def _apply_to(self, model):
"""Apply the transformation."""
m = model
for constr in m.component_data_objects(
ctype=Constraint, active=True, descend_into=True):
if not constr.body.polynomial_degree() == 1:
continue # we currently only process linear constraints
repn = generate_standard_repn(constr.body)
# get the index of all nonzero coefficient variables
nonzero_vars_indx = [
i for i, _ in enumerate(repn.linear_vars)
if not repn.linear_coefs[i] == 0
]
const = repn.constant
# reconstitute the constraint, including only variable terms with
# nonzero coefficients
constr_body = quicksum(repn.linear_coefs[i] * repn.linear_vars[i]
for i in nonzero_vars_indx) + const
if constr.equality:
constr.set_value(constr_body == constr.upper)
elif constr.has_lb() and not constr.has_ub():
constr.set_value(constr_body >= constr.lower)
elif constr.has_ub() and not constr.has_lb():
constr.set_value(constr_body <= constr.upper)
else:
# constraint is a bounded inequality of form a <= x <= b.
constr.set_value(EXPR.inequality(
constr.lower, constr_body, constr.upper))
def _apply_to(self, model):
"""Apply the transformation."""
m = model
for constr in m.component_data_objects(
ctype=Constraint, active=True, descend_into=True):
if not constr.body.polynomial_degree() == 1:
continue # we currently only process linear constraints
repn = generate_standard_repn(constr.body)
# get the index of all nonzero coefficient variables
nonzero_vars_indx = [
i for i, _ in enumerate(repn.linear_vars)
if not repn.linear_coefs[i] == 0
]
const = repn.constant
# reconstitute the constraint, including only variable terms with
# nonzero coefficients
constr_body = quicksum(repn.linear_coefs[i] * repn.linear_vars[i]
for i in nonzero_vars_indx) + const
if constr.equality:
constr.set_value(constr_body == constr.upper)
elif constr.has_lb() and not constr.has_ub():
constr.set_value(constr_body >= constr.lower)
elif constr.has_ub() and not constr.has_lb():
constr.set_value(constr_body <= constr.upper)
else:
# constraint is a bounded inequality of form a <= x <= b.
constr.set_value(EXPR.inequality(
constr.lower, constr_body, constr.upper))
def test_zero_term_removal(self):
"""Test for removing zero terms from linear constraints."""
m = ConcreteModel()
m.v0 = Var()
m.v1 = Var()
m.v2 = Var()
m.v3 = Var()
m.c = Constraint(expr=m.v0 == m.v1 * m.v2 + m.v3)
m.c2 = Constraint(expr=m.v1 * m.v2 + m.v3 <= m.v0)
m.c3 = Constraint(expr=m.v0 <= m.v1 * m.v2 + m.v3)
m.c4 = Constraint(expr=EXPR.inequality(1, m.v1 * m.v2 + m.v3, 3))
m.v1.fix(0)
TransformationFactory('contrib.remove_zero_terms').apply_to(m)
m.v1.unfix()
# Check that the term no longer exists
self.assertFalse(
any(id(m.v1) == id(v) for v in EXPR.identify_variables(m.c.body)))
self.assertFalse(
any(id(m.v1) == id(v) for v in EXPR.identify_variables(m.c2.body)))
self.assertFalse(
any(id(m.v1) == id(v) for v in EXPR.identify_variables(m.c3.body)))
self.assertFalse(
any(id(m.v1) == id(v) for v in EXPR.identify_variables(m.c4.body)))
def test_zero_term_removal(self):
"""Test for removing zero terms from linear constraints."""
m = ConcreteModel()
m.v0 = Var()
m.v1 = Var()
m.v2 = Var()
m.v3 = Var()
m.c = Constraint(expr=m.v0 == m.v1 * m.v2 + m.v3)
m.c2 = Constraint(expr=m.v1 * m.v2 + m.v3 <= m.v0)
m.c3 = Constraint(expr=m.v0 <= m.v1 * m.v2 + m.v3)
m.c4 = Constraint(expr=EXPR.inequality(1, m.v1 * m.v2 + m.v3, 3))
m.v1.fix(0)
TransformationFactory('contrib.remove_zero_terms').apply_to(m)
m.v1.unfix()
# Check that the term no longer exists
self.assertFalse(any(id(m.v1) == id(v)
for v in EXPR.identify_variables(m.c.body)))
self.assertFalse(any(id(m.v1) == id(v)
for v in EXPR.identify_variables(m.c2.body)))
self.assertFalse(any(id(m.v1) == id(v)
for v in EXPR.identify_variables(m.c3.body)))
self.assertFalse(any(id(m.v1) == id(v)
for v in EXPR.identify_variables(m.c4.body)))
