ILOG CPLEX 11.0 User's Manual

Selecting VariablesAfter a node has been selected, the variable selection parameter, VarSel, influences whichvariable is chosen for branching at that node.Table 14.7VarSel Parameter Settings for Branching Variable ChoiceVarSelSettingSymbolic Value Branching Variable Choice-1 CPX_VARSEL_MININFEAS Branch strictly at the nearest integer valuewhich is closest to the fractional variable.1 CPX_VARSEL_MAXINFEAS Branch strictly at the nearest integer valuewhich is furthest from the fractional variable.0(Default)CPX_VARSEL_DEFAULTILOG CPLEX automatically decides eachbranch direction.2 CPX_VARSEL_PSEUDO Use pseudo costs, which derives an estimateabout the effect of each proposed branch fromduality information.3 CPX_VARSEL_STRONG Use strong branching, which investsconsiderable effort in analyzing potentialbranches in the hope of drastically reducingthe number of nodes that will be explored.4 CPX_VARSEL_PSEUDOREDUCED Use pseudo reduced costs, which is acomputationally less-intensive form of pseudocosts.Changing Branching DirectionAfter a variable has been selected for branching, the BrDir parameter influences thedirection, up or down, of the branch on that variable to be explored first.Table 14.8BrDir Parameter Settings for Branching Direction ChoiceBrDirSettingSymbolic ValueBranching Direction Choice-1 CPX_BRANCH_DOWN Branch downward0(Default)CPX_BRANCH_GLOBALILOG CPLEX automatically decides eachbranch direction.1 CPX_BRANCH_UP Branch upwardPriority orders complement the behavior of these parameters. They are introduced in IssuingPriority Orders on page 280. They offer a mechanism by which you supply problem-specificILOG CPLEX 11.0 — USER’ S MANUAL 269