Source code for pyomo.contrib.preprocessing.plugins.remove_zero_terms

#  ___________________________________________________________________________
#  Pyomo: Python Optimization Modeling Objects
#  Copyright 2017 National Technology and Engineering Solutions of Sandia, LLC
#  Under the terms of Contract DE-NA0003525 with National Technology and 
#  Engineering Solutions of Sandia, LLC, the U.S. Government retains certain 
#  rights in this software.
#  This software is distributed under the 3-clause BSD License.
#  ___________________________________________________________________________

# -*- coding: UTF-8 -*-
"""Transformation to remove zero terms from constraints."""
from __future__ import division

from pyomo.core import quicksum
from pyomo.core.base.constraint import Constraint
from pyomo.core.base.plugin import TransformationFactory
from pyomo.core.expr import current as EXPR
from pyomo.core.plugins.transform.hierarchy import IsomorphicTransformation
from pyomo.repn import generate_standard_repn

[docs]@TransformationFactory.register( 'contrib.remove_zero_terms', doc="Remove terms 0 * var in constraints") class RemoveZeroTerms(IsomorphicTransformation): """Looks for :math:`0 v` in a constraint and removes it. Currently limited to processing linear constraints of the form :math:`x_1 = 0 x_3`, occurring as a result of fixing :math:`x_2 = 0`. .. note:: TODO: support nonlinear expressions """ 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))