[Cbc] Fwd: Gomory or not Gomory, that is the question.

[John Forrest]

Giacomo,


I tried swapping GMI for Gomory and the same thing happened.

It just seems to be errors building up, especially with general integer 
variables.

John
On 04/03/15 13:30, Giacomo Nannicini wrote:
> Hi Yves,
> did you try the CglGMI generator? You may want to see if using CglGMI 
> instead of CglGomory helps. In my experience, the cuts from CglGMI are 
> less prone to numerical errors: in fact, that's the reason the 
> generator was developed. See 
> http://link.springer.com/article/10.1007%2Fs12532-013-0057-4
>
> Giacomo
>
> On Wed, Mar 4, 2015 at 7:06 PM, Yves Touchard <ytouch at dxo.com 
> <mailto:ytouch at dxo.com>> wrote:
>
>     Hello,
>
>     Switching off the twomir cuts makes also the problem feasible.
>
>     Cheers
>
>     Yves
>
>
>     -------- Message transféré --------
>     Sujet : 	Gomory or not Gomory, that is the question.
>     Date : 	Tue, 03 Mar 2015 20:03:03 +0100
>     De : 	Yves Touchard <yves.touchard at sfr.fr>
>     <mailto:yves.touchard at sfr.fr>
>     Pour : 	cbc at list.coin-or.org <mailto:cbc at list.coin-or.org>
>
>
>
>     Hello,
>
>     You will find here
>     (https://www.dropbox.com/s/ayo93hi4togpc9m/noGom.lp?dl=0) a
>     constraint file for which cbc founds a solution when Gomory cuts
>     are removed or for specific cutlength values.
>
>     In other words, the following command leads to an infeasible problem:
>     //soft/cbc-trunk-2149/bin/cbc noGom.lp branch printingOptions
>     normal solution noGom.sol/
>
>     and with the following commands, cbc claims that there is a solution:
>     //soft/cbc-trunk-2149/bin/cbc noGom.lp gomory off branch
>     printingOptions normal solution noGom.sol/
>     //soft/cbc-trunk-2149/bin/cbc noGom.lp cutlength xx branch
>     printingOptions normal solution noGom.sol/ (with xx equal to -1,
>     0, 10, 20... and different from 30...)
>
>     Since our problems are dynamically generated, it is very painful
>     to try to solve them with different options, hoping that the right
>     set is in the list.
>
>     So, is there a way to find this set of options.
>     Or could you explain what are the rows that are difficult for cbc.
>     And, does the change of the continuous variables into integer
>     variables help? (for our problems, it makes sense).
>
>     Thanks and regards
>
>     Yves
>
>
>
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