Hi, actually we have been thinking some more, driven also by the fact that we have a non-monotonic propagator ourselves.
So, Gecode 3.0 will support non-monotonic propagators. What we have to do, still, is to spell out the invariants and guarantees one still gets when using non-monotonic propagators (the key here will be that the existence of solutions does not change). It looks reasonably straightforward for all but Gist (so, Gist will warn now and then that it might recompute something slightly different). Cheers Christian -- Christian Schulte, www.ict.kth.se/~cschulte/ -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Guido Tack Sent: Tuesday, July 01, 2008 5:33 PM To: Zampelli Stephane Cc: [EMAIL PROTECTED] Subject: Re: [gecode-users] Non-monotonic propagator. Zampelli Stephane wrote: > Suppose one has a non-monotonic propagator P, because the propagator > uses an approximation (of a NP-Hard problem) of the pruning. > How can Gecode accomodate of this situation? > Does this mean that recomputation cannot be used? Recomputation will almost certainly fail (i.e., segfault or throw an exception) if non-monotonic propagators are present. > Is the result correct if the recomputation is not used (full copying, > c_d=1)? Yes. > What about executing the propag P after the fixpoint of all other > monotonic constraints? That looks like a solution in principle, but won't work in practice. The problem is that the space is not going to be stable (i.e. at a fixpoint) after running P. Spaces in Gecode can only be copied at fixpoints. You could iterate the normal fixpoint computation and the invocation of P until you reach a mutual fixpoint. Still, this is not guaranteed to work with batch recomputation, where only one fixpoint is computed for each backtrack. We have thought a bit about how to accomodate non-monotonic propagators, but it's really not easy. Cheers, Guido _______________________________________________ Gecode users mailing list [EMAIL PROTECTED] https://www.gecode.org/mailman/listinfo/gecode-users _______________________________________________ Gecode users mailing list [EMAIL PROTECTED] https://www.gecode.org/mailman/listinfo/gecode-users
