ = f t + u f and set
G 1 : = ( 2 μ + λ ) div u P ( ρ ) 1 2 | H | 2 , G 2 : = ( 2 μ + λ ) div w , V 1 : = × u , V 2 : = × w . (2.6)
Since ( × H ) × H = H H 1 2 | H | 2 due to (1.1)5, we have from (1.1)2 and (1.1)3 that
{ G 1 = div ( ρ u ˙ H H ) , G 2 4 ξ 2 μ + λ G 2 = div ( ρ w ˙ ) , ( μ + ξ ) V 1 = × ( ρ u ˙ H H ) 2 ξ × V 2 , μ V 2 4 ξ V 2 = × ( ρ w ˙ ) 2 ξ × V 1 . (2.7)
Thus, from the standard L p -estimate of an elliptic system, we have the following lemma.
Lemma 2.4Under the condition (2.4), it holds that
G 1 L 2 + V 1 L 2 + G 2 H 1 + V 2 H 1 C ( ρ u ˙ L 2 + ρ w ˙ L 2 + u L 2 + w L 2 + H H L 2 ) C ( ρ u t L 2 + ρ w t L 2 + u u L 2 + w w L 2 + u L 2 + w L 2 + H H L 2 ) , (2.8)
G 1 L 6 + G 2 L 6 + V 1 L 6 + V 2 L 6 C ( u ˙ L 2 + w ˙ L 2 + ρ u ˙ L 2 + ρ w ˙ L 2 + u L 2 + w L 2 + H H L 2 + H H L 6 ) . (2.9)
Proof In view of standard L 2 -estimates of elliptic system (2.7), one immediately obtains (2.8). By (2.1) and (2.4), we get that
G 1 L 6 + G 2 L 6 + V 1 L 6 + V 2 L 6 C ( ρ u ˙ L 6 + ρ w ˙ L 6 + G 2 L 2 + V 1 L 6 + V 2 L 2 + V 2 L 6 + H H L 6 ) C ( u ˙ L 2 + w ˙ L 2 + G 2 L 2 + V 1 L 2 + V 2 H 1 + H H L 6 ) ,
which, combined with (2.8), yields (2.9) immediately. □
The next lemma is concerned with the higher integrability of H under the assumption (2.4).
Lemma 2.5Under the condition (2.4), it holds for any 0 T T that
H L ( 0 , T ; L q ) C ( q ) for any q [ 2 , ) , (2.10)
where C ( q ) is a positive constant depending onq.
The proof is similar to Lemma 3.3 in [12] and is omitted here.
With the help of (2.4) and Lemmas 2.3-2.5, we can prove the following key lemma.
Lemma 2.6Under the condition (2.4), it holds that for any 0 T < T ,
sup 0 t T ( u L 2 2 + w H 1 2 + H L 2 2 ) + 0 T ( ρ u t L 2 2 + ρ w t L 2 2 + H t L 2 2 + H H 1 2 ) d t C . (2.11)
Proof Multiplying (1.1)2, (1.1)3 and (1.1)4 by u t , w t and H t , respectively, and integrating the resulting equations by parts, one obtains after summing up that
1 2 d d t ( μ | u | 2 + ( μ + λ ) ( div u ) 2 + μ | w | 2 + ( μ + λ ) ( div w ) 2 + σ | H | 2 ) d x + 1 2 d d t ξ ( | × u | 2 + 4 | w | 2 ) d x + ( ρ | u t | 2 + ρ | w t | 2 + | H t | 2 ) d x = P div u t d x + 2 ξ ( × w u t + × u w t ) d x ( ρ u u u t + ρ u w w t ) d x + ( H H 1 2 | H | 2 ) u t d x + H u H t d x u H H t d x H H t div u d x : = i = 1 7 I i . (2.12)
To estimate the first term on the right-hand side of (2.12), we observe that P satisfies
P t + div ( P u ) + ( γ 1 ) P div u = 0 .
Hence, using (2.4), (2.5) and (2.10) yields that
I 1 = d d t P div u d x P u div u d x + ( γ 1 ) P ( div u ) 2 d x = d d t P div u d x 1 2 μ + λ P u G 1 d x + 1 2 ( 2 μ + λ ) P 2 div u d x 1 2 ( 2 μ + λ ) P u | H | 2 d x + ( γ 1 ) P ( div u ) 2 d x d d t P div u d x + C ( P L 3 u L 6 G 1 L 2 + P L P L 2 u L 2 + P L u L 6 H L 3 H L 2 + P L u L 2 2 ) d d t P div u d x + ε G 1 L 2 2 + C ( ε ) ( u L 2 2 + H L 2 2 + 1 ) , (2.13)
where we have used Young’s inequality and (2.1).
For the second term, we have, after integration by parts, that
I 2 = 2 ξ ( w ( × u t ) + ( × u ) w t ) d x = 2 ξ d d t w ( × u ) d x , (2.14)
and by the Cauchy-Schwarz inequality, we have
I 3 1 4 ( ρ u t L 2 2 + ρ w t L 2 2 ) + C ( u u L 2 2 + u w L 2 2 ) . (2.15)
Similarly, integrating by parts and using the fact div H = 0 , one has
I 4 = ( H u t H 1 2 | H | 2 div u t ) d x = d d t ( H u H 1 2 | H | 2 div u ) d x + ( H t u H + H u H t H H t div u ) d x d d t ( H u H 1 2 | H | 2 div u ) d x + 1 4 H t L 2 2 + C H u L 2 2 . (2.16)
For the last three terms on the right-hand side of (2.12), one has from (2.4) that
| i = 5 7 I i | 1 4 H t L 2 2 + C ( u H L 2 2 + H u L 2 2 ) . (2.17)
Thus, putting (2.13)-(2.17) into (2.12) and choosing ε > 0 suitably small, we infer from (2.8) that
d d t ( μ | u | 2 + ( μ + λ ) ( div u ) 2 + μ | w | 2 + ( μ + λ ) ( div w ) 2 + σ | H | 2 ) d x + d d t ξ | × u 2 w | 2 d x + ( ρ | u t | 2 + ρ | w t | 2 + | H t | 2 ) d x d d t ( 2 P div u + | H | 2 div u 2 H u H ) d x + C ( u L 2 2 + w L 2 2 + H L 2 2 ) + C ( u u L 2 2 + u w L 2 2 + u H L 2 2 + H u L 2 2 + H H L 2 2 ) . (2.18)
For any r, s satisfying (1.3), we have by the Hölder and Sobolev inequalities that
f g L 2 C f L r g L 2 r r 2 C f L r g L 2 r 3 r g L 6 3 r δ g L 6 + C ( δ ) ( f L r s 2 + 1 ) g L 2 , r > 3 , (2.19)
for some δ ( 0 , 1 ) .
Taking f = u , H, g = u , ∇w, ∇H into (2.19) and using (2.10), we obtain
u u L 2 2 + u w L 2 2 + u H L 2 2 + H u L 2 2 + H H L 2 2 δ ( u L 6 2 + w L 6 2 + H L 6 2 ) + C ( δ ) ( u L r s + 1 ) ( u L 2 2 + w L 2 2 + H L 2 2 ) . (2.20)
By the standard L p -estimate, one can deduce from (2.1), (2.4), (2.8) and (2.10) that
u L 6 + w L 6 C ( div u L 6 + × u L 6 + div w L 6 + × w L 6 ) C ( G 1 L 6 + G 2 L 6 + V 1 L 6 + V 2 L 6 + P L 6 + | H | 2 L 6 ) C ( 1 + G 1 L 2 + G 2 L 2 + V 1 L 2 + V 2 L 2 ) C ( 1 + ρ u t L 2 + ρ w t L 2 ) + C ( u u L 2 + u u L 2 + H H L 2 ) . (2.21)
Furthermore, it follows from (1.1)4 and Sobolev’s embedding inequality that
H L 6 C H H 1 C ( H t L 2 + u H L 2 + H u L 2 + H L 2 ) , (2.22)
putting (2.21) and (2.22) into (2.20), such that
u u L 2 2 + u w L 2 2 + u H L 2 2 + H u L 2 2 + H H L 2 2 C δ ( ρ u t L 2 2 + ρ w t L 2 2 + H t L 2 2 ) + C ( δ ) ( u L r s + 1 ) ( u L 2 2 + w L 2 2 + H L 2 2 ) , (2.23)
which, together (2.21) and (2.18), choosing δ > 0 suitably small, gives
d d t ( μ | u | 2 + ( μ + λ ) ( div u ) 2 + μ | w | 2 + ( μ + λ ) ( div w ) 2 + σ | H | 2 ) d x + d d t ξ | × u 2 w | 2 d x + ( ρ | u t | 2 + ρ | w t | 2 + | H t | 2 ) d x d d t ( 2 P div u + | H | 2 div u 2 H u H ) d x + C ( u L r s + 1 ) ( u L 2 2 + w L 2 2 + H L 2 2 ) . (2.24)
It is easily seen that
| ( 2 P div u + | H | 2 div u 2 H u H ) d x | μ 4 u L 2 2 + C .
Taking this into account, we conclude from (2.4), (2.24) and Gronwall’s inequality that part of (2.11) holds for any 0 T < T . Note that the estimate of H L 2 ( 0 , T ; H 1 ) is a consequence of (2.4), (2.22) and (2.23). The proof of this lemma is completed. □
Next we prove the boundedness of ρ u ˙ L 2 , ρ w ˙ L 2 , H t L 2 and H H 1 by the compatibility conditions (1.6) and (1.7).
Lemma 2.7Under the condition (2.4), it holds that for any 0 T < T ,
sup 0 t T ( ρ u ˙ L 2 2 + ρ w ˙ L 2 2 + H t L 2 2 + H H 1 2 ) + 0 T ( u ˙ L 2 2 + w ˙ L 2 2 + H t L 2 2 ) d t C . (2.25)
Proof Applying the operator u ˙ j [ t + div ( u ) ] and u ˙ j [ t + div ( u ) ] to both sides of (1.1)2 and (1.1)3, respectively, and using (1.1)1, one can obtain, after a straightforward calculation, that
1 2 d d t ( ρ | u ˙ | 2 + ρ | w ˙ | 2 ) d x = ( μ + ξ ) u ˙ j [ u t j + div ( u u j ) ] d x + ( μ + λ ξ ) u ˙ j [ t j div u + div ( u j div u ) ] d x + μ w ˙ j [ w t j + div ( u w j ) ] d x + ( μ + λ ) w ˙ j [ t j div w + div ( u j div w ) ] d x u ˙ j [ j P t + div ( u j P ) ] d x + 2 ξ u ˙ [ × w t + i ( u i × w ) ] d x + 2 ξ w ˙ [ × u t + i ( u i × u ) ] d x 4 ξ w ˙ j [ w t j + div ( u w j ) ] d x 1 2 u ˙ j [ t j | H | 2 + div ( u j | H | 2 ) ] d x + u ˙ j [ t ( H H j ) + div ( u ( H H j ) ) ] d x : = i = 1 10 J i . (2.26)
We get after integration by parts that
J 1 = ( μ + ξ ) ( | u ˙ j | 2 i u ˙ j i u k k u j i u ˙ j u k k i u j + u u ˙ j u j ) d x = ( μ + ξ ) ( | u ˙ j | 2 i u ˙ j i u k k u j + i u ˙ j k u k i u j i u k k u ˙ j i u j ) d x ( μ + ξ ) u ˙ L 2 2 + C u ˙ L 2 u L 4 2 . (2.27)
Similarly, we also have
j = 2 4 J j ( μ + λ ξ ) div u ˙ L 2 2 μ w ˙ L 2 2 ( μ + λ ) div w ˙ L 2 2 + C u ˙ L 2 u L 4 2 + C w ˙ L 2 u L 4 w L 4 . (2.28)
After integration by parts, using (1.1)1 and (2.11), we obtain
J 5 = ( ρ P ( ρ ) div u div u ˙ P ( ρ ) k ( u k j u ˙ j ) P ( ρ ) j ( u k k u ˙ j ) ) d x C u L 2 u ˙ L 2 C u ˙ L 2 . (2.29)
Using the definition of the material derivation and integrating by parts, we deduce from (2.1), (2.5) and (2.11) that
J 6 = 2 ξ [ w t ( × u ˙ ) u u ˙ ( × w ) ] d x = 2 ξ w ˙ ( × u ˙ ) d x 2 ξ [ u w ( × u ˙ ) + u u ˙ ( × w ) ] d x 2 ξ w ˙ ( × u ˙ ) d x + C u L 6 w L 3 u ˙ L 2 2 ξ w ˙ ( × u ˙ ) d x + C w L 3 u ˙ L 2 , (2.30)
and, similarly,
J 7 = 2 ξ w ˙ ( × u ˙ ) d x 2 ξ [ u u ( × w ˙ ) + u w ˙ ( × u ) ] d x 2 ξ w ˙ ( × u ˙ ) d x + C u L 3 w ˙ L 2 , (2.31)
and
J 8 = 4 ξ | w ˙ | 2 d x + 4 ξ [ u w w ˙ + u w ˙ w ] d x = 4 ξ | w ˙ | 2 d x 4 ξ w w ˙ div u d x 4 ξ | w ˙ | 2 d x + C u L 2 w L 3 w ˙ L 6 4 ξ | w ˙ | 2 d x + C w ˙ L 2 . (2.32)
The ninth term on the right-hand side of (2.26) can be estimated as follows, integrating by parts, using (2.1), (2.5), (2.10), (2.11) and Hölder’s inequality:
J 9 = ( j u ˙ j H H t + k u ˙ j u k j H H ) d x C u ˙ L 2 ( H L 6 H t L 3 + u L 6 H L 6 H L 6 ) C u ˙ L 2 ( H t L 2 1 2 H t L 6 1 2 + u L 2 H H 1 ) δ u ˙ L 2 2 + C ( δ ) ( H t L 2 2 + H t L 2 2 + H H 1 2 ) . (2.33)
In a similar manner, one also has
J 10 = u ˙ j ( H t H j + H H t j + div ( u ( H H j ) ) ) d x = ( ( H t u ˙ j ) H j + ( H u ˙ j ) H t j + u k k u ˙ j ( H H j ) ) d x δ u ˙ L 2 2 + C ( δ ) ( H t L 2 2 + H t L 2 2 + H H 1 2 ) . (2.34)
Putting (2.27)-(2.34) into (2.26), using the Cauchy-Schwarz inequality and choosing δ > 0 suitably small, we get
d d t ( ρ u ˙ L 2 2 + ρ w ˙ L 2 2 ) + ( u ˙ L 2 2 + w ˙ L 2 2 + 2 w ˙ × u ˙ L 2 2 ) C ( 1 + u L 6 3 + w L 6 3 + H t L 2 2 + H t L 2 2 + H H 1 2 ) . (2.35)
To estimate H t L 2 , one can differentiate (1.1)4 with respect to t, multiply the resulting equations by H t in L 2 , and integrate by parts over R 3 to get
1 2 d d t | H t | 2 d x + σ | H t | 2 d x = ( H u t u t H H div u t ) H t d x + ( H t u u H t H t div u ) H t d x : = K 1 + K 2 . (2.36)
Integrating by parts and using (1.1)5, (2.1), (2.10) and (2.11), then we deduce
K 1 = ( H u ˙ u ˙ H H div u ˙ ) H t d x + ( H i i H t j H k j H t k ) ( u u j ) d x C H L 6 H t L 3 u ˙ L 2 + C u ˙ L 6 H L 2 H t L 3 + C H L 12 H t L 2 u L 4 u L 6 C ( H t L 2 1 2 H t L 2 1 2 u ˙ L 2 + H t L 2 u L 4 ) ε 1 H t L 2 2 + ε 2 u ˙ L 2 2 + C ( ε 1 , ε 2 ) ( H t L 2 2 + u L 4 2 )
for some positive constants ε 1 , ε 2 ( 0 , 1 ) . For the second term on the right-hand side of (2.36), integrating by parts and using (2.1) give
K 2 = ( H t u 1 2 H t div u ) H t d x C u L 2 H t L 2 C H t L 2 1 2 H t L 2 3 2 ε 1 H t L 2 2 + C ( ε 1 ) H t L 2 2 .
Putting the estimates of K 1 , K 2 into (2.36) and choosing ε 1 > 0 small enough, one has
1 2 d d t | H t | 2 d x + σ 2 | H t | 2 d x ε 2 u ˙ L 2 2 + C ( ε 2 ) ( H t L 2 2 + u L 4 2 ) . (2.37)
Then, combining (2.35) and (2.37), using Young’s inequality, and choosing ε 2 > 0 suitably small yield that
d d t ( ρ u ˙ L 2 2 + ρ w ˙ L 2 2 + H t L 2 2 ) + ( u ˙ L 2 2 + w ˙ L 2 2 + H t L 2 2 + 2 w ˙ × u ˙ L 2 2 ) C ( 1 + u L 6 3 + w L 6 3 + H t L 2 2 + H H 1 2 ) . (2.38)
Firstly, we use (2.4)-(2.6), (2.9), (2.10), (2.11), (2.1) and (2.2) to infer from the standard L p -estimate that
u L 6 + w L 6 C ( div u L 6 + × u L 6 + div w L 6 + × w L 6 ) C ( 1 + G 1 L 6 + G 2 L 6 + V 1 L 6 + V 2 L 6 + | H | 2 L 6 ) C ( 1 + G 1 L 2 + G 2 L 2 + V 1 L 2 + V 2 L 2 ) C ( 1 + ρ u ˙ L 2 + ρ w ˙ L 2 + H H 1 ) , (2.39)
and
ρ u ˙ L 2 + ρ w ˙ L 2 C ( ρ u t L 2 + ρ w t L 2 ) + C ( ρ u u L 2 + ρ w w L 2 ) C ( ρ u t L 2 + ρ w t L 2 ) + C ( u L u L 2 + w L w L 2 ) C ( ρ u t L 2 + ρ w t L 2 ) + C ( u L 6 1 2 + w L 6 1 2 ) . (2.40)
Moreover, by the standard L 2 -estimate of an elliptic system, we infer from (1.1)4, (2.1), (2.2) and (2.11) that
H H 1 C ( H t L 2 + u H L 2 + H u L 2 + u L 2 ) C ( H t L 2 + u L 6 H L 3 + H L u L 2 + 1 ) C ( H t L 2 + H L 2 1 2 H L 6 1 2 + 1 ) C ( H t L 2 + H H 1 1 2 + 1 ) ,
and hence,
H H 1 C ( H t L 2 + 1 ) . (2.41)
Combining (2.39)-(2.41), we obtain
u L 6 + w L 6 C ( 1 + ρ u t L 2 + ρ w t L 2 + H t L 2 ) . (2.42)
Now, putting (2.41) and (2.42) into (2.38), one has
d d t ( ρ u ˙ L 2 2 + ρ w ˙ L 2 2 + H t L 2 2 ) + ( u ˙ L 2 2 + w ˙ L 2 2 + H t L 2 2 + 2 w ˙ × u ˙ L 2 2 ) C ( 1 + ρ u ˙ L 2 2 + ρ w ˙ L 2 2 + H t L 2 2 ) ( 1 + ρ u t L 2 + ρ w t L 2 ) ,
from which and (2.11), we immediately obtain (2.25) by Gronwall’s inequality, (1.6) and (1.7). As a result of (2.41), we can also deduce the boundedness of H H 1 . □
The next lemma is used to bound the density gradient and u L 1 ( 0 , T ; L ) .
Lemma 2.8Under the condition (2.4), it holds that for any 0 T < T ,
sup 0 t T ( ρ L 2 L q + u H 1 + w H 1 ) + 0 T ( u L + u W 1 , q 2 + w W 1 , q 2 ) d t C (2.43)
for any q ( 3 , 6 ] .
Proof Differentiating (1.1)1 with respect to x i and multiplying it by | i ρ | q 2 i ρ ( q 2 ) in L 2 , we obtain, after integrating by parts and summing up, that
d d t | ρ | q d x C ( q ) ( | u | | ρ | q + ρ | ρ | q 1 | div u | ) d x C ( q ) ( u L ρ L q q + div u L q ρ L q q 1 ) . (2.44)
It follows from (2.1), (2.4), (2.6)-(2.9), (2.25) and the interpolation inequality that for any q ( 3 , 6 ] ,
div u L q C ( G 1 L q + P L q + H L H L q ) C ( 1 + G 1 L 2 + G 1 L 6 + ρ L q ) C ( 1 + u ˙ L 2 + w ˙ L 2 + ρ L q ) ,
where (2.2) and (2.25) were also used to get that H L C . So, putting this into (2.44) yields
d d t ρ L q C ( u L + 1 ) ρ L q + C ( 1 + u ˙ L 2 + w ˙ L 2 ) . (2.45)
We now estimate u L . To do this, we first observe that
( μ + ξ ) u + ( μ + λ ξ ) div u = ρ u ˙ + P 2 ξ × w + ( × H ) × H .
Hence, using the standard L p -estimate of an elliptic system leads to
2 u L q C ( ρ u ˙ L q + P L q + w L q + H H L q ) C ( 1 + u ˙ L 2 + ρ L q + w H 1 ) .
From (1.1)3 and the standard L 2 -estimate of the elliptic system, we have that
w H 1 C ( w H 1 + ρ w ˙ L 2 + u L 2 ) C , (2.46)
and then
2 u L q C ( 1 + u ˙ L 2 + ρ L q ) . (2.47)
This, together with Lemmas 2.2 and 2.6, gives
u L C ( u L 2 + 1 ) + C ( div u L + × u L ) log ( e + 2 u L q ) C + C ( div u L + × u L ) log ( e + u ˙ L 2 ) + C ( div u L + × u L ) log ( e + ρ L q ) . (2.48)
Now, if we set f ( t ) = e + ρ L q and let
g ( t ) = ( 1 + div u L + × u L + u ˙ L 2 + w ˙ L 2 ) log ( e + u ˙ L 2 ) ,
then it is seen from (2.45) and (2.48) that
f ( t ) = C g ( t ) f ( t ) + C g ( t ) f ( t ) ln f ( t )
due to f ( t ) > 1 . Thus,
( ln f ( t ) ) C g ( t ) + C g ( t ) ln f ( t ) . (2.49)
On the other hand, since
g ( t ) C ( 1 + div u L 2 + × u L 2 + u ˙ L 2 2 + w ˙ L 2 ) ,
we thus deduce from (2.11), (2.25), (2.4), (2.8), (2.9) and (2.2) that
0 T g ( t ) d t C 0 T ( 1 + div u L 2 + × u L 2 + u ˙ L 2 2 + w ˙ L 2 ) d t C + C 0 T ( div u L 2 + × u L 2 ) d t C + C 0 T ( G 1 L 2 + V 1 L 2 + P L 2 + H L 4 ) d t C + C 0 T ( G 1 L 2 2 + G 1 L 2 2 + V 1 L 2 2 + V 1 L 2 2 ) d t C + C 0 T ( u ˙ L 2 2 + w ˙ L 2 2 + H H 1 4 ) d t C . (2.50)
As a result, it follows from (2.49) and Gronwall’s inequality that
f ( t ) C for any 0 t T < T ,
and consequently,
sup 0 t T ρ L q C for any q ( 3 , 6 ] . (2.51)
From this and (2.25), (2.48), (2.50), one obtains
0 T u L d t C . (2.52)
Taking q = 2 in (2.45), we get, by using (2.52) and (2.25) and Gronwall’s inequality, that
sup 0 t T ρ L 2 C . (2.53)
Moreover, the standard L 2 -estimate of an elliptic system and (1.1)2, together with (2.4), (2.11) and (2.25), implies
2 u L 2 C ( ρ u ˙ L 2 + P L 2 + H H L 2 + u L 2 + w L 2 ) C ( 1 + ρ L 2 ) C . (2.54)
Similar to the proof of (2.47), there are
2 u L q + 2 w L q C ( 1 + u ˙ L 2 + ρ w ˙ L q + u L q + w L q ) C ( 1 + u ˙ L 2 + w ˙ L 2 ) , q ( 3 , 6 ] ,
where we have used (2.1), (2.11), (2.46), (2.51) and (2.54). From this, together with (2.25), (2.46) and (2.51)-(2.54), we can deduce (2.43). □
As a consequence of Lemmas 2.6-2.8, we have the following lemma.
Lemma 2.9Under the condition (2.4), it holds that for any 0 T < T ,
sup 0 t T ( ρ u t L 2 2 + ρ w t L 2 2 ) + 0 T ( u t L 2 2 + w t L 2 2 ) d t C . (2.55)
The proof is the same as that of Lemma 3.6 in [20] and is omitted here.
With the help of Lemmas 2.3, 2.6-2.9 and the local existence theorem, we can complete the proof of Theorem 1.2 by the contradiction arguments. In fact, in view of Lemmas 2.3, 2.6-2.9, it is easy to see that the functions ( ρ , u , w , H ) ( x , T ) = lim t T ( ρ , u , w , H ) have the same regularities imposed on the initial data (1.5) at the time t = T . This implies that the compatibility conditions (1.6) and (1.7) are satisfied at the time T . Thus, we can take ( ρ , u , w , H ) ( x , T ) as the initial data and apply the local existence theorem to extend the local strong solutions beyond T . This contradicts the assumption that T is the maximal time of existence.
### Competing interests
The author declares that they have no competing interests.
### Acknowledgements
This work is partially supported by the Fundamental Research Funds for the Central Universities (Grant No. 11QZR16), the National Natural Science Foundation of China (Grant No. 11001090).
### References
1. Berkovski, B, Bashtovoy, V: Magnetic Fluids and Applications Handbook, Begell House, New York (1996)
2. Hatzikonstantinou, PM, Vafeas, P: A general theoretical model for the magnetohydrodynamic flow of micropolar magnetic fluids. Application to Stokes flow. Math. Methods Appl. Sci.. 33, 233–248 (2009)
3. Papadopoulos, PK, Vafeas, P, Hatzikonstantinou, PM: Ferrofluid pipe flow under the influence of the magnetic field of a cylindrical coil. Phys. Fluids. 24, Article ID 122002 (2012)
Article ID 122002
Publisher Full Text
4. Rosensweig, RE: Ferrohydrodynamics, Dover Publications, New York (1997)
5. Rojas-Medar, MA: Magneto-micropolar fluid motion: existence and uniqueness of strong solution. Math. Nachr.. 188, 301–319 (1997). Publisher Full Text
6. Ortega-Torres, EE, Rojas-Medar, MA: Magneto-micropolar fluid motion: global existence of strong solutions. Abstr. Appl. Anal.. 4, 109–125 (1999). Publisher Full Text
7. Yuan, J: Existence theorem and blow-up criterion of strong solutions to the magneto-micropolar fluid equations. Math. Methods Appl. Sci.. 31, 1113–1130 (2008). Publisher Full Text
8. Yuan, BQ: Regularity of weak solutions to magneto-micropolar fluid equations. Acta Math. Sci.. 30, 1469–1480 (2010)
9. Gala, S: Regularity criterion for 3D magneto-micropolar fluid equations in the Morrey-Campanato space. Nonlinear Differ. Equ. Appl.. 17, 181–194 (2010). Publisher Full Text
10. Volpert, AI, Khudiaev, SI: On the Cauchy problem for composite system of nonlinear equations. Mat. Sb.. 87, 504–528 (1972)
11. Fan, JS, Yu, WH: Strong solution to the compressible MHD equations with vacuum. Nonlinear Anal., Real World Appl.. 10, 392–409 (2009). Publisher Full Text
12. Xu, XY, Zhang, JW: A blow-up criterion for 3D compressible magnetohydrodynamic equations with vacuum. Math. Models Methods Appl. Sci.. 22, Article ID 1150010 (2012)
13. Mujakovic, N: One-dimensional flow of a compressible viscous micropolar fluid: a local existence theorem. Glas. Mat.. 33(53), 71–91 (1998)
14. Mujakovic, N: One-dimensional flow of a compressible viscous micropolar fluid: a global existence theorem. Glas. Mat.. 33(53), 199–208 (1998)
15. Chen, MT: Global strong solutions for the viscous, micropolar, compressible flow. J. Partial Differ. Equ.. 24, 158–164 (2011)
16. Amirat, Y, Hamdache, K: Weak solutions to the equations of motion for compressible magnetic fluids. J. Math. Pures Appl.. 91, 433–467 (2009)
17. Lions, PL: Mathematical Topics Influid Mechanics. Vol. 2. Compressible Models, Oxford University Press, New York (1998)
18. Feireisl, E, Novotny, A, Petzeltová, H: On the existence of globally defined weak solutions to the Navier-Stokes equations. J. Math. Fluid Mech.. 3, 358–392 (2001). Publisher Full Text
19. Chen, MT: Unique solvability of compressible micropolar viscous fluids. Bound. Value Probl.. 2012, Article ID 32 (2012)
20. Chen, MT, Huang, B, Zhang, JW: Blowup criterion for three-dimensional equations of compressible viscous micropolar fluids with vacuum. Nonlinear Anal.. 79, 1–11 (2013)
21. Huang, XD, Li, J, Xin, ZP: Serrin-type criterion for the three-dimensional viscous compressible flows. SIAM J. Math. Anal.. 43(4), 1872–1886 (2011). Publisher Full Text
22. Choe, JH, Kim, H: Strong solutions of the Navier-Stokes equations for isentropic compressible fluids. J. Differ. Equ.. 190, 504–523 (2003). Publisher Full Text |
# Role of a difference in generating symmetric palindromes
An example : 923456781-123456789=799999992
Now divide it by the difference between the terminal digits, i.e. 9-1=8
So 799999992/8=99999999
Another example : 52314780-02314785=49999995/5=99999999
But if we do : 799999992/9=88888888 and 49999995/9=5555555
So either the difference or 9 itself help in generating symmetric palindromes
Can this be generalized?
-
Looks like you are the same person as math.stackexchange.com/users/47960/pradip-saha math.stackexchange.com/users/48050/pradip-saha Kindly do not create multiple accounts. I have asked the moderators to merge these accounts. – user17762 Nov 4 '12 at 18:36
Ok, thanks @Marvis, any thoughts on this question.. – Pradip Saha Nov 4 '12 at 18:39
Yes, this idea works fine in general.
Given a positive integer $n$ with at least two digits, define its… "outer flip" $o(n)$ to be the number obtained by swapping its first and last digits, so that $o(123456789)=923456781$, $o(52314780)=02314785$ (note that $o$ is not an involution since $o(o(52314780))=5314782$). Also define $d(n)$ to be the difference of the outer digits of $n$, so that $d(n)=0$ exactly if $n=o(n)$ and $d(n)$ achieves a maximum of $9$ for numbers such as $970$.
Fact 1: If $n\ne o(n)$, then $\left|n-o(n)\right|$ is the number starting with the digit $[d(n)-1]$, ending with the digit $[10-d(n)]$, and enough $9$s in between so that it has the same length (counting the leading zero if $d(n)=1$) as $n$. This follows because all the digits in the middle cancel eachother, and then it's a result of the carrying process for differences like $70002-20007$.
Note that if we pick an $n$ with the desired length and $d(n)$ then this way (as $\left|n-o(n)\right|$) we can obtain all numbers that end with some nonzero digit, "begin" with $9$ minus that digit (possibly $0$) and have an arbitrary (possibly empty) string of $9$s in the middle. Call these numbers "nineish". Define the "modified length" of nineish number to be its actual length if it doesn't end in $9$, and one more than its length if it does (to account for the leading zero).
Fact 2: A nineish number $n$ with last digit $\delta$ is the product of a string of $9$s of length one less than the modified length of $n$ and the one-digit-number $10-\delta$ (this corresponds to $d(m)$ if $n=|m-o(m)|$). To show that something is, say, $9999*7$, it suffices to show that when you add $7$ to it, you get $10000*7$. But this follows from the definition of a nineish number because if you add $10-\delta$ to $\delta$, you get $10$ which carries through the whole string of nines producing zeros until the end where we have the sum $(9-\delta)+1=10-\delta\checkmark$.
Fact 3: A nineish number $n$ with last digit $\delta$ is the product of $9$ and a string of the digit $10-\delta$ with length one less than the modified length of $n$. You can argue this fact directly, but it's easier to use fact 2, which says that $n=999\ldots9*(10-\delta)$, so that $n=9*111\ldots1*(10-\delta)$, but $111\ldots1*(10-\delta)$ is exactly the string we wanted to get after division by $9$.
- |
# Representing vertices as spheres in Graphics 3D [closed]
I'm representing a portion of molecule, P3HT, in Mathematica as a pentagon that I build using Polygon and Graphics3D.
I would like to represent the vertices of the pentagon as spheres(corresponding to atoms).
If possible I would like to add a vector perpendicular to the P3HT plane stemming from the centroid of the plane.
Here's what I have so far:
The atomic coordinates:
C1 := {-1.51767 , 2.46541, -0.0036}
C2 := {-1.15943, 1.11229, -0.00326}
C3 := {0.25701, 0.88881, -0.00082}
C4 := {0.9979, 2.09239, 0.00071}
S := {-0.10561, 3.33212, -0.00095}
The molecular plane, defined by the atomic coordinates:
P3HTPlane = Polygon[{{-1.51767, 2.46541, -0.0036}, {-1.15943,
1.11229, -0.00326}, {0.25701, 0.88881, -0.00082}, {0.9979,
2.09239, 0.00071}, {-0.10561, 3.33212, -0.00095}}]
The centroid of the plane:
OO = RegionCentroid[P3HTPlane]
The plot of the plane with the centroid included:
Graphics3D[{LightOrange, P3HTPlane, Red, PointSize[0.02], Point[OO]},
BoxRatios -> {1, 1, 1}]
In case it helps, here's the molecule I'm working with:
ChemicalData["3-hexylthiophene", "MoleculePlot"]
Thanks for the help!
• You can draw a sphere centered at C1 with radius say 0.1 using Sphere[C1, 0.1]. You can draw multiple spheres using Sphere[C1, 0.1], Sphere[C2, 0.1], ... or just Sphere[{C1, C2, ...}, 0.1] for short. You'll want to remove the BoxRatios -> {1, 1, 1}` option though or the spheres won't look like spheres. – Rahul Aug 26 '16 at 23:12
• Awesome! I got the whole thing working. Thank you very much! – Victor Murcia Aug 26 '16 at 23:57 |
# American Institute of Mathematical Sciences
November 2013, 33(11&12): 5293-5303. doi: 10.3934/dcds.2013.33.5293
## How to distinguish a local semigroup from a global semigroup
1 Department of Mathematics, University of North Texas, Denton, TX 76205-5017, United States
Received September 2011 Revised March 2012 Published May 2013
For a given autonomous time-dependent system that generates either a global, in time, semigroup or else only a local, in time, semigroup, a test involving a linear eigenvalue problem is given which determines which of global' or local' holds. Numerical examples are given. A linear transformation $A$ is defined so that one has global' or local' depending on whether $A$ does not or does have a positive eigenvalue. There is a possible application to Navier-Stokes problems..
Citation: J. W. Neuberger. How to distinguish a local semigroup from a global semigroup. Discrete & Continuous Dynamical Systems, 2013, 33 (11&12) : 5293-5303. doi: 10.3934/dcds.2013.33.5293
##### References:
show all references
##### References:
[1] Viorel Nitica, Andrei Török. On a semigroup problem. Discrete & Continuous Dynamical Systems - S, 2019, 12 (8) : 2365-2377. doi: 10.3934/dcdss.2019148 [2] Rui L. Fernandes, Yuxuan Zhang. Local and global integrability of Lie brackets. Journal of Geometric Mechanics, 2021, 13 (3) : 355-384. doi: 10.3934/jgm.2021024 [3] Andrzej Biś. Entropies of a semigroup of maps. Discrete & Continuous Dynamical Systems, 2004, 11 (2&3) : 639-648. doi: 10.3934/dcds.2004.11.639 [4] Michael Blank. Recurrence for measurable semigroup actions. Discrete & Continuous Dynamical Systems, 2021, 41 (4) : 1649-1665. doi: 10.3934/dcds.2020335 [5] Carlos Cabrera, Peter Makienko, Peter Plaumann. Semigroup representations in holomorphic dynamics. Discrete & Continuous Dynamical Systems, 2013, 33 (4) : 1333-1349. doi: 10.3934/dcds.2013.33.1333 [6] Jana Kopfová. Nonlinear semigroup methods in problems with hysteresis. Conference Publications, 2007, 2007 (Special) : 580-589. doi: 10.3934/proc.2007.2007.580 [7] Renato Iturriaga, Héctor Sánchez Morgado. The Lax-Oleinik semigroup on graphs. Networks & Heterogeneous Media, 2017, 12 (4) : 643-662. doi: 10.3934/nhm.2017026 [8] Nobuyuki Kenmochi, Noriaki Yamazaki. Global attractor of the multivalued semigroup associated with a phase-field model of grain boundary motion with constraint. Conference Publications, 2011, 2011 (Special) : 824-833. doi: 10.3934/proc.2011.2011.824 [9] Dongkui Ma, Min Wu. Topological pressure and topological entropy of a semigroup of maps. Discrete & Continuous Dynamical Systems, 2011, 31 (2) : 545-556. doi: 10.3934/dcds.2011.31.545 [10] Bin Chen, Xiongping Dai. On uniformly recurrent motions of topological semigroup actions. Discrete & Continuous Dynamical Systems, 2016, 36 (6) : 2931-2944. doi: 10.3934/dcds.2016.36.2931 [11] Luisa Arlotti. Explicit transport semigroup associated to abstract boundary conditions. Conference Publications, 2011, 2011 (Special) : 102-111. doi: 10.3934/proc.2011.2011.102 [12] Stephen Thompson, Thomas I. Seidman. Approximation of a semigroup model of anomalous diffusion in a bounded set. Evolution Equations & Control Theory, 2013, 2 (1) : 173-192. doi: 10.3934/eect.2013.2.173 [13] Armand Bernou. A semigroup approach to the convergence rate of a collisionless gas. Kinetic & Related Models, 2020, 13 (6) : 1071-1106. doi: 10.3934/krm.2020038 [14] Yujun Ju, Dongkui Ma, Yupan Wang. Topological entropy of free semigroup actions for noncompact sets. Discrete & Continuous Dynamical Systems, 2019, 39 (2) : 995-1017. doi: 10.3934/dcds.2019041 [15] Klara Stokes, Maria Bras-Amorós. Associating a numerical semigroup to the triangle-free configurations. Advances in Mathematics of Communications, 2011, 5 (2) : 351-371. doi: 10.3934/amc.2011.5.351 [16] Gérard Maze, Chris Monico, Joachim Rosenthal. Public key cryptography based on semigroup actions. Advances in Mathematics of Communications, 2007, 1 (4) : 489-507. doi: 10.3934/amc.2007.1.489 [17] Rainer Steinwandt, Adriana Suárez Corona. Cryptanalysis of a 2-party key establishment based on a semigroup action problem. Advances in Mathematics of Communications, 2011, 5 (1) : 87-92. doi: 10.3934/amc.2011.5.87 [18] András Bátkai, Istvan Z. Kiss, Eszter Sikolya, Péter L. Simon. Differential equation approximations of stochastic network processes: An operator semigroup approach. Networks & Heterogeneous Media, 2012, 7 (1) : 43-58. doi: 10.3934/nhm.2012.7.43 [19] Joseph Auslander, Xiongping Dai. Minimality, distality and equicontinuity for semigroup actions on compact Hausdorff spaces. Discrete & Continuous Dynamical Systems, 2019, 39 (8) : 4647-4711. doi: 10.3934/dcds.2019190 [20] Wilson Lamb, Adam McBride, Louise Smith. Coagulation and fragmentation processes with evolving size and shape profiles: A semigroup approach. Discrete & Continuous Dynamical Systems, 2013, 33 (11&12) : 5177-5187. doi: 10.3934/dcds.2013.33.5177
2020 Impact Factor: 1.392 |
### Welcome to our site!
#### Boncuk
##### Banned
I would recommend buy two of them and setting them up as a redundant raid array.. It's not practical to backup that much data, and no one wants to lose 3 terrabytes of data because of a cheap drive. Might seem like a waste to use 2 drives as mirror, but if the raid controller is even halfway decent (most of them are nowdays I think) it'll also increase bulk read speeds.
#### MrAl
##### Well-Known Member
Hi,
I broke out my old TRS80 the other day after cleaning a bit and that thing has
floppy drives that are 180k bytes ha ha.
The hard drive for that thing, when it was available back in the 80's, was 20 megabytes
and cost 400 dollars US.
##### Banned
It really is amazing how good they've gotten at miniturizing electronics. I have an 8 gig USB thumb drive that's as small as a thumb NAIL =\ And the largest SD cards that are out there are insanely huge for something that you could accidentally swallow and come to no harm =P
I junked them a ways back but I used to still have functional RLL hard drives from some old machine I had ages ago.
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#### killivolt
That's an amazing price considering I've been looking at one for viseo editing that was 1TB at 99 US .... hmmmm, your link has me rethinking things. As for never filling a 3TB drive, consider archiving high quality videos. It will fill up... yes after a long time, but still nonetheless. HiTech, you have it wrong I should have worded this better I Purchased Quantity of 3 - 1TB drives. But, there is free shipping. I mostly wanted someone to say a little about the type of drive to see if they were crap or not. One of my CT administrators found it and I bought them for work. Plus, I thought it might be a good deal by the sounds of it you found some @ 99.00 so I didn't get that great of a deal. Thanks for pointing that out I'll re-word that better. kv #### HiTech ##### Well-Known Member My bad! I should stop "skim reading" posts. #### Boncuk ##### New Member What year was that Boncuk? That was 1985. I needed more than 720KB on a 3 1/2" floppy for stock keeping. The computer was an Amstrad Joyce. The HDD wasn't much faster than a floppy though. #### 3v0 ##### Coop Build Coordinator Forum Supporter My first machine had paper tape which I replaced with twin 8 inch floppies. My first hard drive had a removable platter. 3v0 Last edited: #### gabeNC ##### Member Can't wait till i'm as old you farts. I can tell the kids... "back in the day I had to use an actual keyboard... not these neural net transmitters..." #### Boncuk ##### New Member Can't wait till i'm as old you farts. When you have reached that age you'll wish to be young again. BTW, did you intend to write "as old as you"? Last edited: #### davidbball13 ##### Member I filled up a 400 gig drive in less than a year. and now I have a 640 in there too. and the 640 is about 50% full...... #### HiTech ##### Well-Known Member I shudder to think I used to slave infront of a TRS-80III w/ 48K memory! What POS but at that time it was a toy to waste the hours away by. I remember using it to catalog my videotape inventory. It would take approximately 10-12 hours to sort tapes according to title, date, length, etc. Now, that was 10-12 hrs. to arrange them in order under ONE category only. If I wanted to change the sorting category or add a newly recorded tape, it was another 10-12 hrs!!! Oh Lord, then there was that awful printer that always had paper alignment issues! #### birdman0_o ##### Active Member I filled up a 400 gig drive in less than a year. and now I have a 640 in there too. and the 640 is about 50% full...... Sounds like a whole bunch of legal music to me #### jpanhalt ##### Well-Known Member Most Helpful Member94 per TB, what a rip-off
My local computer is offering Samsung F2EG TB drives at \$69.99. By Monday, maybe it will be buy one, get one free. I think I will wait.
Wonder how long it would take to re-build a RAID1 on a whole TB?
John
##### Banned
Raid 1 is full mirror.
So, looking up the specs real fast. It has a Maximum of 166mb's a second media to buffer read speed, that's probably on the inner ring. I'm not sure of the disc size or exactly how to calculate how that would slow down on the outter ring, but lets assume an average read speed of 1/5th of that, or about 30 megs a second average edge to edge. According to my calculator that'd be around 9 hours. But that's just a rough guesstimate.
