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

[Yves Touchard]

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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