Callbacks#
The final example we consider is the callback example, which demonstrates the use of Gurobi
callbacks. Callbacks are used to report on the progress of the optimization
or to modify the behavior of the Gurobi solver. To use a callback, the user
writes a routine that implements the desired behavior. The routine is
passed to the Gurobi Optimizer when optimization begins, and the routine is
called regularly during the optimization process. One argument of the user
routine is a where
value, which indicates from where in the
optimization process the callback is invoked. The user callback routine can
call the optimization library to query certain values. We refer the reader
to the callback section of the Gurobi Reference
Manual for more precise details.
Our callback example implements a simple termination scheme: the user
passes a node count (limit
) into the callback, and the callback asks
the optimizer to terminate when that node count is reached. This is
implemented as follows:
double nodecnt;
GRBcbget(cbdata, where, GRB_CB_MIP_NODCNT, &nodecnt);
if (nodecnt > limit)
GRBterminate(model);
double nodecnt = getDoubleInfo(GRB_CB_MIP_NODCNT);
if (nodecnt > limit)
abort();
double nodecnt = GetDoubleInfo(GRB.Callback.MIP_NODCNT);
if (nodecnt > limit)
Abort();
double nodecnt = getDoubleInfo(GRB.CB_MIP_NODCNT);
if (nodecnt > limit)
abort();
nodecnt = model.cbGet(GRB.Callback.MIP_NODCNT)
if nodecnt > model._mynodelimit:
model.terminate()
Dim nodecnt As Double = GetDoubleInfo(GRB.Callback.MIP_NODCNT)
If nodecnt > limit Then
Abort()
End If
Our callback example also prints progress information.
GRBcbget(cbdata, where, GRB_CB_MIP_NODCNT, &nodecnt);
if (nodecnt - mydata->lastmsg >= 100) {
...
printf("%7.0f ...", nodecnt, ...);
}
double nodecnt = getDoubleInfo(GRB_CB_MIP_NODCNT);
if (nodecnt - lastnode >= 100) {
lastnode = nodecnt;
...
cout << nodecnt << " " << ...;
}
double nodecnt = GetDoubleInfo(GRB.Callback.MIP_NODCNT);
if (nodecnt - lastnode >= 100) {
lastnode = nodecnt;
...
Console.WriteLine(nodecnt + " " ...);
}
double nodecnt = getDoubleInfo(GRB.CB_MIP_NODCNT);
if (nodecnt - lastnode >= 100) {
lastnode = nodecnt;
...
System.out.println(nodecnt + " " ...);
}
nodecnt = model.cbGet(GRB.Callback.MIP_NODCNT)
if nodecnt % 100 == 0:
print(f"{nodecnt} ...")
Dim nodecnt As Double = GetDoubleInfo(GRB.Callback.MIP_NODCNT)
If nodecnt - lastnode >= 100 Then
lastnode = nodecnt
...
Console.WriteLine(nodecnt & " " ...)
End If