variable_expand.h

Go to the documentation of this file.

// Copyright 2010-2025 Google LLC
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
 
#ifndef ORTOOLS_SAT_VARIABLE_EXPAND_H_
#define ORTOOLS_SAT_VARIABLE_EXPAND_H_
 
#include <cstdint>
#include <optional>
#include <vector>
 
#include "absl/container/btree_map.h"
#include "absl/container/flat_hash_set.h"
#include "ortools/sat/presolve_context.h"
#include "ortools/sat/solution_crush.h"
#include "ortools/util/sorted_interval_list.h"
 
namespace operations_research {
namespace sat {
 
class ValueEncoding {
 public:
  ValueEncoding(int var, PresolveContext* context);
  // Build the set of observed values. This cannot be called after
  // CanonicalizeEncodedValuesAndAddEscapeValues() has been called.
  void AddReferencedValueToEncode(int64_t value);
 
  // Add an optional value to encode. An optional value is a value that is not
  // referenced by a linear1 constraint, but that is needed to support hint
  // manipulation.
  void AddOptionalValueToEncode(int64_t value);
 
  // This method is called after all values from lit => var ==/!= value have
  // been added. It canonicalizes the encoded values and adds an escape value
  // if needed. It there is an objective, the escape value is the min or the max
  // of the residual domain of the variable depending on the objective
  // coefficient of the variable. It there are no objective, the escape value is
  // the smallest value of the residual domain.
  // With this escape value, we can safely reduce the domain of the variable to
  // observed + escape values, and add an exactly_one constraint on all the
  // literals involved.
  void CanonicalizeEncodedValuesAndAddEscapeValue(
      bool push_down_when_unconstrained, bool has_le_ge_linear1);
 
  // Getters on the observed values.
  bool empty() const;
  bool is_fully_encoded() const;
  const std::vector<int64_t>& encoded_values() const;
 
  // A unique escape value is defined only if the linear1 are var == value and
  // var != value. In this case, only one escape value is needed.
  std::optional<int64_t> unique_escape_value() const;
 
  // Setters and getters on the value encoding.
  void ForceFullEncoding();
  void CreateAllValueEncodingLiterals();
  int literal(int64_t value) const;
  const absl::btree_map<int64_t, int>& encoding() const;
 
 private:
  const int var_;
  const Domain var_domain_;
  PresolveContext* context_;
  std::vector<int64_t> encoded_values_;
  std::vector<int64_t> referenced_encoded_values_;
  absl::btree_map<int64_t, int> encoding_;
  std::optional<int64_t> unique_escape_value_;
  bool is_closed_ = false;
  bool is_fully_encoded_ = false;
};
 
class OrderEncoding {
 public:
  OrderEncoding(int var, PresolveContext* context,
                SolutionCrush& solution_crush);
  void InsertLeLiteral(int64_t value, int literal);
  void InsertGeLiteral(int64_t value, int literal);
  void CreateAllOrderEncodingLiterals(const ValueEncoding& values);
  int ge_literal(int64_t value) const;
  int le_literal(int64_t value) const;
  int num_encoded_values() const;
 
 private:
  void CollectAllOrderEncodingValues();
 
  const int var_;
  const Domain var_domain_;
  PresolveContext* context_;
  SolutionCrush& solution_crush_;
  absl::btree_map<int64_t, absl::flat_hash_set<int>> tmp_ge_to_literals_;
  absl::btree_map<int64_t, absl::flat_hash_set<int>> tmp_le_to_literals_;
  absl::btree_map<int64_t, int> encoded_le_literal_;
};
 
void TryToReplaceVariableByItsEncoding(int var, PresolveContext* context,
                                       SolutionCrush& solution_crush);
 
}  // namespace sat
}  // namespace operations_research
 
#endif  // ORTOOLS_SAT_VARIABLE_EXPAND_H_