cp_model_copy.h

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// 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_CP_MODEL_COPY_H_
#define ORTOOLS_SAT_CP_MODEL_COPY_H_
 
#include <cstdint>
#include <functional>
#include <utility>
#include <vector>
 
#include "absl/container/flat_hash_map.h"
#include "absl/container/flat_hash_set.h"
#include "absl/types/span.h"
#include "ortools/sat/cp_model.pb.h"
#include "ortools/sat/lrat_proof_handler.h"
#include "ortools/sat/presolve_context.h"
#include "ortools/sat/sat_base.h"
#include "ortools/sat/sat_parameters.pb.h"
#include "ortools/util/sorted_interval_list.h"
 
namespace operations_research {
namespace sat {
 
// This helper class perform copy with simplification from a model and a
// partial assignment to another model. The purpose is to minimize the size of
// the copied model, as well as to reduce the pressure on the memory sub-system.
//
// It is currently used by the LNS part, but could be used with any other scheme
// that generates partial assignments.
class ModelCopy {
 public:
  explicit ModelCopy(PresolveContext* context,
                     LratProofHandler* lrat_proof_handler = nullptr);
 
  // Copies all constraints from in_model to working model of the context.
  //
  // During the process, it will read variable domains from the context, and
  // simplify constraints to minimize the size of the copied model.
  // Thus it is important that the context->working_model already have the
  // variables part copied.
  //
  // It returns false iff the model is proven infeasible.
  //
  // It does not clear the constraints part of the working model of the context.
  //
  // Note(user): If first_copy is true, we will reorder the scheduling
  // constraint so that they only use reference to previously defined intervals.
  // This allow to be more efficient later in a few preprocessing steps.
  bool ImportAndSimplifyConstraints(
      const CpModelProto& in_model, bool first_copy = false,
      std::function<bool(int)> active_constraints = nullptr);
 
  // Copy variables from the in_model to the working model.
  // It reads the 'ignore_names' parameters from the context, and keeps or
  // deletes names accordingly.
  void ImportVariablesAndMaybeIgnoreNames(const CpModelProto& in_model);
 
  // Setup new variables from a vector of domains.
  // Inactive variables will be fixed to their lower bound.
  void CreateVariablesFromDomains(absl::Span<const Domain> domains);
 
  // Advanced usage. When a model was copied, interval_mapping[i] will contain
  // for a copied interval with original index i, its new index.
  absl::Span<const int64_t> InternalIntervalMapping() const {
    return interval_mapping_;
  }
 
 private:
  // Overwrites the out_model to be unsat. Returns false.
  // The arguments are used to log which constraint caused unsat.
  bool CreateUnsatModel(int c, const ConstraintProto& ct);
 
  // Returns false if the constraint is never enforced and can be skipped.
  bool PrepareEnforcementCopy(const ConstraintProto& ct);
  bool PrepareEnforcementCopyWithDup(const ConstraintProto& ct);
  void FinishEnforcementCopy(ConstraintProto* ct);
 
  // All these functions return false if the constraint is found infeasible.
  bool CopyBoolOr(const ConstraintProto& ct);
  bool CopyBoolOrWithDupSupport(const ConstraintProto& ct, ClauseId clause_id);
  bool FinishBoolOrCopy(ClauseId clause_id = kNoClauseId);
 
  bool CopyBoolAnd(const ConstraintProto& ct);
  bool CopyBoolAndWithDupSupport(const ConstraintProto& ct);
 
  bool CopyAtMostOne(const ConstraintProto& ct);
  bool CopyExactlyOne(const ConstraintProto& ct);
 
  bool CopyElement(const ConstraintProto& ct);
  bool CopyIntProd(const ConstraintProto& ct, bool ignore_names);
  bool CopyIntDiv(const ConstraintProto& ct, bool ignore_names);
  bool CopyIntMod(const ConstraintProto& ct, bool ignore_names);
  bool CopyLinear(const ConstraintProto& ct, bool canonicalize);
  bool CopyLinearExpression(const LinearExpressionProto& expr,
                            LinearExpressionProto* dst,
                            absl::Span<const int> enforcement_literals = {});
  bool CopyAutomaton(const ConstraintProto& ct);
  bool CopyTable(const ConstraintProto& ct);
  bool CopyAllDiff(const ConstraintProto& ct);
  bool CopyLinMax(const ConstraintProto& ct);
 