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Open access peer-reviewed chapter
# Absorption of Acoustic Phonons in Fluorinated Carbon Nanotubes with Non-Parabolic, Double Periodic Band
By Daniel Sakyi-Arthur, S. Y. Mensah, N. G. Mensah, Kwadwo A. Dompreh and R. Edziah
Submitted: February 27th 2018Reviewed: May 2nd 2018Published: December 12th 2018
DOI: 10.5772/intechopen.78231
## Abstract
We studied theoretically the absorption of acoustic phonons in the hypersound regime in Fluorine modified carbon nanotube (F-CNT) Γ q F − CNT and compared it to that of undoped single walled carbon nanotube (SWCNT) Γ q SWCNT . Per the numerical analysis, the F-CNT showed less absorption to that of SWCNT, thus ∣ Γ q F − CNT ∣ < ∣ Γ q SWCNT ∣ . This is due to the fact that Fluorine is highly electronegative and weakens the walls of the SWCNT. Thus, the π -electrons associated with the Fluorine causes less free charge carriers to interact with the phonons and hence changing the metallic properties of the SWCNT to semiconductor by the doping process. From the graphs obtained, the ratio of hypersound absorption in SWCNT to F-CNT at T = 45 K is Γ SWCNT Γ F − CNT ≈ 29 while at T = 55 K , is Γ SWCNT Γ F − CNT ≈ 9 and at T = 65 K , is Γ SWCNT Γ F − CNT ≈ 2 . Clearly, the ratio decreases as the temperature increases.
### Keywords
• carbon nanotube
• fluorinated
• acoustic effects
• hypersound
## 1. Introduction
Acoustic effects in bulk and low dimensional materials have attracted lots of attention recently. This is due to the need of finding coherent acoustic phonons for scientific applications as against the use of conventional direct current [1]. Materials such as homogenous semiconductors, superlattices (SL), graphene and carbon nanotubes (CNT) are good candidates for such studies due to their novel properties such as the high scattering mechanism, the high-bias mean-free path (l) and their sizes which enable strong electron-phonon interaction to occur in them resulting in acoustic phonon scattering. Acoustic waves through these materials are characterized by a set of elementary resonance excitations and dynamic nonlinearity which normally leads to an absorption (or amplification), acoustoelectric effect (AE) [2], and acoustomagnetoelectric effect (AME) [3, 4]. The concept of acoustic wave amplification was first predicted in bulk materials [5], and later in n-Ge [6]. In SLs, Mensah et al. [7] studied hypersound absorption (amplification) and established its use as a phonon filter, and in [8], predicted the use of the SL as a hypersound generator which was confirmed in [1]. In Graphene, Nunes et al. [9] treated theoretically hypersound amplification, but Dompreh et al. [10] further proved that absorption also occurs in the material. Experimentally, Miseikis et al. [11] and Bandhu and Nash [12] have studied acoustoelectric effect in Graphene.
Carbon nanotubes (CNTs), on the other hand, are cylindrical hollow rod of graphene sheets whose electronic structures are determined by the localized π-electrons in the sp2- hybridized bonds. Absorption (Amplification) of hypersound in undoped CNT has been carried out theoretically by Dompreh et al. [13, 14] and experimentally by [15, 16]. Other forms of research such as hot-electron effect [17], thermopower in CNT [18] have been carried out. Flourine-modified CNT (F-CNT) is off-late attracting a lot of scientific interest. This is attained by doping the CNT with Fluorine thus forming double periodic band CNT changing from metallic to semiconductor. As per the studies conducted by Jeon et al. [19], absorption in F-CNT is less than that of SWCNT but no studies have been done on the absorption of F-CNT in the hypersound regime. In this paper, the study of absorption of acoustic phonons in metallic SWCNT and F-CNT are theoretically studied. Here, the acoustic wave considered has wavelength λ=2π/q, smaller than the mean-free path of the CNT and then treated as a packet of coherent phonons (monochromatic phonons) having a δ-function distribution as
Nk=2π3ωqvsΦδkqE1
where kis the phonon wavevector, is the Planck’s constant divided by 2π, and Φis the sound flux density, and ωqand vsare respectively the frequency and the group velocity of sound wave with wavevector q. It is assumed that the sound wave is propagated along the z-axis of the CNT.
This paper is organized as follows: In Section 2, the absorption coefficient for F-CNT and SWCNT are calculated. In Section 3, the final equations are analyzed numerically and presented graphically. Section 4 presents the conclusion of the study.
## 2. Theory
Fluorination plays a significant role in the doping process, as it provides a high surface concentration of functional groups, up to C2Fwithout destruction of the tube’s physical structure. Doping is an easy, fast, exothermic reaction and the repulsive interactions of the Fluorine atoms on the surface debundles the nanotube, thus enhancing their electron dispersion [20]. Figure 1 shows a one dimensional SWCNT doped with Fluorine atoms [21]. Consider a Fluorine modified CNT (n,n) with the Fluorine atoms forming a one-dimensional chain. A nanotube of this nature is equivalent to a band with unit cell as shown in Figure 2, where bis the bond length (C-C) [22].
The width for the F-(n,n) tube equals nperiods (with a periodic length of 3b), and this unit cell contains N=4n2carbon atoms which is shown in Figure 3 [22]. Figure 3 shows the atomic numbering in the unit cell of the F-(n,n) nanotube. For a conjugated πsystem, in which there is alternation of single and double bonds along a linear chain, the Hückel matrix approximation is employed to determine the electronic energy band. Proceeding as in [8, 23], we employ the Hamiltonian of the electron-phonon system in the FCNT in the second quantization formalism as
H=p,νενppecAtapν+aνν+kωkbk+bk+1Np,kννnckmννkzapν+apk+ngνbk++bkE2
where ν=1,2and for a chemically modified F-CNT, where the Fluorine atoms form a one-dimensional chain, the energy dispersion can be deduced by using the Huckel matrix method where translational symmetry is accounted for in [22] as
εpz=εo+Ξnγ0cos2N1apzE3
where a=3b/2, Ξis a constant, Nis an integer, and εois the minimum energy of the πelectrons within the first Brillouin zone. For N=2, the energy dispersion for F-CNT at the Fermi surface at the edge of the Brillouin zone is
εpz=απ+8γocos3apzE4
Eq. (4) can be expanded as
εpz=εo+Δ1cos3apz+Δ2cosapzE5
where εois the electron energy in the first Brillouin zone with momentum po, i.e., π/apoπ/a, Δ1=Δ/kBT, Δ2=3Δ/kBTand Δ=2γo. By employing the coulombs gauge, the electromagnetic wave Et=Eosinωtis related to the vector potential Atis the vector potential related to the external electric field of the electromagnetic wave Et=Eosinωtby the relation E=1/cA/tand is directed along the F-CNT tubular axis. ap+and apare the creation and annihilation operators of an electron with quasi-momentum pin the νthminiband respectively, and bk+and bkare the phonon creation and annihilation operators respectively. Nis the number of FCNT periods, g=0,0,2π/dis the FCNT reciprocal vector, and mνν'is given by
mνν'kz=φν'zφνzeikzdzE6
where φνzis the wavefunction of the νthstate in one of the one-dimensional potential wells from which the FCNT potential is formed. The electromagnetic wave frequency is assumed to be large compared with the inverse of the electron mean free time 1/τand the wavelength is taken to be large compared with the FCNT period, electron mean free path and the de Broglie wavelength. This opens the way for us to use the dipole approximation as in [8]. Moreover, the plane electromagnetic wave of frequency ωsatisfies ω/ωp>1, where ωpis the plasma frequency. In the case of the phonons, we confine our considerations to those for which the wavevector q, satisfies the conditions ql1where lis the electron mean free path in FCNT. Such phonons constitute a well-defined elementary excitations of the system.
For ωτ1and ω>ωp, ensures that the electromagnetic wave penetrate the sample and the condition ql1means that the hypersound wavelength is far smaller than the electron mean free path. The phonon dispersion relation then reads as
itbqt=bqHt=ωqbqt+1NCqpmssqzaps+ap+qngstE7
After much simplification, the phonon transition rate in the presence of the electromagnetic reduces to
Γq=ImΩ=2πΦωqVspz,n=J2ξ×fεnpzfεnpz+qδεnpz+qεnpzωqℓΩE8
that is, the imaginary part of the polarization vector. In Eq. (8) Jxis the Bessel function of order and argument x. It follows from Eq. (8) that if Γq>0we have hypersound attenuation, whereas if Γq<0we have hypersound amplification due to absorption Γq>0and emission Γq<0of photons from the intensified laser field.
In the region of an intense laser field, i.e., ξω, only the electron-phonon collisions with the absorption or emission of 1photons are significant. Accordingly, in the case of ξωthe argument of the Bessel function Jξis large. For large values, the Bessel function Jξis small except when the order is equal to the argument.
ξ=eEoa2ΔqΩ2E9
Taking the sum over using the approximation in Eq. (10)
=J2ξδEℓΩ12δEξ+δE+ξE10
where E=εpz+qεpzωq. Using the Fermi Golden Rule, the phonon transition rate reduces Γq=Un,nacwhere
Un,nac=2πΦωqVspz,pzn,n{|Gpzq,pz|2[f(εn(pzq))f(εn(pz))]δ(εn(pzq)εn(pz)+ωqξ)+|Gpz+q,pz|2[f(εn(pz+q))f(εn(pz))]δ(εn(pz+q)εn(pz)ωq+ξ)}E11
fpz=fεn,npzis the unperturbed distribution function, εn,npzis the energy band, nand ndenotes the quantization of the energy band, and Gpz±qpzis the matrix element of the electron-phonon interaction. Letting pz=pz±qand employing the principle of detailed balance, we assume that scattering into a state pzand out of the state pzis the same, and hence
Gp,p2=Gp,p2E12
Substituting Eq. (12) into Eq. (11) and also converting the summation over pz'into an integral, we obtain
Γq=2πΦωqvs.n,n'Gp,p2fεpzfεpz+qδεpz+qεpzωq+ξdpzE13
The matrix element of the electron-phonon interaction is given as
Gp,p=Λq2σωqE14
where Λis the deformation potential constant, and σis the density of F-CNT. Substituting Eq. (14) into Eq. (13), we obtain
Γq=2πΦωqvsΛq2σωq2n,nfεnpzfεnpz+q×δεnpz+qεnpzωq+ξdpzE15
The electron distribution function is obtained by obtained by solving the Boltzmann transport equation in the presence of external electric field
frptt+vp.rfrpt+eEpfrpt=frptfopτE16
and has a solution of
fpz=0dtτexpt/τfopzeaEtE17
and fopzis the Fermi-Dirac distribution given as
fopz=1expεpzμ/kBT+1E18
where μis the chemical potential which ensures the conservation of electrons, kBis the Boltzmann’s constant, Tis the absolute temperature in energy units. Substituting Eqs. (17) and (18) into Eq. (15), we obtain an equation for Γqwhich contains Fermi-Dirac integral of the order 1/2as
F1/2ηf=1Γ1/20ηf1/21+expηηfE19
where EFEc/kBTηf. For nondegenerate electron gas, where the Fermi level is several kBTbelow the energy of the conduction band Ec(i.e., kBTEc), the integral in Eq. (19) approaches 2/πexpηf. Eqs. (18) and (19) then simplifies to
fopz=CexpεpzeaEτ/kBTE20
where Cis the normalization constant to be determined from the normalization condition fpdp=noas
C=3noa22IoΔ1IoΔ2expεoEFkBTE21
where nois the electron density concentration, Tis the absolute temperature in energy units and Ioxis the modified Bessel function of zero order.
From the conservation laws, the momentum (pz) can be deduced from the delta function part of Eq. (15) as
pz=q2+14aarcsinωq12γoaqE22
By substituting pzinto the distribution function in Eq. (15), and after some cumbersome calculations yields
ΓqFCNT=ΓosinhΔ1cos3pasinAsin32aq+Δ2cospasinBsina2q×coshΔ1cos3pacosAcos32aq+Δ2cospacosBcosa2q4Δ2sinpacosBsina2q+Δ1cosAsin3pasin32aq+Δ1Δ2sinpasin3pacosAcosBsina2qsin32aq×sinhΔ1cos3pacosAcos32aq+Δ2cospacosBcosa2q×coshΔ1cos3pasinAsin32aq+Δ2cospasinBsina2qE23
where χ=ωqa/vs, Θis defined to be the Heaviside step function, α=ωq/12γoaq=ωq/6Δ1aq. In the absence of an external electric field
ΓqFCNT=ΓosinhΔ1sin32aqsinA+Δ2sina2qsinB×coshΔ1cos32aqcosA+Δ2cosa2qcosBE24
and
Γo=noa2ΦΛ2qΘ1α248πIo2γoβIo6γoβωq2σvsγo1α2A=34arcsinωq12γoaqB=14arcsinωq12γoaqα=ωq12γoaqE25
To compare the result with an undoped SWCNT, we follow the same procedure as that of F-CNT. Using the tight-binding energy dispersion of the pzorbital which is given as:
εpz=±γo1+4cosνπncospz3b2+4cos2pz3b2E26
where γo=2.6eVis the hopping integral parameter, b=0.142nmis the C-C bonding distance, and (+) and () signs are respectively the conduction and valence band. When ν=0, the conduction and valence bands cross each other near the Fermi points, pF=±2π/33bgiving the metallic nature to the armchair tube. Putting ν=0, and making the substitution, pz=pz+3po/2in Eq. (26) gives
εpz=±γo12cospz3b2E27
where po=2pF=4π/33b1.7×1010m1see [24]. Eq. (27) is equivalent to the energy dispersion in Eq. (5) when n=1, which is
εpz=εo+ΞγocosapzE28
Using Eq. (15), the absorption in SWCNT is calculated as
ΓqSWCNT=π2Λ2q2ΦnoΘ1α24γo2ωq2vsσsinaq/2Io2γoβ1α2×sinhβωqcosh4γoβ1α2cosaq2E29
where
α=ωq4γosinaq/2E30
## 3. Results and discussions
In this formulation, we consider a novel concept of monochromatic acoustic phonon amplification at the THz frequencies regime. Impulsive phonon excitation by a femtosecond optical pulse generates coherent FCNT and SWCNT phonons propagating in the forward and backward direction along the FCNT and SWCNT axis, that is setting up an stationary acoustic wave. Interaction of the propagating acoustic wave with an electrically driven intraminiband transition electron current allows for phonon absorption, connected with electron transitions between states within an electronic miniband. The intravalley or intraminiband character of the electron transport allows for much higher currents than interminiband electron or electron tunneling and thus, a much stronger phonon absorption.
The general expressions for the hypersound absorption in F-CNT (ΓqFCNT) and in SWCNT (ΓqSWCNT) are presented in Eqs. (24) and (29) respectively. In both equations, the absorptions are dependent on the frequency (ωq), the acoustic wavenumber (q), and temperature (T) as well as other parameters such as the inter-atomic distances, the velocity of sound (vs) and the deformation potential (Λ). In both expressions (see Eqs. (24) and (29)) a transparency window is observed: for F-CNT is ωq12γoaq; and for SWCNT is ωqγosin12aq/. These are the consequence of conservation laws. The Eqs. (24) and (29), are analyzed numerically with the following parameters used: Λ=9eV, q=105cm1, ωq=1012s1, vs=5×103m/s, Φ=104Wb/m2, and T=45K. The results are graphically plotted (see Figures 4, 5, 6, 7). Figure 4 shows the dependence of the sound absorption coefficient on the frequency (ωq) for varying q. In both graphs, the absorption is initially high but falls off sharply and then changes slowly at high values of ωq. Increasing the values of qcorrespondingly increases the obtained graph in both doped F-CNT and undoped SWCNT though the magnitude of absorption obtained in SWCNT exceeds that of F-CNT, that is, ΓqSWCNT>ΓqFCNT. This is in accordance with the work of Jeon et al. [19]. In Figure 2, the graph increases to a maximum point then drops off. It then changes again slowly at high qfor both undoped SWCNT and doped F-CNT. By increasing the temperature, the amplitude of the graphs reduces. For T=45K, the maximum absorption in ΓqSWCNT=8.2×104whilst that of ΓqFCNT=2867which gives the ratio of the absorption ΓSWNTΓFCNT29, whilst at T=55K, ΓSWNTΓFCNT9and at T=65K, we had ΓSWNTΓFCNT2. Clearly, we noticed that the ratio decreases with an increase in temperature. The nonlinear behavior in Figure 5 is as a result of the fact that, increasing temperature increases the scattering process in the material. The majority of electrons in this case acquire a higher velocity, shorter collision time, and higher energy. This energetic electrons, which are the majority undergo inter-mini-band transition (tunneling) allowing only a handful to undergo intra-mini-band transition. This allows only the few intra-mini-band electrons to interact with the copropagating phonons leading to a decrease in absorption of the acoustic phonons. To aid a better understanding of the comparison between the absorption obtained in both SWCNT and F-CNT, a semilog plot is presented in Figure 6, which clearly shows that the undoped SWCNT absorbs more than the doped F-CNT. This can be attributed to the fact that the presence of F-CNT atoms leads to chemical activation of a passive surface CNT by adding additional electronic band structure and altering the carbon π-bonds around the Fermi level in a non-linear manner thus forming a band structure of width two periods [22]. As Flourine is highly electronegative it thus weakens the walls of the CNT as it approaches it. The π-electrons attached to the Flourine which causes less free charge carriers to interact with the phonons. Current researches have predicted sp2bonding charge change to sp3by F-functionlization [25, 26, 27]. This bonding charge change would reduce the density of free carriers, consequently leading to the magnitude reduction of the absorption [22] (Figures 4, 5, 6).
In order to put our observations in perspective, we display Figures 4 and 5 in a three-dimensional behavior of the sound coefficient as a function of the frequency (ωq) and the wavevector q(Figure 7).
## 4. Conclusion
Theoretical investigation of strong absorption of coherent acoustic phonons in an FCNT and SWCNT at low temperature utilizing the Boltzmann’s transport equation is carried out in the regime ql1. The absorption coefficient obtained is highly nonlinear and depends on the stimulated absorption of acoustic phonons by electrically determined electrons experiencing intraminiband transport. The study is appropriate and furthermore considers a strong absorption of energized FCNT and SWCNT phonons. The Flourine doping affects the absorption properties of F-CNT, whereas SWCNT absorbs better than the F-CNT as was observed by Jeon et al. [19]. The phonons absorbed in this study have THz frequencies with wavelengths in the nanometer run, and takes into account examinations with high spatial determination, e.g., in phonon filters, spectroscopy (phonon spectrometer), microbiology, micro-nanoelectronic gadgets, tetrahertz adjustment of light, nondestructive testing of microstructures, and acoustic examination.
## More
© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 3.0 License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
## How to cite and reference
### Cite this chapter Copy to clipboard
Daniel Sakyi-Arthur, S. Y. Mensah, N. G. Mensah, Kwadwo A. Dompreh and R. Edziah (December 12th 2018). Absorption of Acoustic Phonons in Fluorinated Carbon Nanotubes with Non-Parabolic, Double Periodic Band, Phonons in Low Dimensional Structures, Vasilios N. Stavrou, IntechOpen, DOI: 10.5772/intechopen.78231. Available from:
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#### Theory of Excitons and Excitonic Quasimolecules Formed from Spatially Separated Electrons and Holes in Quasi-Zero- Dimensional Nanostructures
By Sergey I. Pokutnyi and Włodzimierz Salejda
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# GATE2015-12
For the matrix $\begin{pmatrix} 4 & 3\\ 3& 4 \end{pmatrix}$, if $\begin{pmatrix} 1\\ 1 \end{pmatrix}$ is an eigenvector, the corresponding eigenvalue is __________ . |
# The heat evolved for the rise of water when one end of the capillary tube of radius r is immersed vertically into water is : (Assume surface tension=T and density of water to be p)
$\begin {array} {1 1} (a)\;\frac{2 \pi T}{pg} & \quad (b)\;\frac{\pi T^2}{pg} \\ (c)\;\frac{2 \pi T^2}{pg} & \quad (d)\;none\;of\;these \end {array}$
## 1 Answer
Someone answer this please
answered Apr 24, 2016
1 answer
0 answers
1 answer
1 answer
0 answers
1 answer |
The DXVADDI_VALUERANGE structure describes values of a property (such as, the value spread and default value).
## Syntax
``````typedef struct _DXVADDI_VALUERANGE {
``````
## Members
`MinValue`
[in] A DXVADDI_FIXED32 structure that specifies the minimum value that is allowed for a given property.
`MaxValue`
[in] A DXVADDI_FIXED32 structure that specifies the maximum value that is allowed for a given property.
`DefaultValue`
[in] A DXVADDI_FIXED32 structure that specifies the default value for a given property.
`StepSize`
[in] A DXVADDI_FIXED32 structure that specifies the step size increment for a given property.
## Requirements
Windows version Available in Windows Vista and later versions of the Windows operating systems. Available in Windows Vista and later versions of the Windows operating systems. |
Department of Pre-University Education, KarnatakaPUC Karnataka Science Class 11
# Two Charged Particles Placed at a Separation of 20 Cm Exert 20 N of Coulomb Force on Each Other. What Will Be the Force of the Separation is Increased to 25 Cm? - Physics
Sum
Two charged particles placed at a separation of 20 cm exert 20 N of Coulomb force on each other. What will be the force of the separation is increased to 25 cm?
#### Solution
Two charged particles placed at a separation of 20 cm exert 20 N of Coulomb force on each other.
So, $F_1 = \frac{1}{4\pi \in_0} \cdot \frac{q^2}{r_1^2}$
Also, $F_2 = \frac{1}{4\pi \in_0} \cdot \frac{q^2}{r_2^2}$
According to the question, we have :
$\frac{F_2}{F_1} = \frac{r_1^2}{r_2^2}$
$= \frac{20 \times 20}{25 \times 25} = \frac{16}{25}$
$\therefore F_2 = \frac{16}{25} \times F_1$
$\Rightarrow F_2 = \frac{16}{25} \times 20$
$\Rightarrow F_2 = 12 . 8 N \approx 13 . 0 N$
Therefore, the two charged particles will exert a force of 13.0 N on each other, if the separation is increased to 25 cm.
Concept: Work Done by a Constant Force and a Variable Force
Is there an error in this question or solution?
#### APPEARS IN
HC Verma Class 11, Class 12 Concepts of Physics Vol. 1
Chapter 4 The Forces
Exercise | Q 8 | Page 63
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# Aptitude:: Time and Distance
@ : Home > Aptitude > Time and Distance > General Questions - Discussion
### Exercise
"
#### The ratio between the speeds of two trains is 7 : 8. If the second train runs 400 km in 4 hours, then the speed of the first train is:
A. 70 km/hr B. 75 km/hr C. 84 km/hr D. 87.5 km/hr
Explanation:
Let the speed of two trains be 7x and 8x km/hr.
Explanation:
Let the speed of two trains be 7x and 8x km/hr.
<img src="http://latex.codecogs.com/gif.latex?\frac{5+t}{78}" title="\frac{5+t}{78}" /> |
# How to get rid of units in Partition Function
1. Jul 29, 2014
### "pi"mp
Hi guys,
I'm studying a classical ideal gas trapped in a one-dimensional harmonic potential and I first want to write out the partition function for a single particle. This, I believe, requires two Gaussian integrations, like so:
$$Z=\int_{-\infty}^{\infty} d\dot{x} \int_{-\infty}^{\infty}dx \,\, e^{-\beta E(\dot{x},x)}$$
However, we should like the partition function to be unitless. The above expression has units of (length)^2 divided by (time), as best as I can tell. Now, I know we want to divide by constant parameters of the problem to make it dimensionless. However, there is no characteristic length in this problem! The only constants we have are:
$$\omega = \sqrt{\frac{k}{m}}$$
and I can't figure out how these can be combined to cancel out the (length)^2 units in Z. How does one figure this out. Thanks :)
2. Jul 29, 2014
### DrDu
The length scale is in deed quite arbitrary. That's why we chose the normalisation constant to be m/h with h being Plancks unit of action. In classical mechanics, this is nothing but an arbitrary constant.
3. Jul 29, 2014
### "pi"mp
Right, I knew I could use \hbar for quantum systems. So you're saying for classical ideal gas, I just posit some normalization constant A, claim it has the correct units, and carry it through the entire computation?
4. Jul 29, 2014
### DrDu
In quantities like energy, enthalpy, etc. the constant doesn't enter at all. In others like free energy or entropy, it enters only as an additive constant and has little relevance as we mostly measure entropy differences.
5. Jul 30, 2014
### Jano L.
The partition function does not have to be unitless. Its natural unit is a power of unit of action, since the integrations are over conjugated pairs $q,p$. If you like, you can make it unitless by using arbitrary constant with appropriate dimensions, but there is little reason to do that in classical statistical physics. |
# Simplify $\left({\sum_{k=1}^{2499}\sqrt{10+{\sqrt{50+\sqrt{k}}}}}\right)\left({\sum_{k=1}^{2499}\sqrt{10-{\sqrt{50+\sqrt{k}}}}}\right)^{-1}$
Simplify $$\frac{\displaystyle\sum_{k=1}^{2499}\sqrt{10+{\sqrt{50+\sqrt{k}}}}}{\displaystyle\sum_{k=1}^{2499}\sqrt{10-{\sqrt{50+\sqrt{k}}}}}$$
I don't have any good idea. I need your help.
• How do you sum the denominator for $k>50$? It's a complex number; is this intentional, or are these supposed to be real numbers? – Clayton Aug 5 '13 at 15:18
• I don't believe that this problem has been quoted correctly. – Eric Naslund Aug 5 '13 at 15:19
• Oh! Sorry.I made a mistake. I edited. – mathlove Aug 5 '13 at 17:13
• The ratio seems to be equal to $\tan\left(\frac{7}{16}\pi\right)$. In fact, it seems to hold if you replace $10$ by $2n$, $50$ by $2n^2$ and $2499$ by $4n^4-1$, although I can't see any "obvious" reason why it should be so right now. – Peter Košinár Aug 5 '13 at 22:09
• Thank you for reply. I'm interested in the value. Though I'm trying to find the ratio, I'm facing difficulty. – mathlove Aug 7 '13 at 6:31
Here is my answer. I've just got the following result:$$\frac{\sum_{k=1}^{2499}\sqrt{10+{\sqrt{50+\sqrt k}}}}{\sum_{k=1}^{2499}\sqrt{10-{\sqrt{50+\sqrt k}}}}=1+\sqrt2+\sqrt{4+2\sqrt2}=\cot\frac{\pi}{16}.$$
Proof: Suppose that $\sum$ represents $\sum_{k=1}^{2499}$. Let the numerator and the denominator be $A$ and $B$ respectively. Letting $a_k=\sqrt{10+\sqrt{50+\sqrt k}}, b_k=\sqrt{10-\sqrt{50+\sqrt k}}$, we can represent $A, B$ as $A=\sum a_k, B=\sum b_k.$ Letting $p_k=\sqrt{50+\sqrt k}$ and $q_k=\sqrt{50-\sqrt k}$, since ${p_k}^2+{q_k}^2=10^2$ and $p_k\gt0, q_k\gt0$, there exists a real number $0\lt x_k\lt \frac{\pi}{2}$ such that $p_k=10\cos x_k, q_k=10\sin x_k$. Then, we get $$a_k=\sqrt{10+10\cos x_k}=\sqrt{10+10\left(2{\cos^2{\frac{x_k}{2}}}-1\right)}=\sqrt{20}\cos \frac{x_k}{2},$$$$b_k=\sqrt{10-10\cos x_k}=\sqrt{10-10\left(1-2{\sin^2{\frac{x_k}{2}}}\right)}=\sqrt{20}\sin \frac{x_k}{2}.$$ Then, since $\sum a_k=\sum a_{2500-k}$, let's consider $a_{2500-k}$. \begin{align}a_{2500-k}&=\sqrt{10+\sqrt{50+\sqrt{(50+\sqrt k)(50-\sqrt k)}}}\\&=\sqrt{10+\sqrt{50+{p_kq_k}}}\\&=\sqrt{10+\sqrt{50+100\cos {x_k}\sin {x_k}}}\\&=\sqrt{10+\sqrt{50(\cos {x_k}+\sin {x_k})^2}}\\&=\sqrt{10+\sqrt{50}\cdot\sqrt2\sin \left(x_k+\frac{\pi}{4}\right)}\\&=\sqrt{10+10\cdot2\cos \left(\frac{x_k}{2}+\frac{\pi}{8}\right)\sin \left(\frac{x_k}{2}+\frac{\pi}{8}\right)}\\&=\sqrt{10\left(\cos \left(\frac{x_k}{2}+\frac{\pi}{8}\right)+\sin \left(\frac{x_k}{2}+\frac{\pi}{8}\right)\right)^2}\\&=\sqrt{10}\left(\cos \left(\frac{x_k}{2}+\frac{\pi}{8}\right)+\sin \left(\frac{x_k}{2}+\frac{\pi}{8}\right)\right)\\&=\frac{\left(\cos \left(\frac{\pi}{8}\right)+\sin \left(\frac{\pi}{8}\right)\right)a_k+\left(\cos \left(\frac{\pi}{8}\right)-\sin \left(\frac{\pi}{8}\right)\right)b_k}{\sqrt2}\\&=\sqrt{\frac{\sqrt2+1}{2\sqrt2}}a_k+\sqrt{\frac{\sqrt2-1}{2\sqrt2}}b_k.\end{align} Hence, $$A=\sqrt{\frac{\sqrt2+1}{2\sqrt2}}A+\sqrt{\frac{\sqrt2-1}{2\sqrt2}}B.$$ So, the proof is completed with $$\frac AB=1+\sqrt2+\sqrt{4+2\sqrt2}.$$
Theorem: For any natural number $n$, $$\frac{\sum_{k=1}^{n^2+2n}\sqrt{\sqrt{2n+2}+{\sqrt{n+1+\sqrt k}}}}{\sum_{k=1}^{n^2+2n}\sqrt{\sqrt{2n+2}-{\sqrt{n+1+\sqrt k}}}}=1+\sqrt2+\sqrt{4+2\sqrt2}=\cot {\frac{\pi}{16}}.$$
Note that the case $n=49$ in this theorem is the question at the top.
P.S. I think it's worth adding a link where user mercio provided a background why the theorem holds for any $n$. (it's a background, not a proof. The theorem has already been proved.) |
# 3/4 divided by 4
Let us know about 3/4 divided by 4.
Divided fraction:
3/4 divided by 4: For example, the fraction 3/4 means that 3 is divisible by 4. There is a solution to this segmentation problem. 75 . One can also say that the number 3 is 4 percent of 75.
Similarly, what is divided by 4? In other words – one quarter divided by four = one sixteenth.
What is 4 divided by as a fraction of 3? Using a calculator, if you typed 4 divided by 3, you would get 1.3333. You can also express 4/3 as a mixed fraction: 1 1/3 .
How do you divide 4 by 3? Dividing 4 by 3 is equal to 1 remainder 1 . with (4 / 3 = 1 r 1). When you divide 4 by 3, you don’t have the same number of groups left because 3…
What is the second 4 divided by half? In other words – four divided by one half = eight .
### What is 2 divided by?
Answer: 3/4 of the fraction in 2 is equal to 3 / 8 .
So what is 4 right as an improper fraction? The correct answer is 9/2. To find the answer, you first multiply the whole number by the denominator. (4×2) = 8.
What is 3 divided in half by? In other words – dividing three by one half = six.
#### How is dividing 1 by 3 the same as multiplying by 3?
Remember, 3 is the same as 3/1. Before we can divide, we need to make one more change. We’ll replace the numerator and denominator with the fraction we’re dividing by: 1/3 in this example. So 1/3 becomes 3/1.
What happens in a half of 3/4? 3/4 is half of 3/8 .
What is 1 and 3/4 as a fraction?
The mixed number 1 3/4 will be equal to the improper fraction 7 / 4 .
How do you write 4 divided by 2? Using a calculator, if you divide 4 by 2, you will get 2. You can also express 4/2 as a mixed fraction: 2 0 / 2 .
#### How do you solve improper fractions?
To convert a mixed fraction to an improper fraction, follow these steps:
1. Multiply the whole number part by the denominator of the fraction.
2. Add it to the fraction.
3. Then write the result above the denominator.
How do I solve fractions?
How do you divide improper fractions? To divide mixed fractions, you can first convert each to an improper fraction. Then, switch to the multiplication problem . Multiply by the inverse of the denominator . Simplify your answer and convert to mixed fraction to get your answer!
How do you divide by 4?
#### How do you divide fractions?
What divides the view? The division symbol looks like a dash or double dash (÷) with a dot above and a dot below . This is equivalent to the words “split”. This symbol is found mainly in arithmetic texts at the elementary-school level.
What is the rule for dividing fractions?
Dividing two fractions is the same as multiplying the first fraction by the reciprocal of the second fraction . The first step in dividing fractions is to find the reciprocal (reversing the numerator and denominator) of the second fraction. Next, multiply the two fractions. Then, multiply the two denominators.
What is reciprocal in mathematics? The reciprocal of a number is the number you need to multiply by 1 to get the answer . … Another interesting point is that the inverse of the inverse is the original number.
### How much is half of 3/4 cup in a cup?
Half of 3/4 cup would be 1/4 cup plus 2 Tbsp, or 6 Tbsp.
How do I solve fractions?
How do you multiply fractions?
#### There are 3 simple steps to multiplying fractions
1. Multiply the top numbers (fractions).
2. Multiply the numbers (denominators) at the bottom.
3. Simplify the fraction if necessary.
What is 4/3 as a mixed fraction? Subtract 3 from 4. The result of the division of 43 is 1 and the remainder is 1. with .
algebra examples.
#### How do you divide 3 by 5?
To convert a fraction to a decimal form, we need to divide its numerator by the denominator. Here, the fraction is 3/5, which means we need to do 3 5 . This gives the answer as 0.6 . So, 3/5 is 0.6 as a decimal.
How do you write partition?
The common written symbol for division is (÷) . The ‘/’ (forward slash) symbol is used in spreadsheets and other computer applications. Division is the opposite of multiplication in mathematics. |
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## Adaptive thresholding for binarization
Matlab Image processing blog - 2016, July 25 - 08:01
Despite recent appearances on the blog, I still exist! It's just been a little crazier than usual for the last month or so.
Anyway ... I'm back, and I'm going to try to wrap things up about image binarization. In my 14-Jun-2016 post, I discussed the algorithm underlying imbinarize for the global thresholding case. Today I'm going to talk about the algorithm for the adaptive thresholding case.
Here's an image suffering from an extreme case of nonuniform illumination.
I = imread('printedtext.png'); imshow(I)
Here is the binarization using a global threshold.
bw1 = imbinarize(I); imshow(bw1) title('Global threshold')
And here is the binarization using an adaptive threshold. Note that we have to tell the function that the foreground pixels (representing text characters) are darker than the background pixels (the white paper).
The algorithm used by |imbinarize(I,'adaptive',...) is sometimes called Bradley's method, for the paper by D. Bradley and G. Roth, "Adaptive Thresholding Using Integral Image," Journal of Graphics Tools, vol. 12, issue 2, pp. 13-21, 2007.
This method uses a large-neighborhood mean filter. If the input image pixel is more than a certain percentage greater than the mean filter, then it is set to white.
To perform large-neighborhood mean filtering (also called box filtering) efficiently, the implementation uses something called an integral image. With this technique, time required to perform mean filtering depends only on the number of image pixels. The time is independent of the neighborhood size. Maybe I'll discuss integral images and box filtering in a future post. In the meantime, you can look at integralImage and imboxfilt.
So how big is the mean filter neighborhood? Well, there's no fixed rule. This is another one of those magic numbers that bedevil image processing. The function imbinarize uses a square neighborhood that is about 1/8 of the smallest image dimension. This is just a heuristic rule that works reasonably well for a variety of images.
The function imbinarize does everything for you in one step. It computes the adaptive threshold image and then applies it to produce a binary output image. If you want the adaptive threshold image itself, or if you want more control over the how the adaptive threshold image is computed, then you can use adaptthresh.
Here is the adaptive threshold image for the printed text example shown above.
T = adaptthresh(I,'ForegroundPolarity','dark'); imshow(T) title('Adaptive threshold image')
When you use adaptthresh, you can control the neighborhood size directly. You can also specify other local background measurement methods, including median filtering and Gaussian filter.
Wrapping Up
With the new set of Image Processing Toolbox interfaces, using imbinarize as your one-step solution for both global and adaptive thresholding. Gain finer control over algorithm details, if you need to, by using the underlying functions otsuthresh and adaptthresh. The older functions, im2bw and graythresh, still exist for compatibility, but we encourage you to use the new functions in your new code.
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## EFF is suing the US government to invalidate the DMCA’s DRM provisions
Cory Doctorow - 2016, July 21 - 07:24
The Electronic Frontier Foundation has just filed a lawsuit that challenges the Constitutionality of Section 1201 of the DMCA, the “Digital Rights Management” provision of the law, a notoriously overbroad law that bans activities that bypass or weaken copyright access-control systems, including reconfiguring software-enabled devices (making sure your IoT light-socket will accept third-party lightbulbs; tapping into diagnostic info in your car or tractor to allow an independent party to repair it) and reporting security vulnerabilities in these devices.
EFF is representing two clients in its lawsuit: Andrew “bunnie” Huang, a legendary hardware hacker whose NeTV product lets users put overlays on DRM-restricted digital video signals; and Matthew Green, a heavyweight security researcher at Johns Hopkins who has an NSF grant to investigate medical record systems and whose research plans encompass the security of industrial firewalls and finance-industry “black boxes” used to manage the cryptographic security of billions of financial transactions every day.
