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 treemodel.h 26 * @ingroup PUBLICCOREAPI 27 * @brief Branching rules based on the Single-Variable-Branching (SVB) model 28 * @author Daniel Anderson 29 * @author Pierre Le Bodic 30 * 31 * The Single-Variable-Branching (SVB) model is a simplified model of 32 * Branch & Bound trees, from which several nontrivial variable selection 33 * rules arise. The Treemodel branching rule complements SCIP's hybrid 34 * branching by suggesting improved branching variables given the current 35 * pseudocosts and the current dual gap. 36 * 37 * Given a variable with dual bound changes (l, r) (both positive) 38 * and an absolute gap G, the SVB model describes the tree that needs to be 39 * built by branching on that same variable at every node until the value G 40 * is reached at every leaf, starting from 0 at the root node. 41 * If we do so for every variable, we can select the variable that produces 42 * the smallest tree. 43 * In the case where the gap is not known, then we can compute the growth rate 44 * of the tree, which we call the ratio. 45 * The ratio of a variable (l, r) is the factor by which the size of the tree 46 * built using (l, r) that closes a gap G must be multiplied by to close a gap 47 * G+1. This ratio is not constant for all gaps, but when G tends to infinity, 48 * it converges to a fixed value we can compute numerically using a root finding 49 * algorithm (e.g. Laguerre). 50 * The ratio is used when the gap is too large (e.g. no primal bound known) or 51 * to help approximate the size of the SVB tree for that variable. 52 * 53 * See the following publication for more detail: 54 * 55 * @par 56 * Pierre Le Bodic and George Nemhauser@n 57 * An abstract model for branching and its application to mixed integer programming@n 58 * Mathematical Programming, 2017@n 59 */ 60 61 /*---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8----+----9----+----0----+----1----+----2*/ 62 63 #ifndef __SCIP_TREEMODEL_H__ 64 #define __SCIP_TREEMODEL_H__ 65 66 67 #include "scip/scip.h" 68 69 #ifdef __cplusplus 70 extern "C" { 71 #endif 72 73 /** initialises the Treemodel parameter data structure */ 74 SCIP_EXPORT 75 SCIP_RETCODE SCIPtreemodelInit( 76 SCIP* scip, /**< SCIP data structure */ 77 SCIP_TREEMODEL** treemodel /**< Treemodel parameter data structure */ 78 ); 79 80 /** frees the Treemodel parameter data structure */ 81 SCIP_EXPORT 82 SCIP_RETCODE SCIPtreemodelFree( 83 SCIP* scip, /**< SCIP data structure */ 84 SCIP_TREEMODEL** treemodel /**< Treemodel parameter data structure */ 85 ); 86 87 /** returns TRUE if the Treemodel branching rules are enabled */ 88 SCIP_EXPORT 89 SCIP_Bool SCIPtreemodelIsEnabled( 90 SCIP* scip, /**< SCIP data structure */ 91 SCIP_TREEMODEL* treemodel /**< Treemodel parameter data structure */ 92 ); 93 94 /** apply the Treemodel branching rules to attempt to select a better 95 * branching candidate than the one selected by pseudocost branching */ 96 SCIP_EXPORT 97 SCIP_RETCODE SCIPtreemodelSelectCandidate( 98 SCIP* scip, /**< SCIP data structure */ 99 SCIP_TREEMODEL* treemodel, /**< Treemodel parameter data structure */ 100 SCIP_VAR** branchcands, /**< branching candidate storage */ 101 SCIP_Real* mingains, /**< minimum gain of rounding downwards or upwards */ 102 SCIP_Real* maxgains, /**< maximum gain of rounding downwards or upwards */ 103 SCIP_Real* tiebreakerscore, /**< scores to use for tie breaking */ 104 int nbranchcands, /**< the number of branching candidates */ 105 int* bestcand /**< the best branching candidate found before the call, 106 and the best candidate after the call (possibly the same) */ 107 ); 108 109 #ifdef __cplusplus 110 } 111 #endif 112 113 #endif 114