Re: [Bug-glpk] [Fwd: preprocessing goes into infinite loop]

[glpk xypron]

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