There is a global constraint called value_precede_chain ( https://sofdem.github.io/gccat/gccat/Cint_value_precede_chain.html) which seems to be what you want. It ensures that the first occurrence of the value I must be placed in the array before any values > I. I don't have any ECLiPSe CLP code for this, but there's an MiniZinc code here: https://github.com/MiniZinc/libminizinc/blob/master/share/minizinc/std/fzn_value_precede_chain_int.mzn . And I've ported the MiniZinc code to Picat: http://hakank.org/picat/value_precede_chain.pi . Hope this helps. Best, Hakan On Mon, Mar 27, 2023 at 11:59 AM Panagiotis Stamatopoulos <takis_at_...263....90...> 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 > >> > >> > >> _______________________________________________ > >> ECLiPSe-CLP-Users mailing list > >> ECLiPSe-CLP-Users_at_lists.sourceforge.net > >> https://lists.sourceforge.net/lists/listinfo/eclipse-clp-users > > > > > _______________________________________________ > ECLiPSe-CLP-Users mailing list > ECLiPSe-CLP-Users_at_lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/eclipse-clp-users > -- Hakan Kjellerstrand http://www.hakank.org/ http://www.hakank.org/webblogg/ http://www.hakank.org/constraint_programming_blog/ http://twitter.com/hakankj https://www.facebook.com/hakankjReceived on Mon Mar 27 2023 - 10:08:50 CEST
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