Hi Filip, well, well. Let me just summarize some facts:
- Your idea will work but, as you say yourself, is not going to win any software design beauty contest. It might be good to tinker, but for Gecode itself a design will be needed that does not require to change a space (that's typically a user's model) when using a propagator cum branching. - The idea that this data is just a cache is very helpful. Indeed, we use the very same idea to great advantage in many propagators that ship with Gecode: do not copy the data just reconstruct it when needed, and if the data is already there keep it up to date while doing propagation. If the data becomes to messy, just flush the cache (data) an reconstruct it. - Invoking the status method of a space will always compute a fixpoint, regardless of recomputation or not (as does the attempt to clone a space). This also entails that when the status method of a branching is called, the home is at fixpoint (stable). - Invoking a commit method however will not compute a fixpoint: the very idea of making recomputation efficient relies on this. - You might be able to speed up branching considerably if you take advantage of branching descriptions. They must store information to actually perform a commit operation (as the space is typically not at fixpoint, see above). You have the possibility to add additional information to the branching description that assists in maintaing your data. The idea to maintain the data as a cache is orthogonal to these facts. Hope that helps Christian -- Christian Schulte, http://www.imit.kth.se/~schulte/ -----Original Message----- From: Filip Konvicka [mailto:[EMAIL PROTECTED] Sent: Monday, August 27, 2007 5:55 PM To: [EMAIL PROTECTED] Cc: [EMAIL PROTECTED] Subject: Re: [gecode-users] Schedule Branching Recommendations Hi Christian, > Please do not hesitate to ask more questions of that sort! Do you > consider to only do branching or also propagation? Because there is a > very interesting issue for edge-finding/first-last: both propagation > and branching should share the same data structures to maintain their > information for efficiency. Support for sharing state among several > propagators/branching is on our todo list for a long time but we > decided to only do it when we implement exactly what you are now > appareantly trying to do... > I am in a similar situation now. Could you please explain why (if this is the case indeed) is it not possible to just share the data in some raw data structure inside the Space? I mean, in the above mentioned case, propagation computes some information that can be re-used in the branching. I was under the impression that the following might work in similar cases: - During propagation, store (overwrite) some "raw" data in the Space instance (I know, this is not exactly a good architecture design...) - As soon as the Space is stable, the system looks for active branchings, asking for alternatives - The branching might access the data now, knowing that it is the result of the last propagation (which led to the fixpoint), and return some alternatives The thing I'm not sure about is whether there must always be a propagation step after recomputation. In case that not, the branching should have the possibility to compute the data from scratch, using only the variables' domains (in this case, copying the space should invalidate the data to make sure it is recomputed). The reason I believe this could work is that the shared information is after all just some kind of cache which reflects the current domains. Thanks for any comments, Filip _______________________________________________ Gecode users mailing list [EMAIL PROTECTED] https://www.gecode.org/mailman/listinfo/gecode-users
