[Gecode] Distributors, batch recomputation
Christian Schulte
schulte at imit.kth.se
Wed Jul 14 11:18:00 CEST 2004
I follow your conclusions but I do not follow your concerns. In which way
does branching creation depend on the state of the space? Could you please
elaborate.
Christian
--
Christian Schulte, http://www.imit.kth.se/~schulte/
-----Original Message-----
From: gecode-bounces at ps.uni-sb.de [mailto:gecode-bounces at ps.uni-sb.de] On
Behalf Of Guido Tack
Sent: Tuesday, July 13, 2004 4:49 PM
To: 'Technical discussions about Gecode'
Subject: [Gecode] Distributors, batch recomputation
Hi!
We've been thinking a bit about how distributors and batch recomputation,
and
it seems to be not clear at all. So this is the invariant for batch
recomputation that Christian and I agreed on:
* committing with branch descriptions has to be done in the same order in
which the descriptions were obtained from the space
* if there's more than one distributor, before committing with a description
for distributor no. i+1, enough descriptions have to be committed to make
distributor no. i disappear (completeness)
In the current implementation, after all descriptions for a certain
distributor have been comitted, a fixed point is computed to allow
propagators to dynamically create new distributors. This seems to be
incorrect: The creation of new distributors propably depends on the dynamic
state of the space, so it may make a big difference which commits are done
before and after the propagation! Arbitrarily propagating after one
distributor is finished is just as good or bad as only propagating when
there
are no more active distributors. It seems that dynamically created
distributors just screw up batch recomputation, which is a shame. The way
I'd
suggest to get around this problem is to mark certain branch descriptions
such that we know that before committing to them, we have to compute a fixed
point. The mark would have to be set when a new distributor is created by a
propagator, although I don't see at the moment where to check that.
Guido
--
Guido Tack
Programming Systems Lab
http://www.ps.uni-sb.de/~tack
_______________________________________________
Gecode mailing list
Gecode at ps.uni-sb.de http://www.ps.uni-sb.de/mailman/listinfo/gecode
More information about the gecode-users
mailing list