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"""Laplace Transforms""" | |
import sys | |
import sympy | |
from sympy.core import S, pi, I | |
from sympy.core.add import Add | |
from sympy.core.cache import cacheit | |
from sympy.core.expr import Expr | |
from sympy.core.function import ( | |
AppliedUndef, Derivative, expand, expand_complex, expand_mul, expand_trig, | |
Lambda, WildFunction, diff, Subs) | |
from sympy.core.mul import Mul, prod | |
from sympy.core.relational import ( | |
_canonical, Ge, Gt, Lt, Unequality, Eq, Ne, Relational) | |
from sympy.core.sorting import ordered | |
from sympy.core.symbol import Dummy, symbols, Wild | |
from sympy.functions.elementary.complexes import ( | |
re, im, arg, Abs, polar_lift, periodic_argument) | |
from sympy.functions.elementary.exponential import exp, log | |
from sympy.functions.elementary.hyperbolic import cosh, coth, sinh, asinh | |
from sympy.functions.elementary.miscellaneous import Max, Min, sqrt | |
from sympy.functions.elementary.piecewise import ( | |
Piecewise, piecewise_exclusive) | |
from sympy.functions.elementary.trigonometric import cos, sin, atan, sinc | |
from sympy.functions.special.bessel import besseli, besselj, besselk, bessely | |
from sympy.functions.special.delta_functions import DiracDelta, Heaviside | |
from sympy.functions.special.error_functions import erf, erfc, Ei | |
from sympy.functions.special.gamma_functions import ( | |
digamma, gamma, lowergamma, uppergamma) | |
from sympy.functions.special.singularity_functions import SingularityFunction | |
from sympy.integrals import integrate, Integral | |
from sympy.integrals.transforms import ( | |
_simplify, IntegralTransform, IntegralTransformError) | |
from sympy.logic.boolalg import to_cnf, conjuncts, disjuncts, Or, And | |
from sympy.matrices.matrixbase import MatrixBase | |
from sympy.polys.matrices.linsolve import _lin_eq2dict | |
from sympy.polys.polyerrors import PolynomialError | |
from sympy.polys.polyroots import roots | |
from sympy.polys.polytools import Poly | |
from sympy.polys.rationaltools import together | |
from sympy.polys.rootoftools import RootSum | |
from sympy.utilities.exceptions import ( | |
sympy_deprecation_warning, SymPyDeprecationWarning, ignore_warnings) | |
from sympy.utilities.misc import debugf | |
_LT_level = 0 | |
def DEBUG_WRAP(func): | |
def wrap(*args, **kwargs): | |
from sympy import SYMPY_DEBUG | |
global _LT_level | |
if not SYMPY_DEBUG: | |
return func(*args, **kwargs) | |
if _LT_level == 0: | |
print('\n' + '-'*78, file=sys.stderr) | |
print('-LT- %s%s%s' % (' '*_LT_level, func.__name__, args), | |
file=sys.stderr) | |
_LT_level += 1 | |
if ( | |
func.__name__ == '_laplace_transform_integration' or | |
func.__name__ == '_inverse_laplace_transform_integration'): | |
sympy.SYMPY_DEBUG = False | |
print('**** %sIntegrating ...' % (' '*_LT_level), file=sys.stderr) | |
result = func(*args, **kwargs) | |
sympy.SYMPY_DEBUG = True | |
else: | |
result = func(*args, **kwargs) | |
_LT_level -= 1 | |
print('-LT- %s---> %s' % (' '*_LT_level, result), file=sys.stderr) | |
if _LT_level == 0: | |
print('-'*78 + '\n', file=sys.stderr) | |
return result | |
return wrap | |
def _debug(text): | |
from sympy import SYMPY_DEBUG | |
global _LT_level | |
if SYMPY_DEBUG: | |
print('-LT- %s%s' % (' '*_LT_level, text), file=sys.stderr) | |
def _simplifyconds(expr, s, a): | |
r""" | |
Naively simplify some conditions occurring in ``expr``, | |
given that `\operatorname{Re}(s) > a`. | |
Examples | |
======== | |
>>> from sympy.integrals.laplace import _simplifyconds | |
>>> from sympy.abc import x | |
>>> from sympy import sympify as S | |
>>> _simplifyconds(abs(x**2) < 1, x, 1) | |
False | |
>>> _simplifyconds(abs(x**2) < 1, x, 2) | |
False | |
>>> _simplifyconds(abs(x**2) < 1, x, 0) | |
Abs(x**2) < 1 | |
>>> _simplifyconds(abs(1/x**2) < 1, x, 1) | |
True | |
>>> _simplifyconds(S(1) < abs(x), x, 1) | |
True | |
>>> _simplifyconds(S(1) < abs(1/x), x, 1) | |
False | |
>>> from sympy import Ne | |
>>> _simplifyconds(Ne(1, x**3), x, 1) | |
True | |
>>> _simplifyconds(Ne(1, x**3), x, 2) | |
True | |
>>> _simplifyconds(Ne(1, x**3), x, 0) | |
Ne(1, x**3) | |
""" | |
def power(ex): | |
if ex == s: | |
return 1 | |
if ex.is_Pow and ex.base == s: | |
return ex.exp | |
return None | |
def bigger(ex1, ex2): | |
""" Return True only if |ex1| > |ex2|, False only if |ex1| < |ex2|. | |
Else return None. """ | |
if ex1.has(s) and ex2.has(s): | |
return None | |
if isinstance(ex1, Abs): | |
ex1 = ex1.args[0] | |
if isinstance(ex2, Abs): | |
ex2 = ex2.args[0] | |
if ex1.has(s): | |
return bigger(1/ex2, 1/ex1) | |
n = power(ex2) | |
if n is None: | |
return None | |
try: | |
if n > 0 and (Abs(ex1) <= Abs(a)**n) == S.true: | |
return False | |
if n < 0 and (Abs(ex1) >= Abs(a)**n) == S.true: | |
return True | |
except TypeError: | |
return None | |
def replie(x, y): | |
""" simplify x < y """ | |
if (not (x.is_positive or isinstance(x, Abs)) | |
or not (y.is_positive or isinstance(y, Abs))): | |
return (x < y) | |
r = bigger(x, y) | |
if r is not None: | |
return not r | |
return (x < y) | |
def replue(x, y): | |
b = bigger(x, y) | |
if b in (True, False): | |
return True | |
return Unequality(x, y) | |
def repl(ex, *args): | |
if ex in (True, False): | |
return bool(ex) | |
return ex.replace(*args) | |
from sympy.simplify.radsimp import collect_abs | |
expr = collect_abs(expr) | |
expr = repl(expr, Lt, replie) | |
expr = repl(expr, Gt, lambda x, y: replie(y, x)) | |
expr = repl(expr, Unequality, replue) | |
return S(expr) | |
def expand_dirac_delta(expr): | |
""" | |
Expand an expression involving DiractDelta to get it as a linear | |
combination of DiracDelta functions. | |
""" | |
return _lin_eq2dict(expr, expr.atoms(DiracDelta)) | |
def _laplace_transform_integration(f, t, s_, *, simplify): | |
""" The backend function for doing Laplace transforms by integration. | |
This backend assumes that the frontend has already split sums | |
such that `f` is to an addition anymore. | |
""" | |
s = Dummy('s') | |
if f.has(DiracDelta): | |
return None | |
F = integrate(f*exp(-s*t), (t, S.Zero, S.Infinity)) | |
if not F.has(Integral): | |
return _simplify(F.subs(s, s_), simplify), S.NegativeInfinity, S.true | |
if not F.is_Piecewise: | |
return None | |
F, cond = F.args[0] | |
if F.has(Integral): | |
return None | |
def process_conds(conds): | |
""" Turn ``conds`` into a strip and auxiliary conditions. """ | |
from sympy.solvers.inequalities import _solve_inequality | |
a = S.NegativeInfinity | |
aux = S.true | |
conds = conjuncts(to_cnf(conds)) | |
p, q, w1, w2, w3, w4, w5 = symbols( | |
'p q w1 w2 w3 w4 w5', cls=Wild, exclude=[s]) | |
patterns = ( | |
p*Abs(arg((s + w3)*q)) < w2, | |
p*Abs(arg((s + w3)*q)) <= w2, | |
Abs(periodic_argument((s + w3)**p*q, w1)) < w2, | |
Abs(periodic_argument((s + w3)**p*q, w1)) <= w2, | |
Abs(periodic_argument((polar_lift(s + w3))**p*q, w1)) < w2, | |
Abs(periodic_argument((polar_lift(s + w3))**p*q, w1)) <= w2) | |
for c in conds: | |
a_ = S.Infinity | |
aux_ = [] | |
for d in disjuncts(c): | |
if d.is_Relational and s in d.rhs.free_symbols: | |
d = d.reversed | |
if d.is_Relational and isinstance(d, (Ge, Gt)): | |
d = d.reversedsign | |
for pat in patterns: | |
m = d.match(pat) | |
if m: | |
break | |
if m and m[q].is_positive and m[w2]/m[p] == pi/2: | |
d = -re(s + m[w3]) < 0 | |
m = d.match(p - cos(w1*Abs(arg(s*w5))*w2)*Abs(s**w3)**w4 < 0) | |
if not m: | |
m = d.match( | |
cos(p - Abs(periodic_argument(s**w1*w5, q))*w2) * | |
Abs(s**w3)**w4 < 0) | |
if not m: | |
m = d.match( | |
p - cos( | |
Abs(periodic_argument(polar_lift(s)**w1*w5, q))*w2 | |
)*Abs(s**w3)**w4 < 0) | |
if m and all(m[wild].is_positive for wild in [ | |
w1, w2, w3, w4, w5]): | |
d = re(s) > m[p] | |
d_ = d.replace( | |
re, lambda x: x.expand().as_real_imag()[0]).subs(re(s), t) | |
if ( | |
not d.is_Relational or d.rel_op in ('==', '!=') | |
or d_.has(s) or not d_.has(t)): | |
aux_ += [d] | |
continue | |
soln = _solve_inequality(d_, t) | |
if not soln.is_Relational or soln.rel_op in ('==', '!='): | |
aux_ += [d] | |
continue | |
if soln.lts == t: | |
return None | |
else: | |
a_ = Min(soln.lts, a_) | |
if a_ is not S.Infinity: | |
a = Max(a_, a) | |
else: | |
aux = And(aux, Or(*aux_)) | |
return a, aux.canonical if aux.is_Relational else aux | |
conds = [process_conds(c) for c in disjuncts(cond)] | |
conds2 = [x for x in conds if x[1] != | |
S.false and x[0] is not S.NegativeInfinity] | |
if not conds2: | |
conds2 = [x for x in conds if x[1] != S.false] | |
conds = list(ordered(conds2)) | |
def cnt(expr): | |
if expr in (True, False): | |
return 0 | |
return expr.count_ops() | |
conds.sort(key=lambda x: (-x[0], cnt(x[1]))) | |
if not conds: | |
return None | |
a, aux = conds[0] # XXX is [0] always the right one? | |
def sbs(expr): | |
return expr.subs(s, s_) | |
if simplify: | |
F = _simplifyconds(F, s, a) | |
aux = _simplifyconds(aux, s, a) | |
return _simplify(F.subs(s, s_), simplify), sbs(a), _canonical(sbs(aux)) | |
def _laplace_deep_collect(f, t): | |
""" | |
This is an internal helper function that traverses through the epression | |
tree of `f(t)` and collects arguments. The purpose of it is that | |
anything like `f(w*t-1*t-c)` will be written as `f((w-1)*t-c)` such that | |
it can match `f(a*t+b)`. | |
""" | |
if not isinstance(f, Expr): | |
return f | |
if (p := f.as_poly(t)) is not None: | |
return p.as_expr() | |
func = f.func | |
