[Scip] Postprocessing

Mathieu Larose mat087 at gmail.com
Sun May 22 19:50:15 MEST 2011


Hi Timo,

I implemented a separator which does the bound strenghtening, but I don't
see how it can act like a postprocessing procedure (i.e. called once after
the price-and-cut loop).

The best I can do is to set the "priority" to a negative value, set
"delayed" to true and do some tests whether it should run or not (taken from
sepa_redcost.c lines 115-137).

So the separator acts almost like a postprocessing procedure. But if it is
sucessful (i.e. the domain of at least one variable is reduced), another
round of pricing and separation occurs which I do not want. How can I
prevent this?


Regards,
Mathieu


On Fri, May 20, 2011 at 3:07 AM, Timo Berthold <berthold at zib.de> wrote:

> Hi Mathieu.
>
> Bound strenghtening techniques are automatically applied in the
> propagation callbacks of certain constraint handlers (linear, knapsack,
> quadratic,...) which interacts with the price-and-cut loop of SCIP,
> basically in the following way: propagate->solve LP->price->cut->(if new
> vars or cuts found, start again). Also, reduced cost strengthening (which
> actually is a form of propagation/bound strenghtening) is applied only
> during the separation round. The reason is that this one first needs the
> LP to be solved to optimality.
> If you just use SCIP as a blackbox solver, I hope this answered your
> question.
>
> If you like to set up your own domain propagation routine (node
> pre-processing), you will have to implement a propagation plugin (see How
> to add propagators in the Doxygen-Docs) or the propagation callback of a
> constraint handler (see How to add constraint handlers). If you need a
> solved LP for your method (hend it rather is a post-processing), you
> probably better implement a separator (How to..., see also
> src/scip/sepa_redcost.c) or the separation callbac of a constraint
> handler.
>
>
> Best regards,
> Timo
>
>  > Hello everybody,
> >
> > My apologies if this is obvious, but how can I do some postprocessing
> work
> > (bound strenghtening) after the price-and-cut loop has run?
> >
> >
> > Regards,
> >
> > Mathieu
> > _______________________________________________
> > Scip mailing list
> > Scip at zib.de
> > http://listserv.zib.de/mailman/listinfo/scip
> >
>
>
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