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

[Luigi Malagò]

just one last comment: in the original binpacking example, no double
variables from SCIPgetLPBranchCands
at least the ones i checked...

luigi

On Mon, Aug 22, 2011 at 11:37 AM, Luigi Malagò <luigi.malago at gmail.com>wrote:

> 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
>
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