Both clients reflect the deep constitutional flaws in the DMCA, and both have standing to sue the US government to challenge DMCA 1201 because of its serious criminal provisions (5 years in prison and a $500K fine for a first offense). The US Trade Rep has propagated the DMCA’s anticircumvention rules to most of the world’s industrial nations, and a repeal in the US will strengthen the argument for repealing their international cousins. Huang has written an inspirational essay explaining his reasons for participating in this suit, explaining that he feels it is his duty to future generations: Our recent generation of Makers, hackers, and entrepreneurs have developed under the shadow of Section 1201. Like the parable of the frog in the well, their creativity has been confined to a small patch, not realizing how big and blue the sky could be if they could step outside that well. Nascent 1201-free ecosystems outside the US are leading indicators of how far behind the next generation of Americans will be if we keep with the status quo. Our children deserve better. I can no longer stand by as a passive witness to this situation. I was born into a 1201-free world, and our future generations deserve that same freedom of thought and expression. I am but one instrument in a large orchestra performing the symphony for freedom, but I hope my small part can remind us that once upon a time, there was a world free of such artificial barriers, and that creativity and expression go hand in hand with the ability to share without fear. The EFF’s complaint, filed minutes ago with the US District Court, is as clear and comprehensible an example of legal writing as you could ask for. It builds on two recent Supreme Court precedents (Golan and Eldred), in which the Supremes stated that the only way to reconcile free speech with copyright’s ability to restrict who may utter certain words and expressions is fair use and other exemptions to copyright, which means that laws that don’t take fair use into account fail to pass constitutional muster. In this decade, more and more companies have figured out that the DMCA gives them the right to control follow-on innovation and suppress embarrassing revelations about defects in their products; consequently, DMCA 1201-covered technologies have proliferated into cars and tractors, medical implants and home security systems, thermostats and baby-monitors. With this lawsuit, the EFF has fired a starter pistol in the race to repeal section 1201 of the DMCA and its cousins all over the world: to legitimize the creation of commercial businesses that unlock the value in the gadgets you’ve bought that the original manufacturers want to hoard for themselves; to open up auditing and disclosure on devices that are disappearing into our bodies, and inside of which we place those bodies. Suing on behalf of Huang and Green, EFF’s complaint argues that the wording of the statute requires the Library of Congress to grant exemptions for all conduct that is legal under copyright, including actions that rely on fair use, when that conduct is hindered by the ban on circumvention. Critically, the supreme court has given guidance on this question in two rulings, Eldred and Golan, explaining how copyright law itself is constitutional even though it places limits on free speech; copyright is, after all, a law that specifies who may utter certain combinations of words and other expressive material. The supreme court held that through copyright’s limits, such as fair use, it accommodates the first amendment. The fair-use safety valve is joined by the “idea/expression dichotomy”, a legal principle that says that copyright only applies to expressions of ideas, not the ideas itself. In the 2015 DMCA 1201 ruling, the Library of Congress withheld or limited permission for many uses that the DMCA blocks, but which copyright itself allows – activities that the supreme court has identified as the basis for copyright’s very constitutionality. If these uses had been approved, people such as Huang and Green would not face criminal jeopardy. Because they weren’t approved, Huang and Green could face legal trouble for doing these legitimate things. America’s broken digital copyright law is about to be challenged in court [Cory Doctorow/The Guardian] Why I’m Suing the US Government [Andrew “bunnie” Huang] [Kit Walsh/EFF] (Image: Bunnie Huang, Joi Ito, CC-BY) Categories: Blogs ## Comicon Schedule! Flog - 2016, July 18 - 19:30 Hey all, here’s my COMICON SCHEDULE! Thursday: 12-1pm Geek and Sundry Panel at Indigo Ballroom (Badge needed) 2pm: Nerd HQ Panel Friday 10:30-11:30am: ConMan Panel Hall H (Badge Needed) 2:45pm: Q/A at Petco Park Stage Saturday: 4-4:45pm MST3K Panel at Petco Park Stage 5:15-6:15pm MST3K SHOUT! Book Signing (Badge needed) 8:30-9:30pm MST3K Panel Room 24ABC (Badge needed) Come by and say hi if you have time! Categories: Blogs ## My interview on Utah Public Radio’s “Access Utah” Cory Doctorow - 2016, July 12 - 10:24 Science fiction novelist, blogger and technology activist Cory Doctorow joins us for Tuesday’s AU. In a recent column, Doctorow says that “all the data collected in giant databases today will breach someday, and when it does, it will ruin peoples’ lives. They will have their houses stolen from under them by identity thieves who forge their deeds (this is already happening); they will end up with criminal records because identity thieves will use their personal information to commit crimes (this is already happening); … they will have their devices compromised using passwords and personal data that leaked from old accounts, and the hackers will spy on them through their baby monitors, cars, set-top boxes, and medical implants (this is already happening)…” We’ll talk with Cory Doctorow about technology, privacy, and intellectual property. Cory Doctorow is the co-editor of popular weblog Boing Boing and a contributor to The Guardian, Publishers Weekly, Wired, and many other newspapers, magazines and websites. He is a special consultant to the Electronic Frontier Foundation, a non-profit civil liberties group that defends freedom in technology law, policy, standards and treaties. Doctorow is also an award-winning author of numerous novels, including “Little Brother,” “Homeland,” and “In Real Life.” Categories: Blogs ## As browsers decline in relevance, they’re becoming DRM timebombs Cory Doctorow - 2016, July 8 - 10:08 My op-ed in today’s issue of The Tech, MIT’s leading newspaper, describes how browser vendors and the W3C, a standards body that’s housed at MIT, are collaborating to make DRM part of the core standards for future browsers, and how their unwillingness to take even the most minimal steps to protect academics and innovators from the DMCA will put the MIT community in the crosshairs of corporate lawyers and government prosecutors. If you’re a researcher or security/privacy expert and want to send a message to the W3C that it has a duty to protect the open web from DRM laws, you can sign this open letter to the organization. The W3C’s strategy for “saving the web” from the corporate-controlled silos of apps is to replicate the systems of control that make apps off-limits to innovation and disruption. It’s a poor trade-off, one that sets a time-bomb ticking in the web’s foundations, making the lives of monopolists easier, and the lives of security researchers and entrepreneurs much, much more perilous. The Electronic Frontier Foundation, a W3C member, has proposed a compromise that will protect the rights of academics, entrepreneurs, and security researchers to make new browser technologies and report the defects in the old ones: we asked the W3C to extend its patent policy to the DMCA, so that members who participated in making DRM would have to promise not to use the DMCA to attack implementers or security researchers. But although this was supported by a diverse group of W3C members, the W3C executive did not adopt the proposal. Now, EME has gone to Candidate Recommendation stage, dangerously close to completion. The purpose of HTML5 is to provide the rich interactivity that made apps popular, and to replace apps as the nexus of control for embedded systems, including the actuating, sensing world of “internet of things” devices. We can’t afford to have these devices controlled by a system that is a no-go zone for academic work, security research, and innovative disruption. Although some of the biggest tech corporations in the world today support EME, very few of them could have come into being if EME-style rules had been in place at their inception. A growing coalition of leading international privacy and security researchers have asked the W3C to reconsider and protect the open web from DRM, a proposal supported by many W3C staffers, including Danny Weitzner (CSAIL/W3C), who wrote the W3C’s patent policy. Browsers’ bid for relevance is turning them into time-bombs [Cory Doctorow/The Tech] (Image: Wfm stata center, Raul654, CC-BY-SA) Categories: Blogs ## Peak indifference: privacy as a public health issue Cory Doctorow - 2016, July 3 - 18:57 My latest Locus column, “Peak Indifference”, draws a comparison between the history of the “debate” about the harms of smoking (a debate manufactured by disinformation merchants with a stake in the controversy) and the current debate about the harms of surveillance and data-collection, whose proponents say “privacy is dead,” while meaning, “I would be richer if your privacy were dead.” Smoking’s harms were hard to pin down in part because the gap between cause (a drag on a cigarette) and effect (cancer) was not immediate nor was it absolute. Most drags on cigarettes don’t cause cancer, just like most privacy disclosures don’t harm you. But with enough drags — or enough private information sucked up via surveillance capitalism, disaster is inevitable. Long before smoking became unacceptable, there was a moment of “peak indifference,” the moment when the number of people who weren’t worried about smoking started to decline, and never recover. The privacy wars are reaching that moment now, with millions of people having their lives ruined by data breaches, and that means there’s a new tactical challenge for privacy advocates. Rather than convincing people to care about privacy, now we have to convince them to do something about it. The anti-smoking movement made great strides with this. They made sure that people who had cancer – or whose loved ones did – understood that tobacco’s use wasn’t a blameless, emergent phenomenon. They named names and published documents, showing exactly who conspired to destroy lives with cancer in order to enrich themselves. They surfaced and highlighted the risks to non-smokers’ lives from smoking: not just second-hand smoke, but also the public health burdens and the terrible losses felt by survivors after their loved ones had perished. They demanded architectural changes – bans on smoking – and legal ones, and market ones, and normative ones. Peak indifference let those activists move from convincing to fighting back. That’s why it’s time for privacy activists to start thinking of new tactics. We are past peak indifference to online surveillance: that means that there will never be a moment after today in which fewer people are alarmed by the costs of surveillance. The bad news is that 20 years of failing to convince people of the risks of online privacy has built up a reservoir of inevitable harms: all the data collected in giant databases today will breach someday, and when it does, it will ruin peoples’ lives. They will have their houses stolen from under them by identity thieves who forge their deeds (this is already happening); they will end up with criminal records because identity thieves will use their personal information to commit crimes (this is already happening); they will be accused of terrorism or other life-destroying categories of crimes because an algorithm has mined their data to come to a conclusion they aren’t allowed to see or interrogate (this is already happening); they will have their devices compromised using passwords and personal data that leaked from old accounts, and the hackers will spy on them through their baby monitors, cars, set-top boxes, and medical implants (this is already happening); they will have the sensitive information they disclosed to the government to attain security clearance breached and warehoused by blackmailing enemy states (this is already happening); their employers will fail when their personal information is used to commit industrial espionage (this is already happening). Peak Indifference [Locus Magazine] Categories: Blogs ## I’m profiled in the Globe and Mail Report on Business magazine Cory Doctorow - 2016, June 27 - 10:35 The monthly Report on Business magazine in the Canadian national paper The Globe and Mail profiled my work on DRM reform, as well as my science fiction writing and my work on Boing Boing. I’m grateful to Alec Scott for the coverage, and especially glad that the question of the World Wide Web Consortium’s terrible decision to standardize DRM as part of HTML5 is getting wider attention. If you want learn more, here’s a FAQ, and here’s a letter you can sign onto in which we’re asking the W3C to take steps to protect security disclosures and competition on the web. He doesn’t always have the last word with Berners-Lee, though. “I was surprised and disappointed that he recently announced that W3C was going to start standardizing DRM.…There is a sense among a lot of people that the Web is cooked.” W3C is the World Wide Web Consortium, which Berners-Lee runs, and Doctorow is upset because it’s setting up a standardized regime for digital rights management, or DRM—the locks that tech and entertainment companies put on their products—to prevent people from sharing their wares. Doctorow criticizes American and Canadian legislation that makes it an offence to tamper with these locks. After all, analog publishers can’t control what use purchasers make of their books. And the locks seldom help the creatives who originally produced the content. (1) In joking homage to Isaac Asimov’s laws of robotics, Doctorow has his own law: “Any time someone puts a lock on something that belongs to you and won’t give you the key, that lock isn’t there for your benefit.” The crusader fighting lock-happy entertainment conglomerates [Alec Scott/The Globe and Mail] Categories: Blogs ## How to protect the future web from its founders’ own frailty Cory Doctorow - 2016, June 24 - 11:15 Earlier this month, I gave the afternoon keynote at the Internet Archive’s Decentralized Web Summit, and my talk was about how the people who founded the web with the idea of having an open, decentralized system ended up building a system that is increasingly monopolized by a few companies — and how we can prevent the same things from happening next time. The speech was very well received — it got a standing ovation — and has attracted a lot of discussion since. Jonke Suhr has done me the service of transcribing the talk, which will facilitate translating it into other languages as well as making it accessible to people who struggle with video. Many thanks, Jonke! This is also available as an MP3 and a downloadable video. I’ve included an edited version below: So, as you might imagine, I’m here to talk to you about dieting advice. If you ever want to go on a diet, the first thing you should really do is throw away all your Oreos. It’s not that you don’t want to lose weight when you raid your Oreo stash in the middle of the night. It’s just that the net present value of tomorrow’s weight loss is hyperbolically discounted in favor of the carbohydrate rush of tonight’s Oreos. If you’re serious about not eating a bag of Oreos your best bet is to not have a bag of Oreos to eat. Not because you’re weak willed. Because you’re a grown up. And once you become a grown up, you start to understand that there will be tired and desperate moments in your future and the most strong-willed thing you can do is use the willpower that you have now when you’re strong, at your best moment, to be the best that you can be later when you’re at your weakest moment. And this has a name: It’s called a Ulysses pact. Ulysses was going into Siren-infested waters. When you go into Siren-infested waters, you put wax in your ears so that you can’t hear what the Sirens are singing, because otherwise you’ll jump into the sea and drown. But Ulysses wanted to hear the Sirens. And so he came up with a compromise: He had his sailors tie him to the mast, so that when he heard the call of the Sirens, even though he would beg and gibber and ask them to untie him, so that he could jump into the sea, he would be bound to the mast and he would be able to sail through the infested waters. This is a thing that economists talk about all the time, it’s a really critical part of how you build things that work well and fail well. Now, building a Web that is decentralized is a hard thing to do, and the reason that the web ceases to be decentralized periodically is because it’s very tempting to centralize things. There are lots of short term gains to be had from centralizing things and you want to be the best version of yourself, you want to protect your present best from your future worst. The reason that the Web is closed today is that people just like you, the kind of people who went to Doug Engelbart’s demo in 1968, the kind of people who went to the first Hackers conference, people just like you, made compromises, that seemed like the right compromise to make at the time. And then they made another compromise. Little compromises, one after another. And as humans, our sensory apparatus is really only capable of distinguishing relative differences, not absolute ones. And so when you make a little compromise, the next compromise that you make, you don’t compare it to the way you were when you were fresh and idealistic. You compare it to your current, “stained” state. And a little bit more stained hardly makes any difference. One compromise after another, and before you know it, you’re suing to make APIs copyrightable or you’re signing your name to a patent on one-click purchasing or you’re filing the headers off of a GPL library and hope no one looks too hard at your binaries. Or you’re putting a backdoor in your code for the NSA. And the thing is: I am not better than the people who made those compromises. And you are not better than the people who made those compromises. The people who made those compromises discounted the future costs of the present benefits of some course of action, because it’s easy to understand present benefits and it’s hard to remember future costs. You’re not weak if you eat a bag of Oreos in the middle of the night. You’re not weak if you save all of your friends’ mortgages by making a compromise when your business runs out of runway. You’re just human, and you’re experiencing that hyperbolic discounting of future costs because of that immediate reward in the here and now. If you want to make sure that you don’t eat a bag of Oreos in the middle of the night, make it more expensive to eat Oreos. Make it so that you have to get dressed and find your keys and figure out where the all-night grocery store is and drive there and buy a bag of Oreos. And that’s how you help yourself in the future, in that moment where you know what’s coming down the road. The answer to not getting pressure from your bosses, your stakeholders, your investors or your members, to do the wrong thing later, when times are hard, is to take options off the table right now. This is a time-honored tradition in all kinds of economic realms. Union negotiators, before they go into a tough negotiation, will say: “I will resign as your negotiator, before I give up your pension.” And then they sit down across the table from the other side, and the other side says “It’s pensions or nothing”. And the union leaders say: “I hear what you’re saying. I am not empowered to trade away the pensions. I have to quit. They have to go elect a new negotiator, because I was elected contingent on not bargaining away the pensions. The pensions are off the table.” Brewster has talked about this in the context of code, he suggested that we could build distributed technologies using the kinds of JavaScript libraries that are found in things like Google Docs and Google Mail, because no matter how much pressure is put on browser vendors, or on technology companies in general, the likelihood that they will disable Google Docs or Google Mail is very, very low. And so we can take Google Docs hostage and use it as an inhuman shield for our own projects. The GPL does this. Once you write code, with the GPL it’s locked open, it’s irrevocably licensed for openness and no one can shut it down in the future by adding restrictive terms to the license. The reason the GPL works so well, the reason it became such a force for locking things open, is that it became indispensable. Companies that wanted to charge admission for commodity components like operating systems or file editors or compilers found themselves confronted with the reality that there’s a huge difference between even a small price and no price at all, or no monetary price. Eventually it just became absurd to think that you would instantiate a hundred million virtual machines for an eleventh of a second and get a license and a royalty for each one of them. And at that point, GPL code became the only code that people used in cloud applications in any great volume, unless they actually were the company that published the operating system that wasn’t GPL’d. Communities coalesced around the idea of making free and open alternatives to these components: GNU/Linux, Open- and LibreOffice, git, and those projects benefited from a whole bunch of different motives, not always the purest ones. Sometimes it was programmers who really believed ethically in the project and funded their own work, sometimes talent was tight and companies wanted to attract programmers, and the way that they got them to come through the door is by saying: “We’ll give you some of your time to work on an ethical project and contribute code to it.” Sometimes companies got tactical benefits by zeroing out the margins on their biggest competitor’s major revenue stream. So if you want to fight with Microsoft, just make Office free. And sometimes companies wanted to use but not sell commodity components. Maybe you want to run a cloud service but you don’t want to be in the operating system business, so you put a bunch of programmers on making Linux better for your business, without ever caring about getting money from the operating system. Instead you get it from the people who hire you to run their cloud. Everyone of those entities, regardless of how they got into this situation of contributing to open projects, eventually faced hard times, because hard times are a fact of life. And systems that work well, but fail badly, are doomed to die in flames. The GPL is designed to fail well. It makes it impossible to hyperbolically discount the future costs of doing the wrong thing to gain an immediate benefit. When your investor or your acquisition suitor or your boss say “Screw your ethics, hippie, we need to make payroll”, you can just pull out the GPL and say: “Do you have any idea how badly we will be destroyed if we violate copyright law by violating the GPL?” It’s why Microsoft was right to be freaked out about the GPL during the Free and Open Source wars. Microsoft’s coders were nerds like us, they fell in love with computers first, and became Microsoft employees second. They had benefited from freedom and openness, they had cated out BASIC programs, they had viewed sources, and they had an instinct towards openness. Combining that with the expedience of being able to use FLOSS, like not having to call a lawyer before you could be an engineer, and with the rational calculus, that if they made FLOSS, that when they eventually left Microsoft they could keep using the code that they had made there, meant that Microsoft coders and Microsoft were working for different goals. And the way they expressed that was in how they used and licensed their code. This works so well that for a long time, nobody even knew if the GPL was enforceable, because nobody wanted to take the risk of suing and setting a bad precedent. It took years and years for us to find out in which jurisdictions we could enforce the GPL. That brings me to another kind of computer regulation, something that has been bubbling along under the surface for a long time, at least since the Open Source wars, and that’s the use of Digital Rights Management (DRM) or Digital Restrictions Management, as some people call it. This is the technology that tries to control how you use your computer. The idea is that you have software on the computer that the user can’t override. If there is remote policy set on that computer that the user objects to, the computer rejects the user’s instruction in favor of the remote policy. It doesn’t work very well. It’s very hard to stop people who are sitting in front of a computer from figuring out how it works and changing how it works. We don’t keep safes in bank robbers’ living rooms, not even really good ones. But we have a law that protects it, the Digital Millennium Copyright Act (DMCA), it’s been around since 1998 and it has lots of global equivalents like section 6 of the EUCD in Europe, implemented all across the EU member states. In New Zealand they tried to pass a version of the DMCA and there were uprisings and protests in the streets, they actually had to take the law off the books because it was so unpopular. And then the Christchurch earthquake hit and a member of parliament reintroduced it as a rider to the emergency relief bill to dig people out of the rubble. In Canada it’s Bill C-11 from 2011. And what it does is, it makes it a felony to tamper with those locks, a felony punishable by 500,000 dollars fine and five years in jail for a first offense. It makes it a felony to do security auditing of those locks and publish information about the flaws that are present in them or their systems. This started off as a way to make sure that people who bought DVDs in India didn’t ship them to America. But it is a bad idea whose time has come. It has metastasized into every corner of our world. Because if you put just enough DRM around a product that you can invoke the law, then you can use other code, sitting behind the DRM, to control how the user uses that product, to extract more money. GM uses it to make sure that you can’t get diagnostics out of the car without getting a tool that they license to you, and that license comes with a term that says you have to buy parts from GM, and so all repair shops for GM that can access your diagnostic information have to buy their parts from GM and pay monopoly rents. We see it in insulin pumps, we see it in thermostats and we see it in the “Internet of Things rectal thermometer”, which debuted at CES this year, which means we now have DRM restricted works in our asses. And it’s come to the web. It’s been lurking in the corners of the web for a long time. But now it’s being standardized at the World Wide Web Consortium (W3C) to something called Encrypted Media Extensions (EME). The idea of EME is that there is conduct that users want to engage in that no legislature in the world has banned, like PVR’ing their Netflix videos. But there are companies that would prefer that conduct not to be allowed. By wrapping the video with just enough DRM to invoke the DMCA, you can convert your commercial preference to not have PVRs (which are no more and no less legal than the VCR was when in 1984 the Supreme Court said you can record video off your TV) into something with the force of law, whose enforcement you can outsource to national governments. What that means, is that if you want to do interoperability without permission, if you want to do adversarial interoperability, if you want to add a feature that the manufacturer or the value chain doesn’t want, if you want to encapsulate Gopher inside of the Web to launch a web browser with content form the first day, if you want to add an abstraction layer that lets you interoperate between two different video products so that you can shop between them and find out which one has the better deal, that conduct, which has never been banned by a legislature, becomes radioactively illegal. It also means, that if you want to implement something that users can modify, you will find yourself at the sharp end of the law, because user modifiability for the core components of the system is antithetical to its goals of controlling user conduct. If there’s a bit you can toggle that says “Turn DRM off now”, then if you turn that bit off, the entire system ceases to work. But the worst part of all is that it makes browsers into no-go zones for security disclosures about vulnerabilities in the browser, because if you know about a vulnerability you could use it to weaken EME. But you could also use it to attack the user in other ways. Adding DRM to browsers, standardizing DRM as an open standards organization, that’s a compromise. It’s a little compromise, because after all there’s already DRM in the world, and it’s a compromise that’s rational if you believe that DRM is inevitable. If you think that the choice is between DRM that’s fragmented or DRM that we get a say in, that we get to nudge into a better position, then it’s the right decision to make. You get to stick around and do something to make it less screwed up later, as opposed to being self-marginalized by refusing to participate at all. But if DRM is inevitable, and I refuse to believe that it is, it’s because individually, all across the world, people who started out with the best of intentions made a million tiny compromises that took us to the point where DRM became inevitable, where the computers that are woven into our lives, with increasing intimacy and urgency, are designed to control us instead of being controlled by us. And the reasons those compromises were made is because each one of us thought that we were alone and that no one would have our back, that if we refuse to make the compromise, the next person down the road would, and that eventually, this would end up being implemented, so why not be the one who makes the compromise now. They were good people, those who made those compromises. They were people who were no worse than you and probably better than me. They were acting unselfishly. They were trying to preserve the jobs and livelihoods and projects of people that they cared about. People who believed that others would not back their play, that doing the right thing would be self-limiting. When we’re alone, and when we believe we’re alone, we’re weak. It’s not unusual to abuse standards bodies to attain some commercial goal. The normal practice is to get standards bodies to incorporate your patents into a standard, to ensure that if someone implements your standard, you get a nickel every time it ships. And that’s a great way to make rent off of something that becomes very popular. But the W3C was not armtwisted about adding patents back into standards. That’s because the W3C has the very best patents policy of any standards body in the world. When you come to the W3C to make a standard for the web, you promise not to use your patents against people who implement that standard. And the W3C was able to make that policy at a moment in which it was ascendant, in which people were clamoring to join it, in which it was the first moments of the Web and in which they were fresh. The night they went on a diet, they were able to throw away all the Oreos in the house. They were where you are now, starting a project that people around the world were getting excited about, that was showing up on the front page of the New York Times. Now that policy has become the ironclad signifier of the W3C. What’s the W3C? It’s the open standards body that’s so open, that you don’t get to assert patents if you join it. And it remains intact. How will we keep the DMCA from colonizing the Locked Open Web? How will we keep DRM from affecting all of us? By promising to have each others’ backs. By promising that by participating in the Open Web, we take the DMCA off the table. We take silencing security researchers, we take blocking new entrances to the market off the table now, when we are fresh, when we are insurgent, before we have turned from the pirates that we started out as into the admirals that some of us will become. We take that option off the table. The EFF has proposed a version of this at the W3C and at other bodies, where we say: To be a member, you have to promise not to use the DMCA to aggress against those, who report security vulnerabilities in W3C standards, and people who make interoperable implementations of W3C standards. We’ve also proposed that to the FDA, as a condition of getting approval for medical implants, we’ve asked them to make companies promise in a binding way never to use the DMCA to aggress against security researchers. We’ve taken it to the FCC, and we’re taking it elsewhere. If you want to sign an open letter to the W3C endorsing this, email me: [email protected] But we can go further than that, because Ulysses pacts are fantastically useful tools for locking stuff open. It’s not just the paper that you sign when you start your job, that takes a little bit of money out of your bank account every month for your 401k, although that works, too. The U.S. constitution is a Ulysses pact. It understands that lawmakers will be corrupted and it establishes a principal basis for repealing the laws that are inconsistent with the founding principles as well as a process for revising those principles as need be. A society of laws is a lot harder to make work than a society of code or a society of people. If all you need to do is find someone who’s smart and kind and ask them to make all your decisions for you, you will spend a lot less time in meetings and a lot more time writing code. You won’t have to wrangle and flame or talk to lawyers. But it fails badly. We are all of us a mix of short-sighted and long-term, depending on the moment, our optimism, our urgency, our blood-sugar levels… We must give each other moral support. Literal moral support, to uphold the morals of the Decentralized Web, by agreeing now what an open internet is and locking it open. When we do that, if we create binding agreements to take certain kinds of conduct off the table for anything that interoperates with or is part of what we’re building today, then our wise leaders tomorrow will never be pressurized to make those compromises, because if the compromise can’t be made, there is no point in leaning on them to make it. We must set agreements and principles that allow us to resist the song of the Sirens in the future moments of desperation. And I want to propose two key principles, as foundational as life, liberty, and the pursuit of happiness or the First Amendment: 1) When a computer receives conflicting instructions from its owner and from a remote party, the owner always wins. Systems should always be designed so that their owners can override remote instructions and should never be designed so that remote instructions can be executed if the owner objects to them. Once you create the capacity for remote parties to override the owners of computers, you set the stage for terrible things to come. Any time there is a power imbalance, expect the landlord, the teacher, the parent of the queer kid to enforce that power imbalance to allow them to remotely control the device that the person they have power over uses. You will create security risks, because as soon as you have a mechanism that hides from the user, to run code on the user’s computers, anyone who hijacks that mechanism, either by presenting a secret warrant or by breaking into a vulnerability in the system, will be running in a privileged mode that is designed not to be interdicted by the user. If you want to make sure that people show up at the door of the Distributed Web asking for backdoors, to the end of time, just build in an update mechanism that the user can’t stop. If you want to stop those backdoor requests from coming in, build in binary transparency, so that any time an update ships to one user that’s materially different from the other ones, everybody gets notified and your business never sells another product. Your board of directors will never pressurize you to go along with the NSA or the Chinese secret police to add a backdoor, if doing so will immediately shut down your business. Throw away the Oreos now. Let’s also talk about the Computer Fraud and Abuse Act. This is the act that says if you exceed your authorization on someone else’s computer, where that authorization can be defined as simply the terms of service that you click through on your way into using a common service, you commit a felony and can go to jail. Let’s throw that away, because it’s being used routinely to shut down people who discover security vulnerabilities in systems. 2) Disclosing true facts about the security of systems that we rely upon should never, ever be illegal. We can have normative ways and persuasive ways of stopping people from disclosing recklessly, we can pay them bug bounties, we can have codes of conduct. But we must never, ever give corporations or the state the legal power to silence people who know true things about the systems we entrust our lives, safety, and privacy to. These are the foundational principles. Computers obey their owners, true facts about risks to users are always legal to talk about. And I charge you to be hardliners on these principles, to be called fanatics. If they are not calling you puritans for these principles you are not pushing hard enough. If you computerize the world, and you don’t safeguard the users of computers form coercive control, history will not remember you as the heroes of progress, but as the blind handmaidens of future tyranny. This internet, this distributed internet that we are building, the Redecentralization of the Internet, if it ever succeeds, will someday fail, because everything fails, because overwhelmingly, things are impermanent. What it gives rise to next, is a function of what we make today. There’s a parable about this: The state of Roman metallurgy in the era of chariots, determined the wheel base of a Roman chariot, which determined the width of the Roman road, which determined the width of the contemporary road, because they were built atop the ruins of the Roman roads, which determined the wheel base of cars, which determined the widest size that you could have for a container that can move from a ship, to a truck, to a train, which determined the size of a train car, which determined the maximum size of the Space Shuttle’s disposable rockets. Roman metallurgy prefigured the size of the Space Shuttle’s rockets. This is not entirely true, there are historians who will explain the glosses in which it’s not true. But it is a parable about what happens when empires fall. Empires always fall. If you build a glorious empire, a good empire, an empire we can all be proud to live in, it will someday fall. You cannot lock it open forever. The best you can hope for is to wedge it open until it falls, and to leave behind the materials, the infrastructure that the people who reboot the civilization that comes after ours will use to make a better world. A legacy of technology, norms and skills that embrace fairness, freedom, openness and transparency, is a commitment to care about your shared destiny with every person alive today and all the people who will live in the future. Cory Doctorow: “How Stupid Laws and Benevolent Dictators can Ruin the Decentralized Web, too” [Transcript by Jonke Suhr] Categories: Blogs ## Video: Guarding the Decentralized Web from its founders’ human frailty Cory Doctorow - 2016, June 20 - 13:11 Earlier this month, I gave the afternoon keynote at the Internet Archive’s Decentralized Web Summit, speaking about how the people who are building a new kind of decentralized web can guard against their own future moments of weakness and prevent themselves from rationalizing away the kinds of compromises that led to the centralization of today’s web. The talk was very well-received — it got a standing ovation — and I’ve heard from a lot of people about it since. The video was heretofore only available as a slice of a 9-hour Youtube archive of the day’s proceeding, but thanks to Jeff Kaplan and the Internet Archive, I’ve now got a cut of just my talk, which is on the Internet Archive for your downloading pleasure and mirrored at Youtube (There’s also an MP3). Categories: Blogs ## Image binarization – Otsu’s method Matlab Image processing blog - 2016, June 14 - 14:35 In my 16-May-2016 post about image binarization, I talked about the new binarization functions in R2016a. Today I want to switch gears and talk about Otsu's method, one of the algorithms underlying imbinarize. (A bonus feature of today's blog post is a demo of yyaxis, a new feature of MATLAB R2016a.) Otsu's method is named for Nobuyuki Otsu, who published it in IEEE Transactions on Systems, Man, and Cybernetics, vol. SMC-9, no. 1, January 1979. At this time, researchers had already explored a variety of ways to choose a threshold automatically by examining the histogram of image pixel values. The basic idea is to look for two peaks, representing foreground and background pixel values, and pick a point in between the two peaks as the threshold value. Here's a simple example using the coins image. I = imread('coins.png'); imshow(I) imhist(I) The function imbinarize calls otsuthresh to get a normalized threshold value. t = otsuthresh(histcounts(I,-0.5:255.5)) t = 0.4941 Let's see where that threshold is. hold on plot(255*[t t], ylim, 'r', 'LineWidth', 5) hold off And here is the thresholded coins image. imshow(imbinarize(I,t)) How does this threshold selection work? It is based on entirely on the set of histogram counts. To show the computation, I'll adopt the notation from the paper. Pixels can take on the set of values$i = 1,2,\ldots,L$. The histogram count for pixel value$i$is$n_i$, and the associated probability is$p_i = n_i/N$, where$N$is the number of image pixels. (I'm using the word probability here somewhat loosely, in the relative frequency sense.) The thresholding task is formulated as the problem of dividing image pixels into two classes.$C_0$is the set of pixels with values$[1,\ldots,k]$, and$C_1$is the set of pixels with values in the range$[k+1,\ldots,L]$. The overall class probabilities,$\omega_0$and$\omega_1$, are: $$\omega_0 = \sum_{i=1}^k p_i = \omega(k)$$ $$\omega_1 = \sum_{i=k+1}^L p_i = 1 - \omega_0(k)$$ The class means,$\mu_0$and$\mu_1$, are the mean values of the pixels in$C_0$and$C_1$. They are given by: $$\mu_0 = \sum_{i=1}^k i p_i / \omega_0 = \mu(k)/\omega(k)$$ $$\mu_1 = \sum_{i=k+1}^L i p_i / \omega_1 = \frac{\mu_T - \mu(k)}{1 - \omega(k)}$$ where $$\mu(k) = \sum_{i-1}^k i p_i$$ and$\mu_T$, the mean pixel value for the total image, is: $$\mu_T = \sum_{i=1}^L i p_i.$$ The class variances,$\sigma_0^2$and$\sigma_1^2$, are: $$\sigma_0^2 = \sum_{i = 1}^k (i - \mu_0)^2 p_i / \omega_0$$ $$\sigma_1^2 = \sum_{i = k+1}^L (i - \mu_1)^2 pi / \omega_1.$$ Otsu mentions three measures of "good" class separability: within-class variance ($\lambda$), between-class variance ($\kappa$), and total variance ($\eta$). These are given by: $$\lambda = \sigma_B^2$$ $$\kappa = \sigma_T^2/\sigma_W^2$$ $$\eta = \sigma_B^2/\sigma_T^2$$ where $$\sigma_W^2 = \omega_0 \sigma_0^2 + \omega_1 \sigma_1^2$$ $$\sigma_B^2 = \omega_0 (\mu_0 - \mu_T)^2 + \omega_1 (\mu_1 - \mu_T)^2 = \omega_0 \omega_1 (\mu_1 - \mu_0)^2.$$ He goes on to point out that maximizing any of these criteria is equivalent to maximizing the others. Further, maximizing$\eta$is the same as maximizing$\sigma_B^2$, which can be rewritten in terms of the selected threshold,$k$: $$\sigma_B^2(k) = \frac{[\mu_T \omega(k) - \mu(k)]^2}{\omega(k) [1 - \omega(k)]}.$$ The equation above is the heart of the algorithm.$\sigma_B^2$is computed for all possible threshold values, and we choose as our threshold the value that maximizes it. OK, that was a lot of equations, but there's really not that much involved in computing the key quantity,$\sigma_B^2(k)$. Here's what the computation looks like for the coins image. counts = imhist(I); L = length(counts); p = counts / sum(counts); omega = cumsum(p); mu = cumsum(p .* (1:L)'); mu_t = mu(end); sigma_b_squared = (mu_t * omega - mu).^2 ./ (omega .* (1 - omega)); Using yyaxis, a new R2016a feature, let's plot the histogram and$\sigma_B^2$together. close all yyaxis left plot(counts) ylabel('Histogram') yyaxis right plot(sigma_b_squared) ylabel('\sigma_B^2') xlim([1 256]) Otsu's method chooses the place where$\sigma_B^2$is the highest as the threshold. [~,k] = max(sigma_b_squared); hold on plot([k k],ylim,'LineWidth',5) hold off Here's another example. This is a public-domain light microscope image of Lily mitosis. (The original image is courtesy Andrew S. Bajer, University of Oregon, Eugene, OR. This version is slightly cropped.) url = 'http://blogs.mathworks.com/steve/files/205.jpg'; I = rgb2gray(imread(url)); clf imshow(I) counts = imhist(I); L = length(counts); p = counts / sum(counts); omega = cumsum(p); mu = cumsum(p .* (1:L)'); mu_t = mu(end); sigma_b_squared = (mu_t * omega - mu).^2 ./ (omega .* (1 - omega)); close all yyaxis left plot(counts) ylabel('Histogram') yyaxis right plot(sigma_b_squared) ylabel('\sigma_B^2') [~,k] = max(sigma_b_squared); hold on plot([k k],ylim,'LineWidth',5) hold off xlim([1 256]) clf imshow(imbinarize(I)) title('Thresholded cell image') If imbinarize handles this computation automatically, then why did we also provide a function called otsuthresh? The answer is that imbinarize takes an image as input, although Otsu's method does not require the original image, only the image's histogram. If you have a situation where you want to compute a threshold based only on a histogram, then you can call otsuthresh directly. That's why it is there. To wrap up this week's discussion, I want to point out that a couple of blog readers recommended something called the Triangle method for automatic gray-scale image thresholding. If you want to try this for yourself, there is an implementation on the File Exchange. I have not had a chance yet to experiment with it. Next time I'll talk about the algorithm used by imbinarize for locally adaptive thresholding. \n'); d.write(code_string); // Add copyright line at the bottom if specified. if (copyright.length > 0) { d.writeln(''); d.writeln('%%'); if (copyright.length > 0) { d.writeln('% _' + copyright + '_'); } } d.write('\n'); d.title = title + ' (MATLAB code)'; d.close(); } --> Get the MATLAB code (requires JavaScript) Published with MATLAB® R2016a about image binarization, I talked about the new % binarization functions in R2016a. Today I want to switch gears and talk % about Otsu's method, one of the algorithms underlying % . % % (A bonus feature of today's blog post is a demo of % , a new % feature of MATLAB R2016a.) % % Otsu's method is named for Nobuyuki Otsu, who published it in _IEEE % Transactions on Systems, Man, and Cybernetics_, vol. SMC-9, no. 1, January % 1979. At this time, researchers had already explored a variety of ways to % choose a threshold automatically by examining the histogram of image pixel % values. The basic idea is to look for two peaks, representing foreground % and background pixel values, and pick a point in between the two peaks as % the threshold value. % % Here's a simple example using the coins image. I = imread('coins.png'); imshow(I) %% imhist(I) %% % The function |imbinarize| calls |otsuthresh| to get a normalized threshold % value. t = otsuthresh(histcounts(I,-0.5:255.5)) %% % Let's see where that threshold is. hold on plot(255*[t t], ylim, 'r', 'LineWidth', 5) hold off %% % And here is the thresholded coins image. imshow(imbinarize(I,t)) %% % How does this threshold selection work? It is based on entirely on the set % of histogram counts. To show the computation, I'll adopt the notation from % the paper. Pixels can take on the set of values$i = 1,2,\ldots,L$. The % histogram count for pixel value$i$is$n_i$, and the associated % probability is$p_i = n_i/N$, where$N$is the number of image pixels. % (I'm using the word _probability_ here somewhat loosely, in the relative % frequency sense.) % % The thresholding task is formulated as the problem of dividing image % pixels into two classes.$C_0$is the set of pixels with values %$[1,\ldots,k]$, and$C_1$is the set of pixels with values in the range %$[k+1,\ldots,L]$. % % The overall class probabilities,$\omega_0$and$\omega_1$, are: % % $$\omega_0 = \sum_{i=1}^k p_i = \omega(k)$$ % % $$\omega_1 = \sum_{i=k+1}^L p_i = 1 = \omega(k)$$ % % The class means,$\mu_0$and$\mu_1$, are the mean values of the pixels in %$C_0$and$C_1$. They are given by: % % $$\mu_0 = \sum_{i=1}^k i p_i / \omega_0 = \mu(k)/\omega(k)$$ % % $$\mu_1 = \sum_{i=k+1}^L i p_i / \omega_1 = \frac{\mu_T - \mu(k)}{1 - % \omega(k)}$$ % % where % % $$\mu(k) = \sum_{i-1}^k i p_i$$ % % and$\mu_T$, the mean pixel value for the total image, is: % % $$\mu_T = \sum_{i=1}^L i p_i.$$ % % The class variances,$\sigma_0^2$and$\sigma_1^2$, are: % % $$\sigma_0^2 = \sum_{i = 1}^k (i - \mu_0)^2 p_i / \omega_0$$ % % $$\sigma_1^2 = \sum_{i = k+1}^L (i - \mu_1)^2 pi / \omega_1.$$ % % Otsu mentions three measures of "good" class separability: within-class % variance ($\lambda$), between-class variance ($\kappa$), and total % variance ($\eta$). These are given by: % % $$\lambda = \sigma_B^2$$ % % $$\kappa = \sigma_T^2/\sigma_W^2$$ % % $$\eta = \sigma_B^2/\sigma_T^2$$ % % where % % $$\sigma_W^2 = \omega_0 \sigma_0^2 + \omega_1 \sigma_1^2$$ % % $$\sigma_B^2 = \omega_0 (\mu_0 - \mu_T)^2 + \omega_1 (\mu_1 - \mu_T)^2 = % \omega_0 \omega_1 (\mu_1 - \mu_0)^2.$$ % % He goes on to point out that maximizing any of these criteria is % equivalent to maximizing the others. Further, maximizing$\eta$is the % same as maximizing$\sigma_B^2$, which can be rewritten in terms of the % selected threshold,$k$: % % $$\sigma_B^2(k) = \frac{[\mu_T \omega(k) - \mu(k)]^2}{\omega(k) [1 - % \omega(k)]}.$$ % % The equation above is the heart of the algorithm.$\sigma_B^2$is computed % for all possible threshold values, and we choose as our threshold the % value that maximizes it. % % OK, that was a lot of equations, but there's really not that much involved % in computing the key quantity,$\sigma_B^2(k)$. Here's what the % computation looks like for the coins image. counts = imhist(I); L = length(counts); p = counts / sum(counts); omega = cumsum(p); mu = cumsum(p .* (1:L)'); mu_t = mu(end); sigma_b_squared = (mu_t * omega - mu).^2 ./ (omega .* (1 - omega)); %% % Using |yyaxis|, a new R2016a feature, let's plot the histogram and %$\sigma_B^2$together. close all yyaxis left plot(counts) ylabel('Histogram') yyaxis right plot(sigma_b_squared) ylabel('\sigma_B^2') xlim([1 256]) %% % Otsu's method chooses the place where$\sigma_B^2\$ is the highest as the % threshold. [~,k] = max(sigma_b_squared); hold on plot([k k],ylim,'LineWidth',5) hold off %% % Here's another example. This is a public-domain light microscope image of % Lily mitosis. (The is courtesy Andrew S. Bajer, University of Oregon, Eugene, OR. This % version is slightly cropped.) url = 'http://blogs.mathworks.com/steve/files/205.jpg'; I = rgb2gray(imread(url)); clf imshow(I) %% counts = imhist(I); L = length(counts); p = counts / sum(counts); omega = cumsum(p); mu = cumsum(p .* (1:L)'); mu_t = mu(end); sigma_b_squared = (mu_t * omega - mu).^2 ./ (omega .* (1 - omega)); close all yyaxis left plot(counts) ylabel('Histogram') yyaxis right plot(sigma_b_squared) ylabel('\sigma_B^2') [~,k] = max(sigma_b_squared); hold on plot([k k],ylim,'LineWidth',5) hold off xlim([1 256]) %% clf imshow(imbinarize(I)) title('Thresholded cell image') %% % If |imbinarize| handles this computation automatically, then why did we % also provide a function called % ? % The answer is that |imbinarize| takes an image as input, although Otsu's % method does not require the original image, only the image's histogram. If % you have a situation where you want to compute a threshold based *only* on % a histogram, then you can call |otsuthresh| directly. That's why it is % there. %% % To wrap up this week's discussion, I want to point out that a couple of % blog readers recommended something called the _Triangle method_ for % automatic gray-scale image thresholding. If you want to try this for % yourself, there is an implementation on the File Exchange. I have not had % a chance yet to experiment with it. % % Next time I'll talk about the algorithm used by % for locally % adaptive thresholding. ##### SOURCE END ##### 7a6499d359984c5bbbbf01f04253910a -->
Categories: Blogs
## How we will keep the Decentralized Web decentralized: my talk from the Decentralized Web Summit
Cory Doctorow - 2016, June 9 - 10:24
At yesterday’s Internet Archive Decentralized Web Summit, the afternoon was given over to questions of security and policy.
I gave the opening talk, “How Stupid Laws and Benevolent Dictators can Ruin the Decentralized Web, too,” which was about “Ulysses pacts“: bargains you make with yourself when your willpower is strong to prevent giving into temptation later when you are tired or demoralized, and how these have benefited the web to date, and how new, better ones can protect the decentralized web of the future.
EFF’s Jeremy Gillula and Noah Swartz — who were there to present Certbot, a tool that produces free cryptographic certificates — wrote up the afternoon, including my talk, and did a good job summarizing it:
He called on the audience to act now to make a Ulysses pact for the decentralized web, because everything eventually fails or falls on hard times. If we want to make sure that the principles and values we hold dear survive, we need to design the systems that embody those principles so that they can’t be compromised of weakened. In other words, we need to build things now so that five or ten or twenty years from now, when what we’ve built is successful and someone asks us to add a backdoor or insert malware or track our users, it simply won’t be possible (for either technological or legal or monetary reasons)—no matter how much outside pressure we’re under.
After all, “The reason the web is closed today is because…people just like you made compromises that seemed like the right compromise to make at the time. And then they made another compromise, a little one. And another one.” He continued, pointing out that “We are, all of us, a mix of short-sighted and long-term…We must give each other moral support. Literal support to uphold the morals of the decentralized web, by agreeing now on what an open decentralized web is.” Only by doing this will we be able to resist the siren song of re-centralization.
And what sort of principles should we agree to? Cory suggests two. First, when a computer receives conflicting instructions from its owner and from a remote party, the owner’s wishes should always take precedence. In other words, no DRM (that means you, W3C). Second, disclosing true facts about the security of systems that we rely upon should never ever be illegal. In other words, we need to work to abolish things like the DMCA, which create legal uncertainty for security researchers disclosing vulnerabilities in systems locked behind DRM. The crowd’s response to this passionate call to action? A standing ovation.
[Jeremy Gillula and Noah Swartz/EFF]
Categories: Blogs
## You are not a wallet: complaining considered helpful
Cory Doctorow - 2016, June 7 - 12:49
My new Guardian column, It’s your duty to complain – that’s how companies improve, is a rebuttal to those who greet public complaints about businesses’ actions with, “Well, just don’t buy from them, then.”
This idea posits that your role in the market is to be a kind of ambulatory wallet, whose only options are to buy, or not to buy. But not only does complaining sometimes solve your problems, it also warns others away from bad decisions, helping better companies thrive.
Finally, some business conduct isn’t just bad, it’s wrong, whether that’s discrimination, or unfair trading practices, and in those cases, you not only have the right to choose to do business elsewhere, you also have the right to force that company to change that way it operates, and the people who’ve taken on that challenge have done us all a service, and are the reason that we’re not all dying in a fireball every time our cars get rear-ended.
Whenever a complaint comes up about electronic media – games, ebooks, music, movies – and the ways their publishers restrict playback on devices, the “don’t buy it then” squad starts telling you to take your business elsewhere.
Copyright is a deal between the people and rightsholders. Rightsholders get a copyright – an expansive, long-enduring right to control most copying, display, adaptation and performance – when they create something new and fix it in a tangible medium. All the rights not set out in copyright remain in the public’s hands. That means you can’t sell a book with a license agreement that says, “By buying this book whose copyright expires next week, you agree that you will behave as though the copyright expires in the year 2100.” You can’t say, “By buying this book, you agree to vote for Donald Trump,” or “You agree not to let black people or Jews or women read it.”
You – the person reading that book, playing that game, listening to that music – have rights over that work beyond the right to buy or not buy it. You are more than just your wallet.
You have the right to enjoy the media you buy, even when you travel abroad. You have the right to be private in your enjoyment of that media. You have the right to engage in every activity the law doesn’t prohibit.
When those rights are taken away, you have been wronged. You are still wronged, even when you stop buying from the company that wronged you – and that’s if you have the choice to find a new supplier; if it’s your ISP who’s doing the bad stuff, chances are there aren’t any better ISPs you can switch to. You have options, like contacting a government agency such as the Office of Fair Trading and the Federal Trade Commission, or consumer rights organisation like Which? in the UK and Consumers Union in the USA. You have the option of contacting a lawyer.
It’s your duty to complain – that’s how companies improve
[Cory Doctorow/The Guardian]
(Image: Pixabay, PD)
Categories: Blogs
## How security and privacy pros can help save the web from legal threats over vulnerability disclosure
Cory Doctorow - 2016, June 1 - 09:56
I have a new op-ed in today’s Privacy Tech, the in-house organ of the International Association of Privacy Professionals, about the risks to security and privacy from the World Wide Web Consortium’s DRM project, and how privacy and security pros can help protect people who discover vulnerabilities in browsers from legal aggression.
I’ve got an open letter to the W3C asking it to extend its existing nonaggression policy — which prohibits members from using patents to threaten those who implement web standards — to cover the weird, dangerous rights conferred by laws like the DMCA, which let companies threaten security researchers who come forward with disclosures of dangerous product defects.
If you’re a privacy or security pro and you want to support this initiative, email me, along with the country you’d like listed with your name, and your institutional affiliation (if any).
Last summer, the U.S. Copyright Office solicited comments on problems with DMCA 1201, and heard from some of the nation’s most respected security researchers, from Bruce Schneier to Steve Bellovin (formerly chief technologist at the Federal Trade Commission, now the first technology scholar for the Privacy and Civil Liberties Oversight Board), and Ed Felten (now White House Deputy Chief Technology Officer).
The researchers spoke as one to say that the DMCA has chilled them from reporting on flaws in technologies from cars and tractors to medical implants to voting machines.
The W3C’s decision to standardize DRM puts it on a collision course with this legal system. The U.S. Trade Representative has exported versions of the DMCA to most of the U.S.’s trading partners, meaning that web users all over the world face the risk that the flaws in their browsers will go unreported because researchers fear retaliation from vendors who want to avert commercial embarrassment (and even legal liability) when those flaws come to light.
EFF would prefer that the W3C not standardize DRM at all: anything that makes it easier for companies to attack security researchers is not good for the open web. But since the W3C rejected that proposal, we’ve offered a compromise: asking the W3C to extend its existing policy on IPRs to protect security researchers.
How you can help white hat security researchers [Privacy Tech/IAPP]
Categories: Blogs
## Revealed: the amazing cover for Walkaway, my first adult novel since 2009
Cory Doctorow - 2016, May 26 - 06:54
Next April, Tor Books will publish Walkaway, the first novel I’ve written specifically for adults since 2009; it’s scheduled to be their lead title for the season and they’ve hired the brilliant designer Will Staehle (Yiddish Policeman’s Union, Darker Shade of Magic) for the cover, which Tor has just revealed.
Staehle’s cover features a die-cut dustjacket that offers a peek at the design printed on the boards beneath and highlights the blurb from Edward Snowden (!).
I’ll be going out on a 25-city tour when the book comes out — I hope to see you!
The book was originally titled “Utopia” and you can read about it here; here’s Tor’s summary of the book:
Hubert, Seth, and their ultra-rich heiress friend Natalie are getting a little old to hang out at the “Communist parties,” techno-raveups in abandoned industrial spaces, full of insta-printed drugs and toys. And Natalie was finished, years ago, with her overcontrolling zillionaire dad.
