CPXXgetcallbackinfo and CPXgetcallbackinfo

Description

The routine CPXXgetcallbackinfo/CPXgetcallbackinfo accesses information about the current optimization process from within a user-written legacy callback function.

This routine is the only routine that can access optimization status information from within a nonadvanced, user-written, legacy callback function. It is also the only Callable Library routine that you can call from within a nonadvanced, user-written, legacy callback function. In fact, you can call it only from the legacy callback function.

For LP algorithms:

Crossover from a barrier to a simplex solution reduces the super-basic count. In fact, in a barrier crossover, if the count reaches 0 (zero), the crossover has finished. Thus, the super-basic count serves as a measure of progress for the crossover algorithm.

For Network algorithms:

For Presolve algorithms:

For MIP algorithms and informational callbacks:

The information specified by variations of CPX_CALLBACK_INFO_KAPPA_ is available only when all of these conditions are met:

• The subproblems are solved by simplex.
• The parameter to control MIP kappa computation (CPXPARAM_MIP_Strategy_KappaStats) is set.
• CPLEX has processed at least one LP-basis during the solve.

In all other cases, CPLEX returns the error CPXERR_NO_KAPPASTATS.

You can query the relative MIP gap between the current best primal and dual bounds outside a callback with the routine CPXXgetmiprelgap/CPXgetmiprelgap.

For distributed parallel MIP algorithms and informational callbacks:

For MIP algorithms and advanced callbacks:

For Tuning:

Arguments

env

A pointer to the CPLEX environment as returned by CPXXopenCPLEX/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 CPXXgetlpcallbackfunc/CPXgetlpcallbackfunc , CPXXgetmipcallbackfunc/CPXgetmipcallbackfunc , and CPXXgetnetcallbackfunc/CPXgetnetcallbackfunc for possible values of wherefrom and their meaning.

whichinfo

An integer value specifying the specific information that should be returned by CPXXgetcallbackinfo/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, CPXINT, or CPXLONG, depending on the value of whichinfo, as documented in the following tables.

Return

The routine returns 0 (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.

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);
}