Re: [eclipse-clp-users] On stating a strange constraint

>And, Hakan, thank you very much for the info on the value_precede_chain

This constraint is implemented in Gecode, and is available for ECLiPSe
through lib(gfd) as precede/2:

http://eclipseclp.org/doc/bips/lib/gfd/precede-2.html

Most of Gecode's constraints are available to ECLiiPSe through
lib(gdfd). You can check on which constraints are in the various
ECLiPSe finite domain libraries at:

http://eclipseclp.org/doc/bips/finite-domain_constraints.html

Cheers,

Kish


On Mon, Mar 27, 2023 at 11:28 AM Panagiotis Stamatopoulos
<takis_at_...90...> wrote:
>
> Yes, it worked!!! Marco, thank you very much, indeed!
>
> And, Hakan, thank you very much for the info on the value_precede_chain
> global constraint. It is exactly what I was looking for, but in an
> ECLiPSe environment. Marco's suggestion is actually a simple and
> correct implementation of it.
>
> Best Regards,
> Panagiotis
>
> On 27-Mar-23 12:58 PM, Panagiotis Stamatopoulos wrote:
> > Hi Marco,
> >
> > Yes, you are right. The ultimate purpose of this constraint is
> > symmetry breaking. I 'll try what you suggest. Thanks!
> >
> > Regards,
> > Panagiotis
> >
> > On 27-Mar-23 12:51 PM, Marco Gavanelli wrote:
> >> Hi Panagiotis,
> >>
> >> this constraint reminds me of a symmetry breaking labeling proposed by
> >> Pedro Meseguer.
> >>
> >> Anyway, what about:
> >>
> >> L[0] = 1
> >>
> >> forall i>0
> >>      L[i] <= maxlist(L[0..(i-1)]) + 1
> >> ?
> >>
> >> I hope the intuition is clear, with L[0..(1-i)] I mean the sublist of
> >> the first i elements of the list L.
> >>
> >> Best,
> >> Marco
> >>
> >>
> >> On 27/03/2023 11:34, Panagiotis Stamatopoulos wrote:
> >>> Hello Everybody,
> >>>
> >>> I am seeking ideas on how to implement in ECLiPSe a specific
> >>> constraint in a simple, if possible, and efficient way.
> >>>
> >>> Let L be a list of length N with domain variables ranging
> >>> in 1..M. Acceptable lists are the ones that ...
> >>> 1. ... contain values from 1 up to K (K =< M), but not any
> >>> values from K+1 up to M (K is not given).
> >>> 2. ... satisfy the condition that the first occurrences of
> >>> the values from 1 to K appear in this order in the list.
> >>>
> >>> For example, let N = 8 and M = 5. The lists [1,1,2,1,2,3,2,1]
> >>> and [1,2,1,3,2,4,3,1] are valid. The first one has K = 3 (only
> >>> items 1, 2, 3 appear in the list) and the second one has K = 4
> >>> (just 5 is missing from the list). In the first list, the first
> >>> occurrences of 1, 2, 3 are in positions 1, 3, 6 and in the second
> >>> list, the first occurrences of 1, 2, 3, 4 are in positions 1, 2,
> >>> 4, 6 in the lists. All fine!
> >>>
> >>> I believe that the requirement 1 above could be implemented
> >>> easily with the occurrences constraint (one for each number in
> >>> 1..M) and a set of implication (=>) constraints, stating that
> >>> if the number of occurrences of x in 1..M is 0, then the numbers
> >>> of occurrences of x+1, x+2, ... in the list should also be 0.
> >>> I cannot predict the propagation level of this approach, but
> >>> it seems that, at least, declaratively can be stated.
> >>>
> >>> I don't have any good ideas for the requirement 2. I tried
> >>> something that exploits again the occurrences constraint (for
> >>> every number in 1..M and every prefix list of the given list)
> >>> and then the lex_le constraint. It worked, but if N is around
> >>> 50 or more, the efficiency is unacceptable.
> >>>
> >>> Any ideas on the above would be more than welcome.
> >>>
> >>> Best Regards,
> >>> Panagiotis
> >>>
> >>>
> >>> _______________________________________________
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> >>> ECLiPSe-CLP-Users_at_lists.sourceforge.net
> >>> https://lists.sourceforge.net/lists/listinfo/eclipse-clp-users
> >>
> >
> >
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