103 lines
3.6 KiB
C++
103 lines
3.6 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_BOP_BOP_SOLVER_H_
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#define OR_TOOLS_BOP_BOP_SOLVER_H_
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// Solver for Boolean Optimization Problems built on top of the SAT solver.
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// To optimize a problem the solver uses several optimization strategies like
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// Local Search (LS), Large Neighborhood Search (LNS), and Linear
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// Programming (LP). See bop_parameters.proto to tune the strategies.
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//
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// Note that the BopSolver usage is limited to:
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// - Boolean variables,
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// - Linear constraints and linear optimization objective,
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// - Integral weights for both constraints and objective,
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// - Minimization.
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// To deal with maximization, integral variables and floating weights, one can
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// use the bop::IntegralSolver.
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//
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// Usage example:
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// const LinearBooleanProblem problem = BuildProblem();
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// BopSolver bop_solver(problem);
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// BopParameters bop_parameters;
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// bop_parameters.set_max_deterministic_time(10);
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// bop_solver.SetParameters(bop_parameters);
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// const BopSolveStatus solve_status = bop_solver.Solve();
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// if (solve_status == BopSolveStatus::OPTIMAL_SOLUTION_FOUND) { ... }
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#include <string>
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#include <vector>
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#include "ortools/base/basictypes.h"
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#include "ortools/base/integral_types.h"
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#include "ortools/base/logging.h"
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#include "ortools/base/macros.h"
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#include "ortools/bop/bop_base.h"
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#include "ortools/bop/bop_parameters.pb.h"
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#include "ortools/bop/bop_solution.h"
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#include "ortools/bop/bop_types.h"
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#include "ortools/glop/lp_solver.h"
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#include "ortools/sat/boolean_problem.pb.h"
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#include "ortools/sat/sat_solver.h"
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#include "ortools/util/stats.h"
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#include "ortools/util/time_limit.h"
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namespace operations_research {
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namespace bop {
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// Solver of Boolean Optimization Problems based on Local Search.
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class BopSolver {
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public:
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explicit BopSolver(const sat::LinearBooleanProblem& problem);
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virtual ~BopSolver();
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// Parameters management.
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void SetParameters(const BopParameters& parameters) {
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parameters_ = parameters;
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}
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// Returns the status of the optimization.
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BopSolveStatus Solve();
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BopSolveStatus Solve(const BopSolution& first_solution);
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// Runs the solver with an external time limit.
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BopSolveStatus SolveWithTimeLimit(TimeLimit* time_limit);
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BopSolveStatus SolveWithTimeLimit(const BopSolution& first_solution,
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TimeLimit* time_limit);
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const BopSolution& best_solution() const { return problem_state_.solution(); }
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bool GetSolutionValue(VariableIndex var_id) const {
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return problem_state_.solution().Value(var_id);
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}
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// Returns the scaled best bound.
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// In case of minimization (resp. maximization), the best bound is defined as
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// the lower bound (resp. upper bound).
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double GetScaledBestBound() const;
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double GetScaledGap() const;
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private:
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void UpdateParameters();
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BopSolveStatus InternalMonothreadSolver(TimeLimit* time_limit);
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BopSolveStatus InternalMultithreadSolver(TimeLimit* time_limit);
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const sat::LinearBooleanProblem& problem_;
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ProblemState problem_state_;
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BopParameters parameters_;
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mutable StatsGroup stats_;
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};
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} // namespace bop
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} // namespace operations_research
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#endif // OR_TOOLS_BOP_BOP_SOLVER_H_
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