args = [_laplace_deep_collect(arg, t) for arg in f.args] | |
return func(*args) | |
def _laplace_build_rules(): | |
""" | |
This is an internal helper function that returns the table of Laplace | |
transform rules in terms of the time variable `t` and the frequency | |
variable `s`. It is used by ``_laplace_apply_rules``. Each entry is a | |
tuple containing: | |
(time domain pattern, | |
frequency-domain replacement, | |
condition for the rule to be applied, | |
convergence plane, | |
preparation function) | |
The preparation function is a function with one argument that is applied | |
to the expression before matching. For most rules it should be | |
``_laplace_deep_collect``. | |
""" | |
t = Dummy('t') | |
s = Dummy('s') | |
a = Wild('a', exclude=[t]) | |
b = Wild('b', exclude=[t]) | |
n = Wild('n', exclude=[t]) | |
tau = Wild('tau', exclude=[t]) | |
omega = Wild('omega', exclude=[t]) | |
def dco(f): return _laplace_deep_collect(f, t) | |
_debug('_laplace_build_rules is building rules') | |
laplace_transform_rules = [ | |
(a, a/s, | |
S.true, S.Zero, dco), # 4.2.1 | |
(DiracDelta(a*t-b), exp(-s*b/a)/Abs(a), | |
Or(And(a > 0, b >= 0), And(a < 0, b <= 0)), | |
S.NegativeInfinity, dco), # Not in Bateman54 | |
(DiracDelta(a*t-b), S(0), | |
Or(And(a < 0, b >= 0), And(a > 0, b <= 0)), | |
S.NegativeInfinity, dco), # Not in Bateman54 | |
(Heaviside(a*t-b), exp(-s*b/a)/s, | |
And(a > 0, b > 0), S.Zero, dco), # 4.4.1 | |
(Heaviside(a*t-b), (1-exp(-s*b/a))/s, | |
And(a < 0, b < 0), S.Zero, dco), # 4.4.1 | |
(Heaviside(a*t-b), 1/s, | |
And(a > 0, b <= 0), S.Zero, dco), # 4.4.1 | |
(Heaviside(a*t-b), 0, | |
And(a < 0, b > 0), S.Zero, dco), # 4.4.1 | |
(t, 1/s**2, | |
S.true, S.Zero, dco), # 4.2.3 | |
(1/(a*t+b), -exp(-b/a*s)*Ei(-b/a*s)/a, | |
Abs(arg(b/a)) < pi, S.Zero, dco), # 4.2.6 | |
(1/sqrt(a*t+b), sqrt(a*pi/s)*exp(b/a*s)*erfc(sqrt(b/a*s))/a, | |
Abs(arg(b/a)) < pi, S.Zero, dco), # 4.2.18 | |
((a*t+b)**(-S(3)/2), | |
2*b**(-S(1)/2)-2*(pi*s/a)**(S(1)/2)*exp(b/a*s) * erfc(sqrt(b/a*s))/a, | |
Abs(arg(b/a)) < pi, S.Zero, dco), # 4.2.20 | |
(sqrt(t)/(t+b), sqrt(pi/s)-pi*sqrt(b)*exp(b*s)*erfc(sqrt(b*s)), | |
Abs(arg(b)) < pi, S.Zero, dco), # 4.2.22 | |
(1/(a*sqrt(t) + t**(3/2)), pi*a**(S(1)/2)*exp(a*s)*erfc(sqrt(a*s)), | |
S.true, S.Zero, dco), # Not in Bateman54 | |
(t**n, gamma(n+1)/s**(n+1), | |
n > -1, S.Zero, dco), # 4.3.1 | |
((a*t+b)**n, uppergamma(n+1, b/a*s)*exp(-b/a*s)/s**(n+1)/a, | |
And(n > -1, Abs(arg(b/a)) < pi), S.Zero, dco), # 4.3.4 | |
(t**n/(t+a), a**n*gamma(n+1)*uppergamma(-n, a*s), | |
And(n > -1, Abs(arg(a)) < pi), S.Zero, dco), # 4.3.7 | |
(exp(a*t-tau), exp(-tau)/(s-a), | |
S.true, re(a), dco), # 4.5.1 | |
(t*exp(a*t-tau), exp(-tau)/(s-a)**2, | |
S.true, re(a), dco), # 4.5.2 | |
(t**n*exp(a*t), gamma(n+1)/(s-a)**(n+1), | |
re(n) > -1, re(a), dco), # 4.5.3 | |
(exp(-a*t**2), sqrt(pi/4/a)*exp(s**2/4/a)*erfc(s/sqrt(4*a)), | |
re(a) > 0, S.Zero, dco), # 4.5.21 | |
(t*exp(-a*t**2), | |
1/(2*a)-2/sqrt(pi)/(4*a)**(S(3)/2)*s*erfc(s/sqrt(4*a)), | |
re(a) > 0, S.Zero, dco), # 4.5.22 | |
(exp(-a/t), 2*sqrt(a/s)*besselk(1, 2*sqrt(a*s)), | |
re(a) >= 0, S.Zero, dco), # 4.5.25 | |
(sqrt(t)*exp(-a/t), | |
S(1)/2*sqrt(pi/s**3)*(1+2*sqrt(a*s))*exp(-2*sqrt(a*s)), | |
re(a) >= 0, S.Zero, dco), # 4.5.26 | |
(exp(-a/t)/sqrt(t), sqrt(pi/s)*exp(-2*sqrt(a*s)), | |
re(a) >= 0, S.Zero, dco), # 4.5.27 | |
(exp(-a/t)/(t*sqrt(t)), sqrt(pi/a)*exp(-2*sqrt(a*s)), | |
re(a) > 0, S.Zero, dco), # 4.5.28 | |
(t**n*exp(-a/t), 2*(a/s)**((n+1)/2)*besselk(n+1, 2*sqrt(a*s)), | |
re(a) > 0, S.Zero, dco), # 4.5.29 | |
(exp(-2*sqrt(a*t)), | |
s**(-1)-sqrt(pi*a)*s**(-S(3)/2)*exp(a/s) * erfc(sqrt(a/s)), | |
Abs(arg(a)) < pi, S.Zero, dco), # 4.5.31 | |
(exp(-2*sqrt(a*t))/sqrt(t), (pi/s)**(S(1)/2)*exp(a/s)*erfc(sqrt(a/s)), | |
Abs(arg(a)) < pi, S.Zero, dco), # 4.5.33 | |
(exp(-a*exp(-t)), a**(-s)*lowergamma(s, a), | |
S.true, S.Zero, dco), # 4.5.36 | |
(exp(-a*exp(t)), a**s*uppergamma(-s, a), | |
re(a) > 0, S.Zero, dco), # 4.5.37 | |
(log(a*t), -log(exp(S.EulerGamma)*s/a)/s, | |
a > 0, S.Zero, dco), # 4.6.1 | |
(log(1+a*t), -exp(s/a)/s*Ei(-s/a), | |
Abs(arg(a)) < pi, S.Zero, dco), # 4.6.4 | |
(log(a*t+b), (log(b)-exp(s/b/a)/s*a*Ei(-s/b))/s*a, | |
And(a > 0, Abs(arg(b)) < pi), S.Zero, dco), # 4.6.5 | |
(log(t)/sqrt(t), -sqrt(pi/s)*log(4*s*exp(S.EulerGamma)), | |
S.true, S.Zero, dco), # 4.6.9 | |
(t**n*log(t), gamma(n+1)*s**(-n-1)*(digamma(n+1)-log(s)), | |
re(n) > -1, S.Zero, dco), # 4.6.11 | |
(log(a*t)**2, (log(exp(S.EulerGamma)*s/a)**2+pi**2/6)/s, | |
a > 0, S.Zero, dco), # 4.6.13 | |
(sin(omega*t), omega/(s**2+omega**2), | |
S.true, Abs(im(omega)), dco), # 4,7,1 | |
(Abs(sin(omega*t)), omega/(s**2+omega**2)*coth(pi*s/2/omega), | |
omega > 0, S.Zero, dco), # 4.7.2 | |
(sin(omega*t)/t, atan(omega/s), | |
S.true, Abs(im(omega)), dco), # 4.7.16 | |
(sin(omega*t)**2/t, log(1+4*omega**2/s**2)/4, | |
S.true, 2*Abs(im(omega)), dco), # 4.7.17 | |
(sin(omega*t)**2/t**2, | |
omega*atan(2*omega/s)-s*log(1+4*omega**2/s**2)/4, | |
S.true, 2*Abs(im(omega)), dco), # 4.7.20 | |
(sin(2*sqrt(a*t)), sqrt(pi*a)/s/sqrt(s)*exp(-a/s), | |
S.true, S.Zero, dco), # 4.7.32 | |
(sin(2*sqrt(a*t))/t, pi*erf(sqrt(a/s)), | |
S.true, S.Zero, dco), # 4.7.34 | |
(cos(omega*t), s/(s**2+omega**2), | |
S.true, Abs(im(omega)), dco), # 4.7.43 | |
(cos(omega*t)**2, (s**2+2*omega**2)/(s**2+4*omega**2)/s, | |
S.true, 2*Abs(im(omega)), dco), # 4.7.45 | |
(sqrt(t)*cos(2*sqrt(a*t)), sqrt(pi)/2*s**(-S(5)/2)*(s-2*a)*exp(-a/s), | |
S.true, S.Zero, dco), # 4.7.66 | |
(cos(2*sqrt(a*t))/sqrt(t), sqrt(pi/s)*exp(-a/s), | |
S.true, S.Zero, dco), # 4.7.67 | |
(sin(a*t)*sin(b*t), 2*a*b*s/(s**2+(a+b)**2)/(s**2+(a-b)**2), | |
S.true, Abs(im(a))+Abs(im(b)), dco), # 4.7.78 | |
(cos(a*t)*sin(b*t), b*(s**2-a**2+b**2)/(s**2+(a+b)**2)/(s**2+(a-b)**2), | |
S.true, Abs(im(a))+Abs(im(b)), dco), # 4.7.79 | |
(cos(a*t)*cos(b*t), s*(s**2+a**2+b**2)/(s**2+(a+b)**2)/(s**2+(a-b)**2), | |
S.true, Abs(im(a))+Abs(im(b)), dco), # 4.7.80 | |
(sinh(a*t), a/(s**2-a**2), | |
S.true, Abs(re(a)), dco), # 4.9.1 | |
(cosh(a*t), s/(s**2-a**2), | |
S.true, Abs(re(a)), dco), # 4.9.2 | |
(sinh(a*t)**2, 2*a**2/(s**3-4*a**2*s), | |
S.true, 2*Abs(re(a)), dco), # 4.9.3 | |
(cosh(a*t)**2, (s**2-2*a**2)/(s**3-4*a**2*s), | |
S.true, 2*Abs(re(a)), dco), # 4.9.4 | |
(sinh(a*t)/t, log((s+a)/(s-a))/2, | |
S.true, Abs(re(a)), dco), # 4.9.12 | |
(t**n*sinh(a*t), gamma(n+1)/2*((s-a)**(-n-1)-(s+a)**(-n-1)), | |
n > -2, Abs(a), dco), # 4.9.18 | |
(t**n*cosh(a*t), gamma(n+1)/2*((s-a)**(-n-1)+(s+a)**(-n-1)), | |
n > -1, Abs(a), dco), # 4.9.19 | |
(sinh(2*sqrt(a*t)), sqrt(pi*a)/s/sqrt(s)*exp(a/s), | |
S.true, S.Zero, dco), # 4.9.34 | |
(cosh(2*sqrt(a*t)), 1/s+sqrt(pi*a)/s/sqrt(s)*exp(a/s)*erf(sqrt(a/s)), | |
S.true, S.Zero, dco), # 4.9.35 | |
( | |
sqrt(t)*sinh(2*sqrt(a*t)), | |
pi**(S(1)/2)*s**(-S(5)/2)*(s/2+a) * | |
exp(a/s)*erf(sqrt(a/s))-a**(S(1)/2)*s**(-2), | |
S.true, S.Zero, dco), # 4.9.36 | |
(sqrt(t)*cosh(2*sqrt(a*t)), pi**(S(1)/2)*s**(-S(5)/2)*(s/2+a)*exp(a/s), | |
S.true, S.Zero, dco), # 4.9.37 | |
(sinh(2*sqrt(a*t))/sqrt(t), | |
pi**(S(1)/2)*s**(-S(1)/2)*exp(a/s) * erf(sqrt(a/s)), | |
S.true, S.Zero, dco), # 4.9.38 | |
(cosh(2*sqrt(a*t))/sqrt(t), pi**(S(1)/2)*s**(-S(1)/2)*exp(a/s), | |
S.true, S.Zero, dco), # 4.9.39 | |
(sinh(sqrt(a*t))**2/sqrt(t), pi**(S(1)/2)/2*s**(-S(1)/2)*(exp(a/s)-1), | |
S.true, S.Zero, dco), # 4.9.40 | |
(cosh(sqrt(a*t))**2/sqrt(t), pi**(S(1)/2)/2*s**(-S(1)/2)*(exp(a/s)+1), | |
S.true, S.Zero, dco), # 4.9.41 | |
(erf(a*t), exp(s**2/(2*a)**2)*erfc(s/(2*a))/s, | |
4*Abs(arg(a)) < pi, S.Zero, dco), # 4.12.2 | |
(erf(sqrt(a*t)), sqrt(a)/sqrt(s+a)/s, | |
S.true, Max(S.Zero, -re(a)), dco), # 4.12.4 | |
(exp(a*t)*erf(sqrt(a*t)), sqrt(a)/sqrt(s)/(s-a), | |
S.true, Max(S.Zero, re(a)), dco), # 4.12.5 | |
(erf(sqrt(a/t)/2), (1-exp(-sqrt(a*s)))/s, | |
re(a) > 0, S.Zero, dco), # 4.12.6 | |
(erfc(sqrt(a*t)), (sqrt(s+a)-sqrt(a))/sqrt(s+a)/s, | |
S.true, -re(a), dco), # 4.12.9 | |
(exp(a*t)*erfc(sqrt(a*t)), 1/(s+sqrt(a*s)), | |
S.true, S.Zero, dco), # 4.12.10 | |
(erfc(sqrt(a/t)/2), exp(-sqrt(a*s))/s, | |
re(a) > 0, S.Zero, dco), # 4.2.11 | |
(besselj(n, a*t), a**n/(sqrt(s**2+a**2)*(s+sqrt(s**2+a**2))**n), | |
re(n) > -1, Abs(im(a)), dco), # 4.14.1 | |
(t**b*besselj(n, a*t), | |
2**n/sqrt(pi)*gamma(n+S.Half)*a**n*(s**2+a**2)**(-n-S.Half), | |
And(re(n) > -S.Half, Eq(b, n)), Abs(im(a)), dco), # 4.14.7 | |
(t**b*besselj(n, a*t), | |
2**(n+1)/sqrt(pi)*gamma(n+S(3)/2)*a**n*s*(s**2+a**2)**(-n-S(3)/2), | |
And(re(n) > -1, Eq(b, n+1)), Abs(im(a)), dco), # 4.14.8 | |
(besselj(0, 2*sqrt(a*t)), exp(-a/s)/s, | |
S.true, S.Zero, dco), # 4.14.25 | |
(t**(b)*besselj(n, 2*sqrt(a*t)), a**(n/2)*s**(-n-1)*exp(-a/s), | |
And(re(n) > -1, Eq(b, n*S.Half)), S.Zero, dco), # 4.14.30 | |
(besselj(0, a*sqrt(t**2+b*t)), | |
exp(b*s-b*sqrt(s**2+a**2))/sqrt(s**2+a**2), | |
Abs(arg(b)) < pi, Abs(im(a)), dco), # 4.15.19 | |
(besseli(n, a*t), a**n/(sqrt(s**2-a**2)*(s+sqrt(s**2-a**2))**n), | |
re(n) > -1, Abs(re(a)), dco), # 4.16.1 | |
(t**b*besseli(n, a*t), | |
2**n/sqrt(pi)*gamma(n+S.Half)*a**n*(s**2-a**2)**(-n-S.Half), | |
And(re(n) > -S.Half, Eq(b, n)), Abs(re(a)), dco), # 4.16.6 | |
(t**b*besseli(n, a*t), | |
2**(n+1)/sqrt(pi)*gamma(n+S(3)/2)*a**n*s*(s**2-a**2)**(-n-S(3)/2), | |
And(re(n) > -1, Eq(b, n+1)), Abs(re(a)), dco), # 4.16.7 | |
(t**(b)*besseli(n, 2*sqrt(a*t)), a**(n/2)*s**(-n-1)*exp(a/s), | |
And(re(n) > -1, Eq(b, n*S.Half)), S.Zero, dco), # 4.16.18 | |
(bessely(0, a*t), -2/pi*asinh(s/a)/sqrt(s**2+a**2), | |
S.true, Abs(im(a)), dco), # 4.15.44 | |
