53 lines
2.1 KiB
C++
53 lines
2.1 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_CP_MODEL_POSTSOLVE_H_
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#define OR_TOOLS_SAT_CP_MODEL_POSTSOLVE_H_
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#include <cstdint>
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#include <vector>
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#include "ortools/base/integral_types.h"
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#include "ortools/sat/cp_model.pb.h"
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namespace operations_research {
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namespace sat {
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// Postsolves the given response using information filled by our presolver.
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//
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// This works as follow:
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// - First we fix fixed variables of the mapping_model according to the solution
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// of the presolved problem and the index mapping.
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// - Then, we process the mapping constraints in "reverse" order, and unit
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// propagate each of them when necessary. By construction this should never
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// give rise to any conflicts. And after each constraints, we should have
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// a feasible solution to the presolved problem + all already postsolved
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// constraints. This is the invariant we maintain.
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// - Finally, we arbitrarily fix any free variables left and update the given
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// response with the new solution.
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//
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// Note: Most of the postsolve operations require the constraints to have been
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// written in the correct way by the presolve.
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//
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// TODO(user): We could use the search strategy to fix free variables to some
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// chosen values? The feature might never be needed though.
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void PostsolveResponse(const int64_t num_variables_in_original_model,
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const CpModelProto& mapping_proto,
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const std::vector<int>& postsolve_mapping,
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std::vector<int64_t>* solution);
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} // namespace sat
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} // namespace operations_research
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#endif // OR_TOOLS_SAT_CP_MODEL_POSTSOLVE_H_
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