Re: [eclipse-clp-users] Assignment propagation queue

Lars Kotthoff wrote:
> Dear all,
> 
>  I was wondering whether Eclipse (specifically search/6 from the ic library)
> does any dynamic reordering of the propagation queue. Does it process events in
> the order they're fired or does it use a heuristic like most constrained
> variable first?
> 
> Thanks,
> 
> Lars
> 
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Hi Lars,

The short answer is no, there is no dynamic reordering of the execution 
of the propagation.

Note that ECLiPSe does not implement propagators or propagation queues 
directly. Instead propagation is done by normal ECLiPSe code, with 
suspensions and attributed variables. In many cases, you can view the 
`firing of events' as the waking of suspensions, which are then executed 
  in the order of the execution priority, which is set when the goal is 
suspended -- so you do have some control over the order the suspensions 
are executed, but this is not done dynamically at run-time.

I am not that familiar with this area, but the only heuristics I am 
aware of for ordering propagator execution is based on the constraints
the propagators are involved in, e.g. executing propagators for simple 
constraints first. This can be done using priorities without some 
runtime dynamic reordering, because you know which constraint a 
particular propagator is for.

Cheers,

Kish

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