(besselk(0, a*t), log((s + sqrt(s**2-a**2))/a)/(sqrt(s**2-a**2)), | |
S.true, -re(a), dco) # 4.16.23 | |
] | |
return laplace_transform_rules, t, s | |
def _laplace_rule_timescale(f, t, s): | |
""" | |
This function applies the time-scaling rule of the Laplace transform in | |
a straight-forward way. For example, if it gets ``(f(a*t), t, s)``, it will | |
compute ``LaplaceTransform(f(t)/a, t, s/a)`` if ``a>0``. | |
""" | |
a = Wild('a', exclude=[t]) | |
g = WildFunction('g', nargs=1) | |
ma1 = f.match(g) | |
if ma1: | |
arg = ma1[g].args[0].collect(t) | |
ma2 = arg.match(a*t) | |
if ma2 and ma2[a].is_positive and ma2[a] != 1: | |
_debug(' rule: time scaling (4.1.4)') | |
r, pr, cr = _laplace_transform( | |
1/ma2[a]*ma1[g].func(t), t, s/ma2[a], simplify=False) | |
return (r, pr, cr) | |
return None | |
def _laplace_rule_heaviside(f, t, s): | |
""" | |
This function deals with time-shifted Heaviside step functions. If the time | |
shift is positive, it applies the time-shift rule of the Laplace transform. | |
For example, if it gets ``(Heaviside(t-a)*f(t), t, s)``, it will compute | |
``exp(-a*s)*LaplaceTransform(f(t+a), t, s)``. | |
If the time shift is negative, the Heaviside function is simply removed | |
as it means nothing to the Laplace transform. | |
The function does not remove a factor ``Heaviside(t)``; this is done by | |
the simple rules. | |
""" | |
a = Wild('a', exclude=[t]) | |
y = Wild('y') | |
g = Wild('g') | |
if ma1 := f.match(Heaviside(y) * g): | |
if ma2 := ma1[y].match(t - a): | |
if ma2[a].is_positive: | |
_debug(' rule: time shift (4.1.4)') | |
r, pr, cr = _laplace_transform( | |
ma1[g].subs(t, t + ma2[a]), t, s, simplify=False) | |
return (exp(-ma2[a] * s) * r, pr, cr) | |
if ma2[a].is_negative: | |
_debug( | |
' rule: Heaviside factor; negative time shift (4.1.4)') | |
r, pr, cr = _laplace_transform(ma1[g], t, s, simplify=False) | |
return (r, pr, cr) | |
if ma2 := ma1[y].match(a - t): | |
if ma2[a].is_positive: | |
_debug(' rule: Heaviside window open') | |
r, pr, cr = _laplace_transform( | |
(1 - Heaviside(t - ma2[a])) * ma1[g], t, s, simplify=False) | |
return (r, pr, cr) | |
if ma2[a].is_negative: | |
_debug(' rule: Heaviside window closed') | |
return (0, 0, S.true) | |
return None | |
def _laplace_rule_exp(f, t, s): | |
""" | |
If this function finds a factor ``exp(a*t)``, it applies the | |
frequency-shift rule of the Laplace transform and adjusts the convergence | |
plane accordingly. For example, if it gets ``(exp(-a*t)*f(t), t, s)``, it | |
will compute ``LaplaceTransform(f(t), t, s+a)``. | |
""" | |
a = Wild('a', exclude=[t]) | |
y = Wild('y') | |
z = Wild('z') | |
ma1 = f.match(exp(y)*z) | |
if ma1: | |
ma2 = ma1[y].collect(t).match(a*t) | |
if ma2: | |
_debug(' rule: multiply with exp (4.1.5)') | |
r, pr, cr = _laplace_transform(ma1[z], t, s-ma2[a], | |
simplify=False) | |
return (r, pr+re(ma2[a]), cr) | |
return None | |
def _laplace_rule_delta(f, t, s): | |
""" | |
If this function finds a factor ``DiracDelta(b*t-a)``, it applies the | |
masking property of the delta distribution. For example, if it gets | |
``(DiracDelta(t-a)*f(t), t, s)``, it will return | |
``(f(a)*exp(-a*s), -a, True)``. | |
""" | |
# This rule is not in Bateman54 | |
a = Wild('a', exclude=[t]) | |
b = Wild('b', exclude=[t]) | |
y = Wild('y') | |
z = Wild('z') | |
ma1 = f.match(DiracDelta(y)*z) | |
if ma1 and not ma1[z].has(DiracDelta): | |
ma2 = ma1[y].collect(t).match(b*t-a) | |
if ma2: | |
_debug(' rule: multiply with DiracDelta') | |
loc = ma2[a]/ma2[b] | |
if re(loc) >= 0 and im(loc) == 0: | |
fn = exp(-ma2[a]/ma2[b]*s)*ma1[z] | |
if fn.has(sin, cos): | |
# Then it may be possible that a sinc() is present in the | |
# term; let's try this: | |
fn = fn.rewrite(sinc).ratsimp() | |
n, d = [x.subs(t, ma2[a]/ma2[b]) for x in fn.as_numer_denom()] | |
if d != 0: | |
return (n/d/ma2[b], S.NegativeInfinity, S.true) | |
else: | |
return None | |
else: | |
return (0, S.NegativeInfinity, S.true) | |
if ma1[y].is_polynomial(t): | |
ro = roots(ma1[y], t) | |
if ro != {} and set(ro.values()) == {1}: | |
slope = diff(ma1[y], t) | |
r = Add( | |
*[exp(-x*s)*ma1[z].subs(t, s)/slope.subs(t, x) | |
for x in list(ro.keys()) if im(x) == 0 and re(x) >= 0]) | |
return (r, S.NegativeInfinity, S.true) | |
return None | |
def _laplace_trig_split(fn): | |
""" | |
Helper function for `_laplace_rule_trig`. This function returns two terms | |
`f` and `g`. `f` contains all product terms with sin, cos, sinh, cosh in | |
them; `g` contains everything else. | |
""" | |
trigs = [S.One] | |
other = [S.One] | |
for term in Mul.make_args(fn): | |
if term.has(sin, cos, sinh, cosh, exp): | |
trigs.append(term) | |
else: | |
other.append(term) | |
f = Mul(*trigs) | |
g = Mul(*other) | |
return f, g | |
def _laplace_trig_expsum(f, t): | |
""" | |
Helper function for `_laplace_rule_trig`. This function expects the `f` | |
from `_laplace_trig_split`. It returns two lists `xm` and `xn`. `xm` is | |
a list of dictionaries with keys `k` and `a` representing a function | |
`k*exp(a*t)`. `xn` is a list of all terms that cannot be brought into | |
that form, which may happen, e.g., when a trigonometric function has | |
another function in its argument. | |
""" | |
c1 = Wild('c1', exclude=[t]) | |
c0 = Wild('c0', exclude=[t]) | |
p = Wild('p', exclude=[t]) | |
xm = [] | |
xn = [] | |
x1 = f.rewrite(exp).expand() | |
for term in Add.make_args(x1): | |
if not term.has(t): | |
xm.append({'k': term, 'a': 0, re: 0, im: 0}) | |
continue | |
term = _laplace_deep_collect(term.powsimp(combine='exp'), t) | |
if (r := term.match(p*exp(c1*t+c0))) is not None: | |
xm.append({ | |
'k': r[p]*exp(r[c0]), 'a': r[c1], | |
re: re(r[c1]), im: im(r[c1])}) | |
else: | |
xn.append(term) | |
return xm, xn | |
def _laplace_trig_ltex(xm, t, s): | |
""" | |
Helper function for `_laplace_rule_trig`. This function takes the list of | |
exponentials `xm` from `_laplace_trig_expsum` and simplifies complex | |
conjugate and real symmetric poles. It returns the result as a sum and | |
the convergence plane. | |
""" | |
results = [] | |
planes = [] | |
def _simpc(coeffs): | |
nc = coeffs.copy() | |
for k in range(len(nc)): | |
ri = nc[k].as_real_imag() | |
if ri[0].has(im): | |
nc[k] = nc[k].rewrite(cos) | |
else: | |
nc[k] = (ri[0] + I*ri[1]).rewrite(cos) | |
return nc | |
def _quadpole(t1, k1, k2, k3, s): | |
a, k0, a_r, a_i = t1['a'], t1['k'], t1[re], t1[im] | |
nc = [ | |
k0 + k1 + k2 + k3, | |
a*(k0 + k1 - k2 - k3) - 2*I*a_i*k1 + 2*I*a_i*k2, | |
( | |
a**2*(-k0 - k1 - k2 - k3) + | |
a*(4*I*a_i*k0 + 4*I*a_i*k3) + | |
4*a_i**2*k0 + 4*a_i**2*k3), | |
( | |
a**3*(-k0 - k1 + k2 + k3) + | |
a**2*(4*I*a_i*k0 + 2*I*a_i*k1 - 2*I*a_i*k2 - 4*I*a_i*k3) + | |
a*(4*a_i**2*k0 - 4*a_i**2*k3)) | |
] | |
dc = [ | |
S.One, S.Zero, 2*a_i**2 - 2*a_r**2, | |
S.Zero, a_i**4 + 2*a_i**2*a_r**2 + a_r**4] | |
n = Add( | |
*[x*s**y for x, y in zip(_simpc(nc), range(len(nc))[::-1])]) | |
d = Add( | |
*[x*s**y for x, y in zip(dc, range(len(dc))[::-1])]) | |
return n/d | |
def _ccpole(t1, k1, s): | |
a, k0, a_r, a_i = t1['a'], t1['k'], t1[re], t1[im] | |
nc = [k0 + k1, -a*k0 - a*k1 + 2*I*a_i*k0] | |
dc = [S.One, -2*a_r, a_i**2 + a_r**2] | |
n = Add( | |
*[x*s**y for x, y in zip(_simpc(nc), range(len(nc))[::-1])]) | |
d = Add( | |
*[x*s**y for x, y in zip(dc, range(len(dc))[::-1])]) | |
return n/d | |
def _rspole(t1, k2, s): | |
a, k0, a_r, a_i = t1['a'], t1['k'], t1[re], t1[im] | |
nc = [k0 + k2, a*k0 - a*k2 - 2*I*a_i*k0] | |
dc = [S.One, -2*I*a_i, -a_i**2 - a_r**2] | |
n = Add( | |
*[x*s**y for x, y in zip(_simpc(nc), range(len(nc))[::-1])]) | |
d = Add( | |
*[x*s**y for x, y in zip(dc, range(len(dc))[::-1])]) | |
return n/d | |
def _sypole(t1, k3, s): | |
a, k0 = t1['a'], t1['k'] | |
nc = [k0 + k3, a*(k0 - k3)] | |
dc = [S.One, S.Zero, -a**2] | |
n = Add( | |
*[x*s**y for x, y in zip(_simpc(nc), range(len(nc))[::-1])]) | |
d = Add( | |
*[x*s**y for x, y in zip(dc, range(len(dc))[::-1])]) | |
return n/d | |
def _simplepole(t1, s): | |
a, k0 = t1['a'], t1['k'] | |
n = k0 | |
d = s - a | |
return n/d | |
while len(xm) > 0: | |
t1 = xm.pop() | |
i_imagsym = None | |
i_realsym = None | |
i_pointsym = None | |
# The following code checks all remaining poles. If t1 is a pole at | |
# a+b*I, then we check for a-b*I, -a+b*I, and -a-b*I, and | |
# assign the respective indices to i_imagsym, i_realsym, i_pointsym. | |
# -a-b*I / i_pointsym only applies if both a and b are != 0. | |
for i in range(len(xm)): | |
real_eq = t1[re] == xm[i][re] | |
realsym = t1[re] == -xm[i][re] | |
imag_eq = t1[im] == xm[i][im] | |
imagsym = t1[im] == -xm[i][im] | |
if realsym and imagsym and t1[re] != 0 and t1[im] != 0: | |
i_pointsym = i | |
elif realsym and imag_eq and t1[re] != 0: | |
i_realsym = i | |
elif real_eq and imagsym and t1[im] != 0: | |
i_imagsym = i | |
# The next part looks for four possible pole constellations: | |
# quad: a+b*I, a-b*I, -a+b*I, -a-b*I | |
# cc: a+b*I, a-b*I (a may be zero) | |
# quad: a+b*I, -a+b*I (b may be zero) | |
# point: a+b*I, -a-b*I (a!=0 and b!=0 is needed, but that has been | |
# asserted when finding i_pointsym above.) | |
# If none apply, then t1 is a simple pole. | |
if ( | |
i_imagsym is not None and i_realsym is not None | |
and i_pointsym is not None): | |
results.append( | |
_quadpole(t1, | |
xm[i_imagsym]['k'], xm[i_realsym]['k'], | |
xm[i_pointsym]['k'], s)) | |
planes.append(Abs(re(t1['a']))) | |
