[Scip] [Fwd: Re: Problem with debug solution]

[michael.winkler at zib.de]

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---------------------------- Original Message ----------------------------
Subject: Re: [Scip] Problem with debug solution
From:    bzfwinkm at zib.de
Date:    Mon, May 5, 2014 9:18 pm
To:      "Alexander Schnell" <alexander.schnell at univie.ac.at>
--------------------------------------------------------------------------

Hi Alexander,

> Dear SCIP team,
>
> I implemented a constraint handler and there seems
> to be a problem:
>
> With a certain parameter setting, SCIP tells me that an instance is
> infeasible, whereas I know that there must be an optimal solution for
> that instance. SCIP detects the infeasibility during presolving.
> If I switch off presolving, SCIP finds the optimal solution.
>
> When I try to run SCIP with a debug solution (#define
> SCIP_DEBUG_SOLUTION ... in debug.h), it is read
> but SCIP does not print out any violation detected for the debug
> solution. Is this because the infeasibility was detected during
> presolving?
>
> Do you have an advice for the debugging of such situations, i.e.
> a wrong infeasibility detection during presolving?
>

You can set the verbosity of SCIP to 5 in the interactive shell, this will
hopefully print the plugin that detected the infeasibility.
How numerical stable is your problem?

In SCIP last release 3.1.0 we added SCIPdebugCheckConss() to the debug
mechanism. This can be call from a constraint handler to maybe check if
some presolving step rendered certain constraints to violate the debug
solution.

Best, Michael

> Thank you in advance.
>
> Best regards,
> Alexander Schnell
>
>
>
>
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