And now that anyone can manufacture food, clothing, shelter with equipment comparable to a computer printer, there seems to be little reason to to stick with the world of rules and jobs. So, like hundreds of thousands of others in the mid-21st century, the three of them…walk away.
Mind you, it’s still dangerous out there. Much of the countryside is wrecked by climate change, and predators are with us always. Yet when the initial pioneer walkaways flourish, more people join them. Then the walkaways discover the one thing the ultra-rich have never been able to buy: how to beat death.
Now it’s war—a war that will turn the world upside down.
Fascinating, moving, and darkly humorous, Walkaway is a multi-generation SF thriller about the wrenching changes of the next hundred years…and the very human people who will live their consequences.
[Tor.com]
Categories: Blogs
## Image binarization – new R2016a functions
Matlab Image processing blog - 2016, May 16 - 11:20
In my 09-May-2016 post, I described the Image Processing Toolbox functions im2bw and graythresh, which have been in the product for a long time. I also identified a few weaknesses in the functional designs:
• The function im2bw uses a fixed threshold value (LEVEL) of 0.5 by default. Using graythresh to determine the threshold value automatically would be a more useful behavior most of the time.
• If you don't need to save the value of LEVEL, then you end up calling the functions in a slightly awkward way, passing the input image to each of the two functions: bw = im2bw(I,graythresh(I))
• Although Otsu's method really only needs to know the image histogram, you have to pass in the image itself to the graythresh function. This is awkward for some use cases, such as using the collective histogram of multiple images in a dataset to compute a single threshold.
• Some users wanted to control the number of histogram bins used by graythresh, which does not have that as an option. (I forgot to mention this item in my previous post.)
• There was no locally adaptive thresholding method in the toolbox.
For all of these reasons, the Image Processing Toolbox development undertook a redesign of binarization functionality for the R2016a release. The functional designs are different and the capabilities have been extended. We now encourage the use of a new family of functions:
Binarization using an automatically computed threshold value is now simpler. Instead of two function calls, im2bw(I,graythresh(I)), you can do it with one, imbinarize(I).
I = imread('cameraman.tif'); imshow(I) xlabel('Cameraman image courtesy of MIT') bw = imbinarize(I); imshowpair(I,bw,'montage')
In addition to global thresholding, imbinarize can also do locally adaptive thresholding. Here is an example using an image with a mild illumination gradient from top to bottom.
I = imread('rice.png'); bw = imbinarize(I); imshowpair(I,bw,'montage') title('Original and global threshold')
You can see that the rice grains at the bottom of the image are imperfectly segmented because they are in a darker portion of the image. Now switch to an adaptive threshold.
bw = imbinarize(I,'adaptive'); imshowpair(I,bw,'montage') title('Original and adaptive threshold')
Here is a more extreme example of nonuniform illumination.
I = imread('printedtext.png'); imshow(I) title('Original image') bw = imbinarize(I); imshow(bw) title('Global threshold')
Let's see how using an adaptive threshold can improve the results. Before jumping into it, though, notice that the foreground pixels in this image are darker than the background, which is the opposite of the rice grains image above. The adaptive method works better if it knows whether to look for foreground pixels that are brighter or darker than the background. The optional parameter 'ForegroundPolarity' lets is specify that.
The new functions otsuthresh and adaptthresh are for those who want to have more fine-grained control over the algorithms underlying the global and adaptive thresholding behavior of imbinarize. I'll talk about them next time.
\n'); d.write(code_string); // Add copyright line at the bottom if specified. if (copyright.length > 0) { d.writeln(''); d.writeln('%%'); if (copyright.length > 0) { d.writeln('% _' + copyright + '_'); } } d.write('\n'); d.title = title + ' (MATLAB code)'; d.close(); } -->
Get the MATLAB code (requires JavaScript)
Published with MATLAB® R2016a
Categories: Blogs
## Actor Tailor Soldier Spy
Casey McKinnon - 2016, May 16 - 10:49
I did a quick shoot with the Headshot Truck last week to refresh my headshots and get some photos of character types. My agent was enthusiastic about getting a powerful shot in a suit for roles like manipulative politician, lawyer, and agent (of the FBI, of real estate, of A.C.R.O.N.Y.M.S., etc.). The second look she wanted was a strong army look, which could also work great for roles like resistance fighter, local militia member, or apocalypse survivor. And, thanks to the efficient photographer in the Headshot Truck, and my own over-preparedness, I was able to sneak in a third look... a somewhat period appropriate (and somewhat inappropriate) girl next door type.
I had a good experience with the Headshot Truck, and I may choose to visit them in the future for another look; perhaps doctor/scientist, nerdy intellectual, or Shakespearean ingenue? We shall see. In the meantime, I'm very pleased with the results and I hope they serve their purpose well.
Categories: Blogs
## O’Reilly Hardware Podcast on the risks to the open Web and the future of the Internet of Things
Cory Doctorow - 2016, May 11 - 10:36
I appeared on the O’Reilly Hardware Podcast this week (MP3, talking about the way that DRM has crept into all our smart devices, which compromises privacy, security and competition.
In this episode of the Hardware podcast, we talk with writer and digital rights activist Cory Doctorow. He’s recently rejoined the Electronic Frontier Foundation to fight a World Wide Web Consortium proposal that would add DRM to the core specification for HTML. When we recorded this episode with Cory, the W3C had just overruled the EFF’s objection. The result, he says, is that “we are locking innovation out of the Web.”
“It is illegal to report security vulnerabilities in a DRM,” Doctorow says. “[DRM] is making it illegal to tell people when the devices they depend upon for their very lives are unsuited for that purpose.”
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In our “Tools” segment, Doctorow tells us about tools that can be used for privacy and encryption, including the EFF surveillance self-defense kit, and Wickr, an encrypted messaging service that allows for an expiration date on shared messages and photos. “We need a tool that’s so easy your boss can use it,” he says.
Cory Doctorow on losing the open Web [O’Reilly Hardware Podcast]
Categories: Blogs
## Peace in Our Time: how publishers, libraries and writers could work together
Cory Doctorow - 2016, May 9 - 17:33
Publishing is in a weird place: ebook sales are stagnating; publishing has shrunk to five major publishers; libraries and publishers are at each others’ throats over ebook pricing; and major writers’ groups are up in arms over ebook royalties, and, of course, we only have one major book retailer left — what is to be done?
In my new Locus Magazine column, “Peace in Our Time,” I propose a pair of software projects that could bring all together writers, publishers and libraries to increase competition, give publishers the market intelligence they need to sell more books, triple writers’ ebook royalties, and sell more ebooks to libraries, on much fairer terms.
The first project is a free/open version of Overdrive, the software that publishers insist that libraries use for ebook circulation. A free/open version, collectively created and maintained by the library community, would create a source of data that publishers could use to compete with Amazon, their biggest frenemy, while still protecting patron privacy. The publishers’ quid-pro-quo for this data would be an end to the practice of gouging libraries on ebook prices, leaving them with more capital to buy more books.
The second project is a federated ebook store for writers, that would allow writers to act as retailers for their publishers, selling their own books and keeping the retailer’s share in addition to their traditional royalty: a move that would increase the writer’s share by 300%, without costing the publishers a penny. Writer-operated ebook stores, spread all over the Web but searchable from central portals, do not violate the publishers’ agreements with Amazon, but they do create new sales category: “fair trade ebooks,” whose sale gives the writers you love the money to feed their families and write more books — without costing you anything extra.
Amazon knows, in realtime, how publishers’ books are performing. It knows who is buying them, where they’re buying them, where they’re reading them, what they searched for before buying them, what other books they buy at the same time, what books they buy before and after, whether they read them, how fast they read them, and whether they finish them.
Amazon discloses almost none of this to the publishers, and what information they do disclose to the publishers (the sales data for the publishers’ own books, atomized, without data-mineable associations) they disclose after 30 days, or 90 days, or 180 days. Publishers try to fill in the gaps by buying their own data back from the remaining print booksellers, through subscriptions to point-of-sale databases that have limited relevance to e-book performance.
There is only one database of e-book data that is remotely comparable to the data that Amazon mines to stay ahead of the publishers: e-book circulation data from public libraries. This data is not as deep as Amazon’s – thankfully, since it’s creepy and terrible that Amazon knows about your reading habits in all this depth, and it’s right and fitting that libraries have refused to turn on that kind of surveillance for their own e-book circulation.
Peace in Our Time [Cory Doctorow/Locus]
Categories: Blogs
## Image binarization – im2bw and graythresh
Matlab Image processing blog - 2016, May 9 - 11:41
As I promised last time, I'm writing a series about functional designs for image binarization in the Image Processing Toolbox. Today I'll start by talking about im2bw and graythresh, two functions that have been in the product for a long time.
The function im2bw appeared in Image Processing Toolbox version 1.0, which shipped in early fall 1993. That was about the time I interviewed for my job at MathWorks. (I was a beta tester of version 1.0.)
Here is the help text from that early function:
%IM2BW Convert image to black and white by thresholding. % BW = IM2BW(X,MAP,LEVEL) converts the indexed image X with % colormap MAP to a black and white intensity image BW. % BW is 0 (black) for all pixels with luminance less % than LEVEL and 1 (white) for all other values. % % BW = IM2BW(I,LEVEL) converts the gray level intensity image % I to black and white. BW is 0 (black) for all pixels with % value less than LEVEL and 1 (white) for all other values. % % BW = IM2BW(R,G,B,LEVEL) converts the RGB image to black % and white. BW is 0 (black) for all pixels with luminance % less than LEVEL and 1 (white) for all other values. % % See also IND2GRAY, RGB2GRAY.
At that time, the prefix "im" in the function name meant that the function could take more than one image type (indexed, intensity, RGB).
At this point in the early history of MATLAB, the language really only had one type. Everything in MATLAB was a double-precision matrix. This affected the early functional design in two ways. First, the toolbox established [0,1] as the conventional dynamic range for gray-scale images. This choice was influenced by the mathematical orientation of MATLAB as well as the fact that there was no one-byte-per-element data type. The second impact on functional design can be seen in the syntax IM2BW(R,G,B,LEVEL). RGB (or truecolor) images had to be represented with three different matrices, one for each color component. I really don't miss those days!
Here are two examples, an indexed image and a gray-scale image.
[X,map] = imread('trees.tif'); imshow(X,map); title('Original indexed image') bw = im2bw(X,map,0.5); imshow(bw) title('Output of im2bw') I = imread('cameraman.tif'); imshow(I) title('Original gray-scale image') xlabel('Cameraman image courtesy of MIT') bw = im2bw(I,0.5); imshow(bw) title('Output of im2bw')
It turns out that im2bw had other syntaxes that did not appear in the documentation. Specifically, the LEVEL argument could be omitted. Here is relevant code fragment:
if isempty(level), % Get level from user level = 0.5; % Use default for now end
Experienced software developers will be amused by the code comment above, "Use default for now". This indicates that the developer intended to go back and do something else here before shipping but never did. Anyway, you can see that a LEVEL of 0.5 is used if you don't specify it yourself.
MATLAB 5 and Image Processing Toolbox version 2.0 shipped in early 1998. These were very big releases for both products. MATLAB 5 featured multidimensional arrays, cell arrays, structs, and many other features. MATLAB 5 also had something else that was big for image processing: numeric arrays that weren't double precision. At the time, you could make uint8, int8, uint16, int16, uint32, int32, and single arrays. However, there was almost no functional support or operator support these arrays. The capability was so limited that we didn't even mention it in the MATLAB 5 documentation.
Image Processing Toolbox 2.0 provided support for (and documented) uint8 arrays. The other types went undocumented and largely unsupported in both MATLAB and the toolbox for a while longer.
Multidimensional array and uint8 support affected almost every function in the toolbox, so version 2.0 was a complex release, especially with respect to compatibility. We wanted to be able to handle uint8 and multidimensional arrays smoothly, to the degree possible, with existing user code.
One of the design questions that arose during this transition concerned the LEVEL argument for im2bw. Should the interpretation of LEVEL be different, depending on the data type of the input image? To increase the chance that existing user code would work as expected without change, even if the image data type changed from double to uint8, we adopted the convention that LEVEL would continue to be specified in the range [0,1], independent of the input image data type. That is, a LEVEL of 0.5 has the same visual effect for a double input image as it does for a uint8 input image.
Now, image processing as a discipline is infamous for its "magic numbers," such as threshold values like LEVEL, that need to be tweaked for every data set. Sometime around 1999 or 2000, we reviewed the literature about algorithms to compute thresholds automatically. There were only a handful that seemed to work reasonably well for a broad class of images, and one in particular seemed to be both popular and computationally efficient: N. Otsu, "A Threshold Selection Method from Gray-Level Histograms," IEEE Transactions on Systems, Man, and Cybernetics, vol. 9, no. 1, 1979, pp. 62-66. This is the one we chose to implement for the toolbox. It is the algorithm under the hood of the function graythresh, which was introduced in version 3.0 of the toolbox in 2001.
The function graythresh was designed to work well with the function im2bw. It takes a gray-scale image and returns the same normalized LEVEL value that im2bw uses. For example:
level = graythresh(I) level = 0.3451 bw = im2bw(I,level); imshow(bw) title('Level computed by graythresh')
Aside from multilevel thresholding introduced in R2012b, this has been the state of image binarization in the Image Processing Toolbox for about the last 15 years.
There are a few weaknesses in this set of functional designs, though, and these weaknesses eventually led the development to consider an overhaul.
• Most people felt that the value returned by graythresh would have been a better default LEVEL than 0.5.
• If you don't need to save the value of LEVEL, then you end up calling the functions in a slightly awkward way, passing the input image to each of the two functions: bw = im2bw(I,graythresh(I))
• Although Otsu's method really only needs to know the image histogram, you have to pass in the image itself to the graythresh function. This is awkward for some use cases, such as using the collective histogram of multiple images in a dataset to compute a single threshold.
• There was no locally adaptive thresholding method in the toolbox.
Next time I plan to discuss the new image binarization functional designs in R2016a.
Also, thanks very much to ez, PierreC, Matt, and Mark for their comments on the previous post.
\n'); d.write(code_string); // Add copyright line at the bottom if specified. if (copyright.length > 0) { d.writeln(''); d.writeln('%%'); if (copyright.length > 0) { d.writeln('% _' + copyright + '_'); } } d.write('\n'); d.title = title + ' (MATLAB code)'; d.close(); } -->
Get the MATLAB code (requires JavaScript)
Published with MATLAB® R2016a
Categories: Blogs
## The open web’s guardians are acting like it’s already dead
Cory Doctorow - 2016, May 3 - 11:02
The World Wide Web Consortium — an influential standards body devoted to the open web — used to make standards that would let anyone make a browser that could view the whole Web; now they’re making standards that let the giant browser companies and giant entertainment companies decide which browsers will and won’t work on the Web of the future.
When you ask them why they’re doing this, they say that the companies are going to build technology that locks out new entrants no matter what they do, and by capitulating to them, at least there’s a chance of softening the control the giants will inevitably get.
In my latest Guardian column, Why the future of web browsers belongs to the biggest tech firms, I explain how the decision of the W3C to let giant corporations lock up the Web betrays a belief that the open Web is already dead, and all that’s left to argue about are the terms on which our new overlords will present to us.
Today is the International Day Against DRM. EME, the W3C project that hands control over the Web to giant corporations, uses DRM to assert this control.
We will get the open Web we deserve. If you and I and everyone we know stand up to the bullies who want to use entertainment technology to seize control over the future, we can win.
Otherwise, we’ll be Huxleyed into the full Orwell.
Make it easy for today’s crop of web giants to sue any new entrants into oblivion and you can be pretty certain there won’t be any new entrants.
It marks a turning point in the history of those companies. Where once web giants were incubators for the next generation of entrepreneurs who struck out and started competitors that eclipsed their former employers, now those employees are setting the stage for a future where they can stay where they are, or slide sideways to another giant. Forget overturning the current order, though. Maybe they, too, think the web is cooked.
In case there was any doubt of where the W3C stood on whether the future web needed protection from the giants of today, that doubt was dispelled last month. Working with the Electronic Frontier Foundation, I proposed that the W3C adapt its existing policies – which prohibit members from using their patents to block new web companies – to cover EME, a moved that was supported by many W3C members.
Rather than adopt this proposal or a version of it, last month, the W3C executive threw it out, giving the EME group a green light to go forward with no safeguards whatsoever.
Categories: Blogs |
This blog is powered by Nikola, a Python-based static blog compiler, which I've installed in a Python virtualenv to separate it from the system-wide Python installation of my notebook. Updates of the major version of Python (like from 3.6 to 3.7) inevitably break these virtualenvs, and I have so far accepted that there's no other way to get them back than to rebuild them from scratch. In fact, that's what you get to hear even from experienced Linux developers.
The recent update to Python 3.7 brought that topic back to my attention, and I kind of lost my patience. I just couldn't accept that there shouldn't be a better way, and indeed found a solution for those using the venv module of Python 3.3+:
python -m venv --upgrade <path_of_existing_venv>
Despite the fact that I'm using virtualenv instead of venv, this command worked exactly as I had hoped. ☺
The virtualenv can now be updated as usual. Well, almost – both pip and pip-tools got a lot more conservative and actually have to be told explicitly that they really should upgrade to the latest version. For a particular package, that looks like this:
pip install --upgrade Nikola --upgrade-strategy=eager
A rather weird behavior, if you ask me, but what do I know. ☺
Back to our virtualenv. To really, genuinely and truly update all requirements, the following sequence of commands is necessary:
pip install --upgrade setuptools |
Function for arrange journal club schedule
## Usage
jc_tombola(
data,
members,
papers = 1,
group,
gr_lvl,
status,
st_lvl,
frq,
date,
seed = NULL
)
## Arguments
data
Data frame withe members and their information.
members
Columns with the members names.
papers
Number of paper by meeting
group
Column for arrange the group.
gr_lvl
Levels in the groups for the arrange. See details.
status
Column with the status of the members.
st_lvl
Level to confirm the assistance in the JC. See details.
frq
Number of the day for each session.
date
Date when start the first session of JC.
seed
Number for replicate the results (default = date).
## Value
data frame with the schedule for the JC
## Details
The function could consider n levels for gr_lvl. In the case of two level the third level will be both. The suggested levels for st_lvl are: active or spectator. Only the active members will enter in the schedule. |
# Configuration of IndySDK
## Robot Execution using IndySDK
This is guidance for those who want to run the robot for the first time using pre-built component files of IndySDK.
If the installation is compete, please copy the LeanDeployment folder in /neuromeka/NRMKFoundation/ directory of the development PC (Windows) to the path /home/user/release/ in STEP as illustrated in below.
Note
When users copy component files from development PC to remote server (STEP), users can use Windows Explorer or other SFTP, SCP, FTP client app such as WinSCP to perform SSH file transfer.
After completing the copy, log in to STEP using PuTTY (or other SSH client tool). Then, enter the terminal command as shown below.
• Set execution privilege to the TaskManager file in STEP
1 2 $cd /home/user/release/LeanDeployment$ chmod 777 *
• Execute the TaskManager with root privilege as below. Here, JSON deployment file deployIndy.json must be given as an argument of TaskManager.
1 \$ sudo ./TaskManager -j deployIndy7.json
• Then, the robot turns on and Indy Framework is executed, and basic console logger appears in the terminal shown in below.
• Now, users can use Conty (teach pendant) to control the robot (or virtual robot).
Note
Please refer to IndyFramework chapter for the detailed description about TaskManager and shared library (.so file) which are execution files of Indy Framework.
## JSON Deployment File
deployIndy7.json is a JSON deployment file that configures tasks when operating robot. As shown in the code below, there are three tasks to be executed when the robot operates. Each task contains components as the element of Param.
Example of JSON deployment file of IndySDK
• Path: The path where the shared library files are located. As shown in the aforementioned figure, shared library files (*.so) and Component directory that contains component files (*.comp) should be located in that path.
• Queue: Pre-defined real-time task execution.
• QueueLow has 1Hz execution cycle, and is not used.
• ControlTask will be configured by pre-built (or user-developed) five component files.
• Params: ControlTask is composed of five IndySDK component files.
• The component plug-in files (*.comp) should be located in Component folder in Path.
• When representing component plug-in file in the JSON deployment file, only file name should be specified without extension.
Note
libIndy6DControlTask.so is a task to run real robot, and libIndy6DControlTask_sim.so is a task to run virtual robot in simulation environment. Users can switch the real and simulation modes depending on their purpose.
Warning
Please verify your own control algorithm on simulation environment first, and apply it to a real robot.
## IndySDK Component
IndyFramework includes five types of components such as Robot Model, Joint Controller, Joint Interpolator, Task Controller, and Task Interpolator. Developers can modify the following four items and apply them to IndyFramework using IndySDK development environment provided by a shared library based plug-in.
Component
Deploy Name in JSON
Description
Joint Controller
JController
• Compute command torques for each joint
• Compute gravitational torque in current joint configuration
• Joint Interpolator
JInterpolator
• Path interpolation between waypoints in joint configuration space
• Set maximum velocity and acceleration
TController
• Compute command torques for each joint
TInterpolator
• Path interpolation between waypoints in task space
• Set maximum velocity and acceleration정
• IndyFramework has been implemented to change the control mode (cmode) depending on the situation, and the component suitable for each cmode operates. For example, when the robot is ready state, cmode is 0. During the joint space control, cmode is 1. During the task space control, cmode is 2. During the gravity compensation, cmode is 3. Users can modify component through IndySDK, and implement low-level controllers of each cmode. The following table represents components and their functions called at each cmode.
Control mode (cmode)
Activated IndySDK components
• Joint Control Component (main operating function: computeControlTorq)
• Joint Move (1)
• Joint Trajectory Interpolation Component (main operating function: traj)
• Joint Control Component (main operating function: computeControlTorq)
• Task Trajectory Interpolation Component (main operating function: traj)
• Task Control Component (main operating function: computeControlTorq)
• Direct Teaching (3)
• Joint Control Component (main operating function: computeGravityTorq)
• Components and their function called at each cmode
Each component can be implemented on project template provided by IndySDK. Please see below for details on each component template and related robot control functions.
### 1. Joint Trajectory Interpolation
Joint Trajectory Interpolation component is used to generate a joint-space trajectory passing through all waypoints (a list of pre-defined points). The generated trajectory must satisfy all boundary conditions set by the framework. The APIs are categorized into five groups and are defined in the abstract Joint Trajectory Interpolation class. Here, DIM is a constant representing the dimension of the joint-space waypoint. The user must specify the value of DIM when developing the component.
Functions Description
Set Trajectory Generation Conditions Set the conditions for the trajectory to be calculated, such as the initial time, maximum velocity and acceleration.
Set Waypoint List Set the path by accepting a pointer to the waypoint array as a parameter.
Compute Trajectory
• Generate the desired position, velocity, and acceleration at the moment indicated by the time parameter.
• Note that this function is called every real-time cycle inside the IndyFramework, implying that this function must be real-time compatible.
• Get Trajectory Specification Get the specification and characteristics of the trajectory.
Get Trajectory State Get the current state of the trajectory, such as target reached and repeated motion.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 template class AbstractJPathInterpolator { public: typedef Eigen::Matrix VecType; public: AbstractJPathInterpolator() {} virtual ~AbstractJPathInterpolator() {} /* Setup predefined conditions for the trajectory */ virtual void setPeriod(double delt) = 0; virtual void setInitialTime(double t0) = 0; virtual void setTraj(double t0) = 0; virtual void setupTraj(int mode) {} virtual void setLoop(bool enable) {} virtual void setBoundaryCondAll(const VecType & vel_max, const VecType & acc_max) = 0; /* Setup waypoint list */ virtual void setPath(const VecType *path, int len, double * maxDeviation) = 0; virtual void resetPath() {} /* Compute the desired configuration at a time */ virtual void traj(double time, VecType & posDes, VecType & velDes, VecType & accDes) = 0; /* Get specification of the trajectory */ virtual double getDuration() = 0; virtual int getNTotalSegment() = 0; virtual int getCurrentWaypoint() = 0; /* Get the current status of the trajectory */ virtual bool isTargetReached() = 0; virtual bool isTrajSetFailed() = 0; virtual bool isLoop() { return false; } };
Abstract Joint Trajectory Interpolation Component
### 2. Joint Control
Joint Control component takes the desired and current robot configurations in joint space and determine target torques for all joints. The calculated joint torques are sent directly to the joints’ motor drives. There are three groups of Joint Control API as shown in the following table.
Functions Description
Configure Controller Configure the internal characteristics of the controller.
Reset State 적Reset user-defined internal variables such as integral errors.
Compute Torque
• Calculate the torque value to be applied to the robot joint.
• Note that this function must be real-time compatible because it is called in the middle of real-time cycle.
• 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 template class AbstractJointController { public: typedef AbstractRobotType ROBOT; typedef typename ROBOT::JointVec JointVec; public: AbstractJointController() {} virtual ~AbstractJointController() {} /* Configure Controller */ virtual void setPeriod(double delt) {} virtual void setPassivityMode(bool enable) {} virtual void setGains(JointVec const & kp, JointVec const & kv, JointVec const & ki) {} /* Reset Internal Status */ virtual void reset() {} virtual void reset(int jIndex) {} /* Controlled Torque Computation */ virtual int computeControlTorq(ROBOT & robot, JointVec const & qDesired, JointVec const & qdotDesired, JointVec const & qddotDesired, JointVec & torque) = 0; virtual int computeGravityTorq(ROBOT & robot, JointVec & torque) = 0; };
Abstract Joint Control Component
Task Trajectory Interpolation component is used to generate 6D-space trajectory passing through all waypoints (a list of pre-defined points). The generated trajectory must satisfy all boundary conditions set by the framework. The APIs are categorized into five groups and are defined in the abstract Task Trajectory Interpolation class.
Functions Description
Set Trajectory Generation Conditions Set the conditions for the trajectory to be calculated, such as the initial time, maximum velocity and acceleration.
Set Waypoint List Set the path by accepting a pointer to the waypoint array as a parameter.
Compute Trajectory
• Generate the desired position, velocity, and acceleration at the moment indicated by the time parameter.
• Note that this function is called every real-time cycle inside the IndyFramework, implying that this function must be real-time compatible.
• Get Trajectory Specification Get the specification and characteristics of the trajectory.
Get Trajectory State Get the current state of the trajectory, such as target reached and repeated motion.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 class AbstractFPathInterpolator { public: typedef NRMKFoundation::CompositeHTransformTaskPosition PosType; typedef NRMKFoundation::CompositeHTransformTaskVelocity VelType; typedef VelType AccType; typedef Eigen::Matrix VecType2D; public: AbstractFPathInterpolator() {} virtual ~AbstractFPathInterpolator() {} /* Setup predefined conditions for the trajectory */ virtual void setPeriod(double delt) = 0; virtual void setInitialTime(double t0) = 0; virtual void setTraj(double t0) = 0; virtual void setupTraj(int mode) {} virtual void setBoundaryCondAll(VecType2D const & vel_max, VecType2D const & acc_max) = 0; virtual void setLoop(bool enable) {} virtual void setReadyPos(PosType & pos) {} /* Input the list of waypoints */ virtual void setPath(const PosType *path, const int len, double * maxDeviation, const int *dirAngle = NULL, bool simulCheck = false) = 0; virtual void resetPath() {} /* Compute the desired configuration at a time */ virtual void traj(double time, PosType & pos, VelType & vel, AccType & acc) = 0; /* Get specification of the trajectory */ virtual double getDuration() = 0; virtual int getNTotalSegment() = 0; virtual int getCurrentWaypoint() = 0; /* Check the status of the trajectory */ virtual bool isTargetReached() = 0; virtual bool isTrajSetFailed() = 0; virtual bool isLoop() { return false; } }; |
# Math Overflow Recent Questions
## Primary tabs
most recent 30 from mathoverflow.net 2018-11-16T08:10:03Z
### Lifting Levi Civita connection
Fri, 07/27/2018 - 05:10
When in differential geometry one shows , on a riemannian manifold, that a (unique) connection exists, (Levi Civita connection), is it possible to "lift" that notion to the principal bundle of frames over that manifold?In that case, is that lifted connection unique? (if so, the Yang Mills field would precisely be the LV connection)
Does the bundle of frames always admit a one form, even if the manifold has no metric on it?In that case that would provide a lifting to the LC connection...
### A question on Sobolev spaces and PDE, trading regularity for integrability
Fri, 07/27/2018 - 04:59
Quoting from this blog of Prof Terry
“…as the very useful Sobolev embedding theorem, which allows one to trade regularity for integrability…”
Thats one use of Sobolev spaces. In this context, Fourier and Plancheral methods come very handy, when the corresponding Sobolev space is also a Hilbert space. But that is not always the case…. Only $L^2$ based Sobolev spaces are Hilbert spaces. According to Sobolev emebdding, if the function in $\mathbb{R}^d$ need to be holder continuous, then its gardient needs to be $L^p$ integrable with $p >= d+1$. So for $d >1$, we need $p > 2$, so the associated Sobolev space cannot have a Hilbert space structure. So in this context, we cannot use Fourier Plancheral techniques. “But if” (stress If)… I say, that I can always find a Hilbert space, for any d, (even for cases when d>1), how useful a tool that it would be, in the context of PDE. What would the impact be? Any examples of PDE, on which there would be impact? Appreciate your valuable comment.
### Quotient by a non-free action of a Lie group and manifolds with corners
Fri, 07/27/2018 - 04:06
The quotient manifold theorem says that
If $G$ is a Lie group acting freely and properly on a smooth manifold $M$ then $M/G$ has a (unique) smooth structure such that the projection $\pi:M\to M/G$ is a submersion.
I was wondering what happens when the action is not free. My intuition suggests that we get corners, I have in mind this example: The action of $\frac{\mathbb{Z}}{2\mathbb{Z}}$ over $\mathbb{S}^2$ induced by the reflection wrt the $zy$-plane. The quotient manifold obtained is $\mathbb{D}^2$ and the boundary $\partial\mathbb{D}^2$ can be identified with the fixed points of the action i.e. $\mathbb{S}^2\cap zy \text{-plane}$.
Does anyone know a theorem that covers the non-free case? Where can I read about it?
### Can we define a normal vector field on the level sets of the distance function?
Fri, 07/27/2018 - 03:56
Suppose $M$ is a smooth connected complete Riemannian manifold of dimension $n\geq 2$. Let $d:M\times M\rightarrow \mathbb{R}^+$ be the distance induced by the Riemannian metric on $M$. For $p\in M$ we set $d_p:=d(p,\cdot)$. We know that $d_p$ is smooth on $M\setminus (C_p\cup\{p\})$, where $C_p$ is the cut locus of $p$, which is a null set according to the Riemannian measure on $M$. Moreover, $d_p$ is regular in any point $q\in M\setminus (C_p\cup\{p\})$, since its gradient at $q$ is the derivative of the unique minimal geodesic at $d_p(q)$ joining $p$ and $q$.
For $R>0$ consider the level set $d_p^{-1}(R)$. Since $R$ does not need to be a regular value of $d_p$, we may not be able to define a normal vector field globally on $d_p^{-1}(R)$. Is there some characterisation of the intersection $C_p\cap d_p^{-1}(R)$, which states that set is "small" maybe in the sense of some $N-2$-dimensional Hausdorff measure or in some topological sense? Or is there some other way to define a unit normal vector field "almost everywhere" on $d_p^{-1}(R)$?
### A smooth curve and mean value theorem
Fri, 07/27/2018 - 03:49
Assume that $f$ is smooth function defined in the unit disk $D: x^2+y^2\le 1$, and consider the integral $$I=\int_D f dxdy=\int_0^1r \int_0^{2\pi} f(re^{it})dt.$$
Then it is clear that for $r\in[0,1]$ there is $t_r\in [0,2\pi]$ so that $$I=2\pi \int_0^1 r f(re^{it_r})dr.$$ My question is, can we choose $t_r$ to depend smoothly on $r$.
### how can I solve this geometry problem? [on hold]
Fri, 07/27/2018 - 03:16
enter image description here
Can you solve this problem for me?
### Comparisons of log canonical thresholds
Fri, 07/27/2018 - 02:47
Premise
Let $K$ be a field of characteristic zero and $f\in K[X_1,\dots,X_m]$. By Hironaka's theorem, there exists a log resolution (over $K$) of the ideal $(f)$. Let $\{(N_i,\nu_i)\}_i$ be the numerical data of a fixed log resolution. The quantity $$lct_K(f):=\min_{i}\frac{\nu_i}{N_i}$$ does not depend on the choice of the log resolution and it is called the log canonical threshold of $f$ over $K$.
Questions
Let $f\in \mathbb{Q}[X_1,\dots,X_m]$. By definition, we have $$lct_{\mathbb{Q}}(f)\ge lct_{\mathbb{Q_p}}(f_{\mathbb{Q}_p}) \ge lct_{\mathbb{C}}(f_{\mathbb{C}}).$$ On the other hand, from Denef's formula for the motivic Igusa zeta function it follows that for all but finitely many $p$ one has $$lct_{\mathbb{Q_p}}(f_{\mathbb{Q}_p}) \ge lct_{\mathbb{Q}}(f_{\mathbb{Q}}).$$ This shows that $$lct_{\mathbb{Q_p}}(f_{\mathbb{Q}_p}) = lct_{\mathbb{Q}}(f_{\mathbb{Q}}) \quad \forall\forall p.$$
1. Is this equality actually true for all $p$?
In all the counterexamples I have found in the literature for the validity of Denef's formula for the "bad" primes (in the sense of Denef) one still has $lct_{\mathbb{Q_p}}(f_{\mathbb{Q}_p}) = lct_{\mathbb{Q}}(f_{\mathbb{Q}})$ also for bad primes $p$. Were this not always the case, has anybody a counterexample at hand?
2. What can we say about the comparison with $lct_{\mathbb{C}}(f_{\mathbb{C}})$? |
g07 Chapter Contents
g07 Chapter Introduction
NAG C Library Manual
# NAG Library Function Documentnag_estim_gen_pareto (g07bfc)
## 1 Purpose
nag_estim_gen_pareto (g07bfc) estimates parameter values for the generalized Pareto distribution by using either moments or maximum likelihood.
## 2 Specification
#include #include
void nag_estim_gen_pareto (Integer n, const double y[], Nag_OptimOpt optopt, double *xi, double *beta, double asvc[], double obsvc[], double *ll, NagError *fail)
## 3 Description
Let the distribution function of a set of $n$ observations
$yi , i=1,2,…,n$
be given by the generalized Pareto distribution:
$Fy = 1- 1+ ξy β -1/ξ , ξ≠0 1-e-yβ , ξ=0;$
where
• $\beta >0$ and
• $y\ge 0$, when $\xi \ge 0$;
• $0\le y\le -\frac{\beta }{\xi }$, when $\xi <0$.
Estimates $\stackrel{^}{\xi }$ and $\stackrel{^}{\beta }$ of the parameters $\xi$ and $\beta$ are calculated by using one of:
• method of moments (MOM);
• probability-weighted moments (PWM);
• maximum likelihood estimates (MLE) that seek to maximise the log-likelihood:
$L = -n ln β^ - 1+ 1ξ^ ∑ i=1 n ln 1+ ξ^yi β^ .$
The variances and covariance of the asymptotic Normal distribution of parameter estimates $\stackrel{^}{\xi }$ and $\stackrel{^}{\beta }$ are returned if $\stackrel{^}{\xi }$ satisfies:
• $\stackrel{^}{\xi }<\frac{1}{4}$ for the MOM;
• $\stackrel{^}{\xi }<\frac{1}{2}$ for the PWM method;
• $\stackrel{^}{\xi }<-\frac{1}{2}$ for the MLE method.
If the MLE option is exercised, the observed variances and covariance of $\stackrel{^}{\xi }$ and $\stackrel{^}{\beta }$ is returned, given by the negative inverse Hessian of $L$.
## 4 References
Hosking J R M and Wallis J R (1987) Parameter and quantile estimation for the generalized Pareto distribution Technometrics 29(3)
McNeil A J, Frey R and Embrechts P (2005) Quantitative Risk Management Princeton University Press
## 5 Arguments
1: nIntegerInput
On entry: the number of observations.
Constraint: ${\mathbf{n}}>1$.
2: y[n]const doubleInput
On entry: the $n$ observations ${y}_{\mathit{i}}$, for $\mathit{i}=1,2,\dots ,n$, assumed to follow a generalized Pareto distribution.
Constraints:
• ${\mathbf{y}}\left[i-1\right]\ge 0.0$;
• $\sum _{\mathit{i}=1}^{n}{\mathbf{y}}\left[i-1\right]>0.0$.
3: optoptNag_OptimOptInput
On entry: determines the method of estimation, set:
${\mathbf{optopt}}=\mathrm{Nag_PWM}$
For the method of probability-weighted moments.
${\mathbf{optopt}}=\mathrm{Nag_MOM}$
For the method of moments.
${\mathbf{optopt}}=\mathrm{Nag_MOMMLE}$
For maximum likelihood with starting values given by the method of moments estimates.
${\mathbf{optopt}}=\mathrm{Nag_PWMMLE}$
For maximum likelihood with starting values given by the method of probability-weighted moments.
Constraint: ${\mathbf{optopt}}=\mathrm{Nag_PWM}$, $\mathrm{Nag_MOM}$, $\mathrm{Nag_MOMMLE}$ or $\mathrm{Nag_PWMMLE}$.
4: xidouble *Output
On exit: the parameter estimate $\stackrel{^}{\xi }$.
On exit: the parameter estimate $\stackrel{^}{\beta }$.
6: asvc[$4$]doubleOutput
On exit: the variance-covariance of the asymptotic Normal distribution of $\stackrel{^}{\xi }$ and $\stackrel{^}{\beta }$. ${\mathbf{asvc}}\left[0\right]$ contains the variance of $\stackrel{^}{\xi }$; ${\mathbf{asvc}}\left[3\right]$ contains the variance of $\stackrel{^}{\beta }$; ${\mathbf{asvc}}\left[1\right]$ and ${\mathbf{asvc}}\left[2\right]$ contain the covariance of $\stackrel{^}{\xi }$ and $\stackrel{^}{\beta }$.
7: obsvc[$4$]doubleOutput
On exit: if maximum likelihood estimates are requested, the observed variance-covariance of $\stackrel{^}{\xi }$ and $\stackrel{^}{\beta }$. ${\mathbf{obsvc}}\left[0\right]$ contains the variance of $\stackrel{^}{\xi }$; ${\mathbf{obsvc}}\left[3\right]$ contains the variance of $\stackrel{^}{\beta }$; ${\mathbf{obsvc}}\left[1\right]$ and ${\mathbf{obsvc}}\left[2\right]$ contain the covariance of $\stackrel{^}{\xi }$ and $\stackrel{^}{\beta }$.
8: lldouble *Output
On exit: if maximum likelihood estimates are requested, ll contains the log-likelihood value $L$ at the end of the optimization; otherwise ll is set to $-1.0$.
9: failNagError *Input/Output
The NAG error argument (see Section 3.6 in the Essential Introduction).
## 6 Error Indicators and Warnings
NE_ALLOC_FAIL
Dynamic memory allocation failed.
On entry, argument $〈\mathit{\text{value}}〉$ had an illegal value.
NE_INT
On entry, ${\mathbf{n}}=〈\mathit{\text{value}}〉$.
Constraint: ${\mathbf{n}}>1$.
NE_INTERNAL_ERROR
An internal error has occurred in this function. Check the function call and any array sizes. If the call is correct then please contact NAG for assistance.
NE_OPTIMIZE
The maximum likelihood optimization failed; try a different starting point by selecting the other maximum likelihood estimation option in argument optopt.
Variance of data in y is too low for method of moments optimization.
NE_REAL_ARRAY
On entry, at least one ${\mathbf{y}}\left[i-1\right]\le 0.0$: $i=〈\mathit{\text{value}}〉$, ${\mathbf{y}}\left[i-1\right]=〈\mathit{\text{value}}〉$.
NE_ZERO_SUM
The sum of y is zero within machine precision.
NW_PARAM_DIST
The distribution of maximum likelihood estimates cannot be calculated and the asymptotic distribution is not available for the returned parameter estimates.
NW_PARAM_DIST_ASYM
The asymptotic distribution is not available for the returned parameter estimates.
NW_PARAM_DIST_OBS
The distribution of maximum likelihood estimates cannot be calculated for the returned parameter estimates because the Hessian matrix could not be inverted.
## 7 Accuracy
Not applicable.
The search for maximum likelihood parameter estimates is further restricted by requiring
$1+ ξ^yi β^ > 0 ,$
as this avoids the possibility of making the log-likelihood $L$ arbitrarily high.
## 9 Example
This example calculates parameter estimates for $23$ observations assumed to be drawn from a generalized Pareto distribution.
### 9.1 Program Text
Program Text (g07bfce.c)
### 9.2 Program Data
Program Data (g07bfce.d)
### 9.3 Program Results
Program Results (g07bfce.r) |
# Tag Info
Accepted
### What is the meaning of $V(D,G)$ in the GAN objective function?
To understand this equation first you need to understand the context in which it is first introduced. We have two neural networks (i.e. $D$ and $G$) that are playing a minimax game. This means that ...
• 3,143
Accepted
### Is plain autoencoder a generative model?
An autoencoder is not considered a generative model, because it only reconstructs the given input. You could use the decoder like a generative model by putting in different vectors. However, the ...
• 1,327
Accepted
### How can we process the data from both the true distribution and the generator?
The Focus of This Question "How can ... we process the data from the true distribution and the data from the generative model in the same iteration? Analyzing the Foundational Publication In the ...
• 7,375
### Why diffusion model always use U-Net?
I don't have a definitive answer but I'd state my intuitions anyways: Diffusion models are highly related to the idea of stacked denoising autoencoders [Kumar et al. (2014)]. Additionally, U-Net-like ...
• 1,327
### Why is the variational auto-encoder's output blurred, while GANs output is crisp and has sharp edges?
The key is: VAE usually use a small latent dimension, the information of input is so hard to pass through this bottleneck, meanwhile it tries to minimize the loss with the batch of input data, you ...
• 49
Accepted
### Other deep learning image generation techniques besides GANs?
There are several generative models that have been proposed before or roughly at the same time of the GAN (2014). For example, the deep Boltzman machine (2009), deep generative stochastic network (...
• 37k
Accepted
• 9,037
Accepted
### How can AI be used to more reliably analyze and plan around the tie between climate and emissions?
Can AI provide a more reliable analysis of the gross effects of carbon emissions on extinctions of species ice-cap melting, and other effects? Yes. The work of Judea Pearl and others over the last 20 ...
• 9,037
• 3,143
### What parameters can be tweaked to avoid a generator or discriminator loss collapsing to zero when training a DC-GAN?
GANs are notably hard to train and it is not uncommon to have large bumps in the losses. The learning rate is a good start but the instability may come from a wide variety of reasons. I'm assuming ...
• 256
Accepted
### Does MMD-VAE solve the problem of blurred images of vanilla VAEs?
[Answering my own question after 5 months of studying VAE models] The point of the MMD-VAE or InfoVAE is not exactly to emphasise on the visual quality of generated samples. It is to preserve greater ...
• 148 |
# Jacobian for prior on P-spline transformation
I’m working on a discrete choice model for schools where the probability of a child’s family choosing a school is a monotonic function of distance (i.e. you never like a school more just because it is further away). Its a multinomial logit. My data has D demographic subgroups (cross-classification of ethnicity, socio-economic status etc.) and I want the model to include a flexible B-spline function of d_{ij} that varies by these demographics. So a vector \beta_d for each d \in 1,\dots,D.
Because of sparsity and the monotonicity condition, there are three types of structure on the spline coefficients: hierarchical structure to take account of demographics; a smoothness penalty on second differences; and a hard constraint on first differences (\nabla \beta \leq 0) to enforce monotonicity.
So, at the moment it seems most natural to build each vector from main effects \beta_d = \beta_0 + \beta_{eth(d)} + \beta_{SES(d)} + \dots + b_d to provide hierarchical shrinkage. The components (\beta_0,\beta_{eth(d)},b_d etc.) are raw parameters, and \beta_d are transformed parameters.
