ILOG CPLEX 11.0 User's Manual

◆◆cbdata, a pointer to ILOG CPLEX internal data structures needed byCPXgetcallbackinfo;wherefrom, indicates which optimizer is calling the callback;◆ cbhandle, a pointer supplied when your application calls CPXsetlpcallbackfunc orCPXsetmipcallbackfunc (so that the callback has access to private user data).The arguments wherefrom and cbdata should be used only in calls toCPXgetcallbackinfo.Example: Using Callbacks lpex4.cThis example shows you how to use callbacks effectively with routines from theILOG CPLEX Callable Library. It is based on lpex1.c, a program from the ILOG CPLEXGetting Started manual. This example about callbacks differs from that simpler one inseveral ways:◆◆To make the output more interesting, this example optimizes a slightly different linearprogram.The ILOG CPLEX screen indicator (that is, the parameter CPX_PARAM_SCRIND) is notturned on. Only the callback function produces output. Consequently, this program callsCPXgeterrorstring to retrieve any error messages and then prints them. After theTERMINATE: label, the program uses separate status variables so that if an error occurredearlier, its error status will not be lost or destroyed by freeing the problem object andclosing the ILOG CPLEX environment. Table 30.3 summarizes those status variables.Table 30.3Status Variables in lpex4.cVariablefrstatusclstatusRepresents status returned by this routineCPXfreeprobCPXcloseCPLEX◆The function mycallback at the end of the program is called by the optimizer. Thisfunction tests whether the primal simplex optimizer has been called. If so, then a call toCPXgetcallbackinfo gets the following information:●●●iteration count;feasibility indicator;sum of infeasibilities (if infeasible);● objective value (if feasible).The function then prints these values to indicate progress.ILOG CPLEX 11.0 — USER’ S MANUAL 461