[Help-glpk] Re: GNU LP format

[Andrew Makhorin]

>I have just started using the glpk package. I like your GNU LP format
>but could not find a description for it. I have figured out more or
>less.  I used glpsol program to convert some mps files into glp format
>and I don't understand why the objective function is listed twice, like
>this:
>
>    ...
>    P LP MIN 4 3 9
>    N TESTPROB
>    R 1 F
>    R 2 U 5
>    R 3 L 10
>    R 4 S 7
>    C 1 D 0 4
>    C 2 D -1 1
>    C 3 L 0
>    A 0 1 1
>    A 0 2 4
>    A 0 3 9
>    A 1 1 1
>    A 1 2 4
>    A 1 3 9
>    A 2 1 1
>    A 2 2 1
>    A 3 1 1
>    A 3 3 1
>    A 4 2 -1
>    A 4 3 1
>    I 0 COST
>    ...
>
>Is it a bug or a feature? :-)

In your example the objective does not appear twice; you see the
objective (A 0 ...) and a free row (A 1 ...) which are just identical.
This is because in mps format the objective is specified by means of a
free row while in gnu lp format (as well as in glpk api) the objective
is a separate object (so, in gnu lp format you could change the objective
coefficients not changing the corresponding free row). When lpx_read_mps
reads mps file, by default it uses the first free row as the objective,
however, the free row itself is also included in the problem object.

Andrew Makhorin