The problem is that the first and second differences of \beta_d are transformations of these already-transformed parameters), and it’s those I would like to put priors on, in addition to the priors on the components.
So, my question is, is there a way to put priors on the structure and then also put priors on the first and second differences of the \beta_d? If it entails putting priors on the transformed parameters, do I need a Jacobian adjustment? I’m not sure, but I hope maybe not because the first and second diffs are a linear transformation? Any help would be appreciated.
Below you can see what I’m doing now. I’ve taken out irrelevant parts of the model:
data {
int<lower=1> N; // Number of students
int<lower=2> J; // Number of schools
int<lower=1> D; // Number of demographics
int<lower=1> n_eth; // number of ethnic groups
int<lower=1> n_coef; // Number of spline coefficients
int<lower=1,upper=J> y[N]; //Dependent variable taking values in {1,...,J} ie. NOT binary
int<lower=1,upper=D> demog[N]; // which demographic group is pupil in?
matrix[J, n_coef] X[N]; // Matrix of regressors (spline coefficients)
int<lower=1,upper=n_eth> eth[D]; // which ethnicity does demographic represent?
int<lower=1,upper=2> ses[D]; // which SES group does demographic represent?
matrix[n_coef,n_coef] DD; // structure matrix of spline coefficients
vector[n_coef] zeroes;
}
transformed data{
int<lower=1> n_sigmas;
n_sigmas = 3;
}
parameters {
vector[n_coef] betas; // mean spline coefficients
vector[n_coef] beta_e[n_eth]; // ethnic variations of spline coefficients
vector[n_coef] beta_p[2]; // SES variations of spline coefficients
vector[n_coef] b_d[D]; // Demographic variations of spline coefficients (residual)
real<lower=0> sigmas[n_sigmas]; // variances of all params
}
transformed parameters{
vector[n_coef] beta_d[D];
for(d in 1:D){
beta_d[d] = betas + sigmas[1]*beta_e[eth[d]] + sigmas[2]*beta_p[puppri[d]] + sigmas[3]*b_d[d];
}
}
model {
betas ~ multi_normal_prec(zeroes,DD);
for(i in 1:n_eth){
beta_e[i] ~ multi_normal_prec(zeroes,DD);
}
for(i in 1:2){
beta_p[i] ~ multi_normal_prec(zeroes,DD);
}
for(i in 1:D){
b_d[i] ~ multi_normal_prec(zeroes,DD);
}
for(i in 1:n_sigmas){
sigmas[i] ~ student_t(5,0,5);
}
for(n in 1:N){
y[n] ~ categorical_logit( X[n]*beta_d[demog[n]] );
}
}
NB. the structure matrix is the p-spline formulation DD = tau*crossprod(diff(diag(n_coef),differences=k)) plus a little bit of diag(n_coef)*1e-4 because DD is not a full rank precision matrix. This transformation allows me to put smoothness priors on the original parameters, but I’m not sure there’d be a way to do it with the monotonicity prior. For the moment I’m fixing tau (the smoothness parameter) rather than estimating it.
You can have multiple changes to the posterior log-kernel for the “same” unknowns. And if the Jacobian determinant is constant, then whether you adjust the posterior log-kernel for it or not will not affect what parameters are proposed or accepted. I would check your logic several times though.
Thanks Ben. In that case, I guess that the transformation can be represented by a matrix, so the Jacobian won’t depend on the parameters? I’ll code something up and share.
Is there any reason why cross-classification isn’t discussed and used more frequently?
My “cell membership” indicators eth and ses are arrays of indices of length D, where, say, the values of eth are the ethnicity codes of the members of cross-classification cell d. For concreteness, ethnicity might be binary, SES might be binary, and then D=4. Then eth might be (1,2,1,2) and ses might be (1,1,2,2). If I replace
with
vector[D] eth;
vector[D] ses;
could I then vectorise the statement
for(d in 1:D){
beta_d[d] = betas + sigmas[1]*beta_e[eth[d]] + sigmas[2]*beta_p[ses[d]] + sigmas[3]*b_d[d];
}
as
beta_d = betas + sigmas[1]*beta_e[eth] + sigmas[2]*beta_p[ses] + sigmas[3]*b_d ;
even though each element being indexed is not a scalar but a vector, and I would therefore be using one statement to construct an array of vectors?
No, you cannot index with a vector, but
beta_d = betas + sigmas[1]*beta_e[eth] + sigmas[2]*beta_p[ses] + sigmas[3]*b_d ;
should work if eth and ses are integer arrays.
1 Like |
# Trying to Understand a Remark about Zariski Topology
I'm reading some notes in which following remark is given:
The Zariski topology is quite different from the usual ones. For example, on affine space $\mathbb A^n$ a closed subset that is not equal to $\mathbb A^n$ satisfies at least one non trivial polynomial equation and has therefore necessarily dimension less than $n$, so the closed subsets in Zariski topology are in a sense "very small".
My questions are the following:
1. What is the meaning of dimension here?
2. What is the meaning of 'so the closed subsets in Zariski topology are in a sense "very small"'?
3. What are some other "weird" properties of the Zariski topology?
• An example of "weird" property that might also help for your second question : in the affine space $\mathbb{A}^n$, any open set is dense. So closed sets have no interior point. – Arnaud D. Aug 30 '15 at 9:24
If we consider the Zariski topology on the spectrum of a ring (and not only on its maximal ideals), a point is not necessarily closed. Actually the closed points correspond to maximal ideals. For instance if $A$ is an integral domain,the $0$ prime ideal is dense in $\operatorname{Spec}A$.
Zariski topology is not Hausdorff, but it is Kolmogorov, i.e., given two distinct points there is a neighbourhood of one of them which does not contain the other.
The idea behind Zariski topology is that to know an algebraic variety: we also must know all its subvarieties.
• Zariski topology on Spec(R) is sometimes Hausdorff – Prince M Nov 19 '17 at 2:29
1) Closed sets are defined by some zero set of an ideal, say $I$, so dimension means the dimension of the ring $k[x_1,...,x_n]/I$.
2) For example, closed sets in $\mathbb{A}^1$ are finite set of points as the zero set of a polynomial is bounded by the degree.
3) Zariski topology is not Hausdorff.
One way to explain "very small" is that if you think about $\mathbb A^n$ over $\mathbb C$ as $\mathbb C^n$ with the Euclidean topology (which strictly contains the Zariski topology in the sense that Zariski-closed implies Euclidean-closed), all proper Zariski-closed subsets have Lebesgue measure $0$. |
Dichotomy for measures of maximal entropy
# A dichotomy for measures of maximal entropy near time-one maps of transitive Anosov flows
Jérôme Buzzi, Todd Fisher, and Ali Tahzibi J. Buzzi, Laboratoire de Mathématiques d’Orsay, CNRS - UMR 8628 Université Paris-Sud 11, 91405 Orsay, France, E-mail address:[email protected] T. Fisher, Department of Mathematics, Brigham Young University, Provo, UT 84602, E-mail address:[email protected] A. Tahzibi, Instituto de Ciências Matemáticas e de Computação, Universidade de São Paulo (USP), E-mail address:[email protected]
###### Abstract.
We show that time-one maps of transitive Anosov flows of compact manifolds are accumulated by diffeomorphisms robustly satisfying the following dichotomy: either all of the measures of maximal entropy are non-hyperbolic, or there are exactly two ergodic measures of maximal entropy, one with a positive central exponent and the other with a negative central exponent.
We establish this dichotomy for certain partially hyperbolic diffeomorphisms isotopic to the identity whenever both of their strong foliations are minimal. Our proof builds on the approach developed by Margulis for Anosov flows where he constructs suitable families of measures on the dynamical foliations.
###### 2010 Mathematics Subject Classification:
37C40, 37D30, 37A35, 37D35
T.F. is supported by Simons Foundation grant # 239708. A.T is supported by FAPESP 107/06463-3 and CNPq (PQ) 303025/2015-8
## 1. Introduction
In his pioneering work [27], Margulis studied measures of maximal entropy of geodesic flows in order to count closed geodesics for manifolds with variable negative curvature. More precisely, he constructed a family of measures such that for all the measure is carried by the unstable manifold at , and for all we have
(φt)∗mx=e−t⋅htop(φ)mφtx.
He then built an invariant probability measure which was observed to be a measure of maximal entropy and is now called the Bowen-Margulis measure. It was then proved to be the unique measure of maximal entropy. We refer to Ledrappier [25] for an introduction.
In this paper, we will extend Margulis’ construction to a class of partially hyperbolic maps and obtain a striking dichotomy.
###### Theorem 1.1.
If is a transitive Anosov flow on a compact manifold , then there is an open set in which contains in its closure such that for any we have the following dichotomy:
1. either all the measures of maximal entropy have zero central Lyapunov exponents, or
2. there are exactly two ergodic measures of maximal entropy where one has a positive central exponent and the other has a negative central exponent, and both measures are Bernoulli.
### Related results
These results are part of a larger program to understand properties of entropy beyond uniform hyperbolicity. In that classical setting, say for a transitive Anosov diffeomorphism, there is a unique measure of maximal entropy (MME). Even though there are a number of significant results beyond the hyperbolic setting [29, 9, 10] there are still many fundamental open questions beyond the uniformly hyperbolic setting. Partially hyperbolic diffeomorphisms with one-dimensional center have been studied as the “next nontrivial class”. A MME always exists in this setting by entropy expansivity (see [12, 15, 26]). Its uniqueness is a more delicate question.
Uniqueness of the MME has been shown for certain systems that are derived from Anosov, a subclass introduced by Mañé, first for specific constructions, then in greater and greater generality [7, 13, 38, 16, 8].
The partially hyperbolic diffeomorphisms with a center foliation into circles form another subclass with a more subtle behavior. Assuming accessibility, [31] has established the following dichotomy:
• either the dynamics is isometric in the center direction and there exists a unique MME which is nonhyperbolic; or
• there are multiple hyperbolic MMEs.
### Strategy of proof
We introduce a new subclass of partially hyperbolic diffeomorphisms with one-dimensional center which we call flow type. They are isotopic to the identity and the fundamental examples are the perturbations of time-one maps of Anosov flows. Our main result is Theorem 3.9: the above dichotomy holds for partially hyperbolic flow type diffeomorphisms whose strong foliations are both minimal.
The uniqueness of the MME for a given sign of the central exponent (say nonpositive) follows from a variant of Margulis’ approach. Namely, we first build a family of measures on the center-unstable leaves. Then we construct measures on unstable leaves, which we call Margulis -conditionals. This is more difficult for maps than for flows.
We then use the entropy with respect to the unstable foliation as introduced by Ledrappier and Young [22] and an argument of Ledrappier [24] to show that, when its central exponent is nonpositive, a measure maximizes the entropy if and only if its disintegration along the unstable leaves is given by the Margulis conditionals.
A Hopf argument shows that if there is a MME with negative central exponent, then any MME with nonpositive central exponent must coincide with it. The symmetry between positive and negative central exponents in the hyperbolic case follows from the one-dimensionality of the central leaves: we associate to any measure with, say negative central exponent, an isomorphic one with nonnegative central exponent.
A hyperbolic ergodic MME is isomorphic to a Bernoulli shift times a circular permutation, according to a general result by Ben Ovadia [30]. The triviality of the permutation follows by considering iterates. This concludes the proof of Theorem 3.9.
Finally, to prove Theorem 1.1 we establish Theorem 3.10, i.e., we find open sets of partially hyperbolic flow type diffeomorphisms with both strong foliations minimal near any time-one map of a transitive Anosov flow. We first show that such time-one maps are robustly flow type partially hyperbolic diffeomorphisms. Then Bonatti and Díaz [3] provide a perturbation ensuring robust transitivity. Lastly, by a further perturbation following Bonatti, Díaz, and Urès [4] we can ensure robust minimality of both strong foliations. Theorem 1.1 now follows from Theorem 3.9.
### The use of Margulis conditionals
The construction of Margulis has given rise to a large body of work, mainly devoted to the estimation of the number of periodic orbits, sometimes beyond the uniformly hyperbolic setting [20]. We refer to Sharp’s survey in [28], the long awaited publication of Margulis’ thesis. The works of Hamenstädt [17] and Hasselblatt [18] that give a geometric description of the Margulis conditionals are perhaps closer to our concerns.
While this work was being written, we learned that a different but related approach has been developed in [11]. This approach can deal with equilibrium measures (i.e., generalizations of measures of maximal entropy taking into account a weight function) but requires non-expansion along the center. Separately, Jiagang Yang has told us that he also has results on the MMEs for the same type of diffeomorphisms as we consider.
Let us first note that part of our results could be obtained from symbolic dynamics, using generalizations of ideas going back to the classical works of Sinai, Ruelle, and Bowen (see, e.g., [36, 5, 34]). More precisely, existence of at most one MME with, say, positive central exponent can be deduced from [9, Section 1.6] since, in the terminology of this work, our minimality assumption implies that there is a unique homoclinic class of measures with a given sign of the central exponent. However, the dichotomy does not seem to follow from this approach which is blind to nonhyperbolic measures.
Second, one usually expects that results such as ours can be extended to smoothness, for any , and generalized to equilibrium measures with respect to Hölder-continuous potentials (although uniqueness holds for generic potentials [34]).
### Questions
Our techniques demand a very strong form of irreducibility and the flow type property is somewhat technical. Hence we ask:
###### Question 1.
In Theorem 3.9, can one replace minimality of both strong foliations by minimality of just one or by robust transitivity? Can one replace flow type by isotopic to the identity?
In the volume-preserving setting there is a rigidity result [2]. We think that some version of it may hold for MMEs in the dissipative setting.
###### Question 2.
In the setting of Theorem 3.9, is the hyperbolic case open and dense? When the MME is nonhyperbolic, does this imply that the diffeomorphism is the time one map of a flow? does it at least exclude the existence of hyperbolic periodic points?
Though we will identify the disintegrations of nonhyperbolic MMEs along both strong foliations, their analysis remains incomplete:
###### Question 3.
Consider a partially hyperbolic diffeomorphism with flow type and with minimality of both strong foliations. Can its disintegration along the center be atomic like in the hyperbolic case? Can there be more than one nonhyperbolic MME? Are nonhyperbolic MMEs Bernoulli?
We prove that the hyperbolic MMEs are Bernoulli, hence strongly mixing. One can try to establish some speed (see [39] for a related result).
###### Question 4.
If is a hyperbolic MME for a flow type diffeomorphism with minimality of both strong foliations, does it satisfy exponential decay of correlations for Hölder-continuous functions, i.e., for any Hölder-continuous functions , does there exist a number such that:
∫Mu∘fn.vdμ−∫Mudμ∫Mvdμ=O(κn)?
For Anosov flows, the topological entropy can obviously be changed by perturbations whereas it is locally constant for Anosov diffeomorphisms. What is the situation for the maps we consider?
###### Question 5.
Consider a flow type diffeomorphism whose strong foliations are robustly both minimal. Is it true that the volume growth of each strong leaf is equal to the topological entropy? Does the topological entropy have a homological interpretation? Can an arbitrarily small perturbation make the topological entropy locally constant as a function of the diffeomorphism?
## 2. Background
In this section we review concepts of partial hyperbolicity, Lyapunov exponents, and disintegration of measures.
### 2.1. Partial hyperbolicity
For a diffeomorphism of a compact manifold to itself recall the norm and conorm with respect to a subspace of for some : and
conorm(Df|V):=min{∥Tf(v)∥:v∈V,∥v∥=1}.
A splitting is dominated111This is sometimes called pointwise domination, see [1]. if it is nontrivial, invariant, and if there is some such that, for all :
∥DfN|Ex∥<12conorm(DfN|Fx).
###### Definition 2.1.
A diffeomorphism is (strongly) partially hyperbolic if there is an invariant splitting of the tangent bundle: such that and are dominated, is uniformly contracted, and is uniformly expanded.
The stable and unstable bundles and of a partially hyperbolic diffeomorphism are always uniquely integrable into stable and unstable foliations, respectively, denoted by and . The bundles , , and fail to be integrable for some strongly partially hyperbolic diffeomorphisms.
###### Definition 2.2.
A strongly partially hyperbolic diffeomorphism is dynamically coherent if there exists invariant foliations and that are tangent to the and bundles respectively. In this case there is a center foliation given by for .
We refer to [6] for various other definitions of dynamical coherence and their relationships.
For a dynamically coherent diffeomorphism each leaf of is subfoliated by the leaves of and the leaves of . A similar statement holds for the center-unstable foliation. Then for any points where there is a neighborhood of in the leaf and a homeomorphism such that
hsp,q(x)∈Fs(x)∩Fcloc(q).
The map is the (local) stable holonomy map. We can similarly define the unstable holonomy map.
### 2.2. Center Lyapunov exponents
For a strongly partially hyperbolic diffeomorphism a real number is a center Lyapunov exponent at if there exists a nonzero vector such that
limn→∞1nlog∥Dfn(v)∥=χ.
If , then the limit above only depends on and exists -almost everywhere for any -invariant Borel probability measure . For an ergodic -invariant Borel probability measure the limit takes on a single value for -almost every .
### 2.3. Disintegration of a measure
Let be a Polish space and be a finite Borel measure on . Let be a partition of into measurable sets. Let be the induced measure on the -algebra generated by . A system of conditional measures of with respect to is a family of probability measures on such that
1. for -almost every , and
2. given any continuous function , the function is integrable, and
∫Xψdμ=∫P(∫ψdμP)d^μ(P).
Rokhlin [32, 33] proved that if is a measurable partition, then the disintegration always exists and is essentially unique.
We will consider partitions given by foliations of a manifold. If a foliation has a positive measure set of noncompact leaves, then the result of Rokhlin does not immediately apply. However, one can extend the result of Rokhlin by disintegrating into measures defined up to scaling (see Avila, Viana, and Wilkinson [2]).
Let be a manifold where and be a locally finite measure on . Let be a small foliation box. Then Rokhlin’s result implies there is a disintegration of the restriction of to the foliation box into conditional probability measures along the local leaves of the foliation, i.e., the connected components of for . From [2, Lemma 3.2] we know that if and are foliation boxes and -almost any , then the restriction of and coincide up to a constant factor.
We then know that for -almost every there is a projective measure (i.e., defined up to some scaling possibly depending on ) such that . Furthermore, the function is constant along the leaves of , and the conditional probabilities along the local leaves of any foliation box coincide almost everywhere with the normalized restriction of the to the local leaves of .
Finally, we note that if the foliation is fixed by some diffeomorphism (i.e., ) without fixed points, one can replace the projective measures by true measures using the global normalization: for all .
### 2.4. Continuous systems of measures
We will work with families of measures carried by the leaves of the dynamical foliations up to a union of exceptional leaves.
###### Definition 2.3.
Given a foliation of some manifold and some -saturated subset a continuous system of measures on is a family such that:
1. for all , is a Radon measure on ;
2. for all , if ;
3. is covered by foliation charts such that: is continuous on for any .
The Radon property (i) means that each is a Borel measure and is finite on compact subsets of the leaf (here, and elsewhere, we consider the intrinsic topology on each leaf).
If is the disintegration of some probability measure along a foliation as defined in the previous definition and if is a continuous system of measures on , we will say that they coincide if and for -a.e. , and are proportional.
###### Definition 2.4.
Assume that is a foliation which is invariant under some diffeomorphism , i.e., for all , . Let be -saturated. A continuous system of measures on is dilated if there is some number such that for all :
(1) f∗mx=D−1mf(x).
is called the dilation factor. We call the family a Margulis system on and the measures the Margulis -conditionals.
Our construction (following Margulis) relies on properties of the holonomy between foliations defined as follows:
###### Definition 2.5.
Let be foliations which are invariant under some diffeomorphism . Let be an -saturated subset of . Assume that is a Margulis system of measures on and that is transverse to . The system is invariant, respectively quasi-invariant, along if, for all -holonomies with contained in -leaves included in :
(2) h∗(mx|U)=mh(x)|V for any x∈U,
respectively:
(3) h∗(mx|U) and mh(x)|V are equivalent for any x∈U.
###### Remark 2.6.
The quasi-invariance in (3) can be characterized by the absolute continuity of the holonomies along with respect to a class of transversal measures defined by the Margulis system on .
Though an arbitrary continuous system of measures along the strong unstable foliation does not need to correspond to the disintegration of any invariant probability measure, those we construct in this paper will (see Proposition 5.1.)
## 3. Main Results
This section collects our main results. Our techniques deal with the following type of diffeomorphisms. For convenience, we fix some Riemannian structure on the compact manifold .
###### Definition 3.1.
A diffeomorphism has flow type if:
1. partial hyperbolicity: is strongly partially hyperbolic with splitting and ;
2. Dynamical coherence: there are invariant foliations and tangent to and ;
Let be the foliation whose leaves are the connected components of the intersections , .
1. Center leaves: The center foliation is oriented and has at least one compact leaf.
Let be the continuous flow along with unit positive speed.
1. Flow like dynamics: there is a continuous such that, for all , and .
Following Margulis, we build special measures on most strong stable and strong unstable leaves. Let where is the union of the unstable leaves that intersect some compact center leaf. Define and likewise.
###### Theorem 3.2.
Let be a diffeomorphism with flow type and minimal stable and unstable foliations on a compact manifold . Then there is a continuous system of measures on such that:
1. each is atomless, locally finite, with full support;
2. is a Margulis system along with dilation factor ;
3. the system is -quasi-invariant;
4. is dense with full measure for any ergodic measure with positive entropy.
In the setting of the previous theorem, there is a unique system of measures satisfying the above items (1) and (2). Moreover its dilation factor is .
We call the system of measures the unstable Margulis system and the measures the unstable Margulis conditionals.
We will build such a system in Section 4, show its uniqueness and compute its dilation factor in Section 5.
###### Remarks 3.4.
(1) The above theorem and addendum, applied to , defines a stable Margulis system with dilation factor .
(2) The smoothness assumption is only used by Theorem 4.3 to establish absolute continuity of the -holonomy but it is probably enough to assume smoothness. We do not know how to deal with smoothness.
Using tools from Ledrappier and Young [22], we prove the following result in Section 5.
###### Theorem 3.5.
Let be a diffeomorphism with flow type and minimal stable and unstable foliations on a compact manifold . Let be an ergodic MME.
If , then the disintegration of along is given by the unstable Margulis system from Theorem 3.2. In particular, the measure has have full support.
The above applied to shows that an ergodic MME with has disintegration along given by . In particular, any MME has full support.
###### Remark 3.6.
The above theorem gives more information in the non-hyperbolic case. Indeed, if is an ergodic measure of maximal entropy with , then the disintegrations, along both strong foliations and , are given by the corresponding Margulis systems from Theorem 3.2.
The dichotomy will follow from two results about hyperbolic measures of maximal entropy. The first is a uniqueness result, based on the Hopf argument.
###### Proposition 3.7.
Let be a diffeomorphism with flow type and minimal stable and unstable strong foliations on a compact manifold . Let be some ergodic MME. If is hyperbolic, say , then there is no other ergodic MME with .
The second result is a symmetry argument, using the one-dimensional center leaves. It builds so-called twin measures (see [31, 14]).
###### Proposition 3.8.
Let be a diffeomorphism of a compact manifold . Let be an orientable one-dimensional foliation (with continuously varying leaves). Assume that, for all , maps to itself in an orientation-preserving way. Let satisfy:
1. its Lyapunov exponent along is ;
2. for -a.e. , the following set is relatively compact in the intrinsic topology of :
Wc(x):={y∈Fc(x):limsupn→∞1nlogd(fnx,fny)<0};
3. and for -a.e. , the leaf is noncompact and contains no fixed point.
Then there is another invariant probability measure which is isomorphic to and with exponent .
Finally, we state the abstract version of our main result:
###### Theorem 3.9.
For any diffeomorphism with flow type and minimal stable and unstable foliations on a compact manifold , we have the following dichotomy:
1. either all the measures of maximal entropy have zero central Lyapunov exponents, or
2. there are exactly two ergodic measures of maximal entropy where one has a positive central exponent and one has a negative central exponent, and both are Bernoulli.
The next theorem shows that there is an abundance of diffeomorphisms satisfying the above assumptions. It follows from properties of perturbations of time-one maps of transitive Anosov flows established in [3] and [4], as discussed in Section 6.
###### Theorem 3.10.
If is a transitive Anosov flow on a compact manifold , then for all there exists a open set in such that belongs to the -closure of and every has flow type with both stable and unstable foliations minimal.
## 4. Building Margulis systems of measures
In this section, we consider flow type diffeomorphisms whose strong foliations are both minimal. To begin with, we follow Margulis’ construction of a system of measures on the -leaves that are invariant under stable holonomies. We then deduce from this a system of -conditionals that are quasi-invariant under center-stable holonomies. This proves Theorem 3.2, except for the uniqueness of the Margulis -system and the equality that will be deduced in Section 5 from the analysis of MMEs.
### 4.1. The cu-conditionals
We following Margulis’ construction.
###### Proposition 4.1.
Let on a compact manifold with a dominated splitting with uniformly contracted. Assume that:
1. there are foliations and which are tangent to, resp. and ;
2. is minimal.
Then there is a Margulis system on which is invariant under -holonomy and such that each is atomless, Radon, and fully supported on .
We introduce some convenient definitions. Let . We denote by the intrinsic Riemannian volume on each -leaf: for any subset of a -leaf, is its volume with respect to the Riemannian structure on the leaf. We denote by the distance defined on each leaf by the induced Riemannian structure and defining the intrinsic topology.
The -balls are . For a subset of such a leaf, we set . A -subset is a -bounded subset of a -leaf. A -test function is a nonnegative function such that is a -subset and the restriction of to
supp(ψ):=¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯{x∈M:ψ(x)≠0}
is continuous. We write if and has non-empty interior in the intrinsic topology. We denote by the collection of all -test functions.
Given a -holonomy its size is , and the two subsets are called equivalent along through provided . We say that they are -equivalent if the holonomy has size at most . Two functions are -equivalent along if their supports are equivalent through a -holonomy with size at most and satisfying . Two submanifolds are -transverse if they are transverse and if for every , the angle between any two nonzero vectors in and is at least .
Following Margulis, we consider functionals . Note that is one such functional. The map acts on them by:
∀ψ∈Tcuf(λ)(ψ):=λ(ψ∘f−1).
A key class of such functionals are for any . That is, for any ,
ℓn(ϕ):=∫ϕ∘f−ndλcu.
To normalize, we fix some with . Considering the topology of pointwise convergence (i.e., working in with the product topology), let be the closure of the following set:
L1:={λ=n∑i=1ciℓti:n∈N∗,t1,…,tn∈N,c1,…,cn>0 with λ(ϕ1)=1}.
We will use the following covering numbers. For , a -subset, and , we denote by the smallest integer such that there are with .
We build the -system as a functional.
###### Proposition 4.2.
There exist and such that
f(Λ)=Du⋅Λ
and, for some positive numbers , for any :
1. ;
2. if , then ; and
3. if is -equivalent to , then .
To prove this, we will show that is a convex and compact set and then apply the Schauder-Tychonoff fixed point Theorem to a normalized action of on .
We will relate the iterations of different -test functions by using the invariance under -holonomy and especially the following theorem (see, e.g., [1, Theorem C]).
For convenience let . Observe that for , and .
###### Theorem 4.3.
Let be a diffeomorphism on a compact Riemannian manifold . Assume that there is a dominated splitting with uniformly contracting. Fix and let be two submanifolds -transverse to and -equivalent through . Then is absolutely continuous.
More precisely, writing for the Riemannian volume on , the measures and are equivalent and there are constants and depending only on , , and such that, letting be the size of the holonomy :
(4) ∣∣∣dh∗λ1dλ2−1∣∣∣≤C(ϵα+E(ϵ)).
The second term simply ensures that the above bound holds even for large .
We need two additional lemmas. The first one will give a uniform bound on the volume growth in the center unstable leaves.
###### Lemma 4.4.
For any open, non-empty -subset , there are constants and such that,
(5) ∀x∈M∀n≥0λcu(fnBcu(x,rA))≤CAλcu(fnA).
###### Proof.
Fix so small that is not empty. The minimality implies that any is -equivalent to some point in . The continuity of the foliation and its transversality to yield and such that, for any , is -equivalent to a subset of . The compactness of yields , such that, for any point , is -equivalent to a subset of .
Since is contracted, there are numbers and such that the set is -equivalent to a subset of . Theorem 4.3 proves the claim. ∎
###### Corollary 4.5.
For any with , there are numbers and such that for any and any :
∫ψ∘f−ndλcu≤C(ϕ)rcu(suppψ,R(ϕ))∥ψ∥∞∫ϕ∘f−ndλcu.
###### Proof.
The left hand side is bounded by . Fix some . The previous lemma with yields and . Since is compact in its -leaf , there are with such that . Now
λcu(fn(Bcu(xi,rA)))≤CAλcu(fnA)≤CAλcu(ϕ∘f−n)/t.
Summing over the cover of , the claim follows with and . ∎
The next lemma establishes approximate holonomy invariance.
###### Lemma 4.6.
There are numbers and with the following properties. Let be -equivalent for some .
First, if , then, for all :
(6) ∀λ∈L∣∣λ(ψ∘f−n)−λ(ϕ∘f−n)∣∣≤Cρn(Δα+E(CΔ))λ(ψ∘f−n).
Second, for any with , there are numbers and such that, for any we have
(7) |ℓn(ψ)−ℓn(ϕ)|≤C(ϕ1)r(supp(ψ),R(ϕ1))∥ψ∥∞ρn(Δα+E(CΔ))ℓn(ϕ1).
###### Proof.
Since and are -equivalent, there is with size at most such that . Since is uniformly contracted, and are -equivalent through for some and . Theorem 4.3 yields:
|ℓn(ϕ) −ℓn(ψ)|=∣∣∣∫ϕ∘f−ndλcufny−∫ψ∘f−ndλcufnx∣∣∣ =∣∣ ∣∣∫ϕ∘f−n∘hnd(hn)∗λcufnydλcufnx−ψ∘f−ndλcufnx∣∣ ∣∣ ≤C((CΔκn)α+E(CΔκn))∫|ψ∘f−n|dλcufnx ≤C(Δακαn+E(CΔκn))ℓn(|ψ|).
Let so that . Using the identity , we get: Hence, if ,
|λ(ϕ∘f−n)−λ(ψ∘f−n)|≤C(καnΔα+E(CκnΔ))λ(ψ∘f−n),
proving eq. (6) for all by continuity.
Let with . Applying Corollary 4.5, we obtain and such that eq. (7) holds. ∎
###### Proof of Proposition 4.2.
We prove the first two claims (a) and (b) for arbitrary .
Step 1: Claim (a): .
Corollary 4.5 for yields numbers and such that for any : Therefore, for any :
(8) λ(ψ)=I∑i=1ciℓti(ψ) ≤I∑i=1ciCrcu(suppψ,ρ)∥ψ∥∞ℓti(ϕ1) =Crcu(suppψ,R)∥ψ∥∞λ(ϕ1).
This proves the claim since for . It extends to the closure , concluding Step 1.
Note that eq. (8) implies that is a subset of the compact set
∏ψ∈Tcu[0,C⋅rcu(suppψ,R)∥ψ∥].
Hence its closure is compact.
Step 2: Claim (b): if there is s.t. , .
We assume that and apply again Corollary 4.5, exchanging and . We get new numbers and defined by . Setting , we have . That is, so that, for any :
(9) λ(ψ)≥1C1λ(ϕ1)=1C1.
This again extends to , concluding Step 2 with the lower bound .
Step 3: Existence of with
We now build the functional as a fixed point of the map
¯f:L→L,λ⟼λ(⋅∘f−1)λ(ϕ1∘f−1).
We claim that is well-defined and continuous from to . Indeed, the map from to is well-defined since , is obviously continuous, and is positive by Step 2. Note that is well-defined and is continuous from to . The claim is proved.
Finally, it is obvious that , hence is a well-defined continuous map. Since is a convex, compact subset of the locally convex linear space , the Schauder-Tychonoff Theorem applies and yields with .
Therefore, with .
Step 4: Claim (c): -holonomy invariance of
Let . Writing and likewise for , we can assume . Assume that and are -equivalent. By compactness of their support, they are -equivalent for some and therefore and are -equivalent with . Using the dilation and the approximate holonomy invariance eq. (6) from Lemma 4.6, we get that, for any , for large enough :
|Λ(ϕ)−Λ(ψ)| =D−n|Λ(ϕ∘f−n)−Λ(ψ∘f−n)| ≤D−nϵ⋅Λ(ψ∘f−n)=ϵ⋅Λ(ψ)
As is arbitrarily small this implies , i.e., Claim (c). ∎
We deduce a Margulis system of -measures from the functional .
###### Proof of Proposition 4.1.
Proposition 4.2 yields a functional on , which contains for all . Note that is linear and positive (because this holds for all and extends by continuity to ). Hence, Riesz’s Representation Theorem gives a measure on , for each , by setting:
∀ϕ∈Cc(Fcu(x)),mx(ϕ)=Λ(ϕ).
The local finiteness, full support, and -invariance of each follows from properties (a), (b), (d) of the functional from Proposition 4.2.
We deduce that each is atomless from the holonomy invariance. Assume by contradiction that there is with . Consider the stable leaf . By assumption it is dense in , hence by transversality in . By -invariance, must have a dense set of atoms , all of which have measure . This contradicts the finiteness of on compact sets.
We finally deduce the continuity from the holonomy invariance. As and are transverse, for any , there is a neighborhood of and a continuous map with (in particular, ). Let . By holonomy invariance, . Hence,
|mcux(ϕ|FcuB(x))−mcux0(ϕ|FcuB(x0))|≤∫FcuB(x0)|ϕ∘h0(x,⋅)−ϕ|dmcux0
which converges to as goes to . This is the continuity property. ∎
The next lemma establishes that the constant is larger than .
###### Lemma 4.7.
Let have flow type with both strong foliations minimal. Let be a Margulis -system. The dilation of the Margulis system on satisfies: .
###### Proof.
By assumption (III), there is a compact center leaf . It is contained in the -leaf . Since is a topological attractor for the restriction of to the invariant set , there is a relatively compact neighborhood of in such that has non empty interior. As has full support in , it follows that:
D−1umcux(U)=mcux(f−1U)
proving . ∎
### 4.2. Building the u-conditionals
We complete the proof of Theorem 3.2 (except for the equality and the uniqueness of the Margulis systems, see Propositions 5.5 and 5.8).
We start with the previously built Margulis -system and define the family of measures by extending subsets of -leaves to subsets of -leaves along the center foliation. For flows, Margulis used the formula
mux(A) |
# Recitation 11
Example 1: Dana and Robbie have just been given 20 minutes and 15 tickets each before leaving Funland. Having done some incidental learning while their father worked on this book, they devoted three of their minutes to generating the data in the table below and solving the problem to maximize their fun.
Ride Minutes required Tickets Fun value
Paratroopers 6 4 8
Teacups 4 3 6
Mini Himalayas 4 3 5
Whirling chairs 4 2 6
Helicopters 5 3 3
Merry-go-round 4 2 3
Jungle 5 3 5
Assume that they ride each ride at most once, and solve their problem.
Solution: Let’s use $\{0,1\}$ variables $A, B, C, D, E, F, G$ to indicate whether Dana and Robbie are going to ride each ride separately. We formulate the integer program as follows.
Maximize: $8A+6B+5C+6D+3E+3F+5G$ $6A+4B+4C+4D+5E+4F+5G \le 20-3$ $4A+3B+3C+2D+3E+2F+3G \le 15$ $A, B, C, D, E, F, G\in \{0,1\}$
Example 2: An analytically minded basketball coach selects his starting lineup according to his ratings of his players, and of course, their position and height. His plan for the next game is to maximize the total shooting ability of the starting team while keeping the average height at 6’5″ or more. He also wants to start at least two guards and a center.
The coach’s data is shown in the table below. Determine his starting 5.
Player Height Position Shooting
Bob 6’1″ Guard 9
Clyde 6’6″ Forward 8
Michael 6’4″ Guard 9
David 6’9″ Center 7
Scotty 6’6″ Forward 8
Bill 6’8″ Center 8
Dennis 6’6″ Forward 6
Earl 6’3″ Guard 10
Kareem 6’10” Center 6
Sam 6’1″ Guard 8
Solution: Let’s use $\{0,1\}$ variables $A, B, C, D, E, F, G, H, I, J$ to indicate separately whether each player is in the starting 5. We formulate the integer program as follows.
Maximize: $9A+8B+9C+7D+8E+8F+6G+10H+6I+8J$ $A+B+C+D+E+F+G+H+I+J = 5$ $A + C + H + J \ge 2$ $D + F + I \ge 1$ $-4A+B-C+4D+E+3F+G-2H+5I-4J \ge 0$ $A, B, C, D, E, F, G, H, I, J\in \{0,1\}$ |
# Replace a derivative within partial derivatives
Suppose:
f = a + b g[x, y]
h = D[f, {x, 2}, {y, 1}]
(*Out:= b g^(2,1)[x,y]*)
1. In the function $h=b\frac{\partial^3g}{\partial x^2\partial y}$ I want to replace $\frac{\partial g}{\partial y}$ by $c\frac{\partial u}{\partial t}$ to obtain $h=bc\frac{\partial^3u}{\partial x^2\partial t}$.
2. In the function $h=b\frac{\partial^3g}{\partial x^2\partial y}$ I want to replace $\frac{\partial^2 g}{\partial x^2}$ by $c\frac{\partial u}{\partial t}$ to obtain $h=bc\frac{\partial^2u}{\partial y\partial t}$.
After looking at the Fullform of partial derivatives this seems like a hopeless task. I have also read this post but it hasn't helped. Any suggestions and help is much appreciated.
Clear@Derivative
Derivative[n_, 1][g][x, y] := c D[u[x, t], {x, n}, t]
h
Clear@Derivative
Derivative[2, n_][g][x, y] := c D[u[y, t], t, {y, n}]
h
You can use InternalInheritedBlock to avoid clearing Derivative again and again:
Clear@Derivative
InternalInheritedBlock[{Derivative},
Derivative[n_, 1][g][x, y] := c D[u[x, t], {x, n}, t]; h]
InternalInheritedBlock[{Derivative},
Derivative[2, n_][g][x, y] := c D[u[y, t], t, {y, n}]; h]
• +1 Nice. What does Clear@Derivative exactly do here? – Deep Oct 1 '17 at 9:38
• @Deep Otherwise the rule we created via Derivative[2, n_][g][x, y] := c D[u[y, t], t, {y, n}] etc. will remain. Try removing Clear@Derivative and execute SubValues@Derivative` and you'll know what I mean. – xzczd Oct 1 '17 at 9:44 |
# [OS X TeX] Puzzled by an accented i
Josep Maria Font jmfont at ub.edu
Sun Mar 13 17:05:14 EDT 2011
Hi,
In a typos list, I need to produce an accented "i" where the dot really appears (obviously, to indicate how it should be done in the right way). However, I am not being able to produce one. The obvious, minimal code below gives me two equally accented equally dotless i's. And this without any inputenc or babel trick, and with an up-to-date MacTeX 2010 installation.
Is perhaps the latest (La)TeX even more smart than I ever thought ? Any ideas ?
JMaF
\documentclass{minimal}
\begin{document}
\'{i} vs \'{\i}
\end{document} |
# simplicial approximation theorem
Let $f:|K|\to|L|$ be continuous function, where $|K|$ and $|L|$ are polyhedra having triangulations $K$ and $L$, respectively.
Then there is a barycentric subdivision $K^{(s)}$ of $K$ and a continuous function $g:|K|\to|L|$ such that $g$ is a simplicial map from $K^{(s)}$ to $|L|$ and $g$ is homotopic to $f$.
The theorem is due to J.W. Alexander.
## References
• 1 J.W. Alexander , Combinatorial analysis situs, Trans. Amer. Math. Soc. 28, 301-329, (1926)
Title simplicial approximation theorem SimplicialApproximationTheorem 2013-03-22 16:54:29 2013-03-22 16:54:29 Mathprof (13753) Mathprof (13753) 5 Mathprof (13753) Theorem msc 55U10 |
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# Chi Square Test for Goodness of Fit
So, you've familiarized yourself with the concept of Chi-square distributions and been introduced to the concept of Chi-square tests. Well, now you've come to the good bit. Now it's time to learn how to actually apply these handy little concepts to perform actual statistical testing on sets of data. The first chi-square test that can be performed is the Chi-square test for goodness of fit. In this explanation, you'll learn how you can use this cool little test to check if a distribution actually occurs as projected in reality, or if the distribution, in reality, differs from the projection in a statistically meaningful way.
If you don't feel totally comfortable with the idea of a Chi-Square Distribution or the basic concept of Chi-Square Tests, don't sweat it, there are StudySmarter explanations for both!
No point waiting around then, let's dive into it!
## Chi-Square Test for Goodness of Fit Definition
What is the Chi-square test for goodness of fit then? Well...
The Chi-square test for goodness of fit is a statistical hypothesis test used to determine whether an expected distribution of outcomes is significantly different from the actual observed distribution of outcomes.
This is a lot of talk of outcomes and distributions and all sorts of statistics talk, but what does it all mean?
Well, imagine if you rolled a $$6$$-sided die $$100$$ times. You would expect it to land on each of the sides roughly an equal number of times.
If you actually carried this out and recorded the results, you could then use the Chi-squared goodness of fit test to check if the real-life data matched your expectation, within reasonable limits of course.
Useful right? Ok so now you're hopefully familiar with the what and the why of Chi-square tests for goodness of fit, now let's get into the good stuff. The how.
## Chi-Square Test for Goodness of Fit Hypotheses
The Chi-square test for goodness of fit is a hypothesis test. This means that of course, it must start with a set of hypotheses.
Now, to conduct a hypothesis test like this, you need a null hypothesis and an alternative hypothesis.
A null hypothesis is a hypothesis that states that any statistical difference between populations is down to random chance. For instance
$$H_0:$$ A flipped coin will land on heads $$50\%$$ of the time.
If the null hypothesis proves false through the test, what will have been found? The alternative hypothesis
$$H_a:$$ A flipped coin will not land on heads $$50\%$$ of the time.
How does the Chi-square test for goodness of fit prove or disprove the null hypothesis? Well, it tests how likely the outcome of the sample is to have occurred if the null hypothesis is true. If the probability is low enough, the null hypothesis is considered false, and the alternative hypothesis must be true.
For instance, say your sample was $$100$$ coin flips and you got the following result.
Heads Tails $$99$$ $$1$$
Table 1. Heads vs tails test.
If there was a $$50\%$$ chance of flipping heads with each flip, as the null hypothesis states, then how likely would this result be? It makes sense intuitively that the probability is so low that it's bordering on impossible.
What about if you obtained these results?
Heads Tails $$58$$ $$42$$
Table 2. Heads vs tails test.
Well, this is a bit closer so it's hard to say, but using the Chi-square test for goodness of fit, it could be determined whether this result proved or disproved the null hypothesis.
## Chi-Square Test for Goodness of Fit Assumptions and Conditions
The Chi-square test for goodness of fit is not appropriate to be used on all data. In fact, there are fconditions, (sometimes referred to as assumptions) that must hold true.
• The sampling method is simple random sampling.
• The variable under study is categorical.
• The expected value of observations for each category must be at least five.
• Each outcome in the variable under study must be independent.
Let's take a look at each of these conditions a little more closely.
### Random Sampling
For the Chi-square test for goodness of fit, the sample being analyzed must have constituents that have been chosen at random.
Say you wished to try and predict the frequency at which different types of candy appear in a mixed bag. Well, if you wished to see if your prediction was accurate, you could potentially use a Chi-square test for goodness of fit only if the bags you take to check this are chosen completely at random.
### Categorical Variable
What is a categorical variable? Well, let's take the example of the mixed bags of candy from before. Each of the candies in the bag can be categorized by what type of sweet it is. There is no inherent ordering to these categories, therefore the variable is categorical. If, for instance, your data categories were school years, the variable would be simply ordered from low to high, and thus an ordinal variable, not categorical.
Of these two examples of variables, only the candy example is categorical, and therefore only the candies can be tested using the Chi-squared for the goodness of fit test.