  // If we "copy" an interval for a first time, we make sure to create the
  // linear constraint between the start, size and end. This allow to simplify
  // the input proto and client side code. If there are more than one
  // enforcement literals, we replace them with a new one, made equal to their
  // conjunction with two new constraints.
  bool CopyInterval(const ConstraintProto& ct, int c, bool ignore_names);
  bool AddLinearConstraintForInterval(const ConstraintProto& ct);
  int GetOrCreateVariableForConjunction(std::vector<int>* literals);
 
  // These function remove unperformed intervals. Note that they requires
  // interval to appear before (validated) as they test unperformed by testing
  // if interval_mapping_ is empty.
  void CopyAndMapNoOverlap(const ConstraintProto& ct);
  void CopyAndMapNoOverlap2D(const ConstraintProto& ct);
  bool CopyAndMapCumulative(const ConstraintProto& ct);
 
  // Expands linear expressions with more than one variable in constraints which
  // internally only support affine expressions (such as all_diff, element,
  // interval, reservoir, table, etc). This creates new variables for each such
  // expression, and replaces the original expressions with the new variables in
  // the constraints.
  void ExpandNonAffineExpressions();
  // Replaces the expression sum a_i * x_i + c with gcd * y + c, where y is a
  // new variable defined with an additional constraint y = sum a_i / gcd * x_i.
  void MaybeExpandNonAffineExpression(LinearExpressionProto* expr);
  void MaybeExpandNonAffineExpressions(LinearArgumentProto* linear_argument);
 
  ClauseId NextInferredClauseId();
 
  PresolveContext* context_;
  LratProofHandler* lrat_proof_handler_;
 
  // Temp vectors.
  std::vector<int> non_fixed_variables_;
  std::vector<int64_t> non_fixed_coefficients_;
  std::vector<int64_t> interval_mapping_;
  int starting_constraint_index_ = 0;
 
  std::vector<int> temp_enforcement_literals_;
  absl::flat_hash_set<int> temp_enforcement_literals_set_;
 
  std::vector<int> temp_literals_;
  absl::flat_hash_set<int> temp_literals_set_;
 
  ConstraintProto tmp_constraint_;
 
  // The unit clause IDs of the literals which are fixed to true. Only used if
  // lrat_proof_handler_ is not null.
  absl::flat_hash_map<Literal, ClauseId> unit_clause_ids_;
  // Temp vectors used for LRAT.
  std::vector<Literal> temp_clause_;
  std::vector<Literal> temp_simplified_clause_;
  std::vector<ClauseId> temp_clause_ids_;
  ClauseId next_inferred_clause_id_;
 
  // Map used in GetOrCreateVariableForConjunction() to avoid creating duplicate
  // variables for identical sets of literals.
  absl::flat_hash_map<std::vector<int>, int> boolean_product_encoding_;
  // Map used in ExpandNonAffineExpressions() to avoid creating duplicate
  // variables for the identical non affine expressions.
  absl::flat_hash_map<std::vector<std::pair<int, int64_t>>, int>
      non_affine_expression_to_new_var_;
};
 
// Copy in_model to the model in the presolve context.
// It performs on the fly simplification, and returns false if the
// model is proved infeasible. If reads the parameters 'ignore_names' and keeps
// or deletes variables and constraints names accordingly.
//
// This should only be called on the first copy of the user given model.
// Note that this reorder all constraints that use intervals last. We loose the
// user-defined order, but hopefully that should not matter too much.
bool ImportModelWithBasicPresolveIntoContext(
    const CpModelProto& in_model, PresolveContext* context,
    LratProofHandler* lrat_proof_handler = nullptr);
 
// Same as ImportModelWithBasicPresolveIntoContext() except that variable
// domains are read from domains and constraint might be filtered.
bool ImportModelAndDomainsWithBasicPresolveIntoContext(
    const CpModelProto& in_model, absl::Span<const Domain> domains,
    std::function<bool(int)> active_constraints, PresolveContext* context,
    std::vector<int>* interval_mapping);
 
// Copies the non constraint, non variables part of the model.
void CopyEverythingExceptVariablesAndConstraintsFieldsIntoContext(
    const CpModelProto& in_model, PresolveContext* context);
 
}  // namespace sat
}  // namespace operations_research
 
#endif  // ORTOOLS_SAT_CP_MODEL_COPY_H_