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Re: [Help-glpk] New in this List / Custom output with Printf

From: Andrew Makhorin
Subject: Re: [Help-glpk] New in this List / Custom output with Printf
Date: Mon, 21 Apr 2008 15:07:02 +0400

> I'm a brazilian MsC student (so, sorry for my bad English) from UTFPR
> University.
> First of all, like to say: GLPK + GMPL rules! I'm learning LP/MILP for
> an big research project. After some research and various tests with
> commercial and free software solvers, we adopted GLPK to our project.

Thank you for your interest in glpk.

> For now we use only glpsol at command line to develop models - but we
> are using our custom (incipient for now) build of SciTE to integrate
> glpsol in an friendly IDE in the WinNT platform. I want to use (and
> disseminate) this IDE to teach at this campus in future. When it reach
> a minimum stable status i'll put it on the web (bin and code - with a
> pre-build glpsol too, if has no objection).

> Ok, future is future. 
> After this self-presentation... yes, i have questions =)

> For now, only the crucial: i need to create custom outputs to some
> models, and i'm using printf to do this. Ok, all right. Vars and params
> looks fine, but i don't know how to print important info - like the
> objective value! I've looking at the mail-list archive and found
> herea negative answer to var/constraints attributes. My questions is:
> (1) it is true for objective value too? I'm re-processing the objective
> function after solve to obtain it... And, (2), the answer in the mail
> list still true today? If no, there are plans to implement access to
> this attributes in future glpsol versions?

Currently there is no way to access the objective function value
from mathprog. If you have something like:

   minimize obj: ...some expression...;

you might either use the expression in a printf statement, or, better,
introduce a variable taking on the objective value:

   var foo;
   s.t. bar: foo = ...some expression...;
   minimize obj: foo;

and then use it in printf.

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