[SCIP] After stopping pricing and doing restart, model is becoming unbounded during presolve?

[Franzen, Christian]

Hi Ambros.


Thanks for your reponse and sorry for answering late. I have "switched off" presolving by including no presolver plugins, hence I only got the presolving code from the propagators and constraint handlers. That seems to work properly. I started to include one presolver plugin after the other and there seems to be a problem with "domcol". It fixed a lot of variables and afterwards my problem is reported to be unbounded. I did not test all presolver plugins yet, but I will try to test all of them by the end of this week. Any idea concerning "domcol"?

Regards
Christian

________________________________
Von: Scip <scip-bounces at zib.de> im Auftrag von Ambros Gleixner <gleixner at zib.de>
Gesendet: Mittwoch, 13. Januar 2021 21:15
An: scip at zib.de
Betreff: Re: [SCIP] After stopping pricing and doing restart, model is becoming unbounded during presolve?

Hi Christian,

Strange indeed.  Have you tried to turn off presolving?  Does it still
happen?  Have you tried to successively activate individual presolvers
to see when it starts failing?

Best,
Ambros


Am 04.01.21 um 17:10 schrieb Franzen, Christian:
> Hi Scip Team.
>
>
> Thanks to the help of Gregor, I managed to make SCIP stop pricing after
> some iterations and doing a restart on the reduced master without
> pricing. Unfortunately, I am facing some really strang behaviour.
> Sometime it happens, that my model (for that I already have found a
> feasible solution), is reported to be unbound. I wrote the corresponding
> LP files before and after presolving to disk and I see that some
> variable bounds vanished, which seems to be the reason for the
> unboundness. Furthermore, some of the objective coefficients changed
> their sign. Any ideas how or why that is happening during presolving?
>
>
> Regards
>
> Christian
>
>
> P.S.: I attach the SCIP log for one of these runs.
>
>
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