Scippy

SCIP

Solving Constraint Integer Programs

treemodel.h
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1 /* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
2 /* */
3 /* This file is part of the program and library */
4 /* SCIP --- Solving Constraint Integer Programs */
5 /* */
6 /* Copyright 2002-2022 Zuse Institute Berlin */
7 /* */
8 /* Licensed under the Apache License, Version 2.0 (the "License"); */
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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
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
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
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
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
SCIP_RETCODE SCIPtreemodelSelectCandidate(SCIP *scip, SCIP_TREEMODEL *treemodel, SCIP_VAR **branchcands, SCIP_Real *mingains, SCIP_Real *maxgains, SCIP_Real *tiebreakerscore, int nbranchcands, int *bestcand)
Definition: treemodel.c:920
enum SCIP_Retcode SCIP_RETCODE
Definition: type_retcode.h:63
SCIP_Bool SCIPtreemodelIsEnabled(SCIP *scip, SCIP_TREEMODEL *treemodel)
Definition: treemodel.c:908
SCIP_RETCODE SCIPtreemodelFree(SCIP *scip, SCIP_TREEMODEL **treemodel)
Definition: treemodel.c:892
#define SCIP_Bool
Definition: def.h:93
SCIP_RETCODE SCIPtreemodelInit(SCIP *scip, SCIP_TREEMODEL **treemodel)
Definition: treemodel.c:834
#define SCIP_Real
Definition: def.h:186
SCIP callable library.