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 >>> >>> >>> _______________________________________________ >>> 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-usersReceived on Mon Mar 27 2023 - 10:27:56 CEST
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