Description

This routine is the only routine which can access optimization status information from within a user-written callback function. It is also the only Callable Library routine that may be called from within a user-written callback function, and in fact, may only be called from the callback function.

Return Value

Synopsis

int CPXgetcallbackinfo (CPXENVptr env,
                        void *cbdata,
                        int wherefrom,
                        int whichinfo,
                        void *result_p);

CPXENVptr env

void *cbdata

int wherefrom

int whichinfo

void *result_p

For LP algorithms:

whichinfo	type of *result_p	description
CPX_CALLBACK_INFO_PRIMAL_OBJ	double	primal objective value
CPX_CALLBACK_INFO_DUAL_OBJ	double	dual objective value
CPX_CALLBACK_INFO_PRIM_INFMEAS	double	measure of primal infeasibility
CPX_CALLBACK_INFO_DUAL_INFMEAS	double	measure of dual infeasibility
CPX_CALLBACK_INFO_PRIMAL_FEAS	int	1 if primal feasible, 0 if not
CPX_CALLBACK_INFO_DUAL_FEAS	int	1 if dual feasible, 0 if not
CPX_CALLBACK_INFO_ITCOUNT	int	iteration count
CPX_CALLBACK_INFO_CROSSOVER_PPUSH	int	primal push crossover itn. count
CPX_CALLBACK_INFO_CROSSOVER_PEXCH	int	primal exchange crossover itn. count
CPX_CALLBACK_INFO_CROSSOVER_DPUSH	int	dual push crossover itn. count
CPX_CALLBACK_INFO_CROSSOVER_DEXCH	int	dual exchange crossover itn. count
CPX_CALLBACK_INFO_USER_PROBLEM	CPXLPptr	returns pointer to original user problem available for primal, dual, barrier, mip

For network algorithms:

whichinfo	type of *result_p	description
CPX_CALLBACK_INFO_PRIMAL_OBJ	double	primal objective value
CPX_CALLBACK_INFO_PRIM_INFMEAS	double	measure of primal infeasibility
CPX_CALLBACK_INFO_ITCOUNT	int	iteration count
CPX_CALLBACK_INFO_PRIMAL_FEAS	int	1 if primal feasible, 0 if not

For Presolve algorithms:

whichinfo	type of *result_p	description
CPX_CALLBACK_INFO_PRESOLVE_ROWSGONE	int	number of rows eliminated
CPX_CALLBACK_INFO_PRESOLVE_COLSGONE	int	number of columns eliminated
CPX_CALLBACK_INFO_PRESOLVE_AGGSUBST	int	number of aggregator substitutions
CPX_CALLBACK_INFO_PRESOLVE_COEFFS	int	number of modified coefficients

For MIP algorithms:

whichinfo	type of *result_p	description
CPX_CALLBACK_INFO_BEST_INTEGER	double	obj. value of best integer solution
CPX_CALLBACK_INFO_BEST_REMAINING	double	obj. value of best remaining node
CPX_CALLBACK_INFO_NODE_COUNT	int	total number of nodes solved
CPX_CALLBACK_INFO_NODES_LEFT	int	number of remaining nodes
CPX_CALLBACK_INFO_MIP_ITERATIONS	int	total number of MIP iterations
CPX_CALLBACK_INFO_MIP_FEAS	int	returns 1 if feasible solution exists, otherwise 0
CPX_CALLBACK_INFO_CUTOFF	double	updated cutoff value
CPX_CALLBACK_INFO_CLIQUE_COUNT	int	number of clique inequalities added
CPX_CALLBACK_INFO_COVER_COUNT	int	number of cover inequalities added
CPX_CALLBACK_INFO_USER_PROBLEM	CPXLPptr	returns pointer to original user problem available for primal, dual, Barrier, MIP
CPX_CALLBACK_INFO_COVER_COUNT	int	number of cover inequalities added
CPX_CALLBACK_INFO_USER_PROBLEM	CPXLPptr	returns pointer to original user problem available for primal, dual, Barrier, MIP

Example

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 (CPXENVptr 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 */
   }
   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);
}

CPXsetlpcallbackfunc (env, NULL, NULL);