Nope, don't use advisors. Just do what you did before, that's just fine. You are now even on the safe side as what you did might actually be non-monotonic which is fine for 3.*.
The main advantage of advisors is really to implement propagators for constraints with n variables and getting better asymptotic complexity (for example, when you have to find out which variable has changed for doing propagation, a propagator without advisors will always have O(n) complexity in order to find out which variable has changed and some propagation algorithms are actually constant time). Or, you really care about how the domain has changed. In a way, the reason why advisors are not that essential in your situation is that scheduling propagators and executing them is actually very very efficient in Gecode (okay, I had to brag a little). Cheers Christian -----Original Message----- From: users-boun...@gecode.org [mailto:users-boun...@gecode.org] On Behalf Of Martin Mann Sent: Tuesday, May 19, 2009 6:09 PM To: gecode user list Subject: [gecode-users] Advisors : need your advise if worth a look for my propagator! ; ) Hi everybody, thanks to your answers Mikael and the silent support and mails from Daniel Przybilla I have a better understanding of the Advisors, their use and functionality. Now the question appears: is the effort/overhead worth for me or not? I had a look at Mikaels thesis and the final statement that Advisors are mainly advantageous for n-ary constraint and not that useful for e.g. binary constraints (correct me if I got it wrong). Thus, I would like to get your feeling on my constraint, because you are the experts on your system! ;) ================ My problem: ================ I have a binary constraint propagator p(X,Y) that does a very strong but expensive filtering on the domains of variables X and Y. Thus I would like to delay the application until one of the domain sizes is smaller than a certain threshold. In Gecode 1.3.* I managed like that: - I subscribed the propagator for domain changes on the two variables - within the propagate function I checked if the minimal domain size of both is smaller than my threshold - if so I ran the filtering algorithm, otherwise I returned that nothing could be propagated (I was lazy and know this is kind of a hack.. ;) ) In my Gecode 3.* reimplementation I want to do it in the best way possible. So the question is: Do I stick to the old "hack" or is it worth a look to implement Advisors that do the domain size check for me? ================================= The CSP itself is quite simple: ================================= - n variables : X_i with 1 <= i <= n - one alldiff : distinct( X_1,..,X_n ) - (n-1) binary constraints : p(X_i, X_(i+1)) with 1 <= i < n (for anybody even more interested in details : p encodes a neighboring constraint in a lattice and the whole CSP encodes a self-avoiding-walk of length n on a lattice) ================================= Soo... the again final question: *Is it worth to use an Advisor for my domain size check? Or is the hack nasty but most probably faster?* I know it is hard for you to give a statement without knowledge on the propagator's details but an expert guess would be sufficient for me. ;) Thanks a lot! Martin -- Martin Mann, Dipl. Bioinf. Bioinformatics - Inst. of Computer Science Albert-Ludwigs-University Freiburg Tel: ++49-761-203-8259 Fax: ++49-761-203-7462 http://www.bioinf.uni-freiburg.de/~mmann/ _______________________________________________ Gecode users mailing list us...@gecode.org https://www.gecode.org/mailman/listinfo/gecode-users _______________________________________________ Gecode users mailing list us...@gecode.org https://www.gecode.org/mailman/listinfo/gecode-users
