[Cbc] Pre-Processing Bug

[John Forrest]

Haroldo,

Is this in trunk or stable?

I just tried it in trunk and it stopped at line 154 of main.cpp saying 
INFEASIBLE.  However this is because the code says

   if (ppLP->isProvenOptimal())
    {
       printf("INFEASIBLE.\n");
       exit(1);
    }
    else
    {
       printf("Optimal solution found.\n");
    }

which looks the wrong way round.  So it seems OK in trunk.

John Forrest


On 20/01/12 18:35, Haroldo Santos wrote:
> Hi,
>
> I think I've found a bug in pre-processing phase of CBC.
>
> What I was doing (and worked flawlessly for all MIPs except this one) 
> was to inform to CBC a feasible solution found using a greedy 
> heuristic. This solution was informed considering variables of the 
> pre-processed model (checking for the original variables in 
> originalColumns() ).
>
> What happened is that the pre-processed model for this case included a 
> new set of constraints (expected) which make this valid solution to be 
> considered infeasible (unexpected). When I fix the same set of 
> variables in the original LP there is no problem.
>
> To make it easy to check for this problem I've wrote a small code 
> which fixes the same variables in the original and in the 
> pre-processed problem and made it available here:
>
> http://www.decom.ufop.br/haroldo/files/ppBug.tar.gz
>
> In infRows.txt I listed tree constraints that when removed allows 
> feasibility to be obtained again.
>
> Thanks in advance,
>
> Haroldo
>
> -- 
> =============================================================
> Haroldo Gambini Santos
> Computing Department - Universidade Federal de Ouro Preto - UFOP
> email: haroldo [at ] iceb.ufop.br <http://iceb.ufop.br>
> home/research page: www.decom.ufop.br/haroldo/ 
> <http://www.decom.ufop.br/haroldo/>
>
>
>
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