# The three additional poles have now been used; to pop them | |
# easily we have to do it from the back. | |
indices_to_pop = [i_imagsym, i_realsym, i_pointsym] | |
indices_to_pop.sort(reverse=True) | |
for i in indices_to_pop: | |
xm.pop(i) | |
elif i_imagsym is not None: | |
results.append(_ccpole(t1, xm[i_imagsym]['k'], s)) | |
planes.append(t1[re]) | |
xm.pop(i_imagsym) | |
elif i_realsym is not None: | |
results.append(_rspole(t1, xm[i_realsym]['k'], s)) | |
planes.append(Abs(t1[re])) | |
xm.pop(i_realsym) | |
elif i_pointsym is not None: | |
results.append(_sypole(t1, xm[i_pointsym]['k'], s)) | |
planes.append(Abs(t1[re])) | |
xm.pop(i_pointsym) | |
else: | |
results.append(_simplepole(t1, s)) | |
planes.append(t1[re]) | |
return Add(*results), Max(*planes) | |
def _laplace_rule_trig(fn, t_, s): | |
""" | |
This rule covers trigonometric factors by splitting everything into a | |
sum of exponential functions and collecting complex conjugate poles and | |
real symmetric poles. | |
""" | |
t = Dummy('t', real=True) | |
if not fn.has(sin, cos, sinh, cosh): | |
return None | |
f, g = _laplace_trig_split(fn.subs(t_, t)) | |
xm, xn = _laplace_trig_expsum(f, t) | |
if len(xn) > 0: | |
# TODO not implemented yet, but also not important | |
return None | |
if not g.has(t): | |
r, p = _laplace_trig_ltex(xm, t, s) | |
return g*r, p, S.true | |
else: | |
# Just transform `g` and make frequency-shifted copies | |
planes = [] | |
results = [] | |
G, G_plane, G_cond = _laplace_transform(g, t, s, simplify=False) | |
for x1 in xm: | |
results.append(x1['k']*G.subs(s, s-x1['a'])) | |
planes.append(G_plane+re(x1['a'])) | |
return Add(*results).subs(t, t_), Max(*planes), G_cond | |
def _laplace_rule_diff(f, t, s): | |
""" | |
This function looks for derivatives in the time domain and replaces it | |
by factors of `s` and initial conditions in the frequency domain. For | |
example, if it gets ``(diff(f(t), t), t, s)``, it will compute | |
``s*LaplaceTransform(f(t), t, s) - f(0)``. | |
""" | |
a = Wild('a', exclude=[t]) | |
n = Wild('n', exclude=[t]) | |
g = WildFunction('g') | |
ma1 = f.match(a*Derivative(g, (t, n))) | |
if ma1 and ma1[n].is_integer: | |
m = [z.has(t) for z in ma1[g].args] | |
if sum(m) == 1: | |
_debug(' rule: time derivative (4.1.8)') | |
d = [] | |
for k in range(ma1[n]): | |
if k == 0: | |
y = ma1[g].subs(t, 0) | |
else: | |
y = Derivative(ma1[g], (t, k)).subs(t, 0) | |
d.append(s**(ma1[n]-k-1)*y) | |
r, pr, cr = _laplace_transform(ma1[g], t, s, simplify=False) | |
return (ma1[a]*(s**ma1[n]*r - Add(*d)), pr, cr) | |
return None | |
def _laplace_rule_sdiff(f, t, s): | |
""" | |
This function looks for multiplications with polynoimials in `t` as they | |
correspond to differentiation in the frequency domain. For example, if it | |
gets ``(t*f(t), t, s)``, it will compute | |
``-Derivative(LaplaceTransform(f(t), t, s), s)``. | |
""" | |
if f.is_Mul: | |
pfac = [1] | |
ofac = [1] | |
for fac in Mul.make_args(f): | |
if fac.is_polynomial(t): | |
pfac.append(fac) | |
else: | |
ofac.append(fac) | |
if len(pfac) > 1: | |
pex = prod(pfac) | |
pc = Poly(pex, t).all_coeffs() | |
N = len(pc) | |
if N > 1: | |
oex = prod(ofac) | |
r_, p_, c_ = _laplace_transform(oex, t, s, simplify=False) | |
deri = [r_] | |
d1 = False | |
try: | |
d1 = -diff(deri[-1], s) | |
except ValueError: | |
d1 = False | |
if r_.has(LaplaceTransform): | |
for k in range(N-1): | |
deri.append((-1)**(k+1)*Derivative(r_, s, k+1)) | |
elif d1: | |
deri.append(d1) | |
for k in range(N-2): | |
deri.append(-diff(deri[-1], s)) | |
if d1: | |
r = Add(*[pc[N-n-1]*deri[n] for n in range(N)]) | |
return (r, p_, c_) | |
# We still have to cover the possibility that there is a symbolic positive | |
# integer exponent. | |
n = Wild('n', exclude=[t]) | |
g = Wild('g') | |
if ma1 := f.match(t**n*g): | |
if ma1[n].is_integer and ma1[n].is_positive: | |
r_, p_, c_ = _laplace_transform(ma1[g], t, s, simplify=False) | |
return (-1)**ma1[n]*diff(r_, (s, ma1[n])), p_, c_ | |
return None | |
def _laplace_expand(f, t, s): | |
""" | |
This function tries to expand its argument with successively stronger | |
methods: first it will expand on the top level, then it will expand any | |
multiplications in depth, then it will try all avilable expansion methods, | |
and finally it will try to expand trigonometric functions. | |
If it can expand, it will then compute the Laplace transform of the | |
expanded term. | |
""" | |
r = expand(f, deep=False) | |
if r.is_Add: | |
return _laplace_transform(r, t, s, simplify=False) | |
r = expand_mul(f) | |
if r.is_Add: | |
return _laplace_transform(r, t, s, simplify=False) | |
r = expand(f) | |
if r.is_Add: | |
return _laplace_transform(r, t, s, simplify=False) | |
if r != f: | |
return _laplace_transform(r, t, s, simplify=False) | |
r = expand(expand_trig(f)) | |
if r.is_Add: | |
return _laplace_transform(r, t, s, simplify=False) | |
return None | |
def _laplace_apply_prog_rules(f, t, s): | |
""" | |
This function applies all program rules and returns the result if one | |
of them gives a result. | |
""" | |
prog_rules = [_laplace_rule_heaviside, _laplace_rule_delta, | |
_laplace_rule_timescale, _laplace_rule_exp, | |
_laplace_rule_trig, | |
_laplace_rule_diff, _laplace_rule_sdiff] | |
for p_rule in prog_rules: | |
if (L := p_rule(f, t, s)) is not None: | |
return L | |
return None | |
def _laplace_apply_simple_rules(f, t, s): | |
""" | |
This function applies all simple rules and returns the result if one | |
of them gives a result. | |
""" | |
simple_rules, t_, s_ = _laplace_build_rules() | |
prep_old = '' | |
prep_f = '' | |
for t_dom, s_dom, check, plane, prep in simple_rules: | |
if prep_old != prep: | |
prep_f = prep(f.subs({t: t_})) | |
prep_old = prep | |
ma = prep_f.match(t_dom) | |
if ma: | |
try: | |
c = check.xreplace(ma) | |
except TypeError: | |
# This may happen if the time function has imaginary | |
# numbers in it. Then we give up. | |
continue | |
if c == S.true: | |
return (s_dom.xreplace(ma).subs({s_: s}), | |
plane.xreplace(ma), S.true) | |
return None | |
def _piecewise_to_heaviside(f, t): | |
""" | |
This function converts a Piecewise expression to an expression written | |
with Heaviside. It is not exact, but valid in the context of the Laplace | |
transform. | |
""" | |
if not t.is_real: | |
r = Dummy('r', real=True) | |
return _piecewise_to_heaviside(f.xreplace({t: r}), r).xreplace({r: t}) | |
x = piecewise_exclusive(f) | |
r = [] | |
for fn, cond in x.args: | |
# Here we do not need to do many checks because piecewise_exclusive | |
# has a clearly predictable output. However, if any of the conditions | |
# is not relative to t, this function just returns the input argument. | |
if isinstance(cond, Relational) and t in cond.args: | |
if isinstance(cond, (Eq, Ne)): | |
# We do not cover this case; these would be single-point | |
# exceptions that do not play a role in Laplace practice, | |
# except if they contain Dirac impulses, and then we can | |
# expect users to not try to use Piecewise for writing it. | |
return f | |
else: | |
r.append(Heaviside(cond.gts - cond.lts)*fn) | |
elif isinstance(cond, Or) and len(cond.args) == 2: | |
# Or(t<2, t>4), Or(t>4, t<=2), ... in any order with any <= >= | |
for c2 in cond.args: | |
if c2.lhs == t: | |
r.append(Heaviside(c2.gts - c2.lts)*fn) | |
else: | |
return f | |
elif isinstance(cond, And) and len(cond.args) == 2: | |
# And(t>2, t<4), And(t>4, t<=2), ... in any order with any <= >= | |
c0, c1 = cond.args | |
if c0.lhs == t and c1.lhs == t: | |
if '>' in c0.rel_op: | |
c0, c1 = c1, c0 | |
r.append( | |
(Heaviside(c1.gts - c1.lts) - | |
Heaviside(c0.lts - c0.gts))*fn) | |
else: | |
return f | |
else: | |
return f | |
return Add(*r) | |
def laplace_correspondence(f, fdict, /): | |
""" | |
This helper function takes a function `f` that is the result of a | |
``laplace_transform`` or an ``inverse_laplace_transform``. It replaces all | |
unevaluated ``LaplaceTransform(y(t), t, s)`` by `Y(s)` for any `s` and | |
all ``InverseLaplaceTransform(Y(s), s, t)`` by `y(t)` for any `t` if | |
``fdict`` contains a correspondence ``{y: Y}``. | |
Parameters | |
========== | |
f : sympy expression | |
Expression containing unevaluated ``LaplaceTransform`` or | |
``LaplaceTransform`` objects. | |
fdict : dictionary | |
Dictionary containing one or more function correspondences, | |
e.g., ``{x: X, y: Y}`` meaning that ``X`` and ``Y`` are the | |
Laplace transforms of ``x`` and ``y``, respectively. | |
Examples | |
======== | |
>>> from sympy import laplace_transform, diff, Function | |
>>> from sympy import laplace_correspondence, inverse_laplace_transform | |
>>> from sympy.abc import t, s | |
>>> y = Function("y") | |
>>> Y = Function("Y") | |
>>> z = Function("z") | |
>>> Z = Function("Z") | |
>>> f = laplace_transform(diff(y(t), t, 1) + z(t), t, s, noconds=True) | |
>>> laplace_correspondence(f, {y: Y, z: Z}) | |
s*Y(s) + Z(s) - y(0) | |
>>> f = inverse_laplace_transform(Y(s), s, t) | |
>>> laplace_correspondence(f, {y: Y}) | |
y(t) | |
""" | |
p = Wild('p') | |
s = Wild('s') | |
t = Wild('t') | |
a = Wild('a') | |
if ( | |
not isinstance(f, Expr) | |
or (not f.has(LaplaceTransform) | |
and not f.has(InverseLaplaceTransform))): | |
return f | |
for y, Y in fdict.items(): | |
if ( | |
(m := f.match(LaplaceTransform(y(a), t, s))) is not None | |
and m[a] == m[t]): | |
return Y(m[s]) | |
if ( | |
(m := f.match(InverseLaplaceTransform(Y(a), s, t, p))) | |
is not None | |
and m[a] == m[s]): | |
return y(m[t]) | |
func = f.func | |
