Hi,
I am trying to post a propagator for the constraint
x' = x or x' = epsilon
with x and x' integer variables and epsilon some constant not in dom(x).
I first thought to use reified equality constraints but it would achieve
very few propagation (for example, removing values from x would not
remove them from x' as long as epsilon is in dom(x'))
Then I thought I could do the same with the count constraint: posting
#(X | x_i = y) = 1
with X = [x, epsilon] and y = x'
But the count propagator (for #(X | x_i = y) >= 1) does not seem to
achieve domain-consistency towards y in this case: values that are not
present in the union of the domains of the x_i's are not removed from y.
To test this I wrote this little program:
class TestCount : public Example {
protected:
IntVar v, w, x;
public:
TestCount(const Options& opt)
: v(this, 1, 10), w(this, 2, 4), x(this, 7, 9) {
IntVarArray tab(this, 2);
tab[0] = w; tab[1] = x;
exactly(this, tab, v, 1);
branch(this, tab, INT_VAR_SIZE_MIN, INT_VAL_MIN);
}
// …
}
and I obtain solutions like v=[1..10] w=2 x=7. Shouldn't it propagate
v={2,7} ? Did I do something wrong ?
If what I am trying to do is not possible using count, what is the best
way to implement it, achieving domain consistency ?
Thank you in advance for your help.
Didier
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