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piecemin.py
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piecemin.py
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from constants import *
class PIECEMIN():
'''Establishes Pi.len <= Li.min when Li is not assigned,
and Pi.len <= Li.value when assigned.
Ensures that pieces suitable for a node (Pi) are at least as tall as the
length of the node (Li). Illegal pieces are removed from the domain of Pi.'''
def establish(self, csp, curvar, value, participants, spec):
'''Establishes consistency after curvar: value assignment.
The assumption is that curvar is in the assigned variables.'''
i = curvar[1:]
Li, Pi = "L" + i, "P" + i
A = csp.get_assignment()
if Pi in A:
return REVISED_NONE
D = csp.get_domains()
return self.__revise(csp, Li, Pi, A, D)
def propagate(self, csp, reduced_vars, participants, spec):
'''Establishes consistency after reduction of some variables.'''
for p in participants:
i = p[1:]
break
Li, Pi = "L" + i, "P" + i
A = csp.get_assignment()
if Pi in A:
return REVISED_NONE
D = csp.get_domains()
return self.__revise(csp, Li, Pi, A, D)
def __revise(self, csp, Li, Pi, A, D):
'''Removes illegal values from the domain of Pi, if possible.'''
if Li in A:
min_len = A[Li]
else:
min_len = D[Li]["min"]
new_domain = set([])
for piece in D[Pi]:
_len = piece[1]
if min_len <= _len:
new_domain.add(piece)
if new_domain == set([]):
return (CONTRADICTION, {Pi})
elif len(new_domain) == len(D[Pi]):
return ALREADY_CONSISTENT
csp.update_domain(Pi, new_domain)
return (MADE_CONSISTENT, {Pi})