[Cbc] [CBC] Preprocess causing infeasibility

[John Forrest]

Marco,

Should be fixed.

The dual code correctly thought it should push a variable all the way to 
its upper bound.  Unhappily the upper bound was 1.3.  Then a later part 
of presolve worked out that that was infeasible for an integer variable.

The error occurred in CoinPresolveDoubleton which changed bounds from 
0,infinity to 0,1.3 without checking whether it was integer. I have 
corrected code so bounds would be 0,1.

John Forrest

On 28/09/15 23:46, Haroldo Gambini Santos wrote:
> Hi Marco,
>
> I found out that the problem is related to a presolving procedure 
> which tries to fix bounds using dual information.
>
> A /quick and dirty/ fix is to change in
>
> Osi/src/OsiPresolve.cpp   line    988
>
> if (dual) {
> to
> if ((dual)&&0) {
>
> to temporarily disable this processing...
>
> Hoping that a better fix comes soon,
>
> Cheers,
>
> Haroldo
>
> On 28-09-2015 06:22, mg wrote:
>> Hi all,
>> I've found a case where preprocess says the problem is infeasible, 
>> but if I turn preprocess off, the problem is correctly solved.
>>
>> Attached you can find the LP file (m3.lp). To reproduce the problem 
>> you can use the following code (I use callCbc):
>>
>> OsiClpSolverInterface solver;
>> CbcModel model(solver);
>> model.solver()->readLp("m3.lp");
>> std::string args("-heur off -cuts off -solve");
>> // using these arguments instead it works
>> // std::string args("-heur off -cuts off -preprocess off -solve");
>> callCbc(args, model);
>>
>> The problem happens in both 2.9.5 releaseand 2.9.6 release versions.
>>
>> Thanks in advance,
>> Marco
>>
>>
>> _______________________________________________
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>> Cbc at list.coin-or.org
>> http://list.coin-or.org/mailman/listinfo/cbc
>
> -- 
> ==================================================
> Haroldo Gambini Santos
> D.Sc, Computer Science
> Universidade Federal de Ouro Preto
> http://www.decom.ufop.br/haroldo/
>
>
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