Re: Labeling outside of fd_labeling?

Le 16 juin 2012 à 16:44, Jan Burse a écrit :

> Dear All,
> 
> Small question. I just posed the following query:
> 
> ?- X #< Y, Y #< Z, Z #< X.
> 
> The interpreter then was busy for around ~4 secs
> and then responded with "no".
> 
> The "no" is actually correct, by transitivity we have
> X #< Z which conflicts with Z #< X.
> 
> What I wonder is what keeps the interpreter busy for
> ~4 secs and whether the "no" is reliable.

It is due to the arc-consistency filtering algorithm. Consider X@<Y, Y#<X. Basically for X#<Y the max(X) is set to max(Y)-1 each time the max(Y) is updated. Conversely for Y#<X, the max(Y) is set to max(X)-1 each time max(X) is updated.
This results on a decrement of the max(X) and max(Y) from FD_MAX_INT (e.g. 268435455) to 0 (1 by 1). Once X or Y reaches a domain 0..0 the inconsistency is discovered on the other variable (domain 0..-1, i.e. empty).

This takes 4 sec on your machine.

About the "no": yes it is reliable.

Daniel

> 
> Bye
> 
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