# ___________________________________________________________________________
#
# 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.
# ___________________________________________________________________________
"""Automatically initialize variables."""
from pyomo.core.base.var import Var
from pyomo.core.base.transformation import TransformationFactory
from pyomo.core.expr.numvalue import value
from pyomo.core.plugins.transform.hierarchy import IsomorphicTransformation
[docs]
@TransformationFactory.register(
'contrib.init_vars_midpoint',
doc="Initialize non-fixed variables to the midpoint of their bounds.",
)
class InitMidpoint(IsomorphicTransformation):
"""Initialize non-fixed variables to the midpoint of their bounds.
- If the variable does not have bounds, set the value to zero.
- If the variable is missing one bound, set the value to that of the
existing bound.
"""
def _apply_to(self, instance, overwrite=False):
"""Apply the transformation.
Kwargs:
overwrite: if False, transformation will not overwrite existing
variable values.
"""
for var in instance.component_data_objects(ctype=Var, descend_into=True):
if var.fixed:
continue
if var.value is not None and not overwrite:
continue
if var.lb is None and var.ub is None:
# If LB and UB do not exist, set variable value to 0
var.set_value(0)
elif var.lb is None:
# if one bound does not exist, set variable value to the other
var.set_value(value(var.ub))
elif var.ub is None:
# if one bound does not exist, set variable value to the other
var.set_value(value(var.lb))
else:
var.set_value((value(var.lb) + value(var.ub)) / 2.0)
[docs]
@TransformationFactory.register(
'contrib.init_vars_zero', doc="Initialize non-fixed variables to zero."
)
class InitZero(IsomorphicTransformation):
"""Initialize non-fixed variables to zero.
- If setting the variable value to zero will violate a bound, set the
variable value to the relevant bound value.
"""
def _apply_to(self, instance, overwrite=False):
"""Apply the transformation.
Kwargs:
overwrite: if False, transformation will not overwrite existing
variable values.
"""
for var in instance.component_data_objects(ctype=Var, descend_into=True):
if var.fixed:
continue
if var.value is not None and not overwrite:
continue
if var.lb is not None and value(var.lb) > 0:
var.set_value(value(var.lb))
elif var.ub is not None and value(var.ub) < 0:
var.set_value(value(var.ub))
else:
var.set_value(0)