[Scip] help : How to write dual problem

[Gregor Hendel]

Dear Abdelkader Ouali,

I am afraid there is no ad-hoc method available for this in SCIP. The 
methods available through the linear constraint
handler <http://scip.zib.de/doc/html_devel/cons__linear_8h.php> might be 
sufficient here:

1. Create a secondary SCIP-instance dualscip and a problem inside dualscip.
2. Create variables for every linear constraint in dualscip
3. Create a new linear constraint in dualscip for every variable
4. Iterate over the constraints once in order to have their variables, 
vals (=coefficients), and number, and add
the coefficients for the corresponding dual variable of this constraint 
to every dual constraint it should appear in.
5. Now you can use the LP-writer for the dualscip-Problem.

This is quite a nice SCIP-exercise, isn't it? :)

The reason why SCIP does not come with such a functionality (yet) is its 
constraint-based nature. It does not
always make sense to speak of the dual of a SCIP problem. The dual of 
the LP that SCIP builds internally might
be different from what you exspect, because the problem has already 
undergone a transformation through
various presolving steps.

Kind regards
Gregor


Am 09.07.2014 10:01, schrieb Abdelkader Ouali:
> Hello,
>
> How to write dual problem of the original problem in lp format file
> using SCIP routines
>
> Thanks
>
> ---
> Abdelkader Ouali
>
>
>
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> Scip at zib.de
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