The routine CPXsetheuristiccallbackfunc sets or modifies the user-written callback to be called by ILOG CPLEX during MIP optimization after the subproblem has been solved to optimality. That callback is not called when the subproblem is infeasible or cut off. The callback supplies ILOG CPLEX with heuristically-derived integer solutions.

If a linear program must be solved as part of a heuristic callback, make a copy of the node LP and solve the copy, not the CPLEX node LP.

Example

 status = CPXsetheuristiccallbackfunc(env, myheuristicfunc, mydata);

See also the example admipex2.c in the standard distribution.

Parameters

env

A pointer to the CPLEX environment, as returned by CPXopenCPLEX.

heuristiccallback

A pointer to a user-written heuristic callback. If this callback is set to NULL, no callback is called during optimization.

cbhandle

A pointer to the user's private data. This pointer is passed to the callback.

Callback description

 int callback (CPXENVptr env,
               void      *cbdata,
               int       wherefrom,
               void      *cbhandle,
               double    *objval_p,
               double    *x,
               int       *checkfeas_p,
               int       *useraction_p);
 

The call to the heuristic callback occurs after an optimal solution to the subproblem has been obtained. The user can provide that solution to start a heuristic for finding an integer solution. The integer solution provided to ILOG CPLEX replaces the incumbent if it has a better objective value. The basis that is saved as part of the incumbent is the optimal basis from the subproblem; it may not be a good basis for starting optimization of the fixed problem.

The integer solution returned to CPLEX is for the original problem if the parameter CPX_PARAM_MIPCBREDLP was set to CPX_OFF before the call to CPXmipopt that calls the callback. Otherwise, it is for the presolved problem.

Callback return value

The callback returns zero on success and nonzero if an error occurs.

Callback arguments

env

A pointer to the CPLEX environment, as returned by CPXopenCPLEX.

cbdata

A pointer passed from the optimization routine to the user-written callback to identify the problem being optimized. The only purpose of the cbdata pointer is to pass it to the callback information routines.

wherefrom

An integer value indicating at which point in the optimization this function was called. It has the value CPX_CALLBACK_MIP_HEURISTIC for the heuristic callback.

cbhandle

A pointer to user private data.

objval_p

A pointer to a variable that on entry contains the optimal objective value of the subproblem and on return contains the objective value of the integer solution found, if any.

x

An array that on entry contains primal solution values for the subproblem and on return contains solution values for the integer solution found, if any.

checkfeas_p

A pointer to an integer that indicates whether or not ILOG CPLEX should check the returned integer solution for integer feasibility. The solution is checked if checkfeas_p is nonzero. When the solution is checked and found to be integer infeasible, it is discarded, and optimization continues.

useraction_p

A pointer to an integer to contain the indicator for the action to be taken on completion of the user callback. The table summarizes the possible values.