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Re: [Bug-glpk] Wrong result with MIP presolver - NO PRIMAL FEASIBLE SOLU


From: Andrew Makhorin
Subject: Re: [Bug-glpk] Wrong result with MIP presolver - NO PRIMAL FEASIBLE SOLUTION
Date: Thu, 01 Jan 2015 16:13:35 +0300

Hi Heinrich,

Thank you for your bug report.

> for the appended model I get the following results with glpk 4.55 on Linux 
> 64bit:
> 
> $ glpsol  -m test.mod
> ...
> Preprocessing...
> PROBLEM HAS NO PRIMAL FEASIBLE SOLUTION
> 
> $ glpsol --nointopt -m test.mod
> ...
> +356119: mip =   0.000000000e+00 >=     tree is empty   0.0% (0; 3059)
> INTEGER OPTIMAL SOLUTION FOUND
> Time used:   161.6 secs
> 
> The presolver should not influence reported feasiblity.

It may happen due to insufficient accuracy in the mip presolver. I will
try to inspect your instance more carefully.


Andrew Makhorin





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