args = [laplace_correspondence(arg, fdict) for arg in f.args] | |
return func(*args) | |
def laplace_initial_conds(f, t, fdict, /): | |
""" | |
This helper function takes a function `f` that is the result of a | |
``laplace_transform``. It takes an fdict of the form ``{y: [1, 4, 2]}``, | |
where the values in the list are the initial value, the initial slope, the | |
initial second derivative, etc., of the function `y(t)`, and replaces all | |
unevaluated initial conditions. | |
Parameters | |
========== | |
f : sympy expression | |
Expression containing initial conditions of unevaluated functions. | |
t : sympy expression | |
Variable for which the initial conditions are to be applied. | |
fdict : dictionary | |
Dictionary containing a list of initial conditions for every | |
function, e.g., ``{y: [0, 1, 2], x: [3, 4, 5]}``. The order | |
of derivatives is ascending, so `0`, `1`, `2` are `y(0)`, `y'(0)`, | |
and `y''(0)`, respectively. | |
Examples | |
======== | |
>>> from sympy import laplace_transform, diff, Function | |
>>> from sympy import laplace_correspondence, laplace_initial_conds | |
>>> from sympy.abc import t, s | |
>>> y = Function("y") | |
>>> Y = Function("Y") | |
>>> f = laplace_transform(diff(y(t), t, 3), t, s, noconds=True) | |
>>> g = laplace_correspondence(f, {y: Y}) | |
>>> laplace_initial_conds(g, t, {y: [2, 4, 8, 16, 32]}) | |
s**3*Y(s) - 2*s**2 - 4*s - 8 | |
""" | |
for y, ic in fdict.items(): | |
for k in range(len(ic)): | |
if k == 0: | |
f = f.replace(y(0), ic[0]) | |
elif k == 1: | |
f = f.replace(Subs(Derivative(y(t), t), t, 0), ic[1]) | |
else: | |
f = f.replace(Subs(Derivative(y(t), (t, k)), t, 0), ic[k]) | |
return f | |
def _laplace_transform(fn, t_, s_, *, simplify): | |
""" | |
Front-end function of the Laplace transform. It tries to apply all known | |
rules recursively, and if everything else fails, it tries to integrate. | |
""" | |
terms_t = Add.make_args(fn) | |
terms_s = [] | |
terms = [] | |
planes = [] | |
conditions = [] | |
for ff in terms_t: | |
k, ft = ff.as_independent(t_, as_Add=False) | |
if ft.has(SingularityFunction): | |
_terms = Add.make_args(ft.rewrite(Heaviside)) | |
for _term in _terms: | |
k1, f1 = _term.as_independent(t_, as_Add=False) | |
terms.append((k*k1, f1)) | |
elif ft.func == Piecewise and not ft.has(DiracDelta(t_)): | |
_terms = Add.make_args(_piecewise_to_heaviside(ft, t_)) | |
for _term in _terms: | |
k1, f1 = _term.as_independent(t_, as_Add=False) | |
terms.append((k*k1, f1)) | |
else: | |
terms.append((k, ft)) | |
for k, ft in terms: | |
if ft.has(SingularityFunction): | |
r = (LaplaceTransform(ft, t_, s_), S.NegativeInfinity, True) | |
else: | |
if ft.has(Heaviside(t_)) and not ft.has(DiracDelta(t_)): | |
# For t>=0, Heaviside(t)=1 can be used, except if there is also | |
# a DiracDelta(t) present, in which case removing Heaviside(t) | |
# is unnecessary because _laplace_rule_delta can deal with it. | |
ft = ft.subs(Heaviside(t_), 1) | |
if ( | |
(r := _laplace_apply_simple_rules(ft, t_, s_)) | |
is not None or | |
(r := _laplace_apply_prog_rules(ft, t_, s_)) | |
is not None or | |
(r := _laplace_expand(ft, t_, s_)) is not None): | |
pass | |
elif any(undef.has(t_) for undef in ft.atoms(AppliedUndef)): | |
# If there are undefined functions f(t) then integration is | |
# unlikely to do anything useful so we skip it and given an | |
# unevaluated LaplaceTransform. | |
r = (LaplaceTransform(ft, t_, s_), S.NegativeInfinity, True) | |
elif (r := _laplace_transform_integration( | |
ft, t_, s_, simplify=simplify)) is not None: | |
pass | |
else: | |
r = (LaplaceTransform(ft, t_, s_), S.NegativeInfinity, True) | |
(ri_, pi_, ci_) = r | |
terms_s.append(k*ri_) | |
planes.append(pi_) | |
conditions.append(ci_) | |
result = Add(*terms_s) | |
if simplify: | |
result = result.simplify(doit=False) | |
plane = Max(*planes) | |
condition = And(*conditions) | |
return result, plane, condition | |
class LaplaceTransform(IntegralTransform): | |
""" | |
Class representing unevaluated Laplace transforms. | |
For usage of this class, see the :class:`IntegralTransform` docstring. | |
For how to compute Laplace transforms, see the :func:`laplace_transform` | |
docstring. | |
If this is called with ``.doit()``, it returns the Laplace transform as an | |
expression. If it is called with ``.doit(noconds=False)``, it returns a | |
tuple containing the same expression, a convergence plane, and conditions. | |
""" | |
_name = 'Laplace' | |
def _compute_transform(self, f, t, s, **hints): | |
_simplify = hints.get('simplify', False) | |
LT = _laplace_transform_integration(f, t, s, simplify=_simplify) | |
return LT | |
def _as_integral(self, f, t, s): | |
return Integral(f*exp(-s*t), (t, S.Zero, S.Infinity)) | |
def doit(self, **hints): | |
""" | |
Try to evaluate the transform in closed form. | |
Explanation | |
=========== | |
Standard hints are the following: | |
- ``noconds``: if True, do not return convergence conditions. The | |
default setting is `True`. | |
- ``simplify``: if True, it simplifies the final result. The | |
default setting is `False`. | |
""" | |
_noconds = hints.get('noconds', True) | |
_simplify = hints.get('simplify', False) | |
debugf('[LT doit] (%s, %s, %s)', (self.function, | |
self.function_variable, | |
self.transform_variable)) | |
t_ = self.function_variable | |
s_ = self.transform_variable | |
fn = self.function | |
r = _laplace_transform(fn, t_, s_, simplify=_simplify) | |
if _noconds: | |
return r[0] | |
else: | |
return r | |
def laplace_transform(f, t, s, legacy_matrix=True, **hints): | |
r""" | |
Compute the Laplace Transform `F(s)` of `f(t)`, | |
.. math :: F(s) = \int_{0^{-}}^\infty e^{-st} f(t) \mathrm{d}t. | |
Explanation | |
=========== | |
For all sensible functions, this converges absolutely in a | |
half-plane | |
.. math :: a < \operatorname{Re}(s) | |
This function returns ``(F, a, cond)`` where ``F`` is the Laplace | |
transform of ``f``, `a` is the half-plane of convergence, and `cond` are | |
auxiliary convergence conditions. | |
The implementation is rule-based, and if you are interested in which | |
rules are applied, and whether integration is attempted, you can switch | |
debug information on by setting ``sympy.SYMPY_DEBUG=True``. The numbers | |
of the rules in the debug information (and the code) refer to Bateman's | |
Tables of Integral Transforms [1]. | |
The lower bound is `0-`, meaning that this bound should be approached | |
from the lower side. This is only necessary if distributions are involved. | |
At present, it is only done if `f(t)` contains ``DiracDelta``, in which | |
case the Laplace transform is computed implicitly as | |
.. math :: | |
F(s) = \lim_{\tau\to 0^{-}} \int_{\tau}^\infty e^{-st} | |
f(t) \mathrm{d}t | |
by applying rules. | |
If the Laplace transform cannot be fully computed in closed form, this | |
function returns expressions containing unevaluated | |
:class:`LaplaceTransform` objects. | |
For a description of possible hints, refer to the docstring of | |
:func:`sympy.integrals.transforms.IntegralTransform.doit`. If | |
``noconds=True``, only `F` will be returned (i.e. not ``cond``, and also | |
not the plane ``a``). | |
.. deprecated:: 1.9 | |
Legacy behavior for matrices where ``laplace_transform`` with | |
``noconds=False`` (the default) returns a Matrix whose elements are | |
tuples. The behavior of ``laplace_transform`` for matrices will change | |
in a future release of SymPy to return a tuple of the transformed | |
Matrix and the convergence conditions for the matrix as a whole. Use | |
``legacy_matrix=False`` to enable the new behavior. | |
Examples | |
======== | |
>>> from sympy import DiracDelta, exp, laplace_transform | |
>>> from sympy.abc import t, s, a | |
>>> laplace_transform(t**4, t, s) | |
(24/s**5, 0, True) | |
>>> laplace_transform(t**a, t, s) | |
(gamma(a + 1)/(s*s**a), 0, re(a) > -1) | |
>>> laplace_transform(DiracDelta(t)-a*exp(-a*t), t, s, simplify=True) | |
(s/(a + s), -re(a), True) | |
There are also helper functions that make it easy to solve differential | |
equations by Laplace transform. For example, to solve | |
.. math :: m x''(t) + d x'(t) + k x(t) = 0 | |
with initial value `0` and initial derivative `v`: | |
>>> from sympy import Function, laplace_correspondence, diff, solve | |
>>> from sympy import laplace_initial_conds, inverse_laplace_transform | |
>>> from sympy.abc import d, k, m, v | |
>>> x = Function('x') | |
>>> X = Function('X') | |
>>> f = m*diff(x(t), t, 2) + d*diff(x(t), t) + k*x(t) | |
>>> F = laplace_transform(f, t, s, noconds=True) | |
>>> F = laplace_correspondence(F, {x: X}) | |
>>> F = laplace_initial_conds(F, t, {x: [0, v]}) | |
>>> F | |
d*s*X(s) + k*X(s) + m*(s**2*X(s) - v) | |
>>> Xs = solve(F, X(s))[0] | |
>>> Xs | |
m*v/(d*s + k + m*s**2) | |
>>> inverse_laplace_transform(Xs, s, t) | |
2*v*exp(-d*t/(2*m))*sin(t*sqrt((-d**2 + 4*k*m)/m**2)/2)*Heaviside(t)/sqrt((-d**2 + 4*k*m)/m**2) | |
References | |
========== | |
.. [1] Erdelyi, A. (ed.), Tables of Integral Transforms, Volume 1, | |
Bateman Manuscript Prooject, McGraw-Hill (1954), available: | |
https://resolver.caltech.edu/CaltechAUTHORS:20140123-101456353 | |
See Also | |
======== | |
inverse_laplace_transform, mellin_transform, fourier_transform | |
hankel_transform, inverse_hankel_transform | |
""" | |
_noconds = hints.get('noconds', False) | |
_simplify = hints.get('simplify', False) | |
if isinstance(f, MatrixBase) and hasattr(f, 'applyfunc'): | |