### Expected Value
The next condition for a Chi-square test for goodness of fit is expected sample observations per category of at least five. This one is nice and simple. Basically, this test can only be used on large enough sample sizes. Your hypothesis might be that there is the same number of each sweet spread out amongst the bags. If your sample includes $$200$$ candy and five types of candies, then the expected number of each sweet found in the sample would be $$40$$. This is above five, and therefore meets this condition for the test
### Outcome Independence
The final condition for the Chi-square test for goodness of fit is outcome independence. All this means is that the probability of each outcome is not affected by the outcomes that came before. For instance, when it comes to the bag of candies, each time a sweet is picked from a bag there is a $$\frac{1}{5}$$ chance that it is a cola bottle. This is true no matter how many cola bottles have been picked before, or how many gummy bears. The previous outcomes have no effect on this one, so the outcomes are independent and the condition is met.
## Formula for Chi-Square Goodness of Fit Test Statistic
Once the hypotheses have been formulated and the conditions confirmed to have been met, it's time to calculate the Chi-square test statistic. This is done with this simple formula
$\chi^2 = \sum_{i=1}^n \frac{(O_i-E_i)^2}{E_i}$
Where $$O_i$$ is the $$i^{th}$$ observed value and $$E_i$$ is the $$i^{th}$$ expected value.
For example, with the following expected and observed values, the calculation would be carried out as follows.
Cola Bottle Flying Saucer Gummy Bear Fruit Lace Toffee Expected $$40$$ $$40$$ $$40$$ $$40$$ $$40$$ Observed $$20$$ $$25$$ $$15$$ $$18$$ $$22$$
Table 3. expected and observed values, chi-square test.
\begin{align} \chi^2 &= \sum_{i=1}^n \frac{(O_i-E_i)^2}{E_i} \\\\ &= \frac{(20-40)^2}{40} + \frac{(25-40)^2}{40} + \frac{(15-40)^2}{40}+... \\\\ &= 51.45 \end{align}
## Performing the Test for Goodness of Fit
Firstly, you will need to know the significance level, $$\alpha$$. The significance level sets the strength of the evidence you require to be able to consider the null hypothesis proven. Often significance levels will be set at $$5\%$$, ($$\alpha=0.05$$). A lower significance level indicates that a greater strength of evidence is required.
Secondly, you will need to know the number of degrees of freedom of the problem. The number of degrees of freedom is simply the number of independent groups the variable has. This value is just the number of groups $$-1$$. For example, for a variable with five groups, the number of degrees of freedom is four.
The next step in the test is to either find the Chi-square value or the p-value. Either of these values can be used to complete the test.
### Performing the Test With the Chi-Square Value
From the Chi-square table, you can find the Chi-square value for your test for the significance level and degrees of freedom of your specific problem. Below is a small segment of the table.
Degrees of Freedom Significance Level $$0.2$$ $$0.1$$ $$0.05$$ $$0.025$$ $$0.01$$ $$1$$ $$1.64$$ $$2.71$$ $$3.84$$ $$5.02$$ $$6.64$$ $$2$$ $$3.22$$ $$4.61$$ $$5.99$$ $$7.38$$ $$9.21$$ $$3$$ $$4.64$$ $$6.25$$ $$7.82$$ $$9.35$$ $$11.35$$ $$4$$ $$5.99$$ $$7.78$$ $$9.49$$ $$11.14$$ $$13.28$$
Table 4 - Chi-Square Values
So, back to the candy example. If the significance level is set at $$5\%$$, what is the Chi-square value? Well, the value where $$\alpha = 0.05$$ and $$4$$ meet is $$9.49$$.
The question that now arises, is whether the test statistic is greater, or smaller than the Chi-square value. If your test statistic is lower than the Chi-square value, then you can consider the null hypothesis confirmed.
### Performing the Test With the P-value
The $$p-$$value is the probability that (if the null hypothesis is true) sampling variation would produce an estimate that is further away from the hypothesis value than found in the current sample. It's a bit wordy, In other words, it's the probability that random sampling could produce a less accurate result than the current one.
Once again, the table is consulted. This time, find where your test statistic lies in the table, and extract the corresponding value from the significance level row. For example, for a test statistic of $$5$$ when the degrees of freedom was $$3$$, $$0.2< p <0.1$$. As long as the $$p-$$value is greater than the significance level, the null hypothesis has not been disproven.
## Chi-square Test for Goodness of Fit Example
(1) A biologist hypothesizes that each of the three types of fish occurs in equal numbers in a pond. They take a random sample of $$120$$ fish to test the hypothesis, and the results were as follows
Bass Crappie Sunfish $$32$$ $$52$$ $$36$$
Table 5. Fish data table.
Degrees of Freedom Significance Level $$0.2$$ $$0.1$$ $$0.05$$ $$0.025$$ $$0.01$$ $$1$$ $$1.64$$ $$2.71$$ $$3.84$$ $$5.02$$ $$6.64$$ $$2$$ $$3.22$$ $$4.61$$ $$5.99$$ $$7.38$$ $$9.21$$ $$3$$ $$4.64$$ $$6.25$$ $$7.82$$ $$9.35$$ $$11.35$$ $$4$$ $$5.99$$ $$7.78$$ $$9.49$$ $$11.14$$ $$13.28$$
Table 6. Degrees of freedom and significant level.
(a) State the hypotheses being tested.(b) Does the data being tested meet the conditions for a Chi-square test for goodness of fit?(c) Calculate the Chi-square test statistic.(d) Find the Chi-square value of the data, given the significance level is $$5\%$$.(e) Does the sample disprove the null hypothesis?Solution:(a) The first step is to define the hypotheses.$$H_0$$: Each type of fish occurs in equal numbers in the pond.$$H_a$$: Each type of fish does not occur in equal numbers in the pond.(b) The question states that the sample is random, so the first condition is met.The variable is categorical as it is made up of unordered groups therefore the second condition is met.The expected value of each group is $$\frac{120}{3} = 40$$, which is over five, therefore the third condition is met.Finally, when a fish is pulled out of the water there is always a $$\frac{1}{3}$$ chance of it being any of the types of fish, therefore each outcome is independent, and so the fourth condition is met.Yes, it meets the four conditions(c) \begin{align} \chi^2& = \sum_{i=1}^n \frac{(O_i-E_i)^2}{E_i} \\\\ &=\frac{(32-40)^2}{40} +\frac{(52-40)^2}{40} + \frac{(36-40)^2}{40} \\\\ &= 5.6 \end{align}
(d) \begin{align} df &= n - 1 \\\\ &= 3 - 1 \\\\ &= 2\end{align}
With a significance level of $$5\%$$, $$\alpha = 0.05$$, the Chi-square value from the table is $$5.99$$.
(e) As the test statistic is less than the Chi-square value $$(5.6 < 5.99)$$, the test has shown there is not sufficient evidence to disprove the null hypothesis.
(2) A school does a study about the occurrence of different colored eyes in its pupils. It is hypothesized that $$15\%$$ of pupils will have green eyes, $$25\%$$ of pupils will have blue eyes, and $$60\%$$ of pupils will have brown eyes. Of the $$1000$$ pupils, $$80$$ are chosen at random. The results of the sample are as follows.
Green Blue Brown $$18$$ $$28$$ $$34$$
Table 7. Colour data.
Table 8. Degrees of freedom and significant level.
Degrees of Freedom Significance Level $$0.2$$ $$0.1$$ $$0.05$$ $$0.025$$ $$0.01$$ $$1$$ $$1.64$$ $$2.71$$ $$3.84$$ $$5.02$$ $$6.64$$ $$2$$ $$3.22$$ $$4.61$$ $$5.99$$ $$7.38$$ $$9.21$$ $$3$$ $$4.64$$ $$6.25$$ $$7.82$$ $$9.35$$ $$11.35$$ $$4$$ $$5.99$$ $$7.78$$ $$9.49$$ $$11.14$$ $$13.28$$
(a) State the hypotheses being tested.(b) Does the data being tested meet the conditions for a Chi-square test for goodness of fit?(c) Calculate the Chi-square test statistic.(d) Find the $$p-$$value of the data, given the significance level is $$5\%$$.(e) Does the sample disprove the null hypothesis?
(a) $$H_0$$: $$15\%$$ of pupils will have green eyes, $$25\%$$ of pupils will have blue eyes, and $$60\%$$ of pupils will have brown eyes.
$$H_a$$: It is not the case that $$15\%$$ of pupils will have green eyes, $$25\%$$ of pupils will have blue eyes, and $$60\%$$ of pupils will have brown eyes
(b) The question states that the sample is random, so the first condition is met. The variable is categorical as it is made up of unordered groups therefore the second condition is met. The expected value of each group can be calculated as follows
$Green = 80 \cdot 0.15 = 12$
$Blue = 80 \cdot 0.25 = 20$
$Brown = 80 \cdot 0.6 = 48$
As the expected value of each group is greater than $$5$$, the third condition is met.Finally, the color of one student's eyes is not affected by the color of any other student's eyes, therefore the fourth condition is met.
(c) \begin{align} \chi^2& = \sum_{i=1}^n \frac{(O_i-E_i)^2}{E_i} \\\\ &=\frac{(18-12)^2}{12} +\frac{(28-20)^2}{20} + \frac{(34-48)^2}{48} \\\\ &= 10.28 \end{align}
(d) First, find the degrees of freedom
\begin{align} df &= n - 1 \\\\ &= 3-1 \\\\ &=2 \end{align}
Now, as the test statistic is $$10.28$$, from the table
$p < 0.01$
(e) As the $$p-$$value is smaller than the significance level, sufficient evidence has been provided to disprove the null hypothesis.
$p < 0.01 < 0.05$
## Chi-Square Test for Goodness of Fit - Key takeaways
• The Chi-square test for goodness of fit is a statistical hypothesis test used to determine whether an expected distribution of outcomes is significantly different from the actual observed distribution of outcomes.
• The Chi-square test for goodness of fit can only be carried out on data that meets the four conditions.
• The Chi-square test for goodness of fit can be carried out either by comparing the Chi-square value and test statistic or by comparing the $$p-$$value of the data and the significance level.
## Frequently Asked Questions about Chi Square Test for Goodness of Fit
The Chi-square test for goodness of fit can be used when you wish to test hypotheses about categorical data sets.
A chi-square test for goodness of fit can be conducted to confirm or deny a hypothesis about the distribution of a categorical data set.
1. The sample method must be random
2. The variable under study must be categorical
3. The expected value of observations for each category must be at least five
4. Each outcome in the variable under study must be independent.
The Chi-square test for goodness of fit can only be conducted on data that meets the four conditions.
One.
The Chi-square test for goodness of fit is right tailed because the numerator of the Chi-square test statistic is always positive
A Chi-square test for goodness of fit can be conducted to confirm or deny a hypothesis about the distribution of a categorical data set.
## Final Chi Square Test for Goodness of Fit Quiz
Question
What is the Chi-square test for goodness of fit?
The Chi-square test for goodness of fit is a statistical test that can be used to confirm or deny a hypothesis about the distribution of a categorical data set.
Show question
Question
What is a categorical data set?
Categorical data is data that is divided into discrete, unordered groups.
Show question
Question
Give an example of a categorical data set.
Anything that fits the definition
'Categorical data is data that is divided into discrete, unordered groups.'
Such as types of candy in a bag, the number of people with various eye colors, etc.
Show question
Question
How many conditions need to be met by a data set for a Chi-square test for goodness of fit to be used?
Four.
Show question
Question
What are the conditions that need to be met by a data set for a Chi-square test for goodness of fit to be used?
• The sampling method is simple random sampling.
• The variable under study is categorical.
• The expected value of observations for each category must be at least five.
• Each outcome in the variable under study must be independent.
Show question
Question
What makes a sampling method random?
The constituents of the sample must be chosen totally at random.
Show question
Question
Someone flips a coin a hundred times and records the result of each flip, heads or tails.
Is each outcome in this dataset independent?
Yes, the outcome of any given flip does not impact the probability of that or another outcome arising again.
Show question
Question
What is the formula for calculating the Chi-square test statistic?
$\chi^2 = \sum_{i=1}^n \frac{(O_i - E_i)^2}{E_i}$
Show question
Question
What is the significance level of a Chi-square test for goodness of fit?
The significance level sets the strength of the evidence you require to be able to consider the null hypothesis proven.
Show question
Question
What is a null hypothesis?
A null hypothesis is a hypothesis that states that any statistical difference between populations is down to random chance.
Show question
Question
What is the alternative hypothesis in a Chi-square test for goodness of fit?
The alternative hypothesis is what will be true if your null hypothesis proves wrong.
Show question
Question
How can you find the number of degrees of freedom of a categorical variable?
$df =\text { number of groups} - 1$
Show question
Question
What values do you need to find the Chi-square value for a Chi-square test for goodness of fit?
Degrees of freedom, significance level, and a Chi-square table.
Show question
Question
What makes a group of a categorical variable independent?
The likelihood of a given observation belonging to that group is not affected by the number of observations belonging to any other group.
Show question
Question
Why is a chi-square for goodness of fit test always right-tailed
The Chi-square goodness of fit test is right-tailed because the numerator of the Chi-square test statistic is always positive.
Show question
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1. Dec 18, 2011
Loro
Here is a paradox that came to my mind during my fluid mechanics course last term. I don't know the solution to it:
We have this experiment in which we hold two sheets of paper parallel to each other and blow between them. They are brought closer to each other:
http://sepulki.net/loro/benoulli1.bmp [Broken]
The air outside is stationary, and the air between the sheets moves, so from the Bernoulli theorem it follows that the pressure is higher outside and lower inside - this implies that the forces on the sheets point inwards and bring them closer to each other.
Now let's consider this experiment in the reference frame of the air moving between the sheets of paper:
http://sepulki.net/loro/benoulli2.bmp [Broken]
Now the air in between is stationary, and the air outside is moving, so it would mean that the pressure is higher inside, and lower outside and so now the forces on the sheets point outwards and draw them apart.
What is wrong with this reasoning in the moving frame? To be honest I'm not exactly sure if this situation can really be treated as an irrotational flow (and if the Bernoulli theorem is applicable).
Last edited by a moderator: May 5, 2017
2. Dec 18, 2011
One problem is you're going from velocity = v to velocity = 0 discontinuously - there has to be a gradient as you get near the walls of the tube, pipe, paper, channel, whatever you want to call it.
This is known as a "boundary layer" and its a small region where the fluid goes from the uniform velocity to zero at the edges of the boundary in a very rapid but continuous way.
My guess is that this is where the error lies.
3. Dec 18, 2011
Actually, the error lies in the fact that your thought experiment changes frames but fails to consider that your paper is now moving. Static pressure is frame independent, and that is what gives rise to the forces involved in your problem.
4. Dec 18, 2011
Loro
The thing is that this simple explaination by Bernoulli theorem doesn't take the bounadry layer into account. It would still apply if we used Euler's equations (the ones that neglect viscosity) instead of Navier-Stokes equations.
But if we neglect viscosity - it doesn't matter whether or not the paper is moving - if there's no viscosity, it doesn't interact with air.
In other words the Bernoulli theorem follows from Euler's equations, that are Galilean invariant, and so the pressure calculated from them should also be Galilean invariant, which it isn't...
5. Dec 18, 2011
Loro
I was thinking that maybe it is that the Bernoulli theorem doesn't apply here?
Because what I think we have in the case of no viscosity is a flow which is piecewise irrotational - but if we think of a point on the boundary (paper) there is vorticity around it.
And the Bernoulli theorem holds only in irrotational flows.
But these are just my thoughts.
6. Dec 18, 2011
Studiot
Surely it is a simple case of two distinct bodies of fluid to which you can apply Bernoulli separately.
You cannot pick one variable value from one body and apply it to the other.
7. Dec 18, 2011
rcgldr
Depending on the source of the air stream, that's not what will happen. Hold the end of a hair dryer (in cold mode) between two sheets of paper and facing downwards. When you turn the blow dryer on (in cold mode), the sheets will not be drawn together.
The Bernoulli principle that relates faster moving air to lower pressure only holds when there are no external forces involved and therefore no change in the total energy. In the case of a blow dryer, the total energy of the air is increased, both pressure and velocity are increased at the nozzle of the blow dryer.
If you change the experiement to blow air between two suspended balloons or empty soda cans, the combination of coanda and venturi effects will cause the balloons or cans to converge. The coanda effect is only indirectly related to Bernoulli.
If you blow air into a venturi pipe, then at the narrowest part of the venturi, the velocity will be highest and the pressure the lowest. Ignoring the effects of friction with the walls of the pipe and viscosity, this follows Bernoulli principle. (For a real pipe of constant diameter, pressure decreases with distance moved along the pipe due to friction and viscosity).
Last edited: Dec 18, 2011
8. Dec 18, 2011
Staff: Mentor
Doesn't look like you read this one:
You transformed from one frame to another incorrectly.
9. Dec 19, 2011
Studiot
Yes you can apply Bernoulli, but you have to do it correctly and your analysis does not have enough information.
The simplest form of Bernoulli is
$${p_1} + 1/2\rho v_1^2 = {p_2} + 1/2\rho v_2^2$$
Now the point of this is that condition 1 (LHS) and condition 2 (RHS) have to be taken for different points in the same body of fluid.
The fluid between the sheets and the fluid external to the sheets are different fluid bodies.
A more rigorous statement would be that you have Bernoulli applies along streamlines (1D) stream strips (2D) or stream tubes (3D), but not across them.
What you are proposing tries to apply Bernoulli across the stream tubes.
You can only use Bernoulli to compare when you can trace the streamlines to infinity or a common point. Otherwise it would be equivalent to trying to compare the forces exerted on a pipe by the air outside and some fluid flowing inside by using Bernoulli. You can only do this if you can find some point where the fluid enters or exits at atmospheric pressure.
10. Dec 19, 2011
Loro
rcgldr, thanks this is interesting:
Does it mean, that its energy is increased, because the motor is doing work on it? Isn't it similar to us doing work on the air when we blow it out?
That's exactly what I was thinking
So I guess the main problem is that I don't know how to change reference frames
Ok so now when I think of that, is it just that the Bernoulli potentials for the two stream tubes are different:
In the frame of the paper the air inside has got a high Bernoulli potential and outside - a low Bernoulli potential.
In the moving frame the air outside has got a low Bernoulli potential and inside - a high one.
But the potentials change when I change frames, so in order to change frames correctly I should assume that pressures are invariant, velocities transform as usually, and from that I can calculate the new Bernoulli potentials, which change differently because we're considering different bodies of fluid.
So in fact what happens when I go to the moving frame, is that the Bernoulli potential of the air inside goes up, because its velocity goes up ; the Bernoulli potential of the air outside goes down, because its velocity goes down - but the pressures remain the same and give rise to the same forces?
And does the actual motion of paper really matter in the sense other than just distinguishing the two frames?
11. Dec 19, 2011
Studiot
The information you provide is not enough to solve the problem.
Look at it like this:
Suppose you supply air from a compressed air source to a bicycle tyre.
Air enters the tyre (has a velocity) and the tyre walls expand against the external atmosphere. No one is suprised because the (static) pressure inside the tyre is greater than the external.
Now let the air move the other way - the tyre walls deflate. Again no one is suprised.
In both cases the calculations are a balance of forces due to prevailing static pressures. Bernoulli is not invoked.
There are two bodies of fluid.
Now consider a aerofoil or sphere or other shape moving in an atmosphere.
There is now only one body of fluid viz the atmosphere.
Streamlines start at equal pressure a long way in front of the moving object, flow over and past it in some way, to finally reconnect and return to the same pressure a long way behind the object.
In these circumstances you can apply Bernoulli (along a streamline) to gain an insight into the exchange of energy between static (potential) and velocity energies throughout the process.
Depending upon the shape and other factors this insight can be pretty accurate.
go well
12. Dec 19, 2011
rcgldr
Yes, but the motor in the blow dryer does much more work than a person blowing on the air. The other thing to consider is that if the static pressure inside the blow dryer's nozzle or a persons mouth wasn't higher than the ambient static pressure outside, then the air wouldn't flow (accelerate) outwards.
Static pressure isn't changed by reference frames. Dynamic pressure is relative to a reference frame, just like kinetic energy, but that's not a factor unless the air is going to be accelerated or decelerated to the speed of the reference frame.
I'm not sure what you mean by potential (dynamic pressure?), but the static pressure of the air inside and outside of the two sheets of paper is independent of the frame of reference. Getting back to the point I made above, the pressure of the air being blown is higher than the ambient pressure, so the air accelerates as it's pressure decreases, until momentum of the air ahead of the stream results in an adverse pressure gradient (increasing with distance), slowing the stream down. There is a term called "exit velocity" which refers to the speed of the affected air at the moment it's pressure returns to ambient. This NASA article on propellers explains this.
http://www.grc.nasa.gov/WWW/K-12/airplane/propanl.html
Except that a wing also increases the energy of the air which violates Bernoulli, in the same manner as mentioned in the NASA propeller article linked to above, but on a smaller scale (a smaller pressure jump, with a smaller exit velocity). Also as mentioned in that NASA article outside of the zone near the wing where the energy of the air is increased, then Bernoulli applies (ignoring issues like turbulent flow).
http://home.comcast.net/~clipper-108/Lift_AAPT.pdf [Broken]
A Cessna 172 weighing about 2300 lbs, traveling in level flight at about 140 mph, diverts about 5 tons of air per second downwards at 11.5 mph right at the wing (that 11.5 mph might actually be the exit velocity). This increases the energy of the air by about 44,000 lb-ft per second, which translates into about 80 horsepower. It's engine can produce 180 hp or more, so it can deliver the 80 hp consumed by lift and the power consumed by drag. Bernoulli principle is violated in the zone where the 80 hp is added to the air related to lift, plus the power added to the air related to drag, but Bernoulli would apply outside that zone (again ignoring issues like turbulence).
So the Cessna 172 isn't all that efficient. At the other extreme, a high end glider like a Nimbus 4 (87 foot wingspan), weighing about 1500 lbs with pilot, might have a 60:1 glide ratio at 60 mph forward speed, 1 mph descent rate. This translates into a gravitational power input of only 4 hp, all of which goes into the air, most of it in the form of kinetic energy, some of it into temperature.
Last edited by a moderator: May 5, 2017
13. Dec 19, 2011
Studiot
Perhaps if you read my text more closely you would understand why I wrote
rather than stating that Bernoulli or some other equation is followed exactly.
14. Dec 19, 2011
Loro
This makes sense, because if we consider a more realistic model for my original experiment - that the sheets of paper are of finite size, still no viscosity, and the air between the sheets comes from our mouth - it wouldn't make sense to me to apply Bernoulli in the simplest form across the paper now, if we couldn't do it in the simple model - because we still have two separate bodies of fluid.
Oh by Bernoulli potential I meant this quantity: (I guess it's not really called that...)
$H = p + \frac{1}{2} \rho v^2$
So taking this into account does my reasoning make sense?
15. Dec 19, 2011
olivermsun
If the sheets have finite size, then you can make a statement about which part is moving and which part is not; also, the bodies of air meet at the end, right?
16. Dec 19, 2011
Loro
Yes, but they have different total energies, so my quantity H is still different for the air inside and outside.
17. Dec 19, 2011
olivermsun
Yes, but there is no longer a paradox since there's clearly a difference between the two frames you originally described if the sheets have finite extent.
You would probably also be assuming that the streamlines going between the sheets of paper eventually meet up with streamlines which passed outside the paper.
18. Dec 19, 2011
rcgldr
Which why I mentioned that Bernoulli applies outsize the zone where energy is added to the air.
This is the total energy per unit volume. H is normally used for the energy head in a different form of Bernoulli equation. Bernoulli can have a potential term, but that term is gravitational potential energy per unit volume:
p + (1/2) ρ v2 + ρ g h
http://en.wikipedia.org/wiki/Bernoulli's_principle
They have have different total energies, but the force perpendicular to the sheets of paper is due to the differences in static pressure, not total energies. The difference in speed between the air and paper is the same in any frame, so any friction / viscosity effects between paper and air will be the same in any frame. The difference in speed between the two streams of air is also the same in any frame, so any interaction between those streams is also the same in any frame. Only speed dependent quantities such as kinetic or dynamic energy are frame dependent, but since there's no direct interaction related to the frame of reference it doesn't matter.
Last edited: Dec 19, 2011
19. Dec 19, 2011
Studiot
Could you describe the streamlines which exhibit this behaviour, both before and after the sheets?
Hear! hear!
Several responders have now stated this (or equivalent) in different ways, Loro, please take note - you are getting there, fluid mechanics is a complicated subject.
And yes there is a link between the first law of thermodynamics and Bernoulli, but it is not applicable here.
Last edited: Dec 19, 2011
20. Dec 19, 2011
olivermsun
I imagine there would be a streamline along the inside surface of the channel and one along the outside surface (just like streamlines over a wing), and they would have to meet up at the end of the sheet. Am I confused? |
# How to write recurrence relation for backtracking problem?
I am not able to understand how to write a recurrence relation for n queen problem. I searched on web and everywhere it was given directly without explaining how can we arrive to that. Recurrence relation is for n*n board $$T(n)=n*T(n-1)+O(n^2)$$ but think it should be $$T(n)=T(n-1)+O(n^2)$$ as if we put the queen anywhere in first row, we are left with $$(n-1)*(n-1)$$ board and it is sub-problem for T(n-1). But how n gets multiplied is not understandable. Can anyone help in explaining such recurrence relation.
Recurrence relation is for n*n board $$T(n)=n*T(n-1)+O(n^2)$$ but think it should be $$T(n)=T(n-1)+O(n^2)$$ as if we put the queen anywhere in first row, we are left with $$(n-1)*(n-1)$$ board and it is sub-problem for T(n-1). But how n gets multiplied is not understandable.
How many cells are there in the first row? $$n$$. That is where the factor $$n$$ come from.
• We put the Queen in the first cell of the first row. Removing the first row and first column, we then check the remaining $$(n-1)*(n-1)$$ board.
• We put the Queen in the second cell of the first row. Removing the first row and second column, we then check the remaining $$(n-1)*(n-1)$$ board.
• $$\vdots$$
• We put the Queen in the last cell of the first row. Removing the first row and last column, we then check the remaining $$(n-1)*(n-1)$$ board. |
# A rectangular conductor LMNO
A rectangular conductor LMNO is placed in a uniform magnetic field of 0.5 T. The field is directed perpendicular to the plane of the conductor.
When the arm MN of length of 20 cm is moved towards left with a velocity of 10 m${ s }^{ -1 }, calculate the emf induced in the arm. Given the resistance of the arm to be 5 \Omega$ (assuming that other arms are of negligible resistance) find the value of the current in the arm.
Let ON be at some point x.
The emf induced in the loop = $[\varepsilon ]$
$[\varepsilon =\frac{-d\phi }{dt}=\frac{-d(Blx)}{dt}=Blv]$
$=0.5\times 0.2\times 10=1V$
$[I=\frac{\varepsilon }{R}=\frac{1}{5}=0.2A]$ |
# Problem 2-3: Solving an Inequality
Solve the inequality $|2-3x|<3$.
Solution
$|2-3x|<3$
$2-3x<3$ or $-(2-3x)<3$
$-3x<1$ or $3x<5$
$-\frac{1}{3} < x<\frac{5}{3}$
## Published by Yaz
Hi! Yaz is here. I am passionate about learning and teaching. I try to explain every detail simultaneously with examples to ensure that students will remember them later too.
## Join the Conversation
2 Comments
1. anna says:
The solution should be:
-1/3 < x < 5/3
1. Thank you very much. Yes, I made a mistake.
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# On a new multivariate sampling paradigm and a polyspline Shannon function
Authors
Type
Preprint
Publication Date
Submission Date
Identifiers
arXiv ID: 0809.5153
Source
arXiv
In the monograph Kounchev, O. I., Multivariate Polysplines. Applications to Numerical and Wavelet Analysis, Academic Press, San Diego-London, 2001, and in the paper Kounchev O., Render, H., Cardinal interpolation with polysplines on annuli, Journal of Approximation Theory 137 (2005) 89--107, we have introduced and studied a new paradigm for cardinal interpolation which is related to the theory of multivariate polysplines. In the present paper we show that this is related to a new sampling paradigm in the multivariate case, whereas we obtain a Shannon type function $S(x)$ and the following Shannon type formula: $f(r\theta) =\sum_{j=-\infty}^{\infty}\int_{\QTR{Bbb}{S}^{n-1}}S(e^{-j}r\theta ) f(e^{j}\theta) d\theta .$ This formula relies upon infinitely many Shannon type formulas for the exponential splines arising from the radial part of the polyharmonic operator $\Delta ^{p}$ for fixed $p\geq 1$. Acknowledgement. The first and the second author have been partially supported by the Institutes partnership project with the Alexander von Humboldt Foundation. The first has been partially sponsored by the Greek-Bulgarian bilateral project BGr-17, and the second author by Grant MTM2006-13000-C03-03 of the D.G.I. of Spain. |
# Basic operations on DG Algebras -- Outlines some basic operations on DG Algebras
There are several ways to define a DGAlgebra. One can start by defining one 'from scratch'. One does this by specifying the ring over which the DGAlgebra is defined and the degrees of the generators. The name of the generators of the DGAlgebra by default is $T_i$, but one may change this by specifying the optional (string) argument 'Variable'.
i1 : R = ZZ/101[a,b,c,d]/ideal{a^3,b^3,c^3,d^3} o1 = R o1 : QuotientRing i2 : A = freeDGAlgebra(R,{{1,1},{1,1},{1,1},{1,1}}) o2 = {Ring => R } Underlying algebra => R[T ..T ] 1 4 Differential => null o2 : DGAlgebra
The command freeDGAlgebra only defines the underlying algebra of A, and not the differential. To set the differential of A, one uses the command setDiff.
i3 : setDiff(A, gens R) o3 = {Ring => R } Underlying algebra => R[T ..T ] 1 4 Differential => {a, b, c, d} o3 : DGAlgebra
Note that the above is the (graded) Koszul complex on a set of generators of R. A much easier way to define this is to use the function koszulComplexDGA.
i4 : B = koszulComplexDGA(R, Variable=>"S") o4 = {Ring => R } Underlying algebra => R[S ..S ] 1 4 Differential => {a, b, c, d} o4 : DGAlgebra
One can compute the homology algebra of a DGAlgebra using the homology (or HH) command.
i5 : HB = HH B Finding easy relations : -- used 0.0204119 seconds o5 = HB o5 : PolynomialRing, 4 skew commutative variables i6 : describe HB ZZ o6 = ---[X ..X , Degrees => {4:{1}}, Heft => {1, 0}, MonomialOrder => {MonomialSize => 32}, DegreeRank => 2, SkewCommutative => {0, 1, 2, 3}] 101 1 4 {3} {GRevLex => {4:1} } {Position => Up } i7 : degrees HB o7 = {{1, 3}, {1, 3}, {1, 3}, {1, 3}} o7 : List
Note that since R is a complete intersection, its Koszul homology algebra is an exterior algebra, which is a free graded commutative algebra. Note that the internal degree is preserved in the computation of the homology algebra of B.
One can also adjoin variables to kill cycles in homology. The command killCycles looks for the first positive degree nonzero homology (say i), and adjoins variables in homological degree i+1 that differentiate to a minimal generating set of this homology, so that the resulting DGAlgebra now only has homology in degree greater than i (note of course this could introduce new homology in higher degrees). The command adjoinVariables allows finer control over this procedure. See adjoinVariables for an example.
i8 : HB.cache.cycles 2 2 2 2 o8 = {a S , b S , c S , d S } 1 2 3 4 o8 : List i9 : C = adjoinVariables(B,{first HB.cache.cycles}) o9 = {Ring => R } Underlying algebra => R[T ..T ] 1 5 2 Differential => {a, b, c, d, a T } 1 o9 : DGAlgebra i10 : homologyAlgebra(C,GenDegreeLimit=>4,RelDegreeLimit=>4) Finding easy relations : -- used 0.0443892 seconds ZZ o10 = ---[X ..X ] 101 1 3 o10 : PolynomialRing, 3 skew commutative variables i11 : C = killCycles(B) o11 = {Ring => R } Underlying algebra => R[T ..T ] 1 8 2 2 2 2 Differential => {a, b, c, d, a T , b T , c T , d T } 1 2 3 4 o11 : DGAlgebra i12 : homologyAlgebra(C,GenDegreeLimit=>4,RelDegreeLimit=>4) ZZ o12 = --- 101 o12 : QuotientRing
Again, note that since R is a complete intersection, once we adjoin the variables in homological degree two to kill the cycles in degree one, we obtain a minimal DG Algebra resolution of the residue field of R. Also, note that since C has generators in even degree, one must specify the optional arguments GenDegreeLimit and RelDegreeLimit to specify the max degree of the computation. To do this, one uses the homologyAlgebra command rather than the HH command.
This computation could have also been done with the command acyclicClosure. The command acyclicClosure performs the command killCycles sequentially to ensure that the result has homology in higher and higher degrees, thereby computing (part of) a minimal DG Algebra resolution of the residue field. acyclicClosure has an optional argument EndDegree that allows the user to specify the maximum homological degree with which to perform this adjunction of variables. The default value of this is 3, since if there are any variables of degree 3 that need to be added, then each subsequent homological degree will require some variables to be adjoined (Halperin's rigidity theorem).
i13 : D = acyclicClosure R o13 = {Ring => R } Underlying algebra => R[T ..T ] 1 8 2 2 2 2 Differential => {a, b, c, d, a T , b T , c T , d T } 1 2 3 4 o13 : DGAlgebra i14 : R' = ZZ/101[x,y,z]/ideal{x^2,y^2,z^2,x*y*z} o14 = R' o14 : QuotientRing i15 : E = acyclicClosure(R',EndDegree=>5) o15 = {Ring => R' } Underlying algebra => R'[T ..T ] 1 56 2 2 2 2 2 2 Differential => {x, y, z, x*T , y*T , z*T , y*z*T , y*z*T , -y*z*T T , -y*z*T T , -y*z*T T , -y*z*T T , y*z*T T , y*z*T T , y*z*T T , -y*z*T T T , -y*z*T , -y*z*T T , -y*z*T T , y*z*T T T , y*z*T T T , y*z*T T T , y*z*T T T , -y*z*T T T , -y*z*T T T , -y*z*T T T , -y*z*T T , y*z*T T T , y*z*T T T , y*z*T T , y*z*T T T , y*z*T T , -y*z*T T , -y*z*T T , -y*z*T T , -y*z*T T T , -y*z*T T T , -y*z*T T T , -y*z*T T T , -y*z*T T T , -y*z*T T T , y*z*T T T T , y*z*T T T T , -y*z*T T T T , y*z*T T , -y*z*T T T , -y*z*T T T , -y*z*T T T , - y*z*T T T T - y*z*T T T , -y*z*T T T , y*z*T T T , y*z*T T T , -y*z*T T T , -y*z*T T T , -y*z*T T T , y*z*T T T T } 1 2 3 1 4 1 3 1 2 1 5 1 6 3 4 2 4 1 4 1 2 3 4 4 5 4 6 1 3 5 1 2 5 1 3 6 1 2 6 2 3 4 1 3 4 1 2 4 4 7 1 3 7 1 2 7 1 5 1 5 6 1 6 3 4 2 4 1 4 3 4 5 2 4 5 1 4 5 3 4 6 2 4 6 1 4 6 1 2 3 5 1 2 3 6 1 2 3 4 4 8 1 3 8 1 3 9 1 2 8 1 2 3 7 1 2 9 1 2 10 1 5 7 1 6 7 3 4 7 2 4 7 1 4 7 1 2 3 7 o15 : DGAlgebra i16 : tally degrees E.natural o16 = Tally{{1, 1} => 3 } {2, 2} => 3 {2, 3} => 1 {3, 4} => 3 {4, 5} => 6 {5, 6} => 10 {5, 7} => 3 {6, 7} => 15 {6, 8} => 12 o16 : Tally
As you can see, since R' is not a complete intersection, the acyclic closure of E requires infinitely many variables; we display the degrees of the first 6 here. The tally that is displayed gives the deviations of the ring R. One can compute the deviations directly from any minimal free resolution of the residue field of R', so that using the one provided by res coker vars R is faster. To do this, use the command deviations.
i17 : deviations(R,DegreeLimit=>6) o17 = HashTable{(1, {1}) => 4} (2, {3}) => 4 o17 : HashTable i18 : deviations(R',DegreeLimit=>6) o18 = HashTable{(1, {1}) => 3 } (2, {2}) => 3 (2, {3}) => 1 (3, {4}) => 3 (4, {5}) => 6 (5, {6}) => 10 (5, {7}) => 3 (6, {7}) => 15 (6, {8}) => 12 o18 : HashTable
As a brief warning, the command poincareN which is used in deviations uses the symbols S and T internally, and may cause problems accessing such rings with the user interface. |
We have to solve $$\frac{d^2r}{dt^2} - \frac{h^2}{r^3} = -\frac{GM}{r^2}$$. $h = r^2\frac{d\theta}{dt}$ is constant , so $\frac{d\theta}{dt} = hu^2$Putting $u = \frac{1}{r}$ we have $$\frac{dr}{dt} = \frac{dr}{du}\frac{du}{d\theta}\frac{d\theta}{dt} = -\frac{1}{u^2}\frac{du}{d\theta}\frac{h}{u^2} = -h\frac{du}{d\theta}$$ Therefore $$\frac{d^2r}{dt^2} = -h\frac{d}{dt}\Big(\frac{du}{d\theta}\Big) = -h\frac{d\theta}{dt}\frac{d^2u}{d\theta^2} = -h^2u^2\frac{d^2u}{d\theta^2}$$ Our differential equation now becomes $$h^2u^2\frac{d^2u}{d\theta^2} - h^2u^3 = -\frac{GM}{u^2} \Rightarrow \frac{d^2u}{d\theta^2} - u = -\frac{GM}{h^2}$$ which has a general solution $u(\theta) = \frac{GM}{h^2} + A\cos{\theta} + B\sin{\theta}$ for constants $A$ and $B$.
Now we substitute back to $r$, and get $$r = \frac{1}{\frac{GM}{h^2} + A\cos{\theta} + B\sin{\theta}} = \frac{\frac{h^2}{GM}}{1 + \frac{Ah^2}{GM}\sin{\theta} + \frac{Bh^2}{GM}\cos{\theta}} = \frac{\frac{h^2}{GM}}{1 + e\cos{(\theta + f)}}$$ for some $e$ and $f$. Therefore $h^2 = GMr(1 + e\cos{(\theta + f)})$. We leave sketching this graph for different values of $e$ an open problem. Send in any attempts! |
I have forgotten
• https://me.yahoo.com
# siunitx in the online latex editor
31 Mar 11, 12:16PM
siunitx in the online latex editor
Hi,
Thanks for the suggestion. Its a very good idea.
For security we can't allow users to customise the preamble, however we can automatically include additional packages. Generally we add a package when people ask for it and we deem it to be a logical addition.
We'll include the siunitx package in the next main release. What other key packages would people like? |
# How much work would it take to push a 3 kg weight up a 8 m plane that is at an incline of pi / 3 ?
Nov 10, 2017
$2 \cdot {10}^{2} \text{ J}$
#### Explanation:
We know that the technical, calculus-based definition of work is defined as:
$W = {\int}_{{s}_{0}}^{{s}_{f}} F \cdot \mathrm{ds}$
where $s$ is position.
Assuming a constant force, this expression simplifies to the following (which you are taught if you're not doing a calculus based physics course):
$W = F \left({s}_{f} - {s}_{0}\right)$
We know how far the block travels, but we do not know how much force is acting on the block. Hence, we'll need to set up a free body diagram and use Newton's 2nd Law to figure that out:
Before we start talking about work, let's draw a free body diagram here to analyze the forces acting on the crate as we push it up:
I've assumed that the ramp is frictionless, since taking friction into account would need a bit more information that you don't have.
Hence, the only forces we care about here are those acting along the axis of the ramp. In this case, those are ${F}_{p}$, our pushing force (which we're solving for), and $m g \sin \left(\theta\right)$, a component of gravitational force.
Recall that in order to get the ramp moving, the minimum net force you need to have acting on the object is 0 (meaning that the object would have zero acceleration). Therefore, we can set up the following:
$\Sigma {F}_{x} = m {a}_{x}$
x signifies the direction up the ramp
$\implies {F}_{p} - m g \sin \left(\theta\right) = 0$
Now, we just solve for ${F}_{p}$:
${F}_{p} = m g \sin \left(\theta\right) = \left(3\right) \left(9.8\right) \left(\sin \left(60\right)\right)$
$\implies {F}_{p} = 25.5 N$
That is the minimum force we need to move the block. Now, we can go ahead and set up our work equation:
$W = F \left({s}_{f} - {s}_{0}\right)$
We can set ${s}_{0} = 0$, and ${s}_{f} = 8$:
$W = 25.5 \left(8 - 0\right)$
$\implies W = 203.6 \to 2 \cdot {10}^{2} \text{ J}$.
Rounded to one significant figure
And there you are. Note that this is the minimum amount of work you'd have to do. You could apply a larger force on the block, and move it up faster, but you'd be doing more work in those cases.
Hope that helped :) |
# Find convergence of integral and compute it
Preparing for my calculus exam I found this exercise and I want to see if I'm on the right track
Find out the convergence of the following series and compute it. $$\int_0^\infty \frac {\,dx} {(x+1)\sqrt {x^2 + x + 1}}$$
To find if the integral is convergent or divergent I'm thinking to compute this limit: $$\lim_{t\rightarrow\infty} \int_0^t \frac {\,dx} {(x+1)\sqrt {x^2 + x + 1}}$$
And if that limit is a constant then my integral is convergent if not then the integral is divergent and I should not compute it.
Now, to compute the integral so I can compute that limit I'm thinking to apply integration by parts.
That $\frac {1}{x+1}$ from the integral is $\frac {d}{\,dx}\ln(x+1)$.
Any tips and/or corrections?
-
Let's try an elementary approach and make the substitution: $$\sqrt{x^2+x+1}=x+t$$ and get $$x=\frac{t^2-1}{1-2t}$$ $$dx=-2 \cdot \frac{t^2-t+1}{(1-2t)^2}\ dt$$ Therefore, our integral gets reduced to $$2\int_{1}^{\frac{1}{2}}\frac{1}{t(t-2)} \ dt=[\log(2-t)-\log(t)]_{1}^{\frac{1}{2}}= \ln 3.$$
Note that for the integration limits, particularly for the case when $x$ tends to $\infty$, I used a celebre limit whose limit is well known, namely:
$$\lim_{x\to\infty} \sqrt[k]{x^k+x^{k-1}+\cdots + 1}-x = \frac{1}{k}, \space k\geq 2$$ that is easily deduced by using Taylor expansion. In our case we dealt with $$\lim_{x\to\infty} \sqrt{x^2+x+1}-x = \frac{1}{2}$$ If you are not used to Taylor expansion, use the substitution $\displaystyle x=\frac{1}{u}$ and pay attention that u tends to $0$. Then you may nicely finish it by using L'Hôpital's rule. Finally, if you don't like either way, just use the conjugates.
Q.E.D. (Chris)
-
If the problem is to examine the convergence alone, just observe that for some constant $C > 0$ we have $$\frac{1}{(x+1)\sqrt{x^2+x+1}} \leq C \min\left\{ 1, \frac{1}{x^2}\right\}. \tag{1}$$ Indeed, on $[0, 1]$, continuity of the integrand shows that it is bounded by some constant $C_1$. On $[1, \infty)$, we have $$\frac{1}{(x+1)\sqrt{x^2+x+1}} \leq \frac{1}{x \sqrt{x^2}} = \frac{1}{x^2}.$$ Thus for $C = \max \{ C_1, 1 \}$ we have $(1)$. Therefore \begin{align*} \int_{0}^{\infty} \frac{dx}{(x+1)\sqrt{x^2+x+1}} & \leq C \int_{0}^{\infty} \min\left\{ 1, \frac{1}{x^2}\right\} \; dx \\ & = C \left( \int_{0}^{1} dx + \int_{1}^{\infty} \frac{1}{x^2} \; dx \right) = 2C < \infty. \end{align*}
This method is quite general for convergence analysis. When applying this method, we first list all the singularities (the point where the integrand blows up) of the integrand, including points $\pm \infty$ at infinity. For example, if we are dealing with
$$\int_{0}^{\infty} \frac{dx}{x^{3/2}\sqrt{x + 1}}$$
instead, then our list of singularity will be $\{0, \infty\}$. Then examine the behavior of the integrand near each singularity point $x_0$, by approximating it to familiar functions such as $(x - x_0)^{r}$. In many cases, this information solely determines the convergence behavior of the integral. In our example above, near $x = 0$ the function is approximately $x^{-3/2}$, whose integral near $x = 0$ diverges to infinity. This proves the divergence of the integral above. Rigorous justification of this estimation would be to find a suitable estimation for the integral. In this example, we may argue by
$$\frac{1}{x^{3/2}\sqrt{x + 1}} \geq \frac{1}{x^{3/2}\sqrt{2}} \quad \text{on} \quad (0, 1].$$
But in this case, we are asked to find its value. When we succeed in finding its value, then convergence also follows.
