[Scip] SCIPgetRelaxBranchCands

Gerald Gamrath gamrath at zib.de
Thu Sep 16 17:30:06 MEST 2010


 Hi Christian,

there is an issue in SCIP with the relaxation and relaxation branching
candidates that we fixed after your last mail so that in the new SCIP
release, the problem is probably already fixed. However, if you send me
your complete GCG code and tell me which SCIP-Version you use (is it
still 1.2.0.8?), I will have a look at it. Please send the code directly
to me and not to the mailing list.

The way you use the relaxation branch cands should be right. But when is
your heuristic called? How did you set the HEUR_TIMING parameter? Are
you sure the relaxation was already solved at that node?

Best regards,
Gerald

Am 15.09.2010 12:44, schrieb Christian Puchert:
> Hi all,
>
> I am currently implementing some primal heuristics for Gerald Gamrath's
> GCG which basically replaces the standard SCIP LP relaxation by a
> special relaxator.
>
> At the moment, I am trying to adjust the SCIP diving heuristics such
> that they work with GCG. These heuristics need the fractional variables
> of the current LP (relaxation) solution which they normally access via
> SCIPgetLPBranchCands. Since the standard LP relaxation is not present
> here, I use SCIPgetRelaxBranchCands instead.
>
> While this function works fine on the root node, the returned number of
> fractional variables on deeper nodes is always zero. However, accessing
> the current relaxation solution via SCIPlinkRelaxSol (or
> GCGrelaxGetCurrentOrigSol) works correctly (and having a look at this
> solution reveals that it is actually not integer feasible).
>
> What is the cause of that? Am I using SCIPgetRelaxBranchCands in a wrong
> way, and can I use this function at all in my primal heuristics?
>
> Thanks and regards,
> Christian
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