MagicSeries, Among, two solutions? about jacop HOT 4 CLOSED

Hi,

Both solutions are correct. I do not know MagicSeries problem but the constraints are satisfied.
In the first solution you have 6 zeros, 2 ones, 1 two, zero of other numbers.
In the second solution you have 7 zeros, 2 ones, zero of other numbers.

The constraint model corresponds to the solutions.
Why do you claim there is supposed to be only one solution?

best,
Radek

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If I understood it correctly, a sequence of numbers S = (s_0 , s_1 ,...,s_{n−1}) is a magic series, if each s_i represents the number of occurrences of i within the sequence S. For the first solution that is s_0 ~= 6 occurrences of 0, s_1 ~= 2 occurrences of 1, s_2 ~=1 occurrence of 2, and s_6 ~= 1 occurrence of 6. For the second solution that would be:

s_0 ~= 7 occurences of 0 (ok)
s_1 ~= 1 occurrence of 1 (wrong)
s_7 ¯= 1 occurence of 7 (ok)

The one occurs twice instead of just once.

from jacop.

Hi,

I was too quick in making my judgement. It seems you found a nice program that exhibits a bug in Among. I am able to replicate your results and with your more detail explanation I can see the problem you are facing. Thank you.

The optimizations applied inside Among that remove the constraint from the constraint store are too quick for your example. For one simple reason, you are using the same variable twice in the context of the constraint (in the context of the list, as well as, the counter). Of course, constraint should account for this but it does not in its optimizations.

It may take some time to figure out a bug fix that does not throw the optimization applied in this constraint. In the meantime, I provide you with a simple workaround (a different model) that does not have this problem.

    store = new Store();

    IntVar[] sequence = new IntVar[n+1];
    IntVar[] counters = new IntVar[n+1];
    for (int i = 0; i < sequence.length; i++) {
        sequence[i] = new IntVar(store, "H" + i, 0, n);
        counters[i] = new IntVar(store, "C" + i, 0, n);
    }

    for (int i=0; i < sequence.length; i++) {
        store.impose(new Among(sequence, new IntervalDomain(i, i), counters[i]));
        store.impose(new XeqY(sequence[i], counters[i]));
    }

This workaround introduces an extra list of variables used as counters that are made equal to the original list. In this model no variable is used twice in the context of the constraint and Among works correctly.

Thank you for persisting in explanation of your problem.

best regards,
Radek

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Thanks a lot, works nicely now!
I am looking forward to the fix, which is not urgent though.
Thanks again for looking deeper into the issue.

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