[gecode-users] Schedule Branching Recommendations

[Filip Konvička]

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