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| """For reading in DIMACS file format | |
| www.cs.ubc.ca/~hoos/SATLIB/Benchmarks/SAT/satformat.ps | |
| """ | |
| from sympy.core import Symbol | |
| from sympy.logic.boolalg import And, Or | |
| import re | |
| def load(s): | |
| """Loads a boolean expression from a string. | |
| Examples | |
| ======== | |
| >>> from sympy.logic.utilities.dimacs import load | |
| >>> load('1') | |
| cnf_1 | |
| >>> load('1 2') | |
| cnf_1 | cnf_2 | |
| >>> load('1 \\n 2') | |
| cnf_1 & cnf_2 | |
| >>> load('1 2 \\n 3') | |
| cnf_3 & (cnf_1 | cnf_2) | |
| """ | |
| clauses = [] | |
| lines = s.split('\n') | |
| pComment = re.compile(r'c.*') | |
| pStats = re.compile(r'p\s*cnf\s*(\d*)\s*(\d*)') | |
| while len(lines) > 0: | |
| line = lines.pop(0) | |
| # Only deal with lines that aren't comments | |
| if not pComment.match(line): | |
| m = pStats.match(line) | |
| if not m: | |
| nums = line.rstrip('\n').split(' ') | |
| list = [] | |
| for lit in nums: | |
| if lit != '': | |
| if int(lit) == 0: | |
| continue | |
| num = abs(int(lit)) | |
| sign = True | |
| if int(lit) < 0: | |
| sign = False | |
| if sign: | |
| list.append(Symbol("cnf_%s" % num)) | |
| else: | |
| list.append(~Symbol("cnf_%s" % num)) | |
| if len(list) > 0: | |
| clauses.append(Or(*list)) | |
| return And(*clauses) | |
| def load_file(location): | |
| """Loads a boolean expression from a file.""" | |
| with open(location) as f: | |
| s = f.read() | |
| return load(s) | |