[Scip] scipoptsuite-3.0.0 and ziboptsuite2.1.1 give different results

[Timo Berthold]

tl;dr: Known bug in SCIP 3.0 with ranged rows which are parallel to
objective function

Dear Hélène,

> I have recently upgraded my ziboptsuite version from 2.1.1 to 3.0.0.. I run a
column generation program using version 2.1.1 and version 3.0.0. and I
obtained
> different results (I have changed nothing in my code).

I think that is a known bug of SCIP 3.0.

What happens is that in presolving, the sub-problem gets reduced to
min -y20-y21-y24
s.t.
1 <= y20+y21+y24 <= 2

The SCIP 3.0 release has a known problem with instances for which the
objective function is parallel to a ranged row.

@Stefan: Could you send Hélène a patch for this?

Actually, the output LP-file was wrong for the same reason (the
constraint is incorrectly marked as "unnecessary").

Best regards
Gregor and Timo

Am 29.11.2012 13:58, schrieb Hélène Toussaint:
>
> Dear all,
>
> I have recently upgraded my ziboptsuite version from 2.1.1 to 3.0.0..
> I run a column generation program using version 2.1.1 and version
> 3.0.0. and I obtained different results (I have changed nothing in my
> code).
>
> During the column generation, I have written one of my pricing
> problems into a file  (before SCIPsolve) using SCIPwriteOrigProblem
> and the transformed sub problem (after SCIPsolve()) using
> SCIPwriteTransProblem. I have obtained the enclosed files subPb.lp and
> subPbTrans.lp. In the transformed sub problem the constraints have
> disappeared and so the solution found by SCIP (in solSubPb.txt) does
> not respect the original constraints (all variables are set to 1).
>
>  
>
> If I use SCIPreadProb to read the file written by SCIPwriteOrigProblem
>  and solve it with SCIPsolve then scip give me the exact result !!
>
>  
>
> Could you please help me to understand what happens ?
>
>  
>
> Best regards,
>
>  
>
> Hélène
>
>
>
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