Re: [Help-glpk] not retrieving integer solutions

[Meketon, Marc]

Thanks Robbie.  I wish I saw that wiki earlier (although I have been a big fan 
of the wiki, I didn't remember this item).  It would have saved me several 
hours and a couple of emails!

-----Original Message-----
From: Robbie Morrison [mailto:address@hidden
Sent: Thursday, July 12, 2012 9:45 PM
To: GLPK help
Cc: Meketon, Marc
Subject: Re: [Help-glpk] not retrieving integer solutions


Hello Marc

------------------------------------------------------------
To:          "address@hidden" <address@hidden>
Subject:      [Help-glpk] not retrieving integer solutions
Message-ID:  <address@hidden>
From:        "Meketon, Marc" <address@hidden>
Date:         Thu, 12 Jul 2012 17:14:39 -0500
------------------------------------------------------------

> I am solving a small integer program (37 rows and 29
> columns) using the C# interface from
> http://yoyovicks.blog.free.fr/
>
> I've tested the code on quite a few datasets and it worked fine.  But
> today I changed some objective function coefficients (just changed the
> sign of them), and for one particular problem I'm retrieving
> non-integer results despite the fact that an integer optimal was
> found.
>
> [snip: code and results]
>
> Would anyone have a guess why the output is non-integer despite
> solving to integer optimality and double-checking that these variables
> are integer?
>
> BTW, when I write the problem out to GLPK format, and solve it using
> glpsol, the output is fully integer.

Please see:

  
http://en.wikibooks.org/wiki/GLPK/Troubleshooting#Continuous_solution_to_mixed-integer_problem

Could a be a bug in the C# wrapper or your use of the wrong calls?

(Given C# supports polymorphism, could this wrapper not be written to proved 
the correct recovery using a generic interface?)

Robbie
---
Robbie Morrison
PhD student -- policy-oriented energy system simulation Institute for Energy 
Engineering (IET) Technical University of Berlin (TU-Berlin), Germany 
University email (redirected) : address@hidden
Webmail (preferred)           : address@hidden
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