conds = not hints.get('noconds', False) | |
if conds and legacy_matrix: | |
adt = 'deprecated-laplace-transform-matrix' | |
sympy_deprecation_warning( | |
""" | |
Calling laplace_transform() on a Matrix with noconds=False (the default) is | |
deprecated. Either noconds=True or use legacy_matrix=False to get the new | |
behavior. | |
""", | |
deprecated_since_version='1.9', | |
active_deprecations_target=adt, | |
) | |
# Temporarily disable the deprecation warning for non-Expr objects | |
# in Matrix | |
with ignore_warnings(SymPyDeprecationWarning): | |
return f.applyfunc( | |
lambda fij: laplace_transform(fij, t, s, **hints)) | |
else: | |
elements_trans = [laplace_transform( | |
fij, t, s, **hints) for fij in f] | |
if conds: | |
elements, avals, conditions = zip(*elements_trans) | |
f_laplace = type(f)(*f.shape, elements) | |
return f_laplace, Max(*avals), And(*conditions) | |
else: | |
return type(f)(*f.shape, elements_trans) | |
LT, p, c = LaplaceTransform(f, t, s).doit(noconds=False, | |
simplify=_simplify) | |
if not _noconds: | |
return LT, p, c | |
else: | |
return LT | |
def _inverse_laplace_transform_integration(F, s, t_, plane, *, simplify): | |
""" The backend function for inverse Laplace transforms. """ | |
from sympy.integrals.meijerint import meijerint_inversion, _get_coeff_exp | |
from sympy.integrals.transforms import inverse_mellin_transform | |
# There are two strategies we can try: | |
# 1) Use inverse mellin transform, related by a simple change of variables. | |
# 2) Use the inversion integral. | |
t = Dummy('t', real=True) | |
def pw_simp(*args): | |
""" Simplify a piecewise expression from hyperexpand. """ | |
if len(args) != 3: | |
return Piecewise(*args) | |
arg = args[2].args[0].argument | |
coeff, exponent = _get_coeff_exp(arg, t) | |
e1 = args[0].args[0] | |
e2 = args[1].args[0] | |
return ( | |
Heaviside(1/Abs(coeff) - t**exponent)*e1 + | |
Heaviside(t**exponent - 1/Abs(coeff))*e2) | |
if F.is_rational_function(s): | |
F = F.apart(s) | |
if F.is_Add: | |
f = Add( | |
*[_inverse_laplace_transform_integration(X, s, t, plane, simplify) | |
for X in F.args]) | |
return _simplify(f.subs(t, t_), simplify), True | |
try: | |
f, cond = inverse_mellin_transform(F, s, exp(-t), (None, S.Infinity), | |
needeval=True, noconds=False) | |
except IntegralTransformError: | |
f = None | |
if f is None: | |
f = meijerint_inversion(F, s, t) | |
if f is None: | |
return None | |
if f.is_Piecewise: | |
f, cond = f.args[0] | |
if f.has(Integral): | |
return None | |
else: | |
cond = S.true | |
f = f.replace(Piecewise, pw_simp) | |
if f.is_Piecewise: | |
# many of the functions called below can't work with piecewise | |
# (b/c it has a bool in args) | |
return f.subs(t, t_), cond | |
u = Dummy('u') | |
def simp_heaviside(arg, H0=S.Half): | |
a = arg.subs(exp(-t), u) | |
if a.has(t): | |
return Heaviside(arg, H0) | |
from sympy.solvers.inequalities import _solve_inequality | |
rel = _solve_inequality(a > 0, u) | |
if rel.lts == u: | |
k = log(rel.gts) | |
return Heaviside(t + k, H0) | |
else: | |
k = log(rel.lts) | |
return Heaviside(-(t + k), H0) | |
f = f.replace(Heaviside, simp_heaviside) | |
def simp_exp(arg): | |
return expand_complex(exp(arg)) | |
f = f.replace(exp, simp_exp) | |
return _simplify(f.subs(t, t_), simplify), cond | |
def _complete_the_square_in_denom(f, s): | |
from sympy.simplify.radsimp import fraction | |
[n, d] = fraction(f) | |
if d.is_polynomial(s): | |
cf = d.as_poly(s).all_coeffs() | |
if len(cf) == 3: | |
a, b, c = cf | |
d = a*((s+b/(2*a))**2+c/a-(b/(2*a))**2) | |
return n/d | |
def _inverse_laplace_build_rules(): | |
""" | |
This is an internal helper function that returns the table of inverse | |
Laplace transform rules in terms of the time variable `t` and the | |
frequency variable `s`. It is used by `_inverse_laplace_apply_rules`. | |
""" | |
s = Dummy('s') | |
t = Dummy('t') | |
a = Wild('a', exclude=[s]) | |
b = Wild('b', exclude=[s]) | |
c = Wild('c', exclude=[s]) | |
_debug('_inverse_laplace_build_rules is building rules') | |
def _frac(f, s): | |
try: | |
return f.factor(s) | |
except PolynomialError: | |
return f | |
def same(f): return f | |
# This list is sorted according to the prep function needed. | |
_ILT_rules = [ | |
(a/s, a, S.true, same, 1), | |
( | |
b*(s+a)**(-c), t**(c-1)*exp(-a*t)/gamma(c), | |
S.true, same, 1), | |
(1/(s**2+a**2)**2, (sin(a*t) - a*t*cos(a*t))/(2*a**3), | |
S.true, same, 1), | |
# The next two rules must be there in that order. For the second | |
# one, the condition would be a != 0 or, respectively, to take the | |
# limit a -> 0 after the transform if a == 0. It is much simpler if | |
# the case a == 0 has its own rule. | |
(1/(s**b), t**(b - 1)/gamma(b), S.true, same, 1), | |
(1/(s*(s+a)**b), lowergamma(b, a*t)/(a**b*gamma(b)), | |
S.true, same, 1) | |
] | |
return _ILT_rules, s, t | |
def _inverse_laplace_apply_simple_rules(f, s, t): | |
""" | |
Helper function for the class InverseLaplaceTransform. | |
""" | |
if f == 1: | |
_debug(' rule: 1 o---o DiracDelta()') | |
return DiracDelta(t), S.true | |
_ILT_rules, s_, t_ = _inverse_laplace_build_rules() | |
_prep = '' | |
fsubs = f.subs({s: s_}) | |
for s_dom, t_dom, check, prep, fac in _ILT_rules: | |
if _prep != (prep, fac): | |
_F = prep(fsubs*fac) | |
_prep = (prep, fac) | |
ma = _F.match(s_dom) | |
if ma: | |
c = check | |
if c is not S.true: | |
args = [x.xreplace(ma) for x in c[0]] | |
c = c[1](*args) | |
if c == S.true: | |
return Heaviside(t)*t_dom.xreplace(ma).subs({t_: t}), S.true | |
return None | |
def _inverse_laplace_diff(f, s, t, plane): | |
""" | |
Helper function for the class InverseLaplaceTransform. | |
""" | |
a = Wild('a', exclude=[s]) | |
n = Wild('n', exclude=[s]) | |
g = Wild('g') | |
ma = f.match(a*Derivative(g, (s, n))) | |
if ma and ma[n].is_integer: | |
_debug(' rule: t**n*f(t) o---o (-1)**n*diff(F(s), s, n)') | |
r, c = _inverse_laplace_transform( | |
ma[g], s, t, plane, simplify=False, dorational=False) | |
return (-t)**ma[n]*r, c | |
return None | |
def _inverse_laplace_time_shift(F, s, t, plane): | |
""" | |
Helper function for the class InverseLaplaceTransform. | |
""" | |
a = Wild('a', exclude=[s]) | |
g = Wild('g') | |
if not F.has(s): | |
return F*DiracDelta(t), S.true | |
if not F.has(exp): | |
return None | |
ma1 = F.match(exp(a*s)) | |
if ma1: | |
if ma1[a].is_negative: | |
_debug(' rule: exp(-a*s) o---o DiracDelta(t-a)') | |
return DiracDelta(t+ma1[a]), S.true | |
else: | |
return InverseLaplaceTransform(F, s, t, plane), S.true | |
ma1 = F.match(exp(a*s)*g) | |
if ma1: | |
if ma1[a].is_negative: | |
_debug(' rule: exp(-a*s)*F(s) o---o Heaviside(t-a)*f(t-a)') | |
return _inverse_laplace_transform( | |
ma1[g], s, t+ma1[a], plane, simplify=False, dorational=True) | |
else: | |
return InverseLaplaceTransform(F, s, t, plane), S.true | |
return None | |
def _inverse_laplace_freq_shift(F, s, t, plane): | |
""" | |
Helper function for the class InverseLaplaceTransform. | |
""" | |
if not F.has(s): | |
return F*DiracDelta(t), S.true | |
if len(args := F.args) == 1: | |
a = Wild('a', exclude=[s]) | |
if (ma := args[0].match(s-a)) and re(ma[a]).is_positive: | |
_debug(' rule: F(s-a) o---o exp(-a*t)*f(t)') | |
return ( | |
exp(-ma[a]*t) * | |
InverseLaplaceTransform(F.func(s), s, t, plane), S.true) | |
return None | |
def _inverse_laplace_time_diff(F, s, t, plane): | |
""" | |
Helper function for the class InverseLaplaceTransform. | |
""" | |
n = Wild('n', exclude=[s]) | |
g = Wild('g') | |
ma1 = F.match(s**n*g) | |
if ma1 and ma1[n].is_integer and ma1[n].is_positive: | |
_debug(' rule: s**n*F(s) o---o diff(f(t), t, n)') | |
r, c = _inverse_laplace_transform( | |
ma1[g], s, t, plane, simplify=False, dorational=True) | |
r = r.replace(Heaviside(t), 1) | |
if r.has(InverseLaplaceTransform): | |
return diff(r, t, ma1[n]), c | |
else: | |
return Heaviside(t)*diff(r, t, ma1[n]), c | |
return None | |
def _inverse_laplace_irrational(fn, s, t, plane): | |
""" | |
Helper function for the class InverseLaplaceTransform. | |
""" | |
a = Wild('a', exclude=[s]) | |
b = Wild('b', exclude=[s]) | |
m = Wild('m', exclude=[s]) | |
n = Wild('n', exclude=[s]) | |
result = None | |
condition = S.true | |
fa = fn.as_ordered_factors() | |
ma = [x.match((a*s**m+b)**n) for x in fa] | |
if None in ma: | |
return None | |
constants = S.One | |
zeros = [] | |
poles = [] | |
rest = [] | |
for term in ma: | |
if term[a] == 0: | |
constants = constants*term | |
elif term[n].is_positive: | |
zeros.append(term) | |
elif term[n].is_negative: | |
poles.append(term) | |
else: | |
rest.append(term) | |
# The code below assumes that the poles are sorted in a specific way: | |
poles = sorted(poles, key=lambda x: (x[n], x[b] != 0, x[b])) | |
zeros = sorted(zeros, key=lambda x: (x[n], x[b] != 0, x[b])) | |
if len(rest) != 0: | |
return None | |
if len(poles) == 1 and len(zeros) == 0: | |
if poles[0][n] == -1 and poles[0][m] == S.Half: | |
# 1/(a0*sqrt(s)+b0) == 1/a0 * 1/(sqrt(s)+b0/a0) | |
a_ = poles[0][b]/poles[0][a] | |
k_ = 1/poles[0][a]*constants | |
if a_.is_positive: | |
result = ( | |
k_/sqrt(pi)/sqrt(t) - | |
k_*a_*exp(a_**2*t)*erfc(a_*sqrt(t))) | |
_debug(' rule 5.3.4') | |
elif poles[0][n] == -2 and poles[0][m] == S.Half: | |
# 1/(a0*sqrt(s)+b0)**2 == 1/a0**2 * 1/(sqrt(s)+b0/a0)**2 | |
a_sq = poles[0][b]/poles[0][a] | |
a_ = a_sq**2 | |
k_ = 1/poles[0][a]**2*constants | |
if a_sq.is_positive: | |
result = ( | |
k_*(1 - 2/sqrt(pi)*sqrt(a_)*sqrt(t) + | |
