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Re: [Bug-glpk] write_freemps does not write objective function coefficie

From: Andrew Makhorin
Subject: Re: [Bug-glpk] write_freemps does not write objective function coefficients
Date: Wed, 4 Jul 2007 14:25:23 +0400

> Trying to debug a stack error in GLPK, I am writing the problem out at
> every iteration of a column generation scheme
> Initially only in the free mps format, but then also in the lp format
> One major and one minor error occur:
> major: write_freemps does not write the objective function coefficients,

This is not a bug. If the instance has at least one free (unbounded)
row, by default lpx_write_mps does not write the objective row assuming
that that free row is the objective row. In order to tell lpx_write_mps
to write the objective row in any case you should change the control
parameter LPX_K_MPSOBJ as follows:

   lpx_set_int_parm(lp, LPX_K_MPSOBJ, 1);

For more details please see the glpk reference manual.

> no column has a non-zero in the objective function
> minor: write_cpxlp creates one extra variable in the bounds section that
> does not appear anywhere else in the problem statement

That variable exists in the problem object, however, its column is
empty (as seen in mps file).

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