OR-Tools  8.2
cp_model_symmetries.h
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1// Copyright 2010-2018 Google LLC
2// Licensed under the Apache License, Version 2.0 (the "License");
3// you may not use this file except in compliance with the License.
4// You may obtain a copy of the License at
5//
6// http://www.apache.org/licenses/LICENSE-2.0
7//
8// Unless required by applicable law or agreed to in writing, software
9// distributed under the License is distributed on an "AS IS" BASIS,
10// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
11// See the License for the specific language governing permissions and
12// limitations under the License.
13
14#ifndef OR_TOOLS_SAT_CP_MODEL_SYMMETRIES_H_
15#define OR_TOOLS_SAT_CP_MODEL_SYMMETRIES_H_
16
17#include <limits>
18#include <memory>
19#include <vector>
20
22#include "ortools/sat/cp_model.pb.h"
24#include "ortools/sat/sat_parameters.pb.h"
25
26namespace operations_research {
27namespace sat {
28
29// Returns a list of generators of the symmetry group of the given problem. Each
30// generator is a permutation of the integer range [0, n) where n is the number
31// of variables of the problem. They are permutations of the (index
32// representation of the) problem variables.
33//
34// Note that we ignore the variables that appear in no constraint, instead of
35// outputing the full symmetry group involving them.
36//
37// TODO(user): On SAT problems it is more powerful to detect permutations also
38// involving the negation of the problem variables. So that we could find a
39// symmetry x <-> not(y) for instance.
40//
41// TODO(user): As long as we only exploit symmetry involving only Boolean
42// variables we can make this code more efficient by not detecting symmetries
43// involing integer variable.
45 const SatParameters& params, const CpModelProto& problem,
46 std::vector<std::unique_ptr<SparsePermutation>>* generators,
47 double deterministic_limit = std::numeric_limits<double>::infinity());
48
49// Detects symmetries and fill the symmetry field.
50void DetectAndAddSymmetryToProto(const SatParameters& params,
51 CpModelProto* proto);
52
53// Basic implementation of some symmetry breaking during presolve.
54//
55// Currently this just try to fix variables by detecting symmetries between
56// Booleans in bool_and, at_most_one or exactly_one constraints.
58
59} // namespace sat
60} // namespace operations_research
61
62#endif // OR_TOOLS_SAT_CP_MODEL_SYMMETRIES_H_
CpModelProto proto
GurobiMPCallbackContext * context
bool DetectAndExploitSymmetriesInPresolve(PresolveContext *context)
void FindCpModelSymmetries(const SatParameters &params, const CpModelProto &problem, std::vector< std::unique_ptr< SparsePermutation > > *generators, double deterministic_limit)
void DetectAndAddSymmetryToProto(const SatParameters &params, CpModelProto *proto)
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