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[Help-glpk] Re: [Bug-glpk] glpk 4.11 failed assertion
From: |
Andrew Makhorin |
Subject: |
[Help-glpk] Re: [Bug-glpk] glpk 4.11 failed assertion |
Date: |
Thu, 3 Aug 2006 18:07:53 +0400 |
> I'm having a problem with a failed assertion in glpk 4.11.
>
> I'm using the library interface and after setting up the problem and
> calling
>
> lpx_adv_basis(lp);
>
> I do
>
> lpx_simplex(lp);
>
> and for one particular problem, I get
>
> Assertion failed: spx->p != 0; file glpspx2.c; line 668
>
> When I write out the problem (attached), however, and run gplsol
> on it, I get
>
> lpx_read_freemps: reading problem data from `/tmp/lp.mps'...
> lpx_read_freemps: problem name not specified
> lpx_read_freemps: 43 rows, 12 columns, 198 non-zeros
> lpx_read_freemps: 193 records were read
> lpx_simplex: original LP has 43 rows, 12 columns, 198 non-zeros
> lpx_simplex: presolved LP has 38 rows, 12 columns, 192 non-zeros
> lpx_adv_basis: size of triangular part = 38
> 0: objval = 0.000000000e+00 infeas = 1.000000000e+00 (0)
> 8: objval = 0.000000000e+00 infeas = 1.526958211e-02 (0)
> PROBLEM HAS NO FEASIBLE SOLUTION
> lpx_simplex: cannot recover undefined or non-optimal solution
> Time used: 0.0 secs
> Memory used: 0.1M (106164 bytes)
>
> Now, I was expecting a solution, but I assume it got lost
> because I have to convert the coefficients of the problem
> to doubles as it appears that glpk doesn't support arbitrary
> precision integer arithmetic.
>
> Still, getting an unexpected answer would be nicer than a failed
> assertion.
>
> I can reproduce the problem by running the polyhedron_sample
> program from the latest git version of my barvinok library
> (http://www.liacs.nl/~sverdool/gitweb.cgi?p=barvinok.git;a=summary)
> with the following input:
> 18 8
> 1 0 0 0 0 0 1 -28
> 1 16 13 0 -297 0 -99 -128
> 1 0 0 1 0 0 0 -33
> 1 5 0 0 18 0 6 7
> 1 12 0 0 45 0 12 19
> 1 17 0 0 63 -3 21 27
> 1 6 0 0 20 0 9 16
> 1 -24 -18 0 405 0 135 158
> 1 -29 0 5 -108 0 -36 -41
> 1 0 0 0 0 1 0 -28
> 1 0 0 0 1 0 0 -36
> 1 -102 -56 0 1161 0 387 497
> 1 -51 0 0 -189 9 -63 -73
> 1 -6 0 0 -20 0 -9 -10
> 1 29 0 -5 108 0 36 45
> 1 -8 0 0 -27 0 -9 -92
> 1 7 -7 0 216 0 72 99
> 1 -60 0 0 -225 0 -60 -92
>
> Unfortunately, as decribed above, the error disappears
> after dumping and rereading the problem.
The error appears due to huge constraint coefficients. You can call
lpx_scale_prob to scale the problem (as glpsol does).
To obtain the solution with glpsol you need to disable the lp presolver
(--nopresol), because it cannot recover non-optimal solutions.
Andrew Makhorin
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