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Re: [Bug-glpk] xassert fail in MIR cut back substitution


From: Andrew Makhorin
Subject: Re: [Bug-glpk] xassert fail in MIR cut back substitution
Date: Tue, 4 Dec 2007 23:27:07 +0300

> I have a MIP where an assertion in the new mir cut generation routines
> in GLPK 4.24 is failing.
> Find attached a cplex-lp file. I was able to produce the problem on a
> linux 64bit machine, and it also appear on some other platforms, but not
> on every, e.g., not on linux 32bit.
> It should pop up with

> ./glpsol --cpxlp --intopt --cuts glpk_mirassertfail.lp

> and the output is

> lpx_read_cpxlp: reading problem data from `glpk_mirassertfail.lp'...
> lpx_read_cpxlp: 50 rows, 43 columns, 169 non-zeros
> lpx_read_cpxlp: 14 integer columns, all of which are binary
> lpx_read_cpxlp: 81 lines were read
> ipp_basic_tech:  6 row(s) and 5 column(s) removed
> ipp_reduce_bnds: 3 pass(es) made, 26 bound(s) reduced
> ipp_basic_tech:  0 row(s) and 0 column(s) removed
> ipp_reduce_coef: 1 pass(es) made, 0 coefficient(s) reduced
> lpx_intopt: presolved MIP has 44 rows, 38 columns, 152 non-zeros
> lpx_intopt: 12 integer columns, all of which are binary
> lpx_adv_basis: size of triangular part = 43
> Solving LP relaxation...
>       0:   objval =   2.543860150e+04   infeas =   1.000000000e+00 (0)
>      24:   objval =   6.655303517e+04   infeas =   0.000000000e+00 (0)
> *    24:   objval =   6.655303517e+04   infeas =   0.000000000e+00 (0)
> *    43:   objval =   1.779541789e+01   infeas =   5.079270338e-16 (0)
> OPTIMAL SOLUTION FOUND
> Creating the conflict graph...
> The conflict graph has 2*10 vertices and 15 edges
> Generating cutting planes...
> &    43: obj =   1.779541789e+01   frac =     3   cuts =     0 (0)
> &    95: obj =   1.789692248e+01   frac =     1   cuts =    10 (198)
> 10 Gomory's mixed integer cut(s) added
> Integer optimization begins...
> +    95: mip =     not found yet >=              -inf        (1; 0)
> MIR cuts enabled
> ios_mir_init: warning: debug mode enabled
> GLPK internal error: jj != 0; file glpios05.c, line 1087

> (I had enabled _MIR_DEBUG for testing. The problem comes with or without
>   it.)

Thank you for your bug report.

The bug is caused due to a missed fragment in a routine performing
back substitution.

Now the bug has been fixed. Please replace src/glpios05.c by a new
version (see attachment) and then rebuild the package.

Attachment: glpios05.c.gz
Description: GNU Zip compressed data


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