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Re: [Bug-glpk] glpsol fails to parse a cplex lp file containing constrai

From: Andrew Makhorin
Subject: Re: [Bug-glpk] glpsol fails to parse a cplex lp file containing constraints that evaluate to zero
Date: Thu, 05 May 2011 19:11:04 +0400

> Running glpsol on the attached file fails:
>  > glpsol --cpxlp debug.lp
> GLPSOL: GLPK LP/MIP Solver, v4.43
> Parameter(s) specified in the command line:
>  --cpxlp debug.lp
> Reading problem data from `debug.lp'...
> debug.lp:6: missing variable name
> CPLEX LP file processing error
> Reading some documentation about the cplex lp format [1], I did not
> find something that forbids to but "0<=0" constraints, so I am filing
> a bug here. Pardon me if I am wrong.
> FYI, cbc does not fail on it, which made me suspect a bug in glpsol,
> but nothing proves they are right.
> [1] http://lpsolve.sourceforge.net/5.5/CPLEX-format.htm

Thank you for your report.

I don't think this is a bug, because cplex lp format does not allow
constant terms in the lhs, i.e. the lhs should be a non-empty linear
form. However, something like "0 x1 <= 0" must be valid.

Andrew Makhorin

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