[gecode-users] semantics for count(Home home, const IntVarArgs &x, IntVar y, IntRelType r, IntVar z)

[Kish Shen]

Hi,

I have been looking at the behaviour of

count(Home home, const IntVarArgs &x, IntVar y, IntRelType r, IntVar z)

and cannot understand what is happening when IntVar y has more than one 
value in its domain. Until now, I have only tested this constraint with 
y having a singleton value in its domain, and in this case, the 
constraint behaves the same as the case where y is Int, i.e. the number 
of occurrences of the value y in x is counted.

However, one of my user wanted to use the constraint where y has 
multiple values (i.e. the counts constraint in the global constraint 
catalog). I know this constraint is provided with y being an IntSet, but 
my user did not know about this constraint, so he used the version where 
y is a IntVar instead.

I had expected that mulitple domain values in y would behave like 
multiple values in the IntSet for this constraint, but this does not 
seem to be the case. For example, the constraint succeeds with the 
following (in ECLiPSe syntax, but the argument order of Gecode's 
constraint):

Y :: [3,4], count([3,0,3,3,4], Y, =, 2)

where [3,0,3,3,4] is x, IntRelType is IRT_EQ.

I don't understand why this succeeds -- the count for 3 is 3, and for 4 
is 1, and for both 3 and 4 is 4, none of which is equal to 2. So what is 
the semantics?

The equivalent call using y as an IntSet [3,4] fails as expected. Also, 
for the same count constraint, if y has a single domain value (e.g. 3 or 
4), then the constraint behave as I expected, i.e. z = 3 for y = 3, and 
z = 1 for y = 1.

Thanks and cheers,

Kish


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