[Scip] Column generation + branch and bound (from binpacking example)

[Luigi Malagò]

hi gerald,
your suggestions helped. the same variable has been generated twice by the
pricer problem.
this is unexpected. i'm investigating more. i will let you know.

thanks a again ;-)
luigi

On Mon, Aug 22, 2011 at 2:14 PM, Gerald Gamrath <gamrath at zib.de> wrote:

>  Hi Luigi,
>
> SCIP copies all original variables when creating the transformed problem,
> but they get the prefix "t_" then. Also when negating a variable, a new
> variable with a similar name is created, but it gets the suffix "_neg".
> However, SCIP never copies variables giving them the exact same name.
>
> Thus, it seems that you create two variables with the same name. How are
> your names built? Do you have a counter that you increase or is it the
> meaning of the variable (i.e., the set of items), that defines the name? It
> might happen, that you create two variables for the same set, e.g. due to
> numerical problems or if you have explicit upper bounds on the variables.
>
> The branching candidates are a list of all integer (or binary) variables in
> the LP, that have a fractional value in the current LP solution. Thus, there
> might be an arbitrary number of branching candidates, upon which you have to
> choose a variable to branch on (or in this case two items to branch on).
>
> However, it is strange that not all of the variables are contained in the
> list returned by SCIPgetVars(). Did you update the list right before
> checking? You could also print the LP solution by SCIPprintTransSol(scip,
> NULL, NULL, TRUE) and SCIPprintSol(scip, NULL, NULL, TRUE) and check whether
> the variables appear twice there, too.
>
> I hope that helps a bit to locate the problem.
>
> Best,
> Gerald
>
> Am 22.08.2011 11:37, schrieb Luigi Malagò:
>
> hi list,
> i'm stuck again with my code, even if now the problem is with
> branch and bound and the binpacking example. i have some unexpected
> behavior and i dont understand where is the problem. maybe some of you can
> help...
>
> i'm working on the existing code of binpacking, to add my variables and
> adapt to my problem,
> since my example is similar in practice to the binpacking. i have
> extra variables both in the master and in the pricing problem, all
> continuous.
>
> my question is about the SCIP_DECL_BRANCHEXECLP(branchExeclpRyanFoster)
> callback.
> i understand tha Ryan Foster branching, and i want to implement it also in
> my problem.
> since the binary variables of the master of the binpacking example are the
> only
> binary variables in my master, i think the code should be exacly the same.
> nevertheless i have some problems:
>
> when branching the first time, the SCIPgetLPBranchCands function returns 4
> variables,
> my problem is that the 1st and 3rd, and 2nd and 4th, respectively, have the
> same name, but different
> fractional value that (in both cases) sum to 1 (the value is then saved in
> pairweights).
> as a consequence bestvalue equals 0, and the assert then fails.
>
>
> i dont know if i'm right, but i expect only 2 variables to appear in the
> array
> obtained with SCIPgetLPBranchCands. first i tought i had duplicate
> variables in my problem.
> i checked the value of the pointers to these 4 vars contained in lpcands,
> the 1st and 2nd pointers to vars correspond to some variables that appear
> among the
> vars of probdata, while the other two do not appear among that list.
> i obtained this list with SCIPgetVars(scip), where i correcly see the
> original master variables, plus all that i have added at each iteration of
> the master/pricer loop.
>
> i guess something is wrong with my code, but if the variables are not
> duplicated in the problem, i have no idea why i obtain duplicate variables
> then... any idea that could help?
>
> once again, thanks a lot for your help,
> luigi malagò
>
>
> _______________________________________________
> Scip mailing listScip at zib.dehttp://listserv.zib.de/mailman/listinfo/scip
>
>
>
> _______________________________________________
> Scip mailing list
> Scip at zib.de
> http://listserv.zib.de/mailman/listinfo/scip
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://listserv.zib.de/mailman/private/scip/attachments/20110822/46582c01/attachment.html