<div dir="ltr"><div><div><div><div>Dear Gerald,<br><br></div>thanks for the input (also, thanks to Martin for ccing me his answer to Cristina).<br></div>In the end, I think it was just a matter of solver tolerance: I am using SoPlex 1.7.2, and though I believed its tolerance to be e-12, by means of display/lpinfo I noticed a number of tolerance parameters set to e-06. Since I am not sure how to change the value of all of them, I lowered scip "numerics/epsilon" from the default e-09 to e-06, and so far the problem has not reappeared.<br>
</div><br></div><div>Best,<br></div><div>Marco<br></div></div><div class="gmail_extra"><br><br><div class="gmail_quote">2014-05-16 19:07 GMT+02:00 Gerald Gamrath <span dir="ltr"><<a href="mailto:gamrath@zib.de" target="_blank">gamrath@zib.de</a>></span>:<br>
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<div>Dear Marco,<br>
<br>
sorry for the late reply. What you write sounds quite reasonable
and you already tried most things that I would normally aks you
for. So I don't see an obvious thing that might have gone wrong,
and we probably need to dig a bit more into what happens.<br>
<br>
Therefore, please check the solution status of the LP when your
pricer is called by calling SCIPgetLPSolstat(). Are you already in
reduced cost pricing when the pricer keeps generating the same
column? Also, please enable LP solver output by setting the
parameter "display/lpinfo" to TRUE. When you checked the reduced
cost of the previously generated variables, they were negative?
What is the LP solution value of the "old" variable and what are
its bounds?<br>
<br>
Another thing: did you mark all constraints to be modifiable?<br>
<br>
Best,<br>
Gerald<br>
<br>
Am 06.05.2014 18:59, schrieb Marco Casula:<br>
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<div>Dear all,<br>
<br>
</div>
I am working on a branch and price algorithm
for the VRP with time windows and stochastic
travel times. While on many instances the
algorithm terminates correctly, with a number
of instances/parameters (delay distributions,
penalties) combinations, the algorithm gets
stuck as the pricer keeps regenerating the
same column.<br>
<br>
</div>
I have found a similar case in the mailing list
archives, and I tried every suggestion I found
there, without success:<br>
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the delay flag of the pricer is set to TRUE, as is
the initial flag for the new variables (I had
previously set this to FALSE, with the same
result);<br>
the variables are added via SCIPaddPricedVar;<br>
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I checked SCIPvarIsInLP for the variable added in
the previous iteration of the pricer, and it is
true;<br>
the reduced cost of the variable added in the
previous iteration (via SCIPgetVarRedCost) coincides
with the one i compute for the variable in the
current iteration;<br>
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I changed the upper bound on the variables from 1.0 to
SCIPinfinity, with no effect.<br>
<br>
</div>
I was hoping for some more insight on the matter. <br>
</div>
Please find attached a logfile for a non working instance
(terminated early), and the Pricer code.<br>
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For completeness, here's a link to a full-working folder
(including all source files) <a href="https://www.dropbox.com/sh/664n10xssiicd4o/G0xtWoLH2T" target="_blank">https://www.dropbox.com/sh/664n10xssiicd4o/G0xtWoLH2T</a><br>
<br>
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Thanks for any help<br>
</div>
Marco Casula<br>
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