[SCIP] separating while counting feasible solutions

[Pierre Le Bodic]

Hi James,

My understanding as a scip user is that when switching to counting &
collecting, you're explicitly enumerating all solutions. Therefore,
separation is turned off probably because 1) it would probably slow down
the enumeration without altering the output, and 2) if needed, a provably
optimal solution will be available once the explicit enumeration is
complete.

Since what you would like to achieve is different than enumeration, it may
pay off to play with some of the parameters in limits/, in particular
limits/objective, whether in solve or count mode. I hope this helps!

Kind regards,
Pierre

On 15 May 2018 at 18:34, James Cussens <james.cussens at york.ac.uk> wrote:

> I have noticed that when SCIP is counting (and possibly collecting)
> feasible solutions, separation is turned off.
>
> What is the rationale for this?
>
> In my own SCIP project having no separation led to very poor performance
> when collecting feasible solutions with objective value better than a given
> value. (I just want reasonably 'good' feasible solutions.)
>
> I fixed the problem as follows:
>
> SCIP_CALL( SCIPsetParamsCountsols(scip) );
>          /* put separating back on! */
>          SCIP_CALL( SCIPparamsetSetSeparating(scip->set->paramset,
> scip->set, scip->messagehdlr, SCIP_PARAMSETTING_DEFAULT, TRUE) );
>
> but perhaps keeping separation leads to some other problem I don't realise.
>
> Any advice on this issue gratefully received.
>
> James
>
> --
> James Cussens
> Dept of Computer Science &
> York Centre for Complex Systems Analysis
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