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

[Alexander Schnell]

Hi Michael,

thank you for your suggestions. 


I don't know exactly how to test the numerical stability
of my problem.
What I can say is that I am using big-M constraints where I try to work
with constants which are as small as possible. 
Moreover, I work with the product of two binary variables 
which I model by the and-constraint. 
I think these two features could lead to numerical problems.
However, I tested my approach with 3240 different runs 
(on 270 instances) and the presolving problem only appears in 0,2% of
the runs. 

Best, Alex.
 

On Mon, 2014-05-05 at 23:31 +0200, michael.winkler at zib.de wrote:
> Also for the mailing list...
> 
> ---------------------------- 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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> > Scip at zib.de
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> >
> 
> 
> 
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