We make the substitution $x + \frac{1}{2} = \frac{\sqrt{3}}{2} \tan t$. As $x$ ranges from $0$ to $\infty$, $t$ ranges from $\frac{\pi}{6}$ to $\frac{\pi}{2}$. Also differentiating both sides, we have $dx = \frac{\sqrt{3}}{2} \sec^2 t \; dt$. Thus
\begin{align*} \int \frac{dx}{(x+1)\sqrt{x^2 + x + 1}} &= \int \frac{1}{\left( \frac{1}{2}+\frac{\sqrt{3}}{2} \tan t \right) \left( \frac{\sqrt{3}}{2} \sec t \right)} \cdot \frac{\sqrt{3}}{2} \sec^2 t \; dt \\ &= \int \frac{dt}{\frac{1}{2}\cos t + \frac{\sqrt{3}}{2} \sin t} \\ &= \int \frac{dt}{\sin\left(t+\frac{\pi}{6}\right)}. \end{align*}
This shows that
$$\int_{0}^{\infty} \frac{dx}{(x+1)\sqrt{x^2 + x + 1}} = \int_{\frac{\pi}{6}}^{\frac{\pi}{2}} \frac{dt}{\sin\left(t+\frac{\pi}{6}\right)} = \int_{\frac{\pi}{3}}^{\frac{2\pi}{3}} \frac{du}{\sin u}$$
for $u = t + \frac{\pi}{6}$. Already it is clear that this improper integral converges, for the integrand is bounded. To find its value, we proceed the calculation.
\begin{align*} \int_{\frac{\pi}{3}}^{\frac{2\pi}{3}} \frac{du}{\sin u} &= \int_{\frac{\pi}{3}}^{\frac{2\pi}{3}} \frac{\sin u}{\sin^2 u} \; du = \int_{\frac{\pi}{3}}^{\frac{2\pi}{3}} \frac{\sin u}{1 - \cos^2 u} \; du \\ &= \int_{-\frac{1}{2}}^{\frac{1}{2}} \frac{ds}{1 - s^2} \qquad (s = \cos u) \\ &= \int_{-\frac{1}{2}}^{\frac{1}{2}} \frac{1}{2}\left( \frac{1}{1-s} + \frac{1}{1+s} \right) \; ds \\ &= \frac{1}{2}\left[ \log(1+s) - \log(1-s) \right]_{-\frac{1}{2}}^{\frac{1}{2}} = \log 3. \end{align*}
-
With $C=1$. – Did Sep 1 '12 at 20:47 |
# Abelian groups of order 70 are cyclic
1. Nov 14, 2009
### redone632
1. The problem statement, all variables and given/known data
Show that every abelian group of order 70 is cyclic.
2. Relevant equations
Cannot use the Fundamental Theorem of Finite Abelian Groups.
3. The attempt at a solution
I've tried to prove the contrapositive and suppose that it is not cyclic then it cannot be abelian. But that has lead no where quickly.
Something tells me that I need to use the fact that 2*5*7 = 70 and 2 5 7 are all primes. But nothing is clicking. We haven't done the Fundamental Theorem of Finite Abelian Groups so there must be a way to prove this without it. If someone can point me in the right direction that would help a lot!
Last edited: Nov 15, 2009
2. Nov 14, 2009
### Dick
Use Cauchy's theorem with your three primes.
3. Nov 15, 2009
### redone632
Hmmm I think I got it. I just want to make sure it's right.
Since 2, 5, 7 are primes that divide 70. Then by Cauchy's Theorem there must be an elements of order 2, 5, 7 say, a, b, c respectively. Since $G$ is abelian, then every subgroup must be normal. Therefore, the subgroups generated a, b, c are distinct and normal. $G$ is then the internal direct product $<a> \times <b> \times <c>$. Then by a theorem, $G$ is isomorphic to $<a> \oplus <b> \oplus <c>$. As $|a|$, $|b|$, $|c|$ are relatively prime, $<a> \oplus <b> \oplus <c>$ is cyclic. Therefore $G$ is cyclic.
Last edited: Nov 15, 2009
4. Nov 15, 2009
### Dick
Sure. Or you could just take the direct approach and argue that the element abc must have order 70.
5. Nov 15, 2009
### redone632
Awesome. Thanks!
6. Nov 15, 2009
### Quantumpencil
There are two groups of order 21, even though it's isomorphic to the direct product of the Cyclic Group of Order 3 and the Cyclic Group of order 7. 3 and 7 are co-prime.
EDIT: Nevermind, didn't read the "abelian" in the problem. Your proof is good.
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# Posts tagged as “counting”
You are given the logs for users’ actions on LeetCode, and an integer k. The logs are represented by a 2D integer array logs where each logs[i] = [IDi, timei] indicates that the user with IDi performed an action at the minute timei.
Multiple users can perform actions simultaneously, and a single user can perform multiple actions in the same minute.
The user active minutes (UAM) for a given user is defined as the number of unique minutes in which the user performed an action on LeetCode. A minute can only be counted once, even if multiple actions occur during it.
You are to calculate a 1-indexed array answer of size k such that, for each j (1 <= j <= k), answer[j] is the number of users whose UAM equals j.
Return the array answer as described above.
Example 1:
Input: logs = [[0,5],[1,2],[0,2],[0,5],[1,3]], k = 5
Output: [0,2,0,0,0]
Explanation:
The user with ID=0 performed actions at minutes 5, 2, and 5 again. Hence, they have a UAM of 2 (minute 5 is only counted once).
The user with ID=1 performed actions at minutes 2 and 3. Hence, they have a UAM of 2.
Since both users have a UAM of 2, answer[2] is 2, and the remaining answer[j] values are 0.
Example 2:
Input: logs = [[1,1],[2,2],[2,3]], k = 4
Output: [1,1,0,0]
Explanation:
The user with ID=1 performed a single action at minute 1. Hence, they have a UAM of 1.
The user with ID=2 performed actions at minutes 2 and 3. Hence, they have a UAM of 2.
There is one user with a UAM of 1 and one with a UAM of 2.
Hence, answer[1] = 1, answer[2] = 1, and the remaining values are 0.
Constraints:
• 1 <= logs.length <= 104
• 0 <= IDi <= 109
• 1 <= timei <= 105
• k is in the range [The maximum UAM for a user, 105].
## Solution: Hashsets in a Hashtable
key: user_id, value: set{time}
Time complexity: O(n + k)
Space complexity: O(n + k)
## C++
Given a string s, return the number of homogenous substrings of s. Since the answer may be too large, return it modulo 109 + 7.
A string is homogenous if all the characters of the string are the same.
substring is a contiguous sequence of characters within a string.
Example 1:
Input: s = "abbcccaa"
Output: 13
Explanation: The homogenous substrings are listed as below:
"a" appears 3 times.
"aa" appears 1 time.
"b" appears 2 times.
"bb" appears 1 time.
"c" appears 3 times.
"cc" appears 2 times.
"ccc" appears 1 time.
3 + 1 + 2 + 1 + 3 + 2 + 1 = 13.
Example 2:
Input: s = "xy"
Output: 2
Explanation: The homogenous substrings are "x" and "y".
Example 3:
Input: s = "zzzzz"
Output: 15
Constraints:
• 1 <= s.length <= 105
• s consists of lowercase letters.
Solution: Counting
Let m be the length of the longest homogenous substring, # of homogenous substring is m * (m + 1) / 2.
e.g. aaabb
“aaa” => m = 3, # = 3 * (3 + 1) / 2 = 6
“bb” => m = 2, # = 2 * (2+1) / 2 = 3
Total = 6 + 3 = 9
Time complexity: O(n)
Space complexity: O(1)
## C++
You are given a string s consisting only of the characters '0' and '1'. In one operation, you can change any '0' to '1' or vice versa.
The string is called alternating if no two adjacent characters are equal. For example, the string "010" is alternating, while the string "0100" is not.
Return the minimum number of operations needed to make s alternating.
Example 1:
Input: s = "0100"
Output: 1
Explanation: If you change the last character to '1', s will be "0101", which is alternating.
Example 2:
Input: s = "10"
Output: 0
Example 3:
Input: s = "1111"
Output: 2
Explanation: You need two operations to reach "0101" or "1010".
Constraints:
• 1 <= s.length <= 104
• s[i] is either '0' or '1'.
## Solution: Two Counters
The final string is either 010101… or 101010…
We just need two counters to record the number of changes needed to transform the original string to those two final strings.
Time complexity: O(n)
Space complexity: O(1)
## C++
You are given a string s of even length. Split this string into two halves of equal lengths, and let a be the first half and b be the second half.
Two strings are alike if they have the same number of vowels ('a''e''i''o''u''A''E''I''O''U'). Notice that s contains uppercase and lowercase letters.
Return true if a and b are alike. Otherwise, return false.
Example 1:
Input: s = "book"
Output: true
Explanation: a = "bo" and b = "ok". a has 1 vowel and b has 1 vowel. Therefore, they are alike.
Example 2:
Input: s = "textbook"
Output: false
Explanation: a = "text" and b = "book". a has 1 vowel whereas b has 2. Therefore, they are not alike.
Notice that the vowel o is counted twice.
Example 3:
Input: s = "MerryChristmas"
Output: false
Example 4:
Input: s = "AbCdEfGh"
Output: true
Constraints:
• 2 <= s.length <= 1000
• s.length is even.
• s consists of uppercase and lowercase letters.
## Solution: Counting
Time complexity: O(n)
Space complexity: O(1)
## Python3
You are given a binary string binary consisting of only 0‘s or 1‘s. You can apply each of the following operations any number of times:
• Operation 1: If the number contains the substring "00", you can replace it with "10".
• For example, "00010" -> "10010
• Operation 2: If the number contains the substring "10", you can replace it with "01".
• For example, "00010" -> "00001"
Return the maximum binary string you can obtain after any number of operations. Binary string x is greater than binary string y if x‘s decimal representation is greater than y‘s decimal representation.
Example 1:
Input: binary = "000110"
Output: "111011"
Explanation: A valid transformation sequence can be:
"000110" -> "000101"
"000101" -> "100101"
"100101" -> "110101"
"110101" -> "110011"
"110011" -> "111011"
Example 2:
Input: binary = "01"
Output: "01"
Explanation: "01" cannot be transformed any further.
Constraints:
• 1 <= binary.length <= 105
• binary consist of '0' and '1'.
## Solution: Greedy + Counting
Leading 1s are good, no need to change them.
For the rest of the string
1. Apply operation 2 to make the string into 3 parts, leading 1s, middle 0s and tailing 1s.
e.g. 11010101 => 11001101 => 11001011 => 11000111
2. Apply operation 1 to make flip zeros to ones except the last one.
e.g. 11000111 => 11100111 => 11110111
There will be only one zero (if the input string is not all 1s) is the final largest string, the position of the zero is leading 1s + zeros – 1.
Time complexity: O(n)
Space complexity: O(n) |
Math Help - Primitive Roots
1. Primitive Roots
I have this problem here, and I can't seem to figure out how to do it.
"Suppose that a (mod p) is a primitive root modulo an odd prime p. If p=3(mod4) is prime, then show that -a(mod p) is never a primitive root modulo p."
Is the proper way to go about this by somehow using the legendre symbol? Or Eulers Criterion? I'm pretty confused.
2. I am sorry. Let me explain better. But that link provides an excellent hint to this problem.
I am really not careful in the second to last line it should be a^{(p-1)/2} = -1 (mod p) instead. |
blob: 436cf255b082e424fc408f7820f455b97e601574 [file] [log] [blame]
N4JS Design Specification
4. Tips and Tricks
In this chapter we collect some coding hints and guidelines on how to properly use the APIs of Eclipse, EMF, Xtext and other dependencies we are using, as well as our own utilities and helpers.
This chapter is only about coding; add information on things like Eclipse setup or Maven/Jenkins to one of the preceding chapters. Similarly, this chapter is intended to provide just a quick overview, check-list and reminder; add detailed information and diagrams to one of the succeeding chapters.
4.1. Naming
• The internal handling of N4JS project names is non-trivial (due to the support for npm scopes), see API documentation of ProjectDescriptionUtils#isProjectNameWithScope(String) for a detailed overview. In short:
• IN4JSProject#getProjectName() and IProject#getName() return different values!
• Avoid using the Eclipse project name, i.e. the return value of IProject#getName(), as far as possible (only use it in UI code when actually dealing with what is shown in the Eclipse UI).
• The last segment of an URI or path pointing to an N4JS project is not always the project name; use utilities in ProjectDescriptionUtils instead, e.g. #deriveN4JSProjectNameFromURI()! (However, given an URI or path pointing to a file inside an N4JS project, you can use its last segment to obtain the file name.)
4.2. Logging
In many situations developer needs to use some kind of logging. When in need, follow these rules:
1. Use org.apache.log4j.Logger; for logging. Other logging utilities (like java built in logger) are not configured.
2. do not use System.out nor Sysetem.err for logging. It is ok to use it for debugging purposes, but those calls should never be merged to master. (with exception of headless compiler, which uses them explicitly)
3. There is central logger configuration in org.eclipse.n4js.utils.logging (and org.eclipse.n4js.utils.logging) that should be used
1. log4j.xml used for production
2. log4j_tests.xml used when running tests
4. in Eclipse run configurations logger has to be set properly, e.g. log4j.configuration=file:${workspace_loc:org.eclipse.n4js.utils.logging/log4j_tests.xml} 5. in maven configurations logger has to be set separately, e.g. -Dlog4j.configuration="file:${basedir}/../../plugins/org.eclipse.n4js.utils.logging/log4j_tests.xml
4.3. Cancellation Handling
At various occasions, Xtext provides an instance of class CancelIndicator to allow our code to handle cancellation of long-running task.
Some things to keep in mind:
• whenever a CancelIndicator is available any code that might not return immediately should implement proper cancellation handling (as explained in the next items).
• most importantly: reacting to a cancellation by returning early from a method is an anti-pattern that leads to problems (client code might continue work on a canceled and thus invalid state); instead: throw an OperationCanceledException!
• don’t use CancelIndicator#isCanceled() for cancellation handling, except in certain special cases. A valid exception case might be during logging to show a message like "operation was canceled".
• instead, inject the Xtext service called OperationCanceledManager and invoke its method #checkCanceled(), passing-in the cancel indicator (this method is null-safe; it will throw an OperationCanceledException in case a cancellation has occurred). Don’t directly create and throw an OperationCanceledException yourself.
• use the other methods provided by OperationCanceledManager when appropriate (see code of that class for details).
• in try/catch blocks, when catching exceptions of a super type of OperationCanceledException, be sure to not suppress cancellation exceptions. For example:
// Java code
@Inject private OperationCanceledManager operationCanceledManager;
/** Returns true on success, false otherwise. */
public boolean doSomething(CancelIndicator ci) {
try {
// do something that might be canceled
return true;
} catch(Exception e) {
operationCanceledManager.propagateIfCancelException(e); // <- IMPORTANT!
return false;
}
}
Try/finally blocks, on the other hand, do not need any special handling.
• a cancel indicator can also be stored in the rule environment (see RuleEnvironmentExtensions#addCancelIndicator()). This means:
• if you create a rule environment completely from scratch and you have a cancel indicator at hand, add it to the rule environment via RuleEnvironmentExtensions#addCancelIndicator() (not required when using RuleEnvironmentExtensions#wrap() for deriving a rule environment from an existing one).
• if you have a rule environment available, be sure to use its cancel indicator in long-running operations, i.e. with code like:
// Xtend code
import static extension org.eclipse.n4js.typesystem.utils.RuleEnvironmentExtensions.*
class C {
@Inject private OperationCanceledManager operationCanceledManager;
def void doSomething() {
for(a : aLotOfStuff) {
operationCanceledManager.checkCanceled(G.cancelIndicator);
// main work ...
}
}
4.4. Caching
• Caching of external libraries (implemented in ExternalProjectMappings)
• update only using EclipseExternalLibraryWorkspace#updateState()
• always mind that the diff of current state and cached state is a necessary information for cleaning dependencies of removed npms
• see EclipseExternalIndexSynchronizer#synchronizeNpms() for implementation
• updating also happens when external root locations change (see ExternalIndexUpdater)
• Caching of user workspace projects (implemented in MuliCleartriggerCache)
• caches only some project information and should be refactored along with Core, Model and EclipseBasedN4JSWorkspace
4.5. Dependency Injection
There are some things to keep in mind when using dependency injection in the context of Xtext. This is a longer topic and it is discussed in the appendix Xtext Injection.
4.6. Miscellaneous
• Resource load states: when an N4JS/N4JSD file is loaded, a certain sequence of processing is triggered (parsing, linking, validation, etc.) and thus an N4JSResource transitions through a sequence of "load states". For details, see N4JS Resource Load States. |
### Help Support The Rocketry Forum:
#### Fore Check
##### Well-Known Member
Is this a good pad? Is it durable and have good features? How much are they really worth as an individual item?
Likewise, how much is the AT Interlock controller worth?
Thanks.
#### BlueNinja
##### Well-Known Member
The mantis is OK, i think the leg attachment points are weak (dont hit teh legs on anything) and since AT wants $99 or so for it, I say get a better pad. The interlock is pretty easy to assemble, and it goes for$50 or so. Again, you could scratchbuild a better one for about 20% of the cost.
#### vjp
##### Well-Known Member
I have both. The Mantis pad is "o.k.", but too fragile and wobbly. Build yourself a better one from PVC and misc. hardware, you'll save lots of money and the result will be much more durable.
The launch controller is better, but again, you can make your own from plans, parts will cost about $25 (if that) at Radio Shack. #### JStarStar ##### Well-Known Member TRF Supporter I never have really understood what's the function of that kind-of S-shaped goose-neck thing on the Mantis pad ... looks to me the main result would be to make it wobbly and unstable and more prone to tipping over if you have a heavy rocket on the rod... I have an Estes Porta-Pad E which serves me well - you can easily switch rods from 1/8 to 3/16 to 1/4 depending on the model you're launching, just a few twists on a wing nut and you're good to go. It's also made out of molded plastic and I wouldn't want to see what happens, for example, if somebody accidentally steps on one leg. As Blue_Ninja and vjp say, I think you can probably make a better one yourself, several threads here in this forum have discussed DIY pads made out of PVC piping that look pretty good. The PVC pads also look tougher and probably more resistant to inadvertent damage. Heck, if you want, you could make a pad out of 1 1/2" or 2" PVC that you could probably drive a truck into without damaging too much. I've also seen a lot of people convert photo tripods to launch pads - those look pretty cool and they're also a little higher off the ground so you don't have to crawl around in the weeds to hook up igniter leads ... #### r1dermon ##### Well-Known Member yeah, i've seen those old drum stands used as launch pads, those are pretty durable. the main complaint with the mantis is the poor legs. PVC is a lot cheaper than 99 bucks. #### OKTurbo ##### Well-Known Member TRF Supporter The leg attachments on the Mantis pad are the weak link. I've seen several that are broken. I've had good luck with my Holverson "Slider" pad. www.jonrocket.com had these for sale at one time. It would be easy to "clone" this pad, but for the price, I didn't bother. It comes with 1/8, 3/16, and 1/4" rods. #### rabidsheeep ##### Well-Known Member mine is just a cheap tripod, a quarter inch rod, and a garbage pail that i tore apart to use as a blast plate if i just roll some tape or paper around the base of a 3/16" rod then i can put it in the 1/4 slot and it works fine #### Stymye ##### Well-Known Member The "S" shape puts the rocket back over the center of gravity of the pad I mounted a drill chuck on mine so I can swap out rods in a flash I use mine for all of my local launches and it has served me well for 4 years so far. It's not something you want to toss around and you do have to be carefull not to step on the legs.but If you find a really good deal for one ,like on ebay or somewhere, go for it. #### Hospital_Rocket ##### Well-Known Member I've smashed the leg mounts on 2 of these things. the leftover legs make nice pad standoffs. For what AT wants for them, they are definitely not, IMHO, anything approaching a value. The interlock controller is nice, however as said above, you can build the functional equivalent for a fraction of the price. I have the one that came with my Initiator startup kit and find it dependable and easy to use. A #### Fore Check ##### Well-Known Member I should have added that I now own both the controller and the pad (I got an Initiator starter set, that was clearance priced, for 1/2 off at Hobby Lobby for a total of$47.50)
I own an AWESOME launcher, the Pratt SureFire2 system, and have no use for the Interlock controller. I was more curious as to it's eBay value.
The pad, however, I'm intrigued by. I normally use an Estes Porta Pad for 1/8" and and Estes Porta Pad "E" for 3/16 and 1/4". I'm not to happy with the functionality on 1/4" rod sized rockets, and was considering building the Mantis for use strictly on 1/4" rod sized rockets (so I'd bring all 3 pads to a given launch, if I brought an appropriate assortment of rockets.)
How would you compare the durability issue of the Mantis to the durability of the Estes porta pads? I've had fine luck with the Estes pads. |
# source:docs/Working/icGrep/evaluation.tex@4782
Last change on this file since 4782 was 4782, checked in by cameron, 4 years ago
Figure placement according to Springer
File size: 12.3 KB
Line
1\section{Evaluation}\label{sec:evaluation}
2
3\def\AN{A.N.}
4
5In this section, we report on the evaluation of \icGrep{} performance, looking at three aspects.
6First, we discuss some performance aspects of \icGrep{} internal methods, looking at the impact of optimizations discussed previously.
7Then we move on to a systematic performance study of \icGrep{} with named Unicode property searches in comparison to two contemporary competitors,
8namely, pcre2grep released in January 2015 and ugrep of the ICU 54.1 software distribution.
9Finally, we examine complex expressions and the impact of multithreading \icGrep{} on an
10Intel i7-2600 (3.4GHz) and i7-4700MQ (2.4GHz) processor.
11
12\subsection{Optimizations of Bitwise Methods}
13
14In order to support evaluation of bitwise methods, as well as to support
15the teaching of those methods and ongoing research, \icGrep{} has an array
16of command-line options. This makes it straightforward
17to report on certain performance aspects of \icGrep{}, while others require
18special builds.
19
20For example, the command-line switch \texttt{-disable-matchstar} can be used
21to eliminate the use of the MatchStar operation for handling
22Kleene-* repetition of character classes. In this case, \icGrep{} substitutes
23a while loop that iteratively extends match results.
24Surprisingly, this
25does not change performance much in many practical cases.
26In each block,
27the maximum iteration count is the maximum length run encountered; the
28overall performance is based on the average of these maxima throughout the
29file. But when search for XML tags using the regular expression
30\verb:<[^!?][^>]*>:, a slowdown of more than 2$\times$ may be found in files
31with many long tags.
32
33In order to short-circuit processing when no remaining matches
34are possible in a block, our regular expression compiler periodically inserts
35if-statements to check whether there are any marker bits still in play.
36To control this feature in dynamically
37generated code, the number of pattern elements between each if-test %non-nullable
38can be selected with the {\tt -if-insertion-gap=} option.
39The default value in \icGrep{} is 3; setting the gap to 100 effectively
40turns off if-insertion.
41Eliminating if-insertion sometimes improves performance by avoiding the extra if tests and branch mispredictions.
42For patterns with long strings, however, there can be a substantial slowdown.
43
44
45The precompiled calculations of the various Unicode properties
46are each placed in if-hierarchies as described previously. To assess the
47impact of this strategy, we built a version of icGrep without such
48if-hierarchies. In this case, when a Unicode property class is defined,
49bitwise logic equations are applied for all members of the class independent
50of the Unicode blocks represented in the input document. For the classes
51covering the largest numbers of codepoints, we observed slowdowns of up to 5$\times$.
52
53\subsection{Simple Property Expressions}
54
55A key feature of Unicode level 1 support in regular expression engines
56the support that they provide for property expressions and combinations of property expressions
57using set union, intersection and difference operators. Both {\tt ugrep}
58and {\tt icgrep} provide systematic support for all property expressions
59at Unicode Level 1 as well as set union, intersection and difference.
60Unfortunately, {\tt pcre2grep} does not support the set intersection and difference operators directly.
61However, these operators can be expressed using a regular expression
62feature known as a lookbehind assertion. Set intersection involves a
63regular expression formed with a one of the property expressions and a
64positive lookbehind assertion on the other, while set difference uses
65a negative lookbehind assertion.
66
67We generated a set of regular expressions involving all Unicode values of
68the Unicode general category property ({\tt gc}) and all values of the Unicode
69script property ({\tt sc}).
70We then generated
71expressions involving random pairs of {\tt gc} and {\tt sc}
72values combined with a random set operator chosen from union, intersection and difference.
73All property values are represented at least once.
74A small number of
75expressions were removed because they involved properties not supported by pcre2grep.
76In the end 246 test expressions were constructed in this process.
77
78We selected a set of Wikimedia XML files in several major languages representing
79most of the world's major language families as a test corpus.
80For each program under test, we performed searches for each regular expression against each XML document.
81Performance is reported in CPU cycles per byte on an Intel i7-2600 machine.
82The results are presented in Fig.~\ref{fig:property_test}.
83They were ranked by the percentage of matching lines found in the XML document and grouped in 5\% increments.
84When comparing the three programs, \icGrep{} exhibits dramatically better performance, particularly when searching for rare items.
85The performance of both pcre2grep and ugrep improves (has a reduction in CPU cycles per byte) as the percentage of matching lines increases.
86This occurs because each match allows them to bypass processing the rest of the line.
87On the other hand, \icGrep{} shows a slight drop-off in performance with the number of matches found.
88This is primarily due to property classes that include large numbers of codepoints.
89These classes require more bitstream equations for calculation and also have a greater probability of matching.
90Nevertheless, the performance of \icGrep{} in matching the defined property expressions is stable and well ahead of the competitors in all cases.
91
92\begin{figure}
93\vspace{-0.5em}
94\begin{center}
98
99\begin{tikzpicture}
100\begin{axis}[
101grid=both,
102x tick label style={ /pgf/number format/1000 sep=},
103ylabel={CPU Cycles Per Byte},
104xlabel={Percentage of Matching Lines},
105minor y tick num={1},
106xmax=100,
107height=0.5\textwidth,
108legend style={at={(1.05,0.5)},
109anchor=west,legend columns=1,
110align=left,draw=none,column sep=2ex}
111]
115\legend{icGrep,ugrep541,pcre2grep}
116\end{axis}
117\end{tikzpicture}
118\end{center}
119\vspace{-1em}
120\caption{Matching Performance for Simple Property Expressions}\label{fig:property_test}
121\vspace{-0.5em}
122\end{figure}
123
124\subsection{Complex Expressions}
125
126This study evaluates the comparative performance of the matching engines on a
127series of more complex expressions, shown in Table \ref{table:regularexpr}.
128The first two are alphanumeric (\AN{}) expressions, differing only in that the first
129one is anchored to match the entire line.
130The third searches for lines consisting of text in Arabic script.
131The fourth expression is a published currency expression taken from
132Stewart and Uckelman~\cite{stewart2013unicode}.
133An expression matching runs of six or more Cyrillic script characters enclosed
134in initial/opening and final/ending punctuation is fifth in the list.
135The final expression is an email expression that allows internationalized names.
136
137\begin{table}\centering % requires booktabs
138\small\vspace{-2em}
139\begin{tabular}{@{}p{2cm}p{9.8cm}@{}}
140\textbf{Name}&\textbf{Regular Expression}\\
141\toprule
142\AN{} \#1&\lstinline^[\p{L}\p{N}]*((\p{L}\p{N})|(\p{N}\p{L}))[\p{L}\p{N}]*$\\ 143\midrule 144\AN{} \#2&\lstinline[\p{L}\p{N}]*((\p{L}\p{N})|(\p{N}\p{L}))[\p{L}\p{N}]*\\ 145\midrule 146Arabic&\lstinline^[\p{Arabic}\p{Common}]*\p{Arabic}[\p{Arabic}\p{Common}]*$\\
147\midrule
148Currency&\lstinline(\p{Sc}\s*(\d*|(\d{1,3}([,.]\d{3})*))([,.]\d{2}?)?)|\\
149&\lstinline((\d*|(\d{1,3}([,.]\d{3})*))([,.]\d{2}?)?\s*\p{Sc})\\
150\midrule
151Cyrillic&\lstinline[\p{Pi}\p{Po}]\p{Cyrillic}{6,}[\p{Pf}\p{Pe}]\\
152\midrule
153Email &\lstinline([^\p{Z}<]+@[\p{L}\p{M}\p{N}.-]+\.(\p{L}\p{M}*){2,6})\\
154&\lstinline(>|\p{Z}|$)\\ 155\bottomrule 156\end{tabular} 157\caption{Regular expressions}\label{table:regularexpr} 158\vspace{-2em} 159\end{table} 160 161In Table \ref{table:complexexpr}, we show the performance results obtained 162from an Intel i7-2600 using generic 64-bit binaries for each engine. 163We limit the SIMD ISA within \icGrep{} to SSE2 which is available 164on all Intel/AMD 64-bit machines. 165In each case, we report seconds taken per GB of input averaged over 10 166runs each on our Wikimedia document collection. 167 168\begin{table}[ht]\centering % requires booktabs 169\newcolumntype{T}{c} 170\small\vspace{-2em} 171\begin{tabular}{@{}p{2cm}r@{~--~}rp{4pt}r@{~--~}rp{4pt}r@{~--~}rp{4pt}r@{~--~}rp{4pt}@{}} 172&\multicolumn{6}{c}{\textbf{\icGrep{}}}\\ 173\cmidrule[1pt](lr){2-7} 174\cmidrule[1pt](lr){8-10} 175\cmidrule[1pt](lr){11-13} 176\textbf{Expression}&\multicolumn{3}{T}{\textbf{SEQ}}&\multicolumn{3}{T}{\textbf{MT}}&\multicolumn{3}{T}{\textbf{pcre2grep}}&\multicolumn{3}{T}{\textbf{ugrep541}}\\ 177\toprule 178\AN{} \#1&2.4&5.0&&2.1&4.4&&8.2&11.3&&8.8&11.3&\\ 179\AN{} \#2&2.3&4.9&&2.0&4.1&&209.9&563.5&&182.3&457.9&\\ 180Arabic&1.5&3.4&&1.2&2.6&&7.5&270.8&&8.9&327.8&\\ 181Currency&0.7&2.1&&0.4&1.4&&188.4&352.3&&52.8&152.8&\\ 182Cyrillic&1.6&3.9&&1.3&2.8&&30.5&49.7&&11.2&20.1&\\ 183Email&3.0&6.9&&2.7&6.4&&67.2&1442.0&&108.8&1022.3&\\ 184\bottomrule 185\end{tabular} 186\caption{Matching times for complex expressions (s/GB)}\label{table:complexexpr} 187\vspace{-2em} 188\end{table} 189 190The most striking aspect of Table \ref{table:complexexpr} is that both ugrep and pcregrep 191show dramatic slowdowns with ambiguities in regular expressions. 192This is most clearly illustrated in the different performance figures 193for the two Alphanumeric test expressions but is also evident in the 194Arabic, Currency and Email expressions. 195Contrastingly, \icGrep{} maintains consistently fast performance in all test scenarios. 196The multithreaded \icGrep{} shows speedup in every case but balancing 197of the workload across multiple cores is clearly an area for further work. 198Nevertheless, our three-thread system shows up to a 40\% speedup. % over the single threaded version 199 200Table \ref{table:relperf} shows the speedups obtained with \icGrep{} 201on a newer Intel i7-4700MQ machine, considering three SIMD ISA alternatives 202and both single-threaded and multi-threaded versions. 203All speedups are relative to the base single-threaded SSE2 performance on this machine, 204which is given in seconds per GB in the first column. 205The SSE2 results are again using the generic binaries compiled for compatibility 206with all 64-bit processors. 207The AVX1 results are for Intel AVX instructions 208in 128-bit mode. The main advantage of AVX1 over SSE2 is its support for 3-operand form, 209which helps reduce register pressure. The AVX2 results are for \icGrep{} 210compiled to use the 256-bit AVX2 instructions, processing blocks of 256 bytes at a time. 211 212\begin{table}[h]\centering % requires booktabs,siunitx 213\small\vspace{-2em} 214\begin{tabular}{@{}p{2cm}l@{~}r@{~~}l@{~}r@{~~}l@{~}r@{~~}l@{~}r@{~~}l@{~}r@{~~}l@{~}r@{~~}@{}} 215&\multicolumn{2}{c}{\textbf{Base}}&\multicolumn{4}{c}{\textbf{SEQ}}&\multicolumn{6}{c}{\textbf{MT}}\\ 216\cmidrule[1pt](lr){2-3} 217\cmidrule[1pt](lr){4-7} 218\cmidrule[1pt](lr){8-13} 219\textbf{Expression}&\multicolumn{2}{c}{\textbf{s/GB}}&\multicolumn{2}{c}{\textbf{AVX1}}&\multicolumn{2}{c}{\textbf{AVX2}}&\multicolumn{2}{c}{\textbf{SSE2}}&\multicolumn{2}{c}{\textbf{AVX1}}&\multicolumn{2}{c}{\textbf{AVX2}}\\ 220\toprule 221\AN{} \#1&2.76&(.65)&1.05&(.03)&1.25&(.08)&1.18&(.02)&1.19&(.03)&1.59&(.10)\\ 222\AN{} \#2&2.69&(.66)&1.05&(.02)&1.36&(.09)&1.20&(.03)&1.19&(.04)&1.80&(.11)\\ 223Arabic&1.82&(.39)&1.05&(.03)&1.15&(.08)&1.37&(.03)&1.37&(.04)&1.66&(.10)\\ 224Currency&1.04&(.30)&1.03&(.02)&1.04&(.06)&1.59&(.15)&1.61&(.14)&1.78&(.21)\\ 225Cyrillic&2.10&(.44)&1.06&(.02)&0.96&(.06)&1.27&(.02)&1.33&(.04)&1.23&(.09)\\ 226Email&3.57&(.87)&1.05&(.03)&1.37&(.14)&1.13&(.03)&1.16&(.04)&1.67&(.18)\\ 227\midrule 228\textit{Geomean}&\multicolumn{2}{c}{--}&1.04&&1.18&&1.28&&1.30&&1.61&\\ 229\bottomrule 230\end{tabular} 231\caption{Speedup of complex expressions on i7-4700MQ$(\sigma)\$}\label{table:relperf}
232\vspace{-2em}
233\end{table}
234
235In each case, the use of three-operand form with AVX1 confers a slight
236speedup. The change to use 256 bits with AVX2 gives a further overall improvement,
237but some mixed results due to the limitations of 256 bit addition. Combining
238the AVX2 ISA with multithreading gives and average overall 61\% speedup compared to base.
Note: See TracBrowser for help on using the repository browser. |
## Q. 7.PS.12
Trends in Ionic Sizes
For each of these pairs, choose the smaller atom or ion:
(a) A $Cu$ atom or a $Cu^{2+}$ ion
(b) A $Se$ atom or a $Se^{2-}$ ion
(c) A $Cu^+$ ion or a $Cu^{2+}$ ion
## Verified Solution
(a) $Cu^{2+}$ ion (b) $Se$ atom (c) $Cu^{2+}$ ion
Strategy and Explanation Consider the differences in the sizes of atoms and their corresponding ions based on electron loss or gain.
(a) A cation is smaller than its parent atom; therefore, $Cu^{2+}$ is smaller than a $Cu$ atom.
(b) Anions are larger than their parent atoms, so a $Se^{2-}$ ion is larger than a selenium atom.
(c) Both copper ions contain 26 protons, but $Cu^{2+}$ has one fewer electron than does $Cu^+$.
Correspondingly, the radius of $Cu^{2+}$ is smaller than that of $Cu^+$. |
Test your understanding of the topic with Sphere Question Answers with step-by-step solutions with tricks and shortcuts. These Sphere Objective Questions are framed according to the latest trends as per the curriculum and covers chapter-wise questions of the topic. Study the topic with a complete Sphere MCQ Quiz question bank and ace the topic with 100% accuracy. Candidates can also check out the app to help them with their preparations.
0.1 per cent of 1.728 × 106 spherical droplets of water, each of diameter 2 mm, coalesce to form a spherical bubble. What is the diameter (in cm) of the bubble?
1. 1.2
2. 1.6
3. 1.8
4. 2.4
Option 4 : 2.4
Sphere MCQ Question 1 Detailed Solution
Calculation:
Total small droplets coalesced to form big bubble = 0.1% of 1.728 × 106
= 1728
Let the radius of big bubble be R mm
$$1728 × \frac{4}{3} × \pi × {\left( {\frac{2}{2}} \right)^3} = \frac{4}{3} × \pi × {R^3}$$
⇒ R3 = 1728
⇒ R = 12 mm or 1.2 cm
⇒ Diameter = 2 × R = 2 × 1.2 = 2.4 cm
A metallic solid cuboid of sides 44 cm, 32 cm and 36 cm melted and converted into some number of spheres of radius 12 cm. How many such sphere can be made with the metal (π = 22/7)?
1. 5
2. 6
3. 7
4. 8
Option 3 : 7
Sphere MCQ Question 2 Detailed Solution
Given:
The sides of the cuboid are 44 cm, 32 cm, and 36 cm
The radius of the sphere is 12 cm
Concept Used:
The volume of a cuboid of sides l, b and h = l × b × h
The volume of the sphere of radius r = (4/3)πr3
Calculation:
The volume of the metallic cuboid is (44 × 32 × 36) cm3
The volume of the sphere is (4/3) × π × 123
Let, the total number of such sphere is n
Accordingly,
44 × 32 × 36 = n × (4/3) × π × 123
⇒ 44 × 32 × 36 = n × (4/3) × (22/7) × 12 × 12 × 12
⇒ n = 44 × 32 × 36 × (3/4) × (7/22) × (1/12) × (1/12) × (1/12)
⇒ n = 7
Such 7 spheres can be made by given metallic cuboid.
If the volume of a sphere is 67375/3 cm3, then its surface area (in cm2) is∶ (Take π = 22/7)
1. 3750
2. 3225
3. 3740
4. 3850
Option 4 : 3850
Sphere MCQ Question 3 Detailed Solution
Volume of sphere = (4/3) × πr3
(4/3) × (22/7) × r3 = 67375/3
⇒ r3 = (67375 × 7 × 3) / (3 × 4 × 22)
⇒ r = ∛(35 × 35 × 35) / (2 × 2 × 2)
⇒ r = 35/2
Surface area of sphere = 4 πr2 = 4 × (22/7) × (35/2) × (35/2) = 3850
How many balls of radius 3 cm can be made by melting a big ball whose radius is 6 cm.
1. 8
2. 4
3. 12
4. 16
Option 1 : 8
Sphere MCQ Question 4 Detailed Solution
Given:
Radius of big ball, R = 6 cm
Radius of small ball, r = 3 cm
Concept used:
Volume of sphere = (4/3)πr3
Calculation:
Volume of a small ball = (4/3)π × (3)3
Volume of big ball = (4/3)π × (6)3
Required number of balls = (Volume of big ball)/(Volume of small ball)
⇒ [(4/3)π × (6)3]/[(4/3)π × (3)3]
⇒ 8 balls
∴ The number of balls that can be made is 8.
Important Points
Surface area of sphere = 4πr2
Volume of hollow sphere = [(4/3)π(R3 - r3)] cubic units
The surface area of a sphere is 5544 cm2. The volume of the sphere would be?
1. 38804 cm3
2. 38808 cm3
3. 38818 cm3
4. 38898 cm3
Option 2 : 38808 cm3
Sphere MCQ Question 5 Detailed Solution
GIVEN:
Surface area of sphere = 5544 cm2
FORMULA USED:
Surface area of sphere = 4πr2
Volume of sphere = (4/3)πr3
CALCULATION:
A.T.Q
4πr2 = 5544
r2 = 5544/4 × 7/22
r2 = 63 × 7 = 441
r = 21 cm
Volume = (4/3) × (22/7) × 21 × 21 × 21
Volume = 88 × 21 × 21 = 38808 cm3
Volume of the sphere would be 38808 cm3
As we used π = 22/7 the answer must be divisible by 11
In options, only 38808 is divisible by 11
Volume of the sphere would be 38808 cm3
Total surface area of a sphere is 324π cm2, then find 2/3rd volume of sphere.
1. 920π cm3
2. 1020π cm3
3. 972π cm3
4. 648π cm3
Option 4 : 648π cm3
Sphere MCQ Question 6 Detailed Solution
Given:
Total surface area of sphere = 324π
Formula:
Total surface area of sphere = 4πr2
Volume of sphere = (4/3)πr3
Calculation:
According to the question
4πr2 = 324π
⇒ r2 = 324/4
⇒ r2 = 81
⇒ r = 9
Volume of sphere = (4/3) πr3
⇒ (4/3) × π × 9 × 9 × 9
⇒ 972π cm3
∴ 2/3rd volume of sphere = 972π × (2/3) = 648π cm3
A hollow sphere of outer curved surface area of 324π cm2 is made from 684π cm3 of metal. Find the thickness of the hollow sphere.
1. 2 cm
2. 3 cm
3. 4 cm
4. 5 cm
Option 2 : 3 cm
Sphere MCQ Question 7 Detailed Solution
Let the outer and the inner radii of the sphere be ‘R’ cm and ‘r’ cm respectively.
∵ Curved surface area of sphere = 4π × (radius)2
⇒ 4πR2 = 324π
⇒ R2 = 81
⇒ R = √81 = 9 cm
Now,
Volume of metal used = Volume of outer sphere – Volume of inner sphere
∵ Volume of sphere = 4/3 × π × (radius)3
⇒ 684π = 4/3 × πR3 – 4/3 × πr3
⇒ 3/4 × 684 = (9)3 – r3
⇒ r3 = 729 – 513 = 216
⇒ r = 6 cm
∴ Thickness of hollow sphere = R – r = 9 – 6 = 3 cm
The radius of a solid sphere of a metal is 15 cm. How long wire of diameter 4 cm can be drawn from it?
1. 1125 cm
2. 1025 cm
3. 225 cm
4. 75 cm
Option 1 : 1125 cm
Sphere MCQ Question 8 Detailed Solution
Given:
The radius of a solid sphere = 15 cm
Diameter of wire = 4 cm
Formula Used:
Volume of Sphere = (4/3)πr3
Wire is in the form of cylinder,
Volume of Cylinder = πRH,
Calculation:
According to the question,
⇒ Volume of sphere = Volume of wire
⇒ π × (4/3) × 15 × 15 × 15 = π × 2 × 2 × H
⇒ H = 15 × 15 × 5 = 1125 cm
∴ The length of wire is 1125 cm.
If 3 small spherical balls having radius 3 cm, 4 cm, and 5 cm melt together to form a big spherical ball. What is the radius of big spherical ball?
1. 8 cm
2. 7 cm
3. 6 cm
4. 9 cm
Option 3 : 6 cm
Sphere MCQ Question 9 Detailed Solution
Given:
Radius of 3 small spherical balls are 3 cm, 4 cm and 5 cm respectively.
