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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)
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