[gecode-users] finding number of propagators for s Space, relation to floundering

[Kish Shen]

Hi Christian,

Thanks for your reply.

I wasn't really thinking that there was a bug, but rather if still 
having propagators around after you program finishes is a good indicator 
that there might be problems. For example, there may be some good 
reasons why propagators may remain after they are entailed in Gecode, as 
with the argmin case. I did wonder if it was worthwhile to detect the 
situation I found and remove the propagator (assuming it is not wrong to 
do so, which your reply suggest it is not wrong).

Do propagators always disappear when their variables all have a 
singleton domain? I was trying constraints where variables still have 
more than one domain value after they are entailed because in gfd I 
can't get the degree of a variable that are not bound (i.e. have more 
than one value in its domain).

Cheers,

Kish

On 30/06/2015 10:56, Christian Schulte wrote:
> There is no guarantee that propagators detect entailment perfectly! So, no
> bug.
>
> A space has a function propagators() that returns the number of propagators
> in a space.
>
> Cheers
> Christian
>
> --
> Christian Schulte, www.gecode.org/~schulte
> Professor of Computer Science, KTH, cschulte at kth.se
> Expert Researcher, SICS, cschulte at sics.se
>
>
> -----Original Message-----
> From: users-bounces at gecode.org [mailto:users-bounces at gecode.org] On Behalf
> Of Kish Shen
> Sent: Tuesday, June 30, 2015 5:15 AM
> To: users at gecode.org
> Subject: Re: [gecode-users] finding number of propagators for s Space,
> relation to floundering
>
> On 29/06/2015 23:51, Kish Shen wrote:
>>
>> ?- A :: 1 .. 20, gfd : min([100, A], M), get_constraints_number(M, D).
>>
>> This shows that the variable M (and I also checked A, not shown here)
>> still have a propagator attached to it
>
> Thinking about this, I think the propagator might be a constraint linking M
> and A, as Gecode cannot unify the variables as ic does....
>
> However, I was actually looking at argmin when I noticed that there was a
> propagator attached when the constraint was satisfied, but I decided to look
> at min instead as ic does not have argmin.
>
> I can't show the ECLiPSe execution with argmin, as that is on a VNC window
> that I can't use cut and paste on, but here is what I tried:
>
> min_index([1,2,3,1,4], I), get_constraints_number(I, D).
>
> I = I{[1,4]}
> D = 1
>
> so there is 1 propagator attached to I in this case, when min_index
> (argmin) is entailed.
>
> Cheers,
>
> Kish
>
>
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