84 lines
2.8 KiB
C++
84 lines
2.8 KiB
C++
// Copyright 2010-2022 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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#ifndef OR_TOOLS_SAT_PSEUDO_COSTS_H_
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#define OR_TOOLS_SAT_PSEUDO_COSTS_H_
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#include <vector>
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#include "ortools/base/logging.h"
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#include "ortools/base/strong_vector.h"
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#include "ortools/sat/integer.h"
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#include "ortools/sat/model.h"
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#include "ortools/sat/sat_base.h"
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#include "ortools/sat/sat_parameters.pb.h"
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#include "ortools/sat/util.h"
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#include "ortools/util/strong_integers.h"
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namespace operations_research {
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namespace sat {
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// Pseudo cost of a variable is measured as average observed change in the
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// objective bounds per unit change in the variable bounds.
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class PseudoCosts {
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public:
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// Helper struct to get information relevant for pseudo costs from branching
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// decisions.
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struct VariableBoundChange {
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IntegerVariable var = kNoIntegerVariable;
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IntegerValue lower_bound_change = IntegerValue(0);
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};
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explicit PseudoCosts(Model* model);
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// Updates the pseudo costs for the given decision.
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void UpdateCost(const std::vector<VariableBoundChange>& bound_changes,
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IntegerValue obj_bound_improvement);
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// Returns the variable with best reliable pseudo cost that is not fixed.
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IntegerVariable GetBestDecisionVar();
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// Returns the pseudo cost of given variable. Currently used for testing only.
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double GetCost(IntegerVariable var) const {
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CHECK_LT(var, pseudo_costs_.size());
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return pseudo_costs_[var].CurrentAverage();
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}
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// Returns the number of recordings of given variable. Currently used for
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// testing only.
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int GetRecordings(IntegerVariable var) const {
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CHECK_LT(var, pseudo_costs_.size());
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return pseudo_costs_[var].NumRecords();
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}
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private:
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// Updates the cost of a given variable.
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void UpdateCostForVar(IntegerVariable var, double new_cost);
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// Reference of integer trail to access the current bounds of variables.
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const IntegerTrail& integer_trail_;
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const SatParameters& parameters_;
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absl::StrongVector<IntegerVariable, IncrementalAverage> pseudo_costs_;
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};
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// Returns extracted information to update pseudo costs from the given
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// branching decision.
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std::vector<PseudoCosts::VariableBoundChange> GetBoundChanges(
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LiteralIndex decision, Model* model);
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} // namespace sat
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} // namespace operations_research
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#endif // OR_TOOLS_SAT_PSEUDO_COSTS_H_
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