[gecode-users] posting instead of propagating domain constraints?

[Christian Schulte]

Yep, it means just scheduling. Propagation is always explicit in Gecode,
triggered by status().

Christian

--
Christian Schulte, web.ict.kth.se/~cschulte/



-----Original Message-----
From: Kish Shen [mailto:kisshen at cisco.com] 
Sent: Friday, July 16, 2010 7:40 PM
To: cschulte at kth.se
Cc: users at gecode.org
Subject: Re: [gecode-users] posting instead of propagating domain
constraints?

Christian Schulte wrote:

> Well, dom() and the integer variants of rel() propagate in the sense that
> they immediately modify the variable domain and schedule some propagators
> for later execution. However, they do not lead to full constraint
> propagation computing a fixpoint. The invariant is that only execution of
> the status() function of a space computes a fixpoint. So they are dirt
> cheap, much cheaper than creating a propagator for them.

Yes, I had understood 'propagates' in the manual to mean 'full 
propagation'. I knew that dom() and rel() will do such simple things 
like update the domain and check that the value you are assigning is 
inside the domain, etc., and assumed that you will always do these 
simple checks for all constraints posted, even where the manual says 
'posting the propagator', e.g. for equality between two IntVars, you 
will check that their domains do overlap, etc.

So does 'propagate' in this case only mean 'scheduling some 
propagators', whereas where the manual state 'posting the propagator' 
does not?

Cheers,

Kish



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