[gecode-users] [search engine] Set a starting point !

[Guido Tack]

Hi,

CP Optimizer uses large neighbourhood search (LNS), which can start from an initial solution.  Gecode does not come with an LNS engine.  The only way the Gecode BAB search can take advantage of a starting point is to use its objective value as an upper bound (assuming you're minimising), i.e., simply constraining the upper bound of the variable that represents the objective.
LNS may be a feature of a future release of Gecode, but currently you'd have to implement it yourself if you need it to solve your problem.

Cheers,
Guido

On 05/12/2012, at 4:20 AM, Aribi Noureddine <aribi_noureddine at yahoo.fr> wrote:

> Hi,
> Actually, the idea of a starting point comes from ibm Ilog CP optimizer. Here is an example:
> -------------------------------------
> /* SET A STARTING POINT */
> 		IloIntArray values(env, nb_val, 0, 1, 2, 3, 4);  // a feasible solution <0, 1, 2, 3, 4>
> 		IloSolution sol(env);
>     for(int c = 0; c < nb_val; c++){  
> 			sol.setValue(vars[c], values[c]);
>     }
> 	cp.setStartingPoint(sol);
> cp.solve();
> -------------------------------------
> The feasible solution can be found using some greedy algo, and thus can enhance the B&B search engin.
> 
> Best regards,
> _ _ _ 
> Noureddine ARIBI
> 
> 
> De : Christian Schulte <cschulte at kth.se>
> À : 'Aribi Noureddine' <aribi_noureddine at yahoo.fr> 
> Cc : users at gecode.org 
> Envoyé le : Mardi 4 décembre 2012 17h33
> Objet : RE: [gecode-users] [search engine] Set a starting point !
> 
> Hi,
>  
> I am still not sure what you are referring to but I am guessing it is about best solution search (Branch-and-bound). This does not work by starting from and improving a feasible solution. Maybe you would like to make yourself comfortable with the idea of best solution search in constraint programming.
>  
> Best
> Christian
>  
>  
> --
> Christian Schulte, www.ict.kth.se/~cschulte/
>  
> From: users-bounces at gecode.org [mailto:users-bounces at gecode.org] On Behalf Of Aribi Noureddine
> Sent: Monday, December 03, 2012 8:35 PM
> To: cschulte at kth.se
> Cc: users at gecode.org
> Subject: Re: [gecode-users] [search engine] Set a starting point !
>  
> Hi, 
>  
> I mean by the starting point a feasible solution (not necessarily the best) that I want to improve.
>  
> Best reagrds,
> _ _ _ 
> Noureddine ARIBI
>  
>  
> De : Christian Schulte <cschulte at kth.se>
> À : 'Aribi Noureddine' <aribi_noureddine at yahoo.fr>; users at gecode.org 
> Envoyé le : Lundi 3 décembre 2012 20h08
> Objet : RE: [gecode-users] [search engine] Set a starting point !
>  
> Hi,
>  
> What do you mean by a starting point?
>  
> Christian
>  
> --
> Christian Schulte, www.ict.kth.se/~cschulte/
>  
> From: users-bounces at gecode.org [mailto:users-bounces at gecode.org] On Behalf Of Aribi Noureddine
> Sent: Monday, December 03, 2012 5:10 PM
> To: users at gecode.org
> Subject: [gecode-users] [search engine] Set a starting point !
>  
> Hi all,
>  
> Is there a way to let the search engine explore the search space from a starting point?
>  
> Thank you.
>  
> Best regards,
> _ _ _ 
> Noureddine ARIBI
>  
>  
> 
> 
> _______________________________________________
> Gecode users mailing list
> users at gecode.org
> https://www.gecode.org/mailman/listinfo/gecode-users

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