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[Help-glpk] Re: Different results for the same problem
From: |
Andrew Makhorin |
Subject: |
[Help-glpk] Re: Different results for the same problem |
Date: |
Mon, 4 Dec 2006 03:56:38 +0300 |
> I have a 0-1 MIP formulation of a scheduling problem. I employ the
> GLPK
> C API to represent my problem and use two function calls in the end
> to
> generate two input files in the CPLEX LP and fixed MPS format
> respectively
> for the same problem.
>
> The calls I use are :
>
> lpx_write_mps(lp,"test.mps");
> and
> lpx_write_cpxlp(lp,"test.lpt");
>
> I run them using the following commands.
>
> ./glpsol --intopt --mps test.mps -o out2
>
> and
>
> ./glpsol --intopt --cpxlp test.lpt -o out1
>
> Even though they represent the same problem, but I seem to be giving
> different results in the two cases. The file test.lpt seems to be
> give the
> correct value of the objective function=3 while test.mps gives an
> objective function value of zero.
>
> I have attached the two files. Could you help me out with this
> problem?
This happens because your instance has free (unbounded) rows.
By default lpx_write_mps writes the objective function row only if
the instance has no free rows. To avoid the error you need to set
the control parameter LPX_K_MPSOBJ as follows:
lpx_set_int_parm(lp, LPX_K_MPSOBJ, 1);
before a call to lpx_write_mps.