The routine CPXgetcallbackinfo accesses 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 argument cbdata MUST be the value of cbdata passed to the user-written callback function.

wherefrom

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

whichinfo

An integer value specifying 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 and informational callbacks:

For MIP algorithms and advanced callbacks:

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;
       }
       
     }
     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);
 }
 

The routine returns zero if successful and nonzero if an error occurs. If nonzero, the requested value may not be available for the specific optimization algorithm. For example, the dual objective is not available from primal simplex.