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## Re: [Help-glpk] Assertion failed

**From**: |
Andrew Makhorin |

**Subject**: |
Re: [Help-glpk] Assertion failed |

**Date**: |
Fri, 14 Jul 2006 04:45:30 +0400 |

>* I have a problem with running glpk-4.10:*
>* *
>* I run the following MIP instance using command (glpsol --cpxlp*
>* ~/tmp_prob.lp):*
>* *
>* Minimize*
>* obj: x_1*
>* *
>* Subject To*
>* r_1: - 1003 x_1 + x_2 >= 0*
>* r_2: - 1999 x_2 + x_3 >= 0*
>* r_3: - 4000 x_3 + x_4 >= 0*
>* r_4: + 8000 x_4 + x_5 <= 0*
>* r_5: + 2 x_5 + x_6 >= 0*
>* r_6: - x_1 <= -1002*
>* r_7: - x_2 <= -1005006*
>* r_8: - x_3 <= 138476654*
>* r_9: - x_4 <= -144165184*
>* r_10: - x_6 <= -1*
>* *
>* Bounds*
>* x_1 free*
>* x_2 free*
>* x_3 free*
>* x_4 free*
>* x_5 free*
>* x_6 free*
>* *
>* Generals*
>* x_1*
>* x_2*
>* x_3*
>* x_4*
>* x_5*
>* x_6*
>* *
>* End*
>* *
>* and I get the following output (error):*
>* *
>* lpx_read_cpxlp: 10 rows, 6 columns, 15 non-zeros*
>* lpx_read_cpxlp: 6 integer columns, none of which are binary*
>* lpx_read_cpxlp: 32 lines were read*
>* lpx_simplex: original LP has 10 rows, 6 columns, 15 non-zeros*
>* lpx_simplex: presolved LP has 5 rows, 6 columns, 10 non-zeros*
>* lpx_adv_basis: size of triangular part = 5*
>* 0: objval = 1.002000000e+03 infeas = 1.000000000e-00 (0)*
>* Assertion failed: spx->p != 0; file glpspx2.c; line 668*
>* *
>* It seems like an error in glpk or is there anything I should do to be able*
>* to*
>* solve this problem?*
The error is caused by extremely bad properties of your problem.
Using free integral variables is a not good idea. Besides, as it
follows, for example, from constraint r_9, x4 being declared as
integral variable must be greater than 144165184; it is very
problematic for any solver based on finite precision arithmetic
to satisfy such condition.
Try to reformulate your problem. In particular, if a value of some
variable is expected to be greater than 100 in optimal solution,
there is no reason in most cases to consider it as integral.
Andrew Makhorin