# ___________________________________________________________________________
#
# 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.
# ___________________________________________________________________________
from pyomo.core.base.constraint import Constraint
from pyomo.core.base.set import Set
[docs]def get_piecewise_constant_constraints(inputs, time, sample_points, use_next=True):
"""Returns an IndexedConstraint that constrains the provided variables
to be constant between the provided sample points
Arguments
---------
inputs: list of variables
Time-indexed variables that will be constrained piecewise constant
time: Set
Set of points at which provided variables will be constrained
sample_points: List of floats
Points at which "constant constraints" will be omitted; these are
points at which the provided variables may vary.
use_next: Bool (default True)
Whether the next time point will be used in the constant constraint
at each point in time. Otherwise, the previous time point is used.
Returns
-------
Set, IndexedConstraint
A RangeSet indexing the list of variables provided and a Constraint
indexed by the product of this RangeSet and time.
"""
input_set = Set(initialize=range(len(inputs)))
sample_point_set = set(sample_points)
def piecewise_constant_rule(m, i, t):
if t in sample_point_set:
return Constraint.Skip
else:
# I think whether we want prev or next here depends on whether
# we use an explicit or implicit time discretization. I.e. whether
# an input is applied to the finite element in front of or behind
# its time point. If the wrong direction for a discretization
# is used, we could have different inputs applied within the same
# finite element, which I think we never want.
var = inputs[i]
if use_next:
t_next = time.next(t)
return var[t] - var[t_next] == 0
else:
t_prev = time.prev(t)
return var[t_prev] - var[t] == 0
pwc_con = Constraint(input_set, time, rule=piecewise_constant_rule)
return input_set, pwc_con