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

[Andrew Makhorin]

-------- 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
>

glpsol.c.GLP_NOFEAS.patch
Description: Text document