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Re: [Help-glpk] Compatibility with AMPL suffixes to display properties


From: Germán Ferrari
Subject: Re: [Help-glpk] Compatibility with AMPL suffixes to display properties of variables and constraints
Date: Sun, 2 May 2010 19:45:36 -0300

HelloXypron,

Thank you very much. I will try both suggestions.

In principle, for variables I need: reduced costs, lower bounds and upper bounds; and for constraints I need: dual values, lower bounds and upper bounds.

Thank you again.

Regards,
Germn.


On Sat, May 1, 2010 at 2:12 AM, glpk xypron <address@hidden> wrote:
Hello Germn,

The GMPL language does not support suffixes.

Some sensitity information is provided by
glpsol --bounds filename

Introducing suffixes to GLPK has been proposed before,
but not implemented in the maintenance release.

An unofficial patched version of a last year GLPK release can be
checked out with subversion

svn co http://glpk.dyndns.org/svn/glpk/branches/glpk-4.38-dot/

It supports the following suffixes in the post solution phase:

variables
lb - lower bound
ub - upper bound
val - value
dual - dual value
basic - 1 if variable is basic

constraints
lb - lower bound
ub - upper bound
dual - dual value
value - value

You can use the suffix only on scalars:

set S := {0..10};
var x{S};
...
#legal
display x[3].lb;
printf x[3].dual;
#illegal
display x.lb;

To generate duals for MIP problems the integer variables are fixed
and an extra call to the simplex routine is executed.

It would be interesting to know which suffixes would be of most
value for your use of GLPK.

Best regards

Xypron

> I've a model in Mathprog which I'm solving using `glpsol` and using
> `display` statements to generate a custom output. In AMPL there is a list
> of
> suffixes that one can use to display different properties of variables and
> constraints. For example for a constraint the available suffixes are:
> astatus body defvar dinit
> dinit0 dual lb lbs
> lbs1 lbs2 ldual lslack
> no relax slack sno
> sstatus status ub ubs
> ubs1 ubs2 udual uslack
>
> So, for example, you can write:
> display C.lb;
>
> To display the lower bound of C.
>
> Is there an equivalent functionality in Mathprog? The above syntax does
> not
> work.
>
> Thank you.
>
> Regards,
> Germn.

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