[Scip] Pricer regenerates the same column

[Gerald Gamrath]

Dear Marco,

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.

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?

Another thing: did you mark all constraints to be modifiable?

Best,
Gerald

Am 06.05.2014 18:59, schrieb Marco Casula:
> Dear all,
>
> 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.
>
> I have found a similar case in the mailing list archives, and I tried 
> every suggestion I found there, without success:
> 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);
> the variables are added via SCIPaddPricedVar;
> I checked SCIPvarIsInLP for the variable added in the previous 
> iteration of the pricer, and it is true;
> 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;
> I changed the upper bound on the variables from 1.0 to SCIPinfinity, 
> with no effect.
>
> I was hoping for some more insight on the matter.
> Please find attached a logfile for a non working instance (terminated 
> early), and the Pricer code.
> For completeness, here's a link to a full-working folder (including 
> all source files) https://www.dropbox.com/sh/664n10xssiicd4o/G0xtWoLH2T
>
> Thanks for any help
> Marco Casula
>
>
>
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