# ___________________________________________________________________________
#
# Pyomo: Python Optimization Modeling Objects
# Copyright (c) 2008-2024
# 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.
# ___________________________________________________________________________
"""Transformation to detect variables fixed by bounds and fix them."""
from math import fabs
from pyomo.core.base.transformation import TransformationFactory
from pyomo.common.collections import ComponentMap
from pyomo.common.config import (
ConfigBlock,
ConfigValue,
NonNegativeFloat,
document_kwargs_from_configdict,
)
from pyomo.core.base.var import Var
from pyomo.core.expr.numvalue import value
from pyomo.core.plugins.transform.hierarchy import IsomorphicTransformation
[docs]@TransformationFactory.register(
'contrib.detect_fixed_vars',
doc="Detect variables that are de-facto fixed but not considered fixed.",
)
@document_kwargs_from_configdict('CONFIG')
class FixedVarDetector(IsomorphicTransformation):
"""Detects variables that are de-facto fixed but not considered fixed.
For each variable :math:`v` found on the model, check to see if its lower
bound :math:`v^{LB}` is within some tolerance of its upper bound
:math:`v^{UB}`. If so, fix the variable to the value of :math:`v^{LB}`.
Keyword arguments below are specified for the ``apply_to`` and
``create_using`` functions.
"""
CONFIG = ConfigBlock("FixedVarDetector")
CONFIG.declare(
"tmp",
ConfigValue(
default=False,
domain=bool,
description="True to store the set of transformed variables and "
"their old values so that they can be restored.",
),
)
CONFIG.declare(
"tolerance",
ConfigValue(
default=1e-13,
domain=NonNegativeFloat,
description="tolerance on bound equality (LB == UB)",
),
)
def _apply_to(self, instance, **kwargs):
config = self.CONFIG(kwargs)
if config.tmp:
instance._xfrm_detect_fixed_vars_old_values = ComponentMap()
for var in instance.component_data_objects(ctype=Var, descend_into=True):
if var.fixed or var.lb is None or var.ub is None:
# if the variable is already fixed, or if it is missing a
# bound, we skip it.
continue
if fabs(value(var.lb) - value(var.ub)) <= config.tolerance:
if config.tmp:
instance._xfrm_detect_fixed_vars_old_values[var] = var.value
var.fix(var.lb)
[docs] def revert(self, instance):
"""Revert variables fixed by the transformation."""
for var, var_value in instance._xfrm_detect_fixed_vars_old_values.items():
var.unfix()
var.set_value(var_value)
del instance._xfrm_detect_fixed_vars_old_values