"""
Transformations regarding :class:`~cpmpy.expressions.core.Comparison` constraints (originally).
Now, it is regarding numeric expressions in general, including nested ones.
Let with <op> one of == or !=,<,<=,>,>=
Numeric expressions in Flat Normal Form are of the kind
- NumExpr <op> IV
- BoolVar == NumExpr <op> IV
- BoolVar -> NumExpr <op> IV
- NumExpr <op> IV -> BoolVar
The NumExpr can be a sum, wsum or global function with a non-bool return type.
This file implements:
- :func:`only_numexpr_equality()`: transforms `NumExpr <op> IV` (also reified) to `(NumExpr == A) & (A <op> IV)` if not supported
"""
import copy
from .flatten_model import get_or_make_var
from ..expressions.core import Comparison, Operator
from ..expressions.utils import is_boolexpr
from ..expressions.variables import _NumVarImpl, _BoolVarImpl
[docs]def only_numexpr_equality(constraints, supported=frozenset()):
"""
transforms `NumExpr <op> IV` to `(NumExpr == A) & (A <op> IV)` if not supported
also for the reified uses of NumExpr
:param supported: a (frozen)set of expression names that supports all comparisons in the solver
"""
# shallow copy (could support inplace too this way...)
newcons = copy.copy(constraints)
for i,cpm_expr in enumerate(newcons):
if isinstance(cpm_expr, Operator) and cpm_expr.name == "->":
cond, subexpr = cpm_expr.args
if not isinstance(cond, _BoolVarImpl): # expr -> bv
res = only_numexpr_equality([cond], supported)
if len(res) > 1:
newcons[i] = res[1].implies(subexpr)
newcons.insert(i, res[0])
elif not isinstance(subexpr, _BoolVarImpl): # bv -> expr
res = only_numexpr_equality([subexpr], supported)
if len(res) > 1:
newcons[i] = cond.implies(res[1])
newcons.insert(i, res[0])
else: #bv -> bv
pass
if isinstance(cpm_expr, Comparison):
lhs, rhs = cpm_expr.args
if cpm_expr.name == "==" and is_boolexpr(lhs) and is_boolexpr(rhs): # reification, check recursively
if not isinstance(lhs, _BoolVarImpl): # expr == bv
res = only_numexpr_equality([lhs], supported)
if len(res) > 1:
newcons[i] = res[1] == rhs
newcons.insert(i, res[0])
elif not isinstance(rhs, _BoolVarImpl): # bv == expr
res = only_numexpr_equality([rhs], supported)
if len(res) > 1:
newcons[i] = lhs == res[1]
newcons.insert(i, res[0])
else: # bv == bv
pass
elif cpm_expr.name != "==":
# LHS <op> IV with <op> one of !=,<,<=,>,>=
lhs = cpm_expr.args[0]
if not isinstance(lhs, _NumVarImpl) and lhs.name not in supported:
# LHS is unsupported for LHS <op> IV, rewrite to `(LHS == A) & (A <op> IV)`
(lhsvar, lhscons) = get_or_make_var(lhs)
# replace comparison by A <op> IV
newcons[i] = Comparison(cpm_expr.name, lhsvar, cpm_expr.args[1])
# add lhscon(s), which will be [(LHS == A)]
assert(len(lhscons) == 1), "only_numexpr_eq: lhs surprisingly non-flat"
newcons.insert(i, lhscons[0])
return newcons