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[Bug-glpk] Re: lpx_write_cpxlp and lpx_read_cpx_lp are incompatible
From: |
Andrew Makhorin |
Subject: |
[Bug-glpk] Re: lpx_write_cpxlp and lpx_read_cpx_lp are incompatible |
Date: |
Mon, 25 Jul 2005 14:19:42 +0400 |
> There is a problem in the functions lpx_write_cpxlp and lpx_read_cpx_lp.
> The two operations are not inverses of each other. For instance, when
> compiling and executing the file cpxlp_bug.c, a linear programming
> problem is created, is written to disk as "a.cpxlp", then read and
> written again as "b.cpxlp", and the two files are different.
>
> Also, the program tries to solve the problems with lpx_simplex: the
> original has a solution, not the modified one.
>
> Perhaps the bound x_1 <= 0 in "a.cpxlp" should have been written -inf <=
> x_1 <= 0 instead.
>
> I am using GLPK version 4.8.
Thank you for your bug report.
There is a bug in lpx_read_cpxlp, namely, by default the lower bound
is set to 0, so when you specify x <= 0, both lower and upper bound are
set to 0 that erroneously gives x = 0.
I will fix the bug and post the patch to the list.
Andrew Makhorin