Solving Constraint Integer Programs

treemodel.h File Reference

Detailed Description

Branching rules based on the Single-Variable-Branching (SVB) model.

Daniel Anderson
Pierre Le Bodic

The Single-Variable-Branching (SVB) model is a simplified model of Branch & Bound trees, from which several nontrivial variable selection rules arise. The Treemodel branching rule complements SCIP's hybrid branching by suggesting improved branching variables given the current pseudocosts and the current dual gap.

Given a variable with dual bound changes (l, r) (both positive) and an absolute gap G, the SVB model describes the tree that needs to be built by branching on that same variable at every node until the value G is reached at every leaf, starting from 0 at the root node. If we do so for every variable, we can select the variable that produces the smallest tree. In the case where the gap is not known, then we can compute the growth rate of the tree, which we call the ratio. The ratio of a variable (l, r) is the factor by which the size of the tree built using (l, r) that closes a gap G must be multiplied by to close a gap G+1. This ratio is not constant for all gaps, but when G tends to infinity, it converges to a fixed value we can compute numerically using a root finding algorithm (e.g. Laguerre). The ratio is used when the gap is too large (e.g. no primal bound known) or to help approximate the size of the SVB tree for that variable.

See the following publication for more detail:

Pierre Le Bodic and George Nemhauser
An abstract model for branching and its application to mixed integer programming
Mathematical Programming, 2017

Definition in file treemodel.h.

#include "scip/scip.h"

Go to the source code of this file.


SCIP_RETCODE SCIPtreemodelInit (SCIP *scip, SCIP_TREEMODEL **treemodel)
SCIP_RETCODE SCIPtreemodelFree (SCIP *scip, SCIP_TREEMODEL **treemodel)
SCIP_Bool SCIPtreemodelIsEnabled (SCIP *scip, SCIP_TREEMODEL *treemodel)
SCIP_RETCODE SCIPtreemodelSelectCandidate (SCIP *scip, SCIP_TREEMODEL *treemodel, SCIP_VAR **branchcands, SCIP_Real *mingains, SCIP_Real *maxgains, SCIP_Real *tiebreakerscore, int nbranchcands, int *bestcand)

Function Documentation

◆ SCIPtreemodelInit()

SCIP_RETCODE SCIPtreemodelInit ( SCIP scip,
SCIP_TREEMODEL **  treemodel 

initialises the Treemodel parameter data structure

scipSCIP data structure
treemodelTreemodel parameter data structure

Definition at line 834 of file treemodel.c.

Referenced by selectCandidateUsingSampling().

◆ SCIPtreemodelFree()

SCIP_RETCODE SCIPtreemodelFree ( SCIP scip,
SCIP_TREEMODEL **  treemodel 

frees the Treemodel parameter data structure

scipSCIP data structure
treemodelTreemodel parameter data structure

Definition at line 892 of file treemodel.c.

◆ SCIPtreemodelIsEnabled()

SCIP_Bool SCIPtreemodelIsEnabled ( SCIP scip,

returns TRUE if the Treemodel branching rules are enabled

scipSCIP data structure
treemodelTreemodel parameter data structure

Definition at line 908 of file treemodel.c.

Referenced by execRelpscost().

◆ SCIPtreemodelSelectCandidate()

SCIP_RETCODE SCIPtreemodelSelectCandidate ( SCIP scip,
SCIP_VAR **  branchcands,
SCIP_Real mingains,
SCIP_Real maxgains,
SCIP_Real tiebreakerscore,
int  nbranchcands,
int *  bestcand 

apply the Treemodel branching rules to attempt to select a better branching candidate than the one selected by pseudocost branching

scipSCIP data structure
treemodelTreemodel parameter data structure
branchcandsbranching candidate storage
mingainsminimum gain of rounding downwards or upwards
maxgainsmaximum gain of rounding downwards or upwards
tiebreakerscorescores to use for tie breaking
nbranchcandsthe number of branching candidates
bestcandthe best branching candidate found before the call, and the best candidate after the call (possibly the same)

Definition at line 920 of file treemodel.c.

References SCIP_Treemodel::enabled, SCIP_Treemodel::filterhigh, SCIP_Treemodel::filterlow, findNonDominatedVars(), SCIP_Treemodel::height, SCIP_Treemodel::highrule, SCIP_Treemodel::lowrule, NULL, SCIP_Bool, SCIP_CALL, SCIP_OKAY, SCIP_PARAMETERWRONGVAL, SCIP_Real, SCIPallocBufferArray, SCIPfreeBufferArray, SCIPgetCurrentNode(), SCIPgetNodeLowerbound(), SCIPgetUpperbound(), SCIPinfinity(), SCIPisGT(), SCIPisInfinity(), SCIPisLT(), selectCandidateUsingRatio(), selectCandidateUsingSampling(), and selectCandidateUsingSVTS().

Referenced by execRelpscost().