Concept used:
Volume of 3 small spherical melted balls = Volume of 1 big spherical ball
Formula used:
Volume of sphere = (4/3) × π × r3
where,
Calculations:
Volume of sphere = (4/3) × π × r3
Volume of first small ball = (4/3) × π × (3)3
⇒ (4/3) × π × 27
⇒ 36π cm3
Volume of second small ball = (4/3) × π × (4)3
⇒ (4/3) × π × 64
⇒ 256π/3 cm3
Volume of third small ball = (4/3) × π × (5)3
⇒ (4/3) × π × 125
⇒ 500π/3 cm3
Volume of big ball = (4/3) × π × R3
Total volume of small balls = 36π + (256π/3) + (500π)/3
⇒ (108π + 256π + 500π)/3
⇒ 864π/3
⇒ 288π cm3
Volume of 3 small spherical melted balls = Volume of 1 big spherical ball
⇒ 288π = (4/3) × π × R3
⇒ R3 = 216
⇒ R = ∛216
⇒ R = 6 cm
∴ The radius of big spherical ball is 6 cm.
If the volume of hemisphere is 4 times the volume of sphere Find the ratio of radii of sphere and hemisphere.
1. 1 : 9
2. 1 : 8
3. 1 : 2
4. 6 : 7
Option 3 : 1 : 2
Sphere MCQ Question 10 Detailed Solution
Given
Volume of hemisphere = 4 × volume of sphere
Formula used
Volume of hemisphere = (2/3)πR3
Volume of sphere = (4/3)πr
Calculation
(2/3)πR3 = 4 × (4/3)× π × r3
Where R and r radius of hemisphere and sphere
R3/r3 = (16/2)
⇒ R3/r3 = 8/1
⇒ R/r = 2/1
⇒ r/R = 1 : 2
∴ Ratio of radii of sphere and hemisphere is 1 : 2.
Three spherical balls of radius 9 cm, 12 cm and 15 cm are melted to form a new spherical ball. What is the radius (in cm) of the new ball?
1. 17 cm
2. 28 cm
3. 18 cm
4. 16 cm
Option 3 : 18 cm
Sphere MCQ Question 11 Detailed Solution
Given:
Three spherical balls of radius 9 cm, 12 cm and 15 cm are melted to form a new spherical ball.
Formula used:
The volume of a sphere = (4/3)πr3
Where r → radius of the sphere
Calculations:
The sum of the volume of the three balls = (4/3)π{(9)3 +(12)3 +(15)3}
⇒ (4/3)π (3)3{(3)3 + (4)3 + (5)3}
⇒ (4π/3) × 27 × 216
Let the radius of the new sphere be 'r'.
So, (4/3)πr3 = (4π/3) × 27 × 216
⇒ r3 = 27 × 216
⇒ r = 3 × 6 cm
⇒ r = 18 cm
∴ The radius of the new ball 18 cm.
The surface areas of two spheres are in the ratio of 9 : 4. The ratio of their volume are
1. 3 : 2
2. 27 : 8
3. 81 : 16
4. 3√3 : 2√2
Option 2 : 27 : 8
Sphere MCQ Question 12 Detailed Solution
Let radius of the first sphere be R and second sphere be r
According to the question,
⇒ (4πR2)/(4πr2) = 9/4
⇒ R2/r2 = 9/4
⇒ R/r = 3/2
⇒ R = 3r/2
Ratio of their volumes,
$$\Rightarrow \frac{4}{3} \times \pi {R^3}:\frac{4}{3} \times \pi {r^3}$$
⇒ (3r/2)3 ∶ r3
⇒ 27/8 ∶ 1
⇒ 27 ∶ 8
∴ Required ratio of volumes is 27 : 8
The volume of a sphere is 38808 cm3. If we have to cut a right circular cone of maximum volume, whose radius is 16.5 cm, then what will be the height of the cone? (Appox.)
1. 34 cm
2. 28 cm
3. 31 cm
4. Can’t be determined
Option 1 : 34 cm
Sphere MCQ Question 13 Detailed Solution
Let the perpendicular distance of the centre of sphere from the radius of cone be d cm and O is the centre of the sphere, r radius of the sphere.
Given that,
The volume of sphere = 38808 cm3
(4/3)πr3 = 38808
(4/3) × (22/7) × (r3) = 38808
r3 = 9261
r = 21 cm
Now, the perpendicular distance of the centre of sphere from the radius of cone
d = √(212 - 16.52) = √(441 - 272.25) = √168.75 = 13 cm (approx.)
So, the height of the cone = d + radius of the sphere = 13 + 21 = 34 cm
A spherical metal ball of radius 12 cm is melted and recast into three spherical balls. The radii of two of these balls is 6 cm and 10 cm. What is the radius of the third ball?
1. 9 cm
2. 10 cm
3. 11 cm
4. 8 cm
Option 4 : 8 cm
Sphere MCQ Question 14 Detailed Solution
Let the radius of the third ball be x cm
According to the question,
⇒ 4/3 π × 123 = 4/3 π × 63 + 4/3 π × 103 + 4/3 π × x3
⇒ 1728 = 216 + 1000 + x3
⇒ x3 = 512
⇒ x = 8
∴ Radius of the third ball = 8 cm
A spherical ball of radius 14 cm is melted and recast into small spherical balls of radius 7 cm each, in this process 20% of the material waste, then find how many complete small spherical balls can be made?
1. 5
2. 6
3. 7
4. 4
Option 2 : 6
Sphere MCQ Question 15 Detailed Solution
Radius of bigger spherical ball R = 14 cm
Radius of smaller spherical ball r = 7 cm
Let the number of small spherical ball be n.
According to the question
⇒ (4/3) × π R3 × 80/100 = n × 4/3 × πr3
⇒ R3 × 0.8 = n × r3
⇒ 143 × 0.8 = n × 73
⇒ n = 8 × 0.8 = 6.4
So, complete balls made only 6.
A large spherical ball of radius 6 cm is formed by combining 64 small spherical balls. Find the radius of one small spherical ball.
1. 2 cm
2. 1.5 cm
3. 3 cm
4. 4 cm
Option 2 : 1.5 cm
Sphere MCQ Question 16 Detailed Solution
Given:
Radius of large ball = 6 cm
Number of small balls = 64
Concepts used:
Volume of spherical ball = 4πr3/3
Number of small spherical balls = Volume of large spherical ball/volume of small spherical ball
Calculation:
Let radius of small ball be r cm.
Volume of small ball = 4π × (r)3/3 cm3
Volume of large ball = 4π × (6)3/3 cm3 = 288π cm3
Number of small spherical balls = Volume of large spherical ball/volume of small spherical ball
⇒ 64 = 288π cm3/4π × (r)3/3 cm3
⇒ 64 cm3 = 216 × (r)3 cm3
⇒ r = (216/64)1/3 cm
⇒ r = (6/4)3 × 1/3 cm
⇒ r = 1.5 cm
∴ Radius of small spherical ball is 1.5 cm.
The radius of a solid sphere of a metal is 3 cm. How long wire of diameter 4 mm can be drawn from it?
1. 8.8 mt.
2. 9.0 mt.
3. 9.6 mt.
4. 9.1 mt.
Option 2 : 9.0 mt.
Sphere MCQ Question 17 Detailed Solution
Given
The radius of a solid sphere = 3 cm
Formula Used
Volume of Sphere = (4/3)πR3
Volume of Cylinder = πR2H
Calculation
⇒ volume of sphere = volume of wire
⇒ π × (4/3) × 3 × 3 × 3 = π × .2 × .2 × H
⇒ H = 3 × 3 × 10 × 10 = 900 cm = 9 mt
∴ the length of wire is 9 mt.
A hollow sphere of 4 cm and 6 cm inner and outer diameter, respectively, is melted into a cone of 8 cm base diameter. Find the height of the cone.
1. 4.75 cm
2. 38 cm
3. 9.5 cm
4. 19 cm
Option 1 : 4.75 cm
Sphere MCQ Question 18 Detailed Solution
Given:
The inner diameter of the hollow sphere, (Di) = 4 cm
The outer diameter of the hollow sphere, (Do) = 6 cm
The base diameter of the cone, (D) = 8 cm
Formula used:
The volume of sphere = (4/3)πr3
The volume of the hollow sphere = (4/3)π(ro– ri3)
The volume of cone = (1/3)πR2h
Concept used:
If a sphere is melted and cast into a cone, then the volume of the sphere and cone is the same.
Calculation:
The inner radius of the sphere ri= 4/2 = 2 cm
The outer radius of the sphere ro= 6/2 = 3 cm
The volume of the hollow sphere = 4/3 π (ro3 – ri3)
⇒ 4/3 π (3– 23) = 76π/3
Let the height of the cone be h cm
The volume of cone = (1/3)πR2h
⇒ 1/3 π × 42 × h = 16/3 π h
The volume of the sphere and cone is equal
⇒ 76/3 π = 16h/3 π
⇒ h = 76/16 = 4.75
∴ The height of the cone is 4.75 cm
If the radius of a sphere is 16 cm and is melted and recast into a sphere of radius 4 cm. Then find the number of small spheres that are cast.
1. 16
2. 32
3. 48
4. 64
Option 4 : 64
Sphere MCQ Question 19 Detailed Solution
Given:
Radius of an original sphere = 16 cm
Radius of a recast sphere = 4 cm
Formula Used:
Volume of a sphere = (4/3)πr3
Number of recast spheres = Volume of the original sphere/Volume of the recast sphere
Calculation:
Volume of a original sphere = 4/3 π (16)3
Volume of the recast sphere = 4/3 π (4)3
Hence, number of recast spheres = Volume of the original sphere/Volume of the recast sphere
⇒ [(4/3) π (16)3]/[(4/3) π (4)3] = 64
∴ The number of recast spheres is 64.
An iron sphere of radius 27 cm is melted to form a wire of length 7.29 m. Then find the radius of wire.
1. 6 cm
2. 9 cm
3. 18 cm
4. 36 cm
Option 1 : 6 cm
Sphere MCQ Question 20 Detailed Solution
Given :-
Radius of sphere is = 27 cm
Length of wire = 7.29 m = 729 cm
Concept :-
Volume of sphere = (4/3)πR3
Volume of cylinder = πr2h
Calculation :-
⇒ Volume of sphere before melted = (4/3) × π × 27 × 27 × 27
⇒ Volume of sphere = (36 × 27 × 27)π
Now,
Let radius of wire = r
⇒ Volume of cylinder = Volume of sphere
⇒ π × r2 × 729 = (36 × 27 × 27) × π
⇒ r2 = ((36 × 27 × 27) × π )/(π × 729)
⇒ r2 = 36
⇒ r = √36
⇒ r = 6 cm.
⇒ Radius of wire = 6 cm
∴ Radius of wire = 6 cm |
# Probing the bound on the energy scale of black holes and supersymmetric QFTs
Comments: 19 pages, no figures, v2: minor changes, references to published version
In this paper, we investigate the energy scale of black holes and supersymmetric QFTs in the presence of a bound on the energy scale. We show that the bound on the energy scale can be satisfied only if the energy scale of the black hole is sufficiently large. In this case, the bound on the energy scale can be realized as a Real-Time System. We find that for two specific black holes and one specific supersymmetric QFT, the bound can be satisfied only if the bound on the energy scale is sufficiently large. We also show that the bound can be satisfied in the presence of a bound on the energy scale for two specific black holes and one specific supersymmetric QFT. |
huma pp750 the unplugged alpha chapter 1
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Today
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Created bytokarev tar 12p accessories
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Here I first made a sketch of the two functions: f (t) is non-zero on [-1, 1] and g (t) is non-zero on [-0.5, 0.5], so adding these two we find that (f ∗ g) (t) should be nonzero on [-1.5, 1.5]. The list of change points of (f ∗ g) (t) is {-1.5, -0.5, 0.5, 1.5}. For values t that are outside this range the convolution is zero.
Transcribed image text: Continuity of Piecewise Functions Determine whether a piecewise function is continuous Question Is the following piecewise function continuous? if xS-3 f(x) = { -2x – 3 -3 <xS-1 if if -1<x Select the correct answer below: O f) is continuous. O f(x) is not continuous.
The limit as the piecewise function approaches zero from the left is 0+1=1, and the limit as it approaches from the right is Cos (Pi*0)=Cos (0)=1. The calculator will use the best method available so try out a lot of different types of problems. Since ≤ includes the equality, we would get that f ( 0) = 1 0 − 2 = − 1 2.
It is not continuous if there are holes/jumps. For a piecewise function, these jumps, or "discontinuities" typically happen at the seams, for this function they are at x = 0 and x = pi. ... If the derivatives are continuous, then the original function is differentiable. Note that any points that occur in the middle of these regions, like x = pi.
Set the value of a piecewise function when no condition is true (called otherwise value) by specifying an additional input argument. If an additional argument is not specified, the default otherwise value of the function is NaN. Define the piecewise function. y = {-2 x <-2 0-2 < x < 0 1 o t h e r w i s e. The Absolute Value Function.The Absolute Value Function is a famous Piecewise.
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No, the piecewise function is not continuous at. Find the value of a that makes the function continuous. Show Answer. The answer is. Find the values of a and b that make the function continuous at all points. Show Answer.. "/> how to define repetitions for teststeps.
The default for f_otherwise is 0 Domain of piecewise function calculator Domain of piecewise function calculator. Know the definition of definite integral for a general function To write a piecewise function, use the following syntax: y = {condition: value, condition: value, etc f(3) For problems 3-10, graph each piecewise function.
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Set the value of a piecewise function when no condition is true (called otherwise value) by specifying an additional input argument. If an additional argument is not specified, the default otherwise value of the function is NaN. Define the piecewise function. y = {-2 x <-2 0-2 < x < 0 1 o t h e r w i s e. The Absolute Value Function.The Absolute Value Function is a famous Piecewise.
A piecewise function is defined by multiple functions, one for each part of a domain. A piecewise function may or may not be continuous or differentiable. A piecewise function may have an inverse if it is one-to-one. It may also have extrema (maximum or minimum values), including at its endpoints. Of course, a piecewise function can have two.
(Section 1.5: Piecewise-Defined Functions; Limits and Continuity in Calculus) 1.5.5 Example 3 (Graphing a Piecewise-Defined Function with a Removable Discontinuity) Graph f, if fx()= x +3, x 3 7, x = 3 . § Solution • We graph the line y = x+3, except we leave a hole at the point ()3, 6 , since 3 is deleted from the subdomain of the top rule.
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There are multiple cases for finding the limit of a piecewise function. Updated: 10/31/2019. 2 hours ago Free piecewise functions calculator - explore piecewise function domain, range, intercepts, extreme points and asymptotes step-by-step This website uses cookies to ensure you get the best experience. One-sided and two-sided being supported.
Get the free "Fourier Series of Piecewise Functions" widget for your website, blog, Wordpress, Blogger, or iGoogle. Find more Mathematics widgets in Wolfram|Alpha.
Search: Piecewise Fourier Series Calculator. That said, u(x,t) is piecewise continuous on the entire in-terval [0,1] Applying the inverse Fourier transform we obtain y p = 1 √ 2π Z∞ −∞ −e−ω2/2 ω2+1 eiωx dω Then, there are constants a 0;a m;b m (uniquely de ned by f) such that at each point of continuity of f(x) the expression on Even and odd extensions The following.
A function f : [a,b] → R is called piecewise continuous iff holds, (a) [a,b] can be partitioned in a finite number of sub-intervals such that f is continuous on the interior of these sub-intervals. (b) f has finite limits at the endpoints of all sub-intervals. The Fourier Theorem: Piecewise continuous case. Theorem (Fourier Series).
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There are multiple cases for finding the limit of a piecewise function. Updated: 10/31/2019. 2 hours ago Free piecewise functions calculator - explore piecewise function domain, range, intercepts, extreme points and asymptotes step-by-step This website uses cookies to ensure you get the best experience. One-sided and two-sided being supported.
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Jun 19, 2022 · Search: Piecewise Fourier Series Calculator.Mathematical Formulation and Uniqueness Result; The They are applicable to func-tions that are piecewise continuous with piecewise continuous first derivative EVEN FUNCTION If f (x) = φ (x) in (-l , l) such that φ (− x) = φ (x) , then f (x Free graphing calculator instantly graphs your math problems fourier series and.
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The function is continuous at this point since the function and limit have the same value. Finally ... 1\hspace{0.5in}\mathop {\lim }\limits_{x \to 3} f\left( x \right) = 0\] The function is not continuous at this point. This kind of discontinuity is called a removable discontinuity. Removable discontinuities are. minecraft roleplay ideas.
The limit as the piecewise function approaches zero from the left is 0+1=1, and the limit as it approaches from the right is Cos (Pi*0)=Cos (0)=1. The calculator will use the best method available so try out a lot of different types of problems. Since ≤ includes the equality, we would get that f ( 0) = 1 0 − 2 = − 1 2.
Find b and c so that f x is differentiable at x 1 Let 39 s work on continuity first 5. piecewise function a function defined by using two or more rules on two or more intervals as a result Determine if each function is continuous. org are unblocked. 2. Drill in determining when a piecewise defined function is continuous.
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On this page you can get various actions with a piecewise-defined function, as well as for most services - get the detailed solution. Derivative of a piecewise. Plot a graph. Curve sketching. Defined integral. Indefined integral of similar functions. Limit of piecewises. Fourier series (In common there are piecewises for calculating a series in.
Limits of piecewise functions. AP Calc: LIM‑1 (EU), LIM‑1.D (LO), LIM‑1.D.1 (EK) About. Transcript. When finding a limit of a piecewise defined function, we should make sure we are using the appropriate definition of the function, depending on where the.
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Answer (1 of 2): Firstly, the separate pieces must be joined. That means the function must be continuous. Secondly, at each connection you need to look at the gradient on the left and the gradient on the right. If the left hand derivative equals.
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This means that on average the 10th Fourier coefficient is only 1% in magnitude compared with the first one Fourier series/piecewise functions Derivatives and integrals of Fourier series A-level Mathematics help Making the most of your Casio fx-991ES calculator GCSE Let f(x) be a piecewise C1 function in Per L(R) Example: Consider the piecewise continuous.
Search: Piecewise Integral Calculator. Tutorial which is an introduction to continuous functions It is a sci It helps to gain experience by displaying the full working process of solving the problem and exercises For example, a standard integral in LaTeX looks like \\int_a^b \\! f(x) \\, \\mathrm{d}x Instructions: 1 Instructions: 1.
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A piecewise-defined function is one that is described not by a one (single) equation, but by two or more. Take into account the following function definition: F ( x) = { − 2 x, − 1 ≤ x < 0 X 2, 0 ≤ x < 1. Above mentioned piecewise equation is an example of an equation for piecewise function defined, which states that the function.... Continuity of piecewise functions 2.
Piecewise Functions Limits and Continuity. Andymath.com features free videos, notes, and practice problems with answers! ... Find the values of a and b that make the function continuous at all points. $$f(x) = \begin{cases} 2x^2 & \text{if } x\leq 2 \\ ax+b & \text{if } 2\lt x \lt 4 \\ x^2+4 & \text{if }x\geq 4 \end{cases}$$ Show Answer.
Structure, space, models, and change rule or expression for calculating the you., you can find derivative of piecewise function calculator example, an area inside a curved,. Graph a piecewise function on each of Partial derivative of the piecewise function the., the notation or is used out of 298 pages solve IVP ’ s an input to an output.
This worksheet will help with Piecewise functions. In order to change the graph, you NEED to input it in this format: if [x < #, first equation, second equation] You can change the #, first equation, and second equation for g (x). You can also change the #'s and the three equations for f (x). The format for graphing Piecewise Functions uses an.
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Set the value of a piecewise function when no condition is true (called otherwise value) by specifying an additional input argument. If an additional argument is not specified, the default otherwise value of the function is NaN. Define the piecewise.
A piecewise function is made up of two or more functions, each defined on a specific domain. Piecewise functions follow the following format: f (x) =. -x, x < 0. 0, x = 0. x, x > 0. The piecewise function above is the absolute value function. As you can see, piecewise functions include:.
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The default for f_otherwise is 0 Domain of piecewise function calculator Domain of piecewise function calculator. Know the definition of definite integral for a general function To write a piecewise function, use the following syntax: y = {condition: value, condition: value, etc f(3) For problems 3-10, graph each piecewise function.
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Lets say this signal is periodic with T=2 Get the free "Fourier Series of Piecewise Functions" widget for your website, blog, Wordpress, Blogger, or iGoogle A piecewise function is a function, which is defined by various multiple functions The Fourier series expansion of an even function f (x) with the period of 2π does not involve the terms with sines and has the form: f (x).
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Find b and c so that f x is differentiable at x 1 Let 39 s work on continuity first 5. piecewise function a function defined by using two or more rules on two or more intervals as a result Determine if each function is continuous. org are unblocked. 2. Drill in determining when a piecewise defined function is continuous.
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On this page you can get various actions with a piecewise-defined function, as well as for most services - get the detailed solution. Derivative of a piecewise. Plot a graph. Curve sketching. Defined integral. Indefined integral of similar functions. Limit of piecewises. Fourier series (In common there are piecewises for calculating a series in.
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Continuity and discontinuity of piecewise functions.
The straightforward calculation of the series of f around x =0 can be computed by using the. A function f : [a,b] → R is called piecewise continuous iff holds, (a) [a,b] can be partitioned in a finite number of sub-intervals such that f is continuous on the interior of these sub-intervals. (b) f has finite limits at the endpoints of all sub-intervals.
Find whether a function is continuous step-by-step. Line Equations. Functions. Arithmetic & Composition. Conic Sections. Transformation New. full pad ». x^2. x^ {\msquare}.
Set the value of a piecewise function when no condition is true (called otherwise value) by specifying an additional input argument. If an additional argument is not specified, the default otherwise value of the function is NaN. Define the piecewise function. y = {-2 x <-2 0-2 < x < 0 1 o t h e r w i s e. The Absolute Value Function.The Absolute Value Function is a famous Piecewise.
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Get the free "Fourier Series of Piecewise Functions" widget for your website, blog, Wordpress, Blogger, or iGoogle. Find more Mathematics widgets in Wolfram|Alpha.
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A piecewise function is a function consisting of sub-functions (pieces) defined on a sequence of intervals (domains). It is also known as a piecewise-defined function or hybrid function. The domain of each sub-function must not overlap. Ask students why the domains must not overlap.. "/> lairds boar stud; vados fanfiction lemon; bolt with hole.
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On-Line Fourier Series Calculator is an interactive app to calculate Fourier Series coefficients (Up to 10000 elements) for user-defined piecewise functions up to 5 pieces, for example Example: Fourier series of piecewise continuous function • (c) The Fourier sine series converges to the odd extension of f (see the graph) Fourier series.
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Example 2. Graph the piecewise function shown below. Using the graph, determine its domain and range. 2x , for x ≠ 0. 1, for x = 0. Solution. For all intervals of x other than when it is equal to 0, f (x) = 2x (which is a linear function). To graph the linear function, we can use two points to connect the line.
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In most cases, we should look for a discontinuity at the point where a piecewise defined function changes its formula. You will have to take one-sided limits separately since different formulas will apply depending on from which side you are approaching the point. Here is an example. Let us examine where f has a discontinuity. f(x)={(x^2 if x<1),(x if 1 le x < 2),(2x-1 if.
Let us illustrate this by the following example. 5: Piecewise-Defined Functions; Limits and Continuity in Calculus) 1. 2 hours ago Free piecewise functions calculator - explore piecewise function domain, range, intercepts, extreme points and asymptotes step-by-step This website uses cookies to ensure you get the best experience.
A typical use of continuous piecewise linear functions is when we link several points in a graph using segments. This kind of approximation to a curve is known as Linear Interpolation. Example of a continuous piecewise linear function is the definition of the absolute value function. We can consider now the derivative of each piece (in this.
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Fourier series make use of the orthogonality relationships of the sine and cosine functions To write a piecewise function, use the following syntax: y = {condition: value, condition: value, etc At points of continuity the series converges to the true Fourier series calculator with steps Fourier series calculator with steps Fourier Series of Piecewise Smooth Functions Some.
a small number of points, are called piecewise continuous functions. We usually write piecewise continuous functions by defining them case by case on different intervals. For example, h(x) = 8 >> >> >> < >> >> >>: x2 +4x+3 x < ¡3 x+3 ¡3 • x < 1 ¡2 x = 1 ex 1 < x • ln2 e¡x x > ln2 is a piecewise continuous function. As an exercise.
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Piecewise Laplace Transform + Online Solver With Free Steps. A piecewise Laplace transform calculator is a calculator used to find out the s-domain complex solution for a piecewise time domain signal which is not continuous at some point in time, and thus exists in more than one definition.. Where the solution of this piecewise function is expressed in the proper s-domain.
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Search: Piecewise Fourier Series Calculator. The following simulation shows the partial sum (up to 20 terms) of the Fourier series for a given function defined on the interval [a,b] to know under which conditions one can di erentiate or integrate the Fourier series of a function • The Fourier cosine series of f is therefore just f(x) = 1 Fourier Series of Piecewise Smooth.
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Pass conds=’ piecewise ’, ‘separate’ or ‘none’ to have these returned, respectively, as a Piecewise function , as a separate result (i Example: Fourier series of piecewise continuous function Equations (4) and (5) can be easily implemented on a programmable calculator of just about any type A piecewise function is a function , which is.
Added Apr 28, 2015 by sam The calculator will evaluate the definite (i Piecewise Functions Taylor series has applications ranging from classical and modern physics to the computations that your hand-held calculator makes when evaluating trigonometric expressions A piecewise continuous function f(x), defined on the interval (a 1 2x + 4 for 151.
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Pass conds='piecewise', 'separate' or 'none' to have these returned, respectively, as a Piecewise function, as a separate result (i Example: Fourier series of piecewise continuous function Equations (4) and (5) can be easily implemented on a programmable calculator of just about any type A piecewise function is a function, which is.Examples 3.5 – Piecewise Functions 1.
A piecewise function is made up of two or more functions , each defined on a specific domain. Piecewise functions follow the following format: f (x) =. -x, x < 0. 0, x = 0. x, x > 0. The piecewise ... online backpropagation calculator; tesla band logo; menstruation in the 1700s; eda yildiz outfits zara; r15 gui pastebin; viridian green laser.
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A function f is continuous when, for every value c in its Domain: f (c) is defined, and. lim x→c f (x) = f (c) "the limit of f (x) as x approaches c equals f (c) ". The limit says: "as x gets closer and closer to c. then f (x) gets closer and closer to f (c)" And we have to check from both directions:.
Step 1. Evaluate the one-sided limits. lim x → 4 − f ( x) = lim x → 4 − ( 2 x + 3) = 2 ( 4) + 3 = 11 lim x → 4 + f ( x) = lim x → 4 + ( 5 x − 9) = 5 ( 4) − 9 = 11. Step 2. If the one-sided limits are the same, the limit exists. Answer: lim x → 4 f ( x) = 11 when f is defined as above. Example 2.
Piecewise Laplace Transform + Online Solver With Free Steps. A piecewise Laplace transform calculator is a calculator used to find out the s-domain complex solution for a piecewise time domain signal which is not continuous at some point in time, and thus exists in more than one definition.. Where the solution of this piecewise function is expressed in the proper s-domain.
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A piecewise function is a function consisting of sub-functions (pieces) defined on a sequence of intervals (domains). It is also known as a piecewise-defined function or hybrid function. The domain of each sub-function must not overlap. Ask students why the domains must not overlap.. "/> lairds boar stud; vados fanfiction lemon; bolt with hole.
Solution : Here we are going to check the continuity between 0 and π/2. For the values of x lesser than or equal to π/4, we have to choose the function sin x. lim x->π/4- f (x) = lim x->π/4- sin x. = sin ( π/4) = 1/√2. For the values of x greater than π/4, we have to choose the function cos x. command line arguments in shell script examples.
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Added Apr 28, 2015 by sam The calculator will evaluate the definite (i Piecewise Functions Taylor series has applications ranging from classical and modern physics to the computations that your hand-held calculator makes when evaluating trigonometric expressions A piecewise continuous function f(x), defined on the interval (a 1 2x + 4 for 151.
A piecewise function behaves differently in different intervals of its domains. One example of a piecewise function is the absolute value function. ... Calculator solution Since x = 2 is in the interval x > 0, plug 2 into f(x) = x^2 - 2. The limit is f(2) = 2^2 - 2 = 2.
In the second example we consider a continuous piecewise linear function f and a continuous piecewise linear fuzzy set A depicted on Fig. 4. The first 30 iterations of the fuzzy set A induced by these maps are depicted on Fig. 5. It can be easily seen that the trajectory tends to be periodic. Example 4.
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Free piecewise functions calculator - explore piecewise function domain, range, intercepts, extreme points and asymptotes step-by-step.
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Search: Piecewise Fourier Series Calculator. Expansion in a Fourier Series Dirac delta, Fourier, Fourier integral, Fourier series, integral representations Notes: For ( 1 The Fourier series of an even function contains only cosine terms and is known as Fourier Series and is given by - [Voiceover] Many videos ago, we first looked at the idea of representing a periodic function as.
A piecewise-defined function is one that is described not by a one (single) equation, but by two or more. Take into account the following function definition: F ( x) = { − 2 x, − 1 ≤ x < 0 X 2, 0 ≤ x < 1. Above mentioned piecewise equation is an example of an equation for piecewise function defined, which states that the function.... Continuity of piecewise functions 2.
Lets say this signal is periodic with T=2 Get the free "Fourier Series of Piecewise Functions" widget for your website, blog, Wordpress, Blogger, or iGoogle A piecewise function is a function, which is defined by various multiple functions The Fourier series expansion of an even function f (x) with the period of 2π does not involve the terms with sines and has the form: f (x).
piecewise continuous function calculator. my favorite city london essay April 2, 2022. Piecewise Functions. Evaluate the function for the given value of x. Match the piecewise function with its graph. Graph the function. 19. 20. Step 1.
Feb 24, 2021 · A piecewise function is a function in which more than one formula is used to define the output over different pieces of the domain. Free piecewise functions calculator - explore piecewise function domain range intercepts extreme points and asymptotes step-by-step This website uses cookies to ensure you get the best experience.. "/>.
For piecewise defined functions, we often have to be very careful in com-puting the derivatives. The di↵erentiation rules (product, quotient, chain rules) can only be applied if the function is defined by ONE formula in a neighborhood of the point where we evaluate the derivative. If we want to calculate the derivative at a point where two.
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A piecewise-defined function is one that is described not by a one (single) equation, but by two or more. Take into account the following function definition: F ( x) = { − 2 x, − 1 ≤ x < 0 X 2, 0 ≤ x < 1. Above mentioned piecewise equation is an example of an equation for piecewise function defined, which states that the function.... Continuity of piecewise functions 2.
Set the value of a piecewise function when no condition is true (called otherwise value) by specifying an additional input argument. If an additional argument is not specified, the default otherwise value of the function is NaN. Define the piecewise.
Free piecewise functions calculator - explore piecewise function domain, range, intercepts, extreme points and asymptotes step-by-step. piecewise function continuous and differentiable calculator. mail January 23, 2018. 0. ... A piecewise continuous function is a function that is continuous except at a finite number of points in its domain.
study how a piecewise continuous function can be constructed using step functions. Then we will see how the Laplace transform and its inverse interact with the said construct. Step Functions Definition: The unit step function (or Heaviside function), is defined by ≥ < = t c t c u c t 1, 0, (), c ≥ 0. Often the unit step function u.
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G x interval x∈ ( −4, 7 ) and has a left of. ( iii ) Let us check whether the piece wise function is continuous on the entire line! Mastery, rather than a percentage grade 1. is ( a ) b! The laplace transformation of a piecewise function may or may not be a continuous function is continuous at this is! 1 & lt ; 1 if 1 6 5, if 2 6.
Search: Piecewise Fourier Series Calculator. The following simulation shows the partial sum (up to 20 terms) of the Fourier series for a given function defined on the interval [a,b] to know under which conditions one can di erentiate or integrate the Fourier series of a function • The Fourier cosine series of f is therefore just f(x) = 1 Fourier Series of Piecewise Smooth.
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Step 1. Evaluate the one-sided limits. lim x → 4 − f ( x) = lim x → 4 − ( 2 x + 3) = 2 ( 4) + 3 = 11 lim x → 4 + f ( x) = lim x → 4 + ( 5 x − 9) = 5 ( 4) − 9 = 11. Step 2. If the one-sided limits are the same, the limit exists. Answer: lim x → 4 f ( x) = 11 when f is defined as above. Example 2.
Piecewise Functions 1 - Cool Math has free online cool math lessons, cool math games and fun math activities. Really clear math lessons (pre-algebra, algebra, precalculus), cool math games, online graphing calculators, geometry art, fractals, polyhedra, parents and teachers areas too.
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Solution : Here we are going to check the continuity between 0 and π/2. For the values of x lesser than or equal to π/4, we have to choose the function sin x. lim x->π/4- f (x) = lim x->π/4- sin x. = sin ( π/4) = 1/√2. For the values of x greater than π/4, we have to choose the function cos x. By Annie Gowen generalized least squares vs ols.
Pass conds=’ piecewise ’, ‘separate’ or ‘none’ to have these returned, respectively, as a Piecewise function , as a separate result (i Example: Fourier series of piecewise continuous function Equations (4) and (5) can be easily implemented on a programmable calculator of just about any type A piecewise function is a function , which is.
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Piecewise functions will be useful to us in the study of limits, continuity, and the derivative as examples and counterexamples of functions having certain properties. If you don’t find enough time to complete this article in a single read, make sure to BOOKMARK this page for future saturation if you don’t want to miss this useful content.
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Request PDF | Calculations of Zadeh’s Extension of Piecewise Linear Functions | Zadeh’s extension principle is one of the most classical techniques in fuzzy set theory. It.
()1 2 =1, so the right endpoint of this piece is at ()1,1. 2 - Activity 2 - Piecewise Functions, Continuity, and Differentiability. The first thing we need to do is decide which piece. Piecewise Function Limit Calculator Piecewise, domain, function. Module 26 -.
Search: Piecewise Fourier Series Calculator. Example: Consider the piecewise continuous function, defined on the interval $$[-2,2] Finding the fourier series of a piecewise function mathematics 5 is a smoothing factor which indicates how good the fit should be (check out the documentation for more info on it) In this next series of blog posts, I will be discussing. Abstract. We obtain conditions under which the modulus of continuity of a piecewise analytic function given on a closed interval of the real axis is an analytic function in a neighborhood of zero. Graphing piecewise functions is like graphing functions on restricted domains. Restricted domains limit the x-values which are defined for the function. Piecewise functions can be continuous or discontinuous. Piecewise functions can be graphed in the following 3 ways: by hand, using an online calculator such as Desmos, or using a TI calculator. Example: Fourier series of piecewise continuous function That said, u(x,t) is piecewise continuous on the entire in-terval [0,1] a homogeneous space), and decompose them as a (discrete or continuous) superposition of much more symmetric functions on the domain, such as a homogeneous space), and decompose them as a (discrete or continuous. Find whether a function is continuous step-by-step. Line Equations. Functions. Arithmetic & Composition. Conic Sections. Transformation New. full pad ». x^2. x^ {\msquare}. #### neuroanatomy netter pdf Free piecewise functions calculator - explore piecewise function domain, range, intercepts, extreme points and asymptotes step-by-step. piecewise function continuous and differentiable calculator. mail January 23, 2018. 0. ... A piecewise continuous function is a function that is continuous except at a finite number of points in its domain. The function is continuous at this point since the function and limit have the same value. Finally ... 1\hspace{0.5in}\mathop {\lim }\limits_{x \to 3} f\left( x \right) = 0\] The function is not continuous at this point. This kind of discontinuity is called a removable discontinuity. Removable discontinuities are. minecraft roleplay ideas. #### patty mayo new episodes Piecewise functions will be useful to us in the study of limits, continuity, and the derivative as examples and counterexamples of functions having certain properties. If you don’t find enough time to complete this article in a single read, make sure to BOOKMARK this page for future saturation if you don’t want to miss this useful content. Set the value of a piecewise function when no condition is true (called otherwise value) by specifying an additional input argument. If an additional argument is not specified, the default otherwise value of the function is NaN. Define the piecewise. ## envision integrated mathematics 1 A piecewise function is a function consisting of sub-functions (pieces) defined on a sequence of intervals (domains). It is also known as a piecewise-defined function or hybrid function. The domain of each sub-function must not overlap. Ask students why the domains must not overlap. A function is called piecewise continuous on an interval if the interval can be broken into a nite number of subintervals on which the function is continuous on each open subinterval (i. Piecewise functions [2. Calculators for plane geometry, solid geometry and trigonometry. 2 -. 8. Continuity of Piecewise Functions Evaluate limits analytically for plecewise functions Question Given the following piecewise function, evaluate lim f(x). f(x) = x² + 2x + 2 x² + x - 2 (x²+1 if X <-3 if -35x<3 if x23 ments 8. Continuity of Piecewise Functions Select the correct answer below: O 4 O 10 O 17 O The limit does not exist. (Section 1.5: Piecewise-Defined Functions; Limits and Continuity in Calculus) 1.5.5 Example 3 (Graphing a Piecewise-Defined Function with a Removable Discontinuity) Graph f, if fx()= x +3, x 3 7, x = 3 . § Solution • We graph the line y = x+3, except we leave a hole at the point ()3, 6 , since 3 is deleted from the subdomain of the top rule. Show Solution. Since we know that exponentials are continuous everywhere we can use the fact above. lim x → 0 e sin x = e lim x → 0 sin x = e 0 = 1 lim x → 0 e sin x = e lim x → 0 sin x = e 0 = 1. Another very nice consequence of continuity is the Intermediate Value Theorem. Request PDF | Calculations of Zadeh’s Extension of Piecewise Linear Functions | Zadeh’s extension principle is one of the most classical techniques in fuzzy set theory. It. ## roast beef tiktok girl A typical use of continuous piecewise linear functions is when we link several points in a graph using segments. This kind of approximation to a curve is known as Linear Interpolation. Example of a continuous piecewise linear function is the definition of the absolute value function. We can consider now the derivative of each piece (in this. Find b and c so that f x is differentiable at x 1 Let 39 s work on continuity first 5. piecewise function a function defined by using two or more rules on two or more intervals as a result Determine if each function is continuous. org are unblocked. 2. Drill in determining when a piecewise defined function is continuous. Set the value of a piecewise function when no condition is true (called otherwise value) by specifying an additional input argument. If an additional argument is not specified, the default otherwise value of the function is NaN. Define the piecewise function. y = {-2 x <-2 0-2 < x < 0 1 o t h e r w i s e. The Absolute Value Function.The Absolute Value Function is a famous Piecewise. 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Expansion in a Fourier Series Dirac delta, Fourier, Fourier integral, Fourier series, integral representations Notes: For ( 1 The Fourier series of an even function contains only cosine terms and is known as Fourier Series and is given by - [Voiceover] Many videos ago, we first looked at the idea of representing a periodic function as. 4. bellazon model id 23) Limits of Piecewise Defined Functions; 24) Piecewise Defined with "Hole" 25) Piecewise Defined with "Jump" 26) Piecewise Limit without Graph; 27) Practice with Piecewise; 28) Continuity, Part I; 29) Continuity, Part II; 30) Continuity, Part III; 31) Definition of Continuous; 32) Example: "Discuss Continuity" 33) Differentiability and Continuity. 2011.marriner yarns 5. turo towing policy Jun 19, 2022 · Search: Piecewise Fourier Series Calculator.Mathematical Formulation and Uniqueness Result; The They are applicable to func-tions that are piecewise continuous with piecewise continuous first derivative EVEN FUNCTION If f (x) = φ (x) in (-l , l) such that φ (− x) = φ (x) , then f (x Free graphing calculator instantly graphs your math problems fourier series and. 2017.sans ics summit 2021 6. lywsd03mmc custom firmwarea ambetter of arkansas provider login Search: Piecewise Function Calculator. (a)Graph the functions f(x) = 2x and g(x) = 2 x and give the domains and range of each function Sometimes an equation can’t be described by a single equation, and instead we have to describe it using a combination of equations Piecewise Functions it' x > 3 3 To find such that is continuous at , we need to find such that In this case, in. 2022.maxon dc motor catalog 7. capella university cost per semester Search: Piecewise Fourier Series Calculator. Expansion in a Fourier Series Dirac delta, Fourier, Fourier integral, Fourier series, integral representations Notes: For ( 1 The Fourier series of an even function contains only cosine terms and is known as Fourier Series and is given by - [Voiceover] Many videos ago, we first looked at the idea of representing a periodic function as. . New York City: Harper Collins. p. factors influencing health pdf. shopify ios app dayz slotted planks.lionel dahmer book 8. bloxburg scripts 2022 Search: Piecewise Fourier Series Calculator. Expansion in a Fourier Series Dirac delta, Fourier, Fourier integral, Fourier series, integral representations Notes: For ( 1 The Fourier series of an even function contains only cosine terms and is known as Fourier Series and is given by - [Voiceover] Many videos ago, we first looked at the idea of representing a periodic function as. 9. jonsered 920 specs The default for f_otherwise is 0 Domain of piecewise function calculator Domain of piecewise function calculator. Know the definition of definite integral for a general function To write a piecewise function, use the following syntax: y = {condition: value, condition: value, etc f(3) For problems 3-10, graph each piecewise function. 10. index of parent directory dcim On this page you can get various actions with a piecewise-defined function, as well as for most services - get the detailed solution. Derivative of a piecewise. Plot a graph. Curve sketching. Defined integral. Indefined integral of similar functions. Limit of piecewises. Fourier series (In common there are piecewises for calculating a series in. 2020.full version of onenote for android 11. buy alpha lithium stock The function is continuous at this point since the function and limit have the same value. Finally \(x = 3$$. $f\left( 3 \right) = - 1\hspace{0.5in}\mathop {\lim }\limits_{x \to 3} f\left( x \right) = 0$ The function is not continuous at this point. This kind of discontinuity is called a removable discontinuity. Removable discontinuities are.
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80. tradingview copy drawings to another chart 18 Answers. #1. +9421. +3. We put one open curly brace beside the "pieces" of the piecewise function, for example: \ (f (x)=\begin {cases} x+2 & \text {if}&x> 2 \\ x^2 &\text {if}& -3< x\leq 2 \\ 9 &\text {if}& x\leq-3 \end {cases}\) This is the way to show the pieces of a piecewise function. On the other hand, domains and ranges (and, of. 2018.hustlers real college girl videos free
81. bose soundbar 700 remote pairing without app The function is continuous at this point since the function and limit have the same value. Finally $$x = 3$$. $f\left( 3 \right) = - 1\hspace{0.5in}\mathop {\lim }\limits_{x \to 3} f\left( x \right) = 0$ The function is not continuous at this point. This kind of discontinuity is called a removable discontinuity. Removable discontinuities are. ". CNNmexico pprno 2018.herrega kutaa 8 pdf
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87. common problems with dd13 engine This calculus review video tutorial explains how to evaluate limits using piecewise functions and how to make a piecewise function continuous by finding the. 2011.o hobbit filmes
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89. jellyfin ombi integration Search: Piecewise Fourier Series Calculator. Expansion in a Fourier Series Dirac delta, Fourier, Fourier integral, Fourier series, integral representations Notes: For ( 1 The Fourier series of an even function contains only cosine terms and is known as Fourier Series and is given by - [Voiceover] Many videos ago, we first looked at the idea of representing a periodic function as. 2011.fc1178bc firmware
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Question
# Two particle held at different height $$a$$ and $$b$$ above the ground are allowed to fall from rest. The ratio of their velocities on reaching the ground is
A
a:b
B
a:b
C
a2:b2
D
b:a
Solution
## The correct option is B $$\sqrt{a}:\sqrt{b}$$Let we assume that both particles takes time $$t_1$$ & respectively to reach the ground.$$S = ut + \dfrac{1}{2} at^2$$$$g = 10 \,m/s$$For first particle, $$a = 5t_1^2$$ ...(1)For second particle, $$b = 5t_2^2$$ ...(2)By dividing $$eq^n (1)/ eq^n (2)$$$$\dfrac{t_1}{t_2} = \sqrt{\dfrac{a}{b}} = \dfrac{\sqrt{a}}{\sqrt{b}}$$Now applying, $$V = u + at$$$$10 t_1 = V-1$$ ...(3)$$10 t_2 = V_2$$ ...(4)Dividing $$eq^n (3)/(4)$$$$\dfrac{V_1}{V_2} = \dfrac{t_1}{t_2} = \dfrac{\sqrt{a}}{\sqrt{b}}$$$$V_1 : V_b = \sqrt{a}:\sqrt{b}$$Physics
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