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Re: [Bug-glpk] [Fwd: preprocessing goes into infinite loop]
From: |
glpk xypron |
Subject: |
Re: [Bug-glpk] [Fwd: preprocessing goes into infinite loop] |
Date: |
Sat, 14 Jan 2012 13:58:45 +0100 |
Hello Andrew,
when running glp_simplex on the problem, I get this output:
GLPK Simplex Optimizer, v4.47
45 rows, 5 columns, 123 non-zeros
0: obj = 5.000000000e+00 infeas = 3.750e+01 (0)
37: obj = 1.400000000e+01 infeas = 8.833e+00 (0)
PROBLEM HAS NO FEASIBLE SOLUTION
I then used John's coding to write the appended file in CPLEX format.
glpsol --lp test.lp leads to the following error in the presolver:
Preprocessing...
Assertion failed: q->lb < q->ub
Error detected in file ..\src\glpnpp03.c at line 556
I would not have expected such an error.
@John: Please, check your problem formulation.
Best regards
Xypron
> -------- Forwarded Message --------
> To: address@hidden <address@hidden>
> Subject: preprocessing goes into infinite loop
> Date: Fri, 13 Jan 2012 17:28:32 -0600
>
> Hello!
>
> I work with the Sage computer algebra system, which can use GLPK as a
> backend to solve mixed integer linear programs. Unfortunately, Sage sometimes
> crashes when I am trying to solve some linear systems that are
> machine-generated for a problem of interest to me.
>
> I managed to reproduce one of these problems directly in GLPK, linking via
> C++. I have placed a copy of the program at
>
> www.math.usm.edu/perry/glpk_bug.cpp
>
> The problem creates an LP w/45 rows and 5 columns that apparently sends
> GLPK's preprocessing into an infinite loop. If the 45th row is not added
> (comment out the BOOM macro at the beginning of the file) then the LP finds a
> solution.
>
> We believe this is a bug in GLPK. If it is a problem with how we are
> accessing GLPK from Sage, please let us know.
>
> Thank you for your attention to this!
>
> regards
> john perry
>
>
>
>
> _______________________________________________
> Bug-glpk mailing list
> address@hidden
> https://lists.gnu.org/mailman/listinfo/bug-glpk
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test.lp
Description: Binary data