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[Fwd: glpsol.c: MIP-return code possibly ignored (overwritten)?]

From: Andrew Makhorin
Subject: [Fwd: glpsol.c: MIP-return code possibly ignored (overwritten)?]
Date: Fri, 04 Feb 2022 02:49:28 +0300

-------- Forwarded Message --------
From: Eeri Kask <Eeri.Kask@mailbox.tu-dresden.de>
To: bug-glpk@gnu.org
Subject: glpsol.c: MIP-return code possibly ignored (overwritten)?
Date: Wed, 2 Feb 2022 09:33:20 +0100

> Dear Professor Makhorin,
> we tested glpsol version 5.0 executable and discovered a possible bug,
> please see attached patch which is not a clean bugfix but only
> demonstrates our finding and provides a quick workaround (for us). :-)
> We are very successfully using glpsol as an external solver in a
> vehicle
> fleet routing application and heavily rely on the return code of the
> standalone glpsol executable: if this return code is not EXIT_SUCCESS
> (i.e. 0) then the rest of the system assumes that particular traffic
> routing setting has no (mixed integer programming) solution.
> Now, due to the issue we discovered, in some situations the simplex
> method (as the first part in your implementation) returns a LP-
> solution,
> but then the MIP-refinement which follows, does not find a MIP-
> solution,
> and this failure does not reflect in the return code of the glpsol
> executable.
> P.S. In the patch I marked with /* !! */ that place which affects us.
> With kind regards,
>     Eeri Kask

Attachment: glpsol.c.GLP_NOFEAS.patch
Description: Text document

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