[gecode-users] channel constraint posting not initially domain consistent?

[Kish Shen]

Hi,

I have been testing the constraints implemented in the ECLiPSe Gecode 
interface, and I have run into this puzzling behaviour for the channel() 
constraint (the version that maps BoolVarArgs to an IntVar),
i.e.

Gecode::channel (Home home, const BoolVarArgs &x, IntVar y, int o=0, 
IntConLevel icl=ICL_DEF)
  	Post domain consistent propagator for channeling Boolean and integer 
variables

In one of my tests, I assigned 0 to one of the BoolVarArgs, which is 
done by something like:

x[i] = BoolVar(home, 0, 0);

so I expected the value represented by i+o to be excluded from the 
domain of y, but it does not seem to be. Concretely, here is what
I used at the ECLiPSe level:

bool_channeling(V, [B1,B2,B3,0,B5], 0).

where V is the IntVar, and the Bs are the BoolVarArgs, and o is set to 
0. When this is posted, I get the domain 0..4 for V, i.e. 3 was not 
excluded from the domain (home.status() has been called -- propagation 
happens by default after the posting of every constraint,  also 
propagation must have occurred because V is given the domain 0..4, which 
came from the channel constraint, as V was initially given a default 
domain that is much larger)

however, if I set the boolean to 0 after posting the constraint first, 
then I do get 3 being excluded:

bool_channeling(V, [B1,B2,B3,B4,B5], 0), B4 = 0.

In this case V has the domain [0..2, 4]

and furthermore,

bool_channeling(V, [B1,B2,B3,0,B5], 0), B2 = 0.

I get [0,2,4] for the domain of V, which shows that 0 was correctly 
assigned to B4 (x[3] where x is the BoolVarArgs), and that somehow the 
initial posting of the constraint does not achieve domain consistency, 
but subsequent posting seem to.

I am using Gecode 3.7.1.
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