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<div class="moz-cite-prefix">Yves,<br>
<br>
Running the code with debug I get - <br>
<br>
Cut with 3 coefficients, cuts off known solutions by 1.57182e-06,
lo=-1.79769e+308, ub=22<br>
( 315 , -1 ) ( 1266 , -1 ) ( 1406 , 2 ) <br>
Non zero solution values are<br>
( 315 , 1 ) ( 1266 , 25 ) ( 1406 , 24 ) <br>
<br>
which looks impossible - however looking more closely the actual
coefficients are <br>
<br>
{-0.99999999999988898, -1, 2.0000001209088585}<br>
<br>
I will think harder what to do, but I may find it difficult to fix
elegantly.<br>
<br>
My proposed immediate fix would be to add a bit of code, to be
turned on at Cbc configuration time to weaken all cuts where
coefficients are not integral and variables are not all 0-1. I
have coded it and tried it on your problem - so that cut gets
weakened by 1.0e-7*(1+25+24).<br>
<br>
If that solution will work for you, I will look at its effect on
other problems and check code into trunk. I would think it should
fix all your problems and not make anything significantly slower.<br>
<br>
John <br>
On 03/03/15 19:06, Yves Touchard wrote:<br>
</div>
<blockquote cite="mid:54F60624.70601@dxo.com" type="cite">
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With the right reply address!<br>
<div class="moz-forward-container"><br>
<br>
-------- Message transféré --------
<table class="moz-email-headers-table">
<tbody>
<tr>
<th nowrap="nowrap">Sujet : </th>
<td>Gomory or not Gomory, that is the question.</td>
</tr>
<tr>
<th nowrap="nowrap">Date : </th>
<td>Tue, 03 Mar 2015 20:03:03 +0100</td>
</tr>
<tr>
<th nowrap="nowrap">De : </th>
<td>Yves Touchard <a moz-do-not-send="true"
class="moz-txt-link-rfc2396E"
href="mailto:yves.touchard@sfr.fr">
<yves.touchard@sfr.fr></a></td>
</tr>
<tr>
<th nowrap="nowrap">Pour : </th>
<td><a moz-do-not-send="true"
class="moz-txt-link-abbreviated"
href="mailto:cbc@list.coin-or.org">cbc@list.coin-or.org</a></td>
</tr>
</tbody>
</table>
<br>
<br>
Hello,<br>
<br>
You will find here (<a moz-do-not-send="true"
class="moz-txt-link-freetext"
href="https://www.dropbox.com/s/ayo93hi4togpc9m/noGom.lp?dl=0">https://www.dropbox.com/s/ayo93hi4togpc9m/noGom.lp?dl=0</a>)
a constraint file for which cbc founds a solution when Gomory
cuts are removed or for specific cutlength values.<br>
<br>
In other words, the following command leads to an infeasible
problem:<br>
<i>/soft/cbc-trunk-2149/bin/cbc noGom.lp branch printingOptions
normal solution noGom.sol</i><br>
<br>
and with the following commands, cbc claims that there is a
solution:<br>
<i>/soft/cbc-trunk-2149/bin/cbc noGom.lp gomory off branch
printingOptions normal solution noGom.sol</i><br>
<i>/soft/cbc-trunk-2149/bin/cbc noGom.lp cutlength xx branch
printingOptions normal solution noGom.sol</i> (with xx equal
to -1, 0, 10, 20... and different from 30...)<br>
<br>
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.<br>
<br>
So, is there a way to find this set of options.<br>
Or could you explain what are the rows that are difficult for
cbc.<br>
And, does the change of the continuous variables into integer
variables help? (for our problems, it makes sense).<br>
<br>
Thanks and regards<br>
<br>
Yves<br>
<br>
</div>
<br>
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