1 /* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */ 2 /* */ 3 /* This file is part of the program and library */ 4 /* SCIP --- Solving Constraint Integer Programs */ 5 /* */ 6 /* Copyright (c) 2002-2023 Zuse Institute Berlin (ZIB) */ 7 /* */ 8 /* Licensed under the Apache License, Version 2.0 (the "License"); */ 9 /* you may not use this file except in compliance with the License. */ 10 /* You may obtain a copy of the License at */ 11 /* */ 12 /* http://www.apache.org/licenses/LICENSE-2.0 */ 13 /* */ 14 /* Unless required by applicable law or agreed to in writing, software */ 15 /* distributed under the License is distributed on an "AS IS" BASIS, */ 16 /* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. */ 17 /* See the License for the specific language governing permissions and */ 18 /* limitations under the License. */ 19 /* */ 20 /* You should have received a copy of the Apache-2.0 license */ 21 /* along with SCIP; see the file LICENSE. If not visit scipopt.org. */ 22 /* */ 23 /* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */ 24 25 /**@file heuristics.h 26 * @ingroup PUBLICCOREAPI 27 * @brief methods commonly used by primal heuristics 28 * @author Gregor Hendel 29 */ 30 31 /*---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8----+----9----+----0----+----1----+----2*/ 32 33 #ifndef __SCIP_HEURISTICS_H__ 34 #define __SCIP_HEURISTICS_H__ 35 36 #include "scip/def.h" 37 #include "scip/type_scip.h" 38 #include "scip/type_heur.h" 39 #include "scip/type_misc.h" 40 #include "scip/type_retcode.h" 41 #include "scip/type_sol.h" 42 #include "scip/type_var.h" 43 44 #ifdef __cplusplus 45 extern "C" { 46 #endif 47 48 /**@defgroup PublicSpecialHeuristicMethods Special Methods 49 * @ingroup PublicHeuristicMethods 50 * @brief methods commonly used by primal heuristics 51 * 52 * @{ 53 */ 54 55 /** performs a diving within the limits of the @p diveset parameters 56 * 57 * This method performs a diving according to the settings defined by the diving settings @p diveset; Contrary to the 58 * name, SCIP enters probing mode (not diving mode) and dives along a path into the tree. Domain propagation 59 * is applied at every node in the tree, whereas probing LPs might be solved less frequently. 60 * 61 * Starting from the current LP solution, the algorithm selects candidates which maximize the 62 * score defined by the @p diveset and whose solution value has not yet been rendered infeasible by propagation, 63 * and propagates the bound change on this candidate. 64 * 65 * The algorithm iteratively selects the the next (unfixed) candidate in the list, until either enough domain changes 66 * or the resolve frequency of the LP trigger an LP resolve (and hence, the set of potential candidates changes), 67 * or the last node is proven to be infeasible. It optionally backtracks and tries the 68 * other branching direction. 69 * 70 * After the set of remaining candidates is empty or the targeted depth is reached, the node LP is 71 * solved, and the old candidates are replaced by the new LP candidates. 72 * 73 * @see heur_guideddiving.c for an example implementation of a dive set controlling the diving algorithm. 74 * 75 * @note the node from where the algorithm is called is checked for a basic LP solution. If the solution 76 * is non-basic, e.g., when barrier without crossover is used, the method returns without performing a dive. 77 * 78 * @note currently, when multiple diving heuristics call this method and solve an LP at the same node, only the first 79 * call will be executed, @see SCIPgetLastDiveNode(). 80 */ 81 SCIP_EXPORT 82 SCIP_RETCODE SCIPperformGenericDivingAlgorithm( 83 SCIP* scip, /**< SCIP data structure */ 84 SCIP_DIVESET* diveset, /**< settings for diving */ 85 SCIP_SOL* worksol, /**< non-NULL working solution */ 86 SCIP_HEUR* heur, /**< the calling primal heuristic */ 87 SCIP_RESULT* result, /**< SCIP result pointer */ 88 SCIP_Bool nodeinfeasible, /**< is the current node known to be infeasible? */ 89 SCIP_Longint iterlim, /**< nonnegative iteration limit for the LP solves, or -1 for dynamic setting */ 90 int nodelimit, /**< nonnegative probing node limit or -1 if no limit should be used */ 91 SCIP_Real lpresolvedomchgquot, /**< percentage of immediate domain changes during probing to trigger LP resolve or -1 92 if diveset specific default should be used */ 93 SCIP_DIVECONTEXT divecontext /**< context for diving statistics */ 94 ); 95 96 /** get a sub-SCIP copy of the transformed problem */ 97 SCIP_EXPORT 98 SCIP_RETCODE SCIPcopyLargeNeighborhoodSearch( 99 SCIP* sourcescip, /**< source SCIP data structure */ 100 SCIP* subscip, /**< sub-SCIP used by the heuristic */ 101 SCIP_HASHMAP* varmap, /**< a hashmap to store the mapping of source variables to the corresponding 102 * target variables */ 103 const char* suffix, /**< suffix for the problem name */ 104 SCIP_VAR** fixedvars, /**< source variables whose copies should be fixed in the target SCIP environment, or NULL */ 105 SCIP_Real* fixedvals, /**< array of fixing values for target SCIP variables, or NULL */ 106 int nfixedvars, /**< number of source variables whose copies should be fixed in the target SCIP environment, or NULL */ 107 SCIP_Bool uselprows, /**< should the linear relaxation of the problem defined by LP rows be copied? */ 108 SCIP_Bool copycuts, /**< should cuts be copied (only if uselprows == FALSE) */ 109 SCIP_Bool* success, /**< was the copying successful? */ 110 SCIP_Bool* valid /**< pointer to store whether the copying was valid, or NULL */ 111 ); 112 113 /** adds a trust region neighborhood constraint to the @p targetscip 114 * 115 * a trust region constraint measures the deviation from the current incumbent solution \f$x^*\f$ by an auxiliary 116 * continuous variable \f$v \geq 0\f$: 117 * \f[ 118 * \sum\limits_{j\in B} |x_j^* - x_j| = v 119 * \f] 120 * Only binary variables are taken into account. The deviation is penalized in the objective function using 121 * a positive \p violpenalty. 122 * 123 * @note: the trust region constraint creates an auxiliary variable to penalize the deviation from 124 * the current incumbent solution. This variable can afterwards be accessed using SCIPfindVar() by its name 125 * 'trustregion_violationvar' 126 */ 127 SCIP_EXPORT 128 SCIP_RETCODE SCIPaddTrustregionNeighborhoodConstraint( 129 SCIP* scip, /**< the SCIP data structure */ 130 SCIP* subscip, /**< SCIP data structure of the subproblem */ 131 SCIP_VAR** subvars, /**< variables of the subproblem, NULL entries are ignored */ 132 SCIP_Real violpenalty /**< the penalty for violating the trust region */ 133 ); 134 135 /** @} */ 136 137 #ifdef __cplusplus 138 } 139 #endif 140 141 #endif 142