The routine CPXgetcallbackinfo is used to access information about the current optimization process from within a user-written callback function.

Parameters

env

A pointer to the CPLEX environment as returned by CPXopenCPLEX.

cbdata

The cbdata pointer passed to the user-written callback function. The parameter cbdata MUST be the value of cbdata passed to the user-written callback function.

wherefrom

An integer value indicating the optimization algorithm from which the user-written callback function was called. The parameter wherefrom MUST be the value of wherefrom passed to the user-written callback function. See CPXgetlpcallbackfuncCPXgetmipcallbackfunc, and CPXgetnetcallbackfunc for possible values of wherefrom and their meaning.

whichinfo

An integer value indicating the specific information that should be returned by CPXgetcallbackinfo to the result argument. Values for whichinfo, the type of the information returned into *result_p, plus a description appear in the table.

result_p

A generic pointer to a variable of type double or int, dependent on the value of whichinfo, as documented in the following tables.

For LP algorithms:

For Network algorithms:

For Presolve algorithms:

For MIP algorithms:

Example

See lpex4.c in the CPLEX User's Manual.

Suppose you want to know the objective value on each iteration for a graphical user display. In addition, if primal simplex is not feasible after 1000 iterations, you want to stop the optimization. The function mycallback is a callback function to do this.

 int mycallback (CPXCENVptr env, void *cbdata, int wherefrom,
 	               void *cbhandle)
 {
  int	itcount;
  double objval;
  int	ispfeas;
  int	status = 0;

  if ( wherefrom == CPX_CALLBACK_PRIMAL ) {
     status = CPXgetcallbackinfo (env, cbdata, wherefrom,
                                  CPX_CALLBACK_INFO_PRIMAL_FEAS,
                                  &ispfeas);
     if ( status ) {
        fprintf (stderr,"error %d in CPXgetcallbackinfo\n", status);
        status = 1;
        goto TERMINATE;
     }
     if ( ispfeas ) {
        status = CPXgetcallbackinfo (env, cbdata, wherefrom,
                 CPX_CALLBACK_INFO_PRIMAL_OBJ,
                 &objval) )
       if ( status ) {
          fprintf (stderr,"error %d in CPXgetcallbackinfo\n",
                   status);
          status = 1;
          goto TERMINATE;
       }
       /* Do some graphics with the value of objval */
     }
     else {
          status = CPXgetcallbackinfo (env, cbdata, wherefrom,
 	                                     CPX_CALLBACK_INFO_ITCOUNT, &itcount);
          if ( status ) {
             fprintf (stderr,"error %d in CPXgetcallbackinfo\n", status);
             status = 1;
             goto TERMINATE;
          }
          if ( itcount > 1000 )  status = 1;
     }
  }

 TERMINATE:
   return (status);
 }