CPXgetcallbackinfo

Description

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

This routine is the only routine that 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.

The routine returns a zero on success, and a 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 when using primal simplex.

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

Arguments

The pointer to the CPLEX environment as returned by CPXopenCPLEX().

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.

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 CPXgetlpcallbackfunc() for possible values of wherefrom and their meaning.

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 below.

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

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); }

Before optimization, the call CPXsetlpcallbackfunc (env, mycallback, NULL); would be made to tell CPLEX to call the function mycallback() once per iteration. To turn off that capability, the following statement would be included:

CPXsetlpcallbackfunc (env, NULL, NULL);