5bf70b691f
* CMake has not been updated yet * bazel was compiling at least last week bazel: disable math opt facility_location.py missing some dependencies...
86 lines
3.0 KiB
Python
86 lines
3.0 KiB
Python
# Copyright 2010-2025 Google LLC
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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"""Utilities for working with linear and quadratic expressions."""
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import typing
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from typing import Iterable, Mapping, Union
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from ortools.math_opt.python import variables
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@typing.overload
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def fast_sum(summands: Iterable[variables.LinearTypes]) -> variables.LinearSum: ...
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@typing.overload
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def fast_sum(
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summands: Iterable[variables.QuadraticTypes],
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) -> Union[variables.LinearSum, variables.QuadraticSum]: ...
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# TODO(b/312200030): There is a pytype bug so that for the code:
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# m = mathopt.Model()
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# x = m.Variable()
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# s = expressions.fast_sum([x*x, 4.0])
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# pytype picks the wrong overload and thinks s has type variables.LinearSum,
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# rather than Union[variables.LinearSum, variables.QuadraticSum]. Once the bug
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# is fixed, confirm that the overloads actually work.
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def fast_sum(summands):
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"""Sums the elements of summand into a linear or quadratic expression.
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Similar to Python's sum function, but faster for input that not just integers
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and floats.
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Unlike sum(), the function returns a linear expression when all inputs are
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floats and/or integers. Importantly, the code:
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model.add_linear_constraint(fast_sum(maybe_empty_list) <= 1.0)
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is safe to call, while:
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model.add_linear_constraint(sum(maybe_empty_list) <= 1.0)
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fails at runtime when the list is empty.
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Args:
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summands: The elements to add up.
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Returns:
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A linear or quadratic expression with the sum of the elements of summand.
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"""
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summands_tuple = tuple(summands)
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for s in summands_tuple:
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if isinstance(s, variables.QuadraticBase):
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return variables.QuadraticSum(summands_tuple)
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return variables.LinearSum(summands_tuple)
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def evaluate_expression(
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expression: variables.QuadraticTypes,
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variable_values: Mapping[variables.Variable, float],
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) -> float:
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"""Evaluates a linear or quadratic expression for given variable values.
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E.g. if expression = 3 * x + 4 and variable_values = {x: 2.0}, then
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evaluate_expression(expression, variable_values) equals 10.0.
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Args:
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expression: The expression to evaluate.
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variable_values: Must contain a value for every variable in expression.
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Returns:
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The value of the expression when replacing variables by their value.
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"""
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if isinstance(expression, variables.QuadraticBase):
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return variables.as_flat_quadratic_expression(expression).evaluate(
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variable_values
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)
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return variables.as_flat_linear_expression(expression).evaluate(variable_values)
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