[Scip] How to deal with "branching decisions"

[gamrath@zib.de]

Tobias Achterberg schrieb:
> This is easy: use the constraints as you do, but instead of fixing the
variables to zero
> in the scip_active() method, do so in the scip_prop() method, i.e., the
domain propagation
> callback. This is exactly where this stuff belongs to. Just make sure
that your constraint
> handler has a propagation frequency of 1, such that the propagator is
always called.
>
>
> Tobias
>


In addition to that, you have to make sure that the node is propagated
again, if it is entered again. Normally, the propagation method is only
called once, only when the node is entered the first time.
You could remember the number of variables that existed, the last time the
constraint was propagated. Each time it is activated, you can check
whether new variables were created in the meantime and it should be
propagated again. You can mark the node at which the constraint is
sticking to be propagated again by SCIPrepropagateNode(). In the
propagation callback, you can then fix variables to zero by SCIPchgVarUb()
and update the number of variables for the last propagation.

This is also done in the Coloring example of the current SCIP-release in
the file cons_storeGraph.c.

Best regards,
Gerald