(1-2*a_*t)*exp(a_*t)*(erf(sqrt(a_)*sqrt(t))-1))) | |
_debug(' rule 5.3.10') | |
elif poles[0][n] == -3 and poles[0][m] == S.Half: | |
# 1/(a0*sqrt(s)+b0)**3 == 1/a0**3 * 1/(sqrt(s)+b0/a0)**3 | |
a_ = poles[0][b]/poles[0][a] | |
k_ = 1/poles[0][a]**3*constants | |
if a_.is_positive: | |
result = ( | |
k_*(2/sqrt(pi)*(a_**2*t+1)*sqrt(t) - | |
a_*t*exp(a_**2*t)*(2*a_**2*t+3)*erfc(a_*sqrt(t)))) | |
_debug(' rule 5.3.13') | |
elif poles[0][n] == -4 and poles[0][m] == S.Half: | |
# 1/(a0*sqrt(s)+b0)**4 == 1/a0**4 * 1/(sqrt(s)+b0/a0)**4 | |
a_ = poles[0][b]/poles[0][a] | |
k_ = 1/poles[0][a]**4*constants/3 | |
if a_.is_positive: | |
result = ( | |
k_*(t*(4*a_**4*t**2+12*a_**2*t+3)*exp(a_**2*t) * | |
erfc(a_*sqrt(t)) - | |
2/sqrt(pi)*a_**3*t**(S(5)/2)*(2*a_**2*t+5))) | |
_debug(' rule 5.3.16') | |
elif poles[0][n] == -S.Half and poles[0][m] == 2: | |
# 1/sqrt(a0*s**2+b0) == 1/sqrt(a0) * 1/sqrt(s**2+b0/a0) | |
a_ = sqrt(poles[0][b]/poles[0][a]) | |
k_ = 1/sqrt(poles[0][a])*constants | |
result = (k_*(besselj(0, a_*t))) | |
_debug(' rule 5.3.35/44') | |
elif len(poles) == 1 and len(zeros) == 1: | |
if ( | |
poles[0][n] == -3 and poles[0][m] == S.Half and | |
zeros[0][n] == S.Half and zeros[0][b] == 0): | |
# sqrt(az*s)/(ap*sqrt(s+bp)**3) | |
# == sqrt(az)/ap * sqrt(s)/(sqrt(s+bp)**3) | |
a_ = poles[0][b] | |
k_ = sqrt(zeros[0][a])/poles[0][a]*constants | |
result = ( | |
k_*(2*a_**4*t**2+5*a_**2*t+1)*exp(a_**2*t) * | |
erfc(a_*sqrt(t)) - 2/sqrt(pi)*a_*(a_**2*t+2)*sqrt(t)) | |
_debug(' rule 5.3.14') | |
if ( | |
poles[0][n] == -1 and poles[0][m] == 1 and | |
zeros[0][n] == S.Half and zeros[0][m] == 1): | |
# sqrt(az*s+bz)/(ap*s+bp) | |
# == sqrt(az)/ap * (sqrt(s+bz/az)/(s+bp/ap)) | |
a_ = zeros[0][b]/zeros[0][a] | |
b_ = poles[0][b]/poles[0][a] | |
k_ = sqrt(zeros[0][a])/poles[0][a]*constants | |
result = ( | |
k_*(exp(-a_*t)/sqrt(t)/sqrt(pi)+sqrt(a_-b_) * | |
exp(-b_*t)*erf(sqrt(a_-b_)*sqrt(t)))) | |
_debug(' rule 5.3.22') | |
elif len(poles) == 2 and len(zeros) == 0: | |
if ( | |
poles[0][n] == -1 and poles[0][m] == 1 and | |
poles[1][n] == -S.Half and poles[1][m] == 1 and | |
poles[1][b] == 0): | |
# 1/((a0*s+b0)*sqrt(a1*s)) | |
# == 1/(a0*sqrt(a1)) * 1/((s+b0/a0)*sqrt(s)) | |
a_ = -poles[0][b]/poles[0][a] | |
k_ = 1/sqrt(poles[1][a])/poles[0][a]*constants | |
if a_.is_positive: | |
result = (k_/sqrt(a_)*exp(a_*t)*erf(sqrt(a_)*sqrt(t))) | |
_debug(' rule 5.3.1') | |
elif ( | |
poles[0][n] == -1 and poles[0][m] == 1 and poles[0][b] == 0 and | |
poles[1][n] == -1 and poles[1][m] == S.Half): | |
# 1/(a0*s*(a1*sqrt(s)+b1)) | |
# == 1/(a0*a1) * 1/(s*(sqrt(s)+b1/a1)) | |
a_ = poles[1][b]/poles[1][a] | |
k_ = 1/poles[0][a]/poles[1][a]/a_*constants | |
if a_.is_positive: | |
result = k_*(1-exp(a_**2*t)*erfc(a_*sqrt(t))) | |
_debug(' rule 5.3.5') | |
elif ( | |
poles[0][n] == -1 and poles[0][m] == S.Half and | |
poles[1][n] == -S.Half and poles[1][m] == 1 and | |
poles[1][b] == 0): | |
# 1/((a0*sqrt(s)+b0)*(sqrt(a1*s)) | |
# == 1/(a0*sqrt(a1)) * 1/((sqrt(s)+b0/a0)"sqrt(s)) | |
a_ = poles[0][b]/poles[0][a] | |
k_ = 1/(poles[0][a]*sqrt(poles[1][a]))*constants | |
if a_.is_positive: | |
result = k_*exp(a_**2*t)*erfc(a_*sqrt(t)) | |
_debug(' rule 5.3.7') | |
elif ( | |
poles[0][n] == -S(3)/2 and poles[0][m] == 1 and | |
poles[0][b] == 0 and poles[1][n] == -1 and | |
poles[1][m] == S.Half): | |
# 1/((a0**(3/2)*s**(3/2))*(a1*sqrt(s)+b1)) | |
# == 1/(a0**(3/2)*a1) 1/((s**(3/2))*(sqrt(s)+b1/a1)) | |
# Note that Bateman54 5.3 (8) is incorrect; there (sqrt(p)+a) | |
# should be (sqrt(p)+a)**(-1). | |
a_ = poles[1][b]/poles[1][a] | |
k_ = 1/(poles[0][a]**(S(3)/2)*poles[1][a])/a_**2*constants | |
if a_.is_positive: | |
result = ( | |
k_*(2/sqrt(pi)*a_*sqrt(t)+exp(a_**2*t)*erfc(a_*sqrt(t))-1)) | |
_debug(' rule 5.3.8') | |
elif ( | |
poles[0][n] == -2 and poles[0][m] == S.Half and | |
poles[1][n] == -1 and poles[1][m] == 1 and | |
poles[1][b] == 0): | |
# 1/((a0*sqrt(s)+b0)**2*a1*s) | |
# == 1/a0**2/a1 * 1/(sqrt(s)+b0/a0)**2/s | |
a_sq = poles[0][b]/poles[0][a] | |
a_ = a_sq**2 | |
k_ = 1/poles[0][a]**2/poles[1][a]*constants | |
if a_sq.is_positive: | |
result = ( | |
k_*(1/a_ + (2*t-1/a_)*exp(a_*t)*erfc(sqrt(a_)*sqrt(t)) - | |
2/sqrt(pi)/sqrt(a_)*sqrt(t))) | |
_debug(' rule 5.3.11') | |
elif ( | |
poles[0][n] == -2 and poles[0][m] == S.Half and | |
poles[1][n] == -S.Half and poles[1][m] == 1 and | |
poles[1][b] == 0): | |
# 1/((a0*sqrt(s)+b0)**2*sqrt(a1*s)) | |
# == 1/a0**2/sqrt(a1) * 1/(sqrt(s)+b0/a0)**2/sqrt(s) | |
a_ = poles[0][b]/poles[0][a] | |
k_ = 1/poles[0][a]**2/sqrt(poles[1][a])*constants | |
if a_.is_positive: | |
result = ( | |
k_*(2/sqrt(pi)*sqrt(t) - | |
2*a_*t*exp(a_**2*t)*erfc(a_*sqrt(t)))) | |
_debug(' rule 5.3.12') | |
elif ( | |
poles[0][n] == -3 and poles[0][m] == S.Half and | |
poles[1][n] == -S.Half and poles[1][m] == 1 and | |
poles[1][b] == 0): | |
# 1 / (sqrt(a1*s)*(a0*sqrt(s+b0)**3)) | |
# == 1/(sqrt(a1)*a0) * 1/(sqrt(s)*(sqrt(s+b0)**3)) | |
a_ = poles[0][b] | |
k_ = constants/sqrt(poles[1][a])/poles[0][a] | |
result = k_*( | |
(2*a_**2*t+1)*t*exp(a_**2*t)*erfc(a_*sqrt(t)) - | |
2/sqrt(pi)*a_*t**(S(3)/2)) | |
_debug(' rule 5.3.15') | |
elif ( | |
poles[0][n] == -1 and poles[0][m] == 1 and | |
poles[1][n] == -S.Half and poles[1][m] == 1): | |
# 1 / ( (a0*s+b0)* sqrt(a1*s+b1) ) | |
# == 1/(sqrt(a1)*a0) * 1 / ( (s+b0/a0)* sqrt(s+b1/a1) ) | |
a_ = poles[0][b]/poles[0][a] | |
b_ = poles[1][b]/poles[1][a] | |
k_ = constants/sqrt(poles[1][a])/poles[0][a] | |
result = k_*( | |
1/sqrt(b_-a_)*exp(-a_*t)*erf(sqrt(b_-a_)*sqrt(t))) | |
_debug(' rule 5.3.23') | |
elif len(poles) == 2 and len(zeros) == 1: | |
if ( | |
poles[0][n] == -1 and poles[0][m] == 1 and | |
poles[1][n] == -1 and poles[1][m] == S.Half and | |
zeros[0][n] == S.Half and zeros[0][m] == 1 and | |
zeros[0][b] == 0): | |
# sqrt(za0*s)/((a0*s+b0)*(a1*sqrt(s)+b1)) | |
# == sqrt(za0)/(a0*a1) * s/((s+b0/a0)*(sqrt(s)+b1/a1)) | |
a_sq = poles[1][b]/poles[1][a] | |
a_ = a_sq**2 | |
b_ = -poles[0][b]/poles[0][a] | |
k_ = sqrt(zeros[0][a])/poles[0][a]/poles[1][a]/(a_-b_)*constants | |
if a_sq.is_positive and b_.is_positive: | |
result = k_*( | |
a_*exp(a_*t)*erfc(sqrt(a_)*sqrt(t)) + | |
sqrt(a_)*sqrt(b_)*exp(b_*t)*erfc(sqrt(b_)*sqrt(t)) - | |
b_*exp(b_*t)) | |
_debug(' rule 5.3.6') | |
elif ( | |
poles[0][n] == -1 and poles[0][m] == 1 and | |
poles[0][b] == 0 and poles[1][n] == -1 and | |
poles[1][m] == S.Half and zeros[0][n] == 1 and | |
zeros[0][m] == S.Half): | |
# (az*sqrt(s)+bz)/(a0*s*(a1*sqrt(s)+b1)) | |
# == az/a0/a1 * (sqrt(z)+bz/az)/(s*(sqrt(s)+b1/a1)) | |
a_num = zeros[0][b]/zeros[0][a] | |
a_ = poles[1][b]/poles[1][a] | |
if a_+a_num == 0: | |
k_ = zeros[0][a]/poles[0][a]/poles[1][a]*constants | |
result = k_*( | |
2*exp(a_**2*t)*erfc(a_*sqrt(t))-1) | |
_debug(' rule 5.3.17') | |
elif ( | |
poles[1][n] == -1 and poles[1][m] == 1 and | |
poles[1][b] == 0 and poles[0][n] == -2 and | |
poles[0][m] == S.Half and zeros[0][n] == 2 and | |
zeros[0][m] == S.Half): | |
# (az*sqrt(s)+bz)**2/(a1*s*(a0*sqrt(s)+b0)**2) | |
# == az**2/a1/a0**2 * (sqrt(z)+bz/az)**2/(s*(sqrt(s)+b0/a0)**2) | |
a_num = zeros[0][b]/zeros[0][a] | |
a_ = poles[0][b]/poles[0][a] | |
if a_+a_num == 0: | |
k_ = zeros[0][a]**2/poles[1][a]/poles[0][a]**2*constants | |
result = k_*( | |
1 + 8*a_**2*t*exp(a_**2*t)*erfc(a_*sqrt(t)) - | |
8/sqrt(pi)*a_*sqrt(t)) | |
_debug(' rule 5.3.18') | |
elif ( | |
poles[1][n] == -1 and poles[1][m] == 1 and | |
poles[1][b] == 0 and poles[0][n] == -3 and | |
poles[0][m] == S.Half and zeros[0][n] == 3 and | |
zeros[0][m] == S.Half): | |
# (az*sqrt(s)+bz)**3/(a1*s*(a0*sqrt(s)+b0)**3) | |
# == az**3/a1/a0**3 * (sqrt(z)+bz/az)**3/(s*(sqrt(s)+b0/a0)**3) | |
a_num = zeros[0][b]/zeros[0][a] | |
a_ = poles[0][b]/poles[0][a] | |
if a_+a_num == 0: | |
k_ = zeros[0][a]**3/poles[1][a]/poles[0][a]**3*constants | |
result = k_*( | |
2*(8*a_**4*t**2+8*a_**2*t+1)*exp(a_**2*t) * | |
erfc(a_*sqrt(t))-8/sqrt(pi)*a_*sqrt(t)*(2*a_**2*t+1)-1) | |
_debug(' rule 5.3.19') | |
elif len(poles) == 3 and len(zeros) == 0: | |
if ( | |
poles[0][n] == -1 and poles[0][b] == 0 and poles[0][m] == 1 and | |
poles[1][n] == -1 and poles[1][m] == 1 and | |
poles[2][n] == -S.Half and poles[2][m] == 1): | |
# 1/((a0*s)*(a1*s+b1)*sqrt(a2*s)) | |
# == 1/(a0*a1*sqrt(a2)) * 1/((s)*(s+b1/a1)*sqrt(s)) | |
a_ = -poles[1][b]/poles[1][a] | |
k_ = 1/poles[0][a]/poles[1][a]/sqrt(poles[2][a])*constants | |
if a_.is_positive: | |
result = k_ * ( | |
a_**(-S(3)/2) * exp(a_*t) * erf(sqrt(a_)*sqrt(t)) - | |
2/a_/sqrt(pi)*sqrt(t)) | |
_debug(' rule 5.3.2') | |
elif ( | |
poles[0][n] == -1 and poles[0][m] == 1 and | |
poles[1][n] == -1 and poles[1][m] == S.Half and | |
poles[2][n] == -S.Half and poles[2][m] == 1 and | |
poles[2][b] == 0): | |
# 1/((a0*s+b0)*(a1*sqrt(s)+b1)*(sqrt(a2)*sqrt(s))) | |
# == 1/(a0*a1*sqrt(a2)) * 1/((s+b0/a0)*(sqrt(s)+b1/a1)*sqrt(s)) | |
a_sq = poles[1][b]/poles[1][a] | |
a_ = a_sq**2 | |
b_ = -poles[0][b]/poles[0][a] | |
k_ = ( | |
1/poles[0][a]/poles[1][a]/sqrt(poles[2][a]) / | |
(sqrt(b_)*(a_-b_))) | |
if a_sq.is_positive and b_.is_positive: | |
result = k_ * ( | |
sqrt(b_)*exp(a_*t)*erfc(sqrt(a_)*sqrt(t)) + | |
sqrt(a_)*exp(b_*t)*erf(sqrt(b_)*sqrt(t)) - | |
sqrt(b_)*exp(b_*t)) | |
_debug(' rule 5.3.9') | |
if result is None: | |
return None | |
else: | |
return Heaviside(t)*result, condition | |
def _inverse_laplace_early_prog_rules(F, s, t, plane): | |
""" | |
Helper function for the class InverseLaplaceTransform. | |
""" | |
prog_rules = [_inverse_laplace_irrational] | |
for p_rule in prog_rules: | |
