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Re: [Help-glpk] "lpx_simplex" fails to find a feasible-point
From: |
Andrew Makhorin |
Subject: |
Re: [Help-glpk] "lpx_simplex" fails to find a feasible-point |
Date: |
Mon, 8 Jan 2007 22:42:39 +0300 |
>
> I have a fairly trivial LP problem that I'm trying to
> solve using GLPK,
> but it says there's no feasible-point even though I can compute one by
> hand. Here is the coefficient matrix:
>
> 1 0 -0.5055 0.0000 0.0000 0 0 0 0 0 0
> 0 1 -0.4207 0.0000 0.0000 0 0 0 0 0 0
> 1 0 0.0000 -0.4779 0.0000 0 0 0 0 0 0
> 0 1 0.0000 -0.3355 0.0000 0 0 0 0 0 0
> 1 0 0.0000 0.0000 -0.4023 0 0 0 0 0 0
> 0 1 0.0000 0.0000 -0.1920 0 0 0 0 0 0
> 1 0 -252.9900 0.0000 0.0000 1 0 0 0 0 0
> 0 1 -210.5600 0.0000 0.0000 0 1 0 0 0 0
> 1 0 0.0000 -239.1900 0.0000 0 0 1 0 0 0
> 0 1 0.0000 -167.9000 0.0000 0 0 0 1 0 0
> 1 0 0.0000 0.0000 -201.3400 0 0 0 0 1 0
> 0 1 0.0000 0.0000 -96.0900 0 0 0 0 0 1
>
> The first six rows are set as >=0.0 and the second six are set as
> =0.0.
> I'm minimizing the sum of the last six column-variables, that absorb
> the "residue" of what might otherwise make the last six rows nonzero.
> All variables are set as >=0.0. An example of a feasible-point is the
> following, in order of the columns they mutliply with:
>
> 201.34
> 96.09
> 0.796
> 0.842
> 1
> 0.05
> 89.84
> 0.07
> 53.78
> 0
> 0
>
> Is this matrix degenerate in some way that breaks GLPK? I've
> tried the
> various combinations of lpx_simplex, lpx_interior, lpx_scale_prob, and
> LPX_K_PRESOL=1. I assume that GLPK is working as designed, since the
> "make check" passes okay. I'm running on an IBM Thinkpad
> running RHEL 4
Please write the problem data to a text file, say, in mps or cplex
format (lpx_write_mps, lpx_write_cpxlp) and post it to me.
Andrew Makhorin