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<p>Hi again,</p>
<p> After compiling Cbc with Nauty, I got a solution of 298244 in 3
minutes, which is very nice. This only happens with some
additional cuts and Vnd heuristic:</p>
<p>-RINS on -Vnd on -probing on -two on -residual on -reduce on
-constraint on -orbit on</p>
<p>I tried other combinations of parameters and this was the best
result by far, so I'm not very positive about this. I've to try
with other instances of the same problem to see if it was just a
fluke.</p>
<p> Anyway, I don't think I'm getting the optimum solution (two
hours running and no new solutions so far) with this approach.<br>
</p>
<p> I'll try the preprocessing 'trick' next to see if there are some
improvements.</p>
<p>Best,</p>
<p>Rui Patrocínio<br>
</p>
<br>
<div class="moz-cite-prefix">On 11/23/2019 11:15 AM, Rui Patrocínio
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:3453631c3b62eff5242c0f5d3cedf986@siscog.pt">
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<p>John,</p>
<p> I also got that solution after two hours while activating some
of the cuts and heuristics that are off by default. Can you tell
me what you tried related with symmetry? Apparently you got the
same solution must faster. After getting that solution, I left
it to run for a day and it didn't got any better (not closing
the gap). The best solution is a little above 284000 if I
remember correctly, so we are not that far away from the
optimum.</p>
<p> Regarding the presolver, I may be able to integrate that
"process" (presolving, exporting and presolving again) calling
CBC several times while solving our problem, if that helps. I'll
make some tests.</p>
<p>Haroldo,</p>
<p> I could get a valid solution after some minutes, even with the
default parameters and activating some of the heuristics and
additional cuts helped getting better solutions faster. The
manual you linked is useful, obrigado.</p>
<p> Best regards,</p>
<p>Rui Patrocínio</p>
<p>A 2019-11-23 10:00, John Forrest escreveu:</p>
<blockquote type="cite" style="padding: 0 0.4em; border-left:
#1010ff 2px solid; margin: 0"><!-- html ignored --><!-- head ignored --><!-- meta ignored -->
<div class="pre" style="margin: 0; padding: 0; font-family:
monospace">My guess is that Cbc is very bad at handling
symmetry. There is a lot of symmetry and trying some of the
ways that Cbc can deal with symmetry I can get a solution of
296773 fairly quickly, but after an hour it does not seem to
be closing the gap. The other area where Cbc is failing
somewhat is preprocessing - if I export the model several
times (each time doing presolve) then I can make it smaller -
this obviously wrong.<br>
<br>
<span style="white-space: nowrap;">John Forrest</span><br>
<br>
<span style="white-space: nowrap;">On 22/11/2019 15:44, Rui Patrocínio wrote:</span>
<blockquote type="cite" style="padding: 0 0.4em; border-left:
#1010ff 2px solid; margin: 0"><span style="white-space:
nowrap;">Hi,</span><br>
<br>
I'm trying to solve one instance of a problem that is
taking a long time to obtain a good solution. Since all
variables are binary, probing and implication cuts are doing
some work and RINS and Vnd are apparently also improving
solutions. For other instances of the problem we are
solving, CBC has an acceptable performance but for this
instance apparently there's something going wrong (~20
seconds to get the optimum solution with a commercial solver
versus never getting the optimum solution with CBC).<br>
<br>
If someone can take a look at the model and give me a hint
of what is going on, I would appreciate it.<br>
<br>
The model is at <a
href="https://drive.google.com/open?id=1bd4jWONmoyAKIi0oLa-AU-ZTu7_8qhb6"
target="_blank" rel="noopener noreferrer"
moz-do-not-send="true">https://drive.google.com/open?id=1bd4jWONmoyAKIi0oLa-AU-ZTu7_8qhb6</a><br>
<br>
-- SISCOG - Sistemas Cognitivos, SA<br>
<br>
<span style="white-space: nowrap;">*Rui Patrocínio*</span><br>
<br>
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