if (r := p_rule(F, s, t, plane)) is not None: | |
return r | |
return None | |
def _inverse_laplace_apply_prog_rules(F, s, t, plane): | |
""" | |
Helper function for the class InverseLaplaceTransform. | |
""" | |
prog_rules = [_inverse_laplace_time_shift, _inverse_laplace_freq_shift, | |
_inverse_laplace_time_diff, _inverse_laplace_diff, | |
_inverse_laplace_irrational] | |
for p_rule in prog_rules: | |
if (r := p_rule(F, s, t, plane)) is not None: | |
return r | |
return None | |
def _inverse_laplace_expand(fn, s, t, plane): | |
""" | |
Helper function for the class InverseLaplaceTransform. | |
""" | |
if fn.is_Add: | |
return None | |
r = expand(fn, deep=False) | |
if r.is_Add: | |
return _inverse_laplace_transform( | |
r, s, t, plane, simplify=False, dorational=True) | |
r = expand_mul(fn) | |
if r.is_Add: | |
return _inverse_laplace_transform( | |
r, s, t, plane, simplify=False, dorational=True) | |
r = expand(fn) | |
if r.is_Add: | |
return _inverse_laplace_transform( | |
r, s, t, plane, simplify=False, dorational=True) | |
if fn.is_rational_function(s): | |
r = fn.apart(s).doit() | |
if r.is_Add: | |
return _inverse_laplace_transform( | |
r, s, t, plane, simplify=False, dorational=True) | |
return None | |
def _inverse_laplace_rational(fn, s, t, plane, *, simplify): | |
""" | |
Helper function for the class InverseLaplaceTransform. | |
""" | |
x_ = symbols('x_') | |
f = fn.apart(s) | |
terms = Add.make_args(f) | |
terms_t = [] | |
conditions = [S.true] | |
for term in terms: | |
[n, d] = term.as_numer_denom() | |
dc = d.as_poly(s).all_coeffs() | |
dc_lead = dc[0] | |
dc = [x/dc_lead for x in dc] | |
nc = [x/dc_lead for x in n.as_poly(s).all_coeffs()] | |
if len(dc) == 1: | |
r = nc[0]*DiracDelta(t) | |
terms_t.append(r) | |
elif len(dc) == 2: | |
r = nc[0]*exp(-dc[1]*t) | |
terms_t.append(Heaviside(t)*r) | |
elif len(dc) == 3: | |
a = dc[1]/2 | |
b = (dc[2]-a**2).factor() | |
if len(nc) == 1: | |
nc = [S.Zero] + nc | |
l, m = tuple(nc) | |
if b == 0: | |
r = (m*t+l*(1-a*t))*exp(-a*t) | |
else: | |
hyp = False | |
if b.is_negative: | |
b = -b | |
hyp = True | |
b2 = list(roots(x_**2-b, x_).keys())[0] | |
bs = sqrt(b).simplify() | |
if hyp: | |
r = ( | |
l*exp(-a*t)*cosh(b2*t) + (m-a*l) / | |
bs*exp(-a*t)*sinh(bs*t)) | |
else: | |
r = l*exp(-a*t)*cos(b2*t) + (m-a*l)/bs*exp(-a*t)*sin(bs*t) | |
terms_t.append(Heaviside(t)*r) | |
else: | |
ft, cond = _inverse_laplace_transform( | |
term, s, t, plane, simplify=simplify, dorational=False) | |
terms_t.append(ft) | |
conditions.append(cond) | |
result = Add(*terms_t) | |
if simplify: | |
result = result.simplify(doit=False) | |
return result, And(*conditions) | |
def _inverse_laplace_transform(fn, s_, t_, plane, *, simplify, dorational): | |
""" | |
Front-end function of the inverse Laplace transform. It tries to apply all | |
known rules recursively. If everything else fails, it tries to integrate. | |
""" | |
terms = Add.make_args(fn) | |
terms_t = [] | |
conditions = [] | |
for term in terms: | |
if term.has(exp): | |
# Simplify expressions with exp() such that time-shifted | |
# expressions have negative exponents in the numerator instead of | |
# positive exponents in the numerator and denominator; this is a | |
# (necessary) trick. It will, for example, convert | |
# (s**2*exp(2*s) + 4*exp(s) - 4)*exp(-2*s)/(s*(s**2 + 1)) into | |
# (s**2 + 4*exp(-s) - 4*exp(-2*s))/(s*(s**2 + 1)) | |
term = term.subs(s_, -s_).together().subs(s_, -s_) | |
k, f = term.as_independent(s_, as_Add=False) | |
if ( | |
dorational and term.is_rational_function(s_) and | |
(r := _inverse_laplace_rational( | |
f, s_, t_, plane, simplify=simplify)) | |
is not None or | |
(r := _inverse_laplace_apply_simple_rules(f, s_, t_)) | |
is not None or | |
(r := _inverse_laplace_early_prog_rules(f, s_, t_, plane)) | |
is not None or | |
(r := _inverse_laplace_expand(f, s_, t_, plane)) | |
is not None or | |
(r := _inverse_laplace_apply_prog_rules(f, s_, t_, plane)) | |
is not None): | |
pass | |
elif any(undef.has(s_) for undef in f.atoms(AppliedUndef)): | |
# If there are undefined functions f(t) then integration is | |
# unlikely to do anything useful so we skip it and given an | |
# unevaluated LaplaceTransform. | |
r = (InverseLaplaceTransform(f, s_, t_, plane), S.true) | |
elif ( | |
r := _inverse_laplace_transform_integration( | |
f, s_, t_, plane, simplify=simplify)) is not None: | |
pass | |
else: | |
r = (InverseLaplaceTransform(f, s_, t_, plane), S.true) | |
(ri_, ci_) = r | |
terms_t.append(k*ri_) | |
conditions.append(ci_) | |
result = Add(*terms_t) | |
if simplify: | |
result = result.simplify(doit=False) | |
condition = And(*conditions) | |
return result, condition | |
class InverseLaplaceTransform(IntegralTransform): | |
""" | |
Class representing unevaluated inverse Laplace transforms. | |
For usage of this class, see the :class:`IntegralTransform` docstring. | |
For how to compute inverse Laplace transforms, see the | |
:func:`inverse_laplace_transform` docstring. | |
""" | |
_name = 'Inverse Laplace' | |
_none_sentinel = Dummy('None') | |
_c = Dummy('c') | |
def __new__(cls, F, s, x, plane, **opts): | |
if plane is None: | |
plane = InverseLaplaceTransform._none_sentinel | |
return IntegralTransform.__new__(cls, F, s, x, plane, **opts) | |
def fundamental_plane(self): | |
plane = self.args[3] | |
if plane is InverseLaplaceTransform._none_sentinel: | |
plane = None | |
return plane | |
def _compute_transform(self, F, s, t, **hints): | |
return _inverse_laplace_transform_integration( | |
F, s, t, self.fundamental_plane, **hints) | |
def _as_integral(self, F, s, t): | |
c = self.__class__._c | |
return ( | |
Integral(exp(s*t)*F, (s, c - S.ImaginaryUnit*S.Infinity, | |
c + S.ImaginaryUnit*S.Infinity)) / | |
(2*S.Pi*S.ImaginaryUnit)) | |
def doit(self, **hints): | |
""" | |
Try to evaluate the transform in closed form. | |
Explanation | |
=========== | |
Standard hints are the following: | |
- ``noconds``: if True, do not return convergence conditions. The | |
default setting is `True`. | |
- ``simplify``: if True, it simplifies the final result. The | |
default setting is `False`. | |
""" | |
_noconds = hints.get('noconds', True) | |
_simplify = hints.get('simplify', False) | |
debugf('[ILT doit] (%s, %s, %s)', (self.function, | |
self.function_variable, | |
self.transform_variable)) | |
s_ = self.function_variable | |
t_ = self.transform_variable | |
fn = self.function | |
plane = self.fundamental_plane | |
r = _inverse_laplace_transform( | |
fn, s_, t_, plane, simplify=_simplify, dorational=True) | |
if _noconds: | |
return r[0] | |
else: | |
return r | |
def inverse_laplace_transform(F, s, t, plane=None, **hints): | |
r""" | |
Compute the inverse Laplace transform of `F(s)`, defined as | |
.. math :: | |
f(t) = \frac{1}{2\pi i} \int_{c-i\infty}^{c+i\infty} e^{st} | |
F(s) \mathrm{d}s, | |
for `c` so large that `F(s)` has no singularites in the | |
half-plane `\operatorname{Re}(s) > c-\epsilon`. | |
Explanation | |
=========== | |
The plane can be specified by | |
argument ``plane``, but will be inferred if passed as None. | |
Under certain regularity conditions, this recovers `f(t)` from its | |
Laplace Transform `F(s)`, for non-negative `t`, and vice | |
versa. | |
If the integral cannot be computed in closed form, this function returns | |
an unevaluated :class:`InverseLaplaceTransform` object. | |
Note that this function will always assume `t` to be real, | |
regardless of the SymPy assumption on `t`. | |
For a description of possible hints, refer to the docstring of | |
:func:`sympy.integrals.transforms.IntegralTransform.doit`. | |
Examples | |
======== | |
>>> from sympy import inverse_laplace_transform, exp, Symbol | |
>>> from sympy.abc import s, t | |
>>> a = Symbol('a', positive=True) | |
>>> inverse_laplace_transform(exp(-a*s)/s, s, t) | |
Heaviside(-a + t) | |
See Also | |
======== | |
laplace_transform | |
hankel_transform, inverse_hankel_transform | |
""" | |
_noconds = hints.get('noconds', True) | |
_simplify = hints.get('simplify', False) | |
if isinstance(F, MatrixBase) and hasattr(F, 'applyfunc'): | |
return F.applyfunc( | |
lambda Fij: inverse_laplace_transform(Fij, s, t, plane, **hints)) | |
r, c = InverseLaplaceTransform(F, s, t, plane).doit( | |
noconds=False, simplify=_simplify) | |
if _noconds: | |
return r | |
else: | |
return r, c | |
def _fast_inverse_laplace(e, s, t): | |
"""Fast inverse Laplace transform of rational function including RootSum""" | |
a, b, n = symbols('a, b, n', cls=Wild, exclude=[s]) | |
def _ilt(e): | |
if not e.has(s): | |
return e | |
elif e.is_Add: | |
return _ilt_add(e) | |
elif e.is_Mul: | |
return _ilt_mul(e) | |
elif e.is_Pow: | |
return _ilt_pow(e) | |
elif isinstance(e, RootSum): | |
return _ilt_rootsum(e) | |
else: | |
raise NotImplementedError | |
def _ilt_add(e): | |
return e.func(*map(_ilt, e.args)) | |
def _ilt_mul(e): | |
coeff, expr = e.as_independent(s) | |
if expr.is_Mul: | |
raise NotImplementedError | |
return coeff * _ilt(expr) | |
def _ilt_pow(e): | |
match = e.match((a*s + b)**n) | |
if match is not None: | |
nm, am, bm = match[n], match[a], match[b] | |
if nm.is_Integer and nm < 0: | |
return t**(-nm-1)*exp(-(bm/am)*t)/(am**-nm*gamma(-nm)) | |
if nm == 1: | |
return exp(-(bm/am)*t) / am | |
raise NotImplementedError | |
def _ilt_rootsum(e): | |
expr = e.fun.expr | |
[variable] = e.fun.variables | |
return RootSum(e.poly, Lambda(variable, together(_ilt(expr)))) | |
return _ilt(e) | |