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XPRSsetcbchgbranch

Purpose

Declares a branching variable callback function, called every time a new branching variable is set or selected during the MIP search.

Synopsis

               int XPRS_CC XPRSsetcbchgbranch(XPRSprob prob, void (XPRS_CC *fucb)(XPRSprob my_prob, void *my_object, int 
               *entity, int *up, double *estdeg), void *object);
               

Arguments

prob	The current problem.
fucb	The callback function, which takes five arguments, my_prob, my_object, entity, up and estdeg, and has no return value. This function is called every time a new branching variable or set is selected.
my_prob	The problem passed to the callback function, fucb.
my_object	The user-defined object passed as object when setting up the callback with XPRSsetcbchgbranch.
entity	A pointer to the variable or set on which to branch. Ordinary global variables are identified by their column index, i.e. 0, 1,...(COLS- 1) and by their set index, i.e. 0, 1,...,(SETS- 1).
up	If entity is a variable, this is 1 if the upward branch is to be made first, or 0 otherwise. If entity is a set, this is 3 if the upward branch is to be made first, or 2 otherwise.
estdeg	The estimated degradation at the node.
object	A user-defined object to be passed to the callback function, fucb.

Example

The following example demonstrates use of the branching rule to branch on the most violated integer of binary during the global search:

typedef struct {
  double* soln;
  char* type;
  double tol;
  int cols;
} solutionData;
...
solutionData nodeData;
...
XPRSminim(prob,"");
XPRSsetintcontrol(prob, XPRS_MIPLOG, 3);
XPRSsetintcontrol(prob, XPRS_CUTSTRATEGY, 0); 

/* setup data */
XPRSgetintattrib(prob, XPRS_COLS, &(nodeData.cols));
XPRSgetdblcontrol(prob, XPRS_MATRIXTOL, &(nodeData.tol));
nodeData.soln = 
  (double*) malloc(sizeof(double)*nodeData.cols);
nodeData.type = 
  (char*) malloc(sizeof(char)*nodeData.cols);
XPRSgetcoltype(prob, nodeData.type, 0, nodeData.cols-1);

XPRSsetcbchgbranch(prob, varSelection, &nodeData);
XPRSglobal(prob);

The callback function might resemble:

void XPRS_CC varSelection(XPRSprob prob, void* vdata, 
  int *iColumn, int *iUp, double *dEstimate)
{
  double dDist, dUpDist, dDownDist, dGreatestDist=0;
  int iCol;   

  solutionData *nodeData = (solutionData*) vdata;
  XPRSgetpresolvesol(prob, (*nodeData).soln, NULL, NULL, 
                     NULL);
  for(iCol=0;iCol<(*nodeData).cols;iCol++) 
  if((*nodeData).type[iCol]=='I' || 
     (*nodeData).type[iCol]=='B')
  {
    dUpDist=ceil((*nodeData).soln[iCol]) -
              (*nodeData).soln[iCol];
    dDownDist = (*nodeData).soln[iCol] - 
                  floor((*nodeData).soln[iCol]);
    dDist = (dUpDist>dDownDist)?dUpDist:dDownDist;
    if(dDownDist > (*nodeData).tol &&
       dUpDist > (*nodeData).tol)
      if( dDist > dGreatestDist ) 
      {
        *iColumn = iCol;
        dGreatestDist = dDist;
      }
  }
}

Further information

The arguments initially contain the default values of the branching variable, branching variable, branching direction and estimated degradation. If they are changed then the Optimizer will use the new values, if they are not changed then the default values will be used.