[Cbc] [CBC] Preprocess causing infeasibility

[mg]

Ok, so if I understood correctly you've only changed CoinPresolveDoubleton.cpp,
am I right ?

Thanks a lot for the quick fix !

Marco

2015-09-29 15:41 GMT+02:00 John Forrest <john.forrest at fastercoin.com>:

> 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 release and 2.9.6 release versions.
>
> Thanks in advance,
> Marco
>
>
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>
> --
> ==================================================
> Haroldo Gambini Santos
> D.Sc, Computer Science
> Universidade Federal de Ouro Pretohttp://www.decom.ufop.br/haroldo/
>
>
>
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