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

[Alexander Schnell]

Hi, 

I increased the verbosity level.
Now, SCIP tells me that the probing propagator 
detected the infeasibility. If I switch off probing during
presolving, this leads to the optimal solution.

The function SCIPdebugCheckConss() has no effect in my constraint
handler. 
Is there a possibility to print out the reason for the infeasibility
during probing?

Best, Alex.
 


On Tue, 2014-05-06 at 09:23 +0200, Alexander Schnell wrote:
> 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
> > > http://listserv.zib.de/mailman/listinfo/scip
> > >
> > 
> > 
> > 
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> 
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