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

[Christian Schulte]

Hi,

Yes there was a bug in posting the propagator for channel. It is fixed in
the trunk.

It's really small and also appended as a patch.

Thanks!
Christian

--
Christian Schulte, www.ict.kth.se/~cschulte/


-----Original Message-----
From: users-bounces at gecode.org [mailto:users-bounces at gecode.org] On Behalf
Of Kish Shen
Sent: Friday, October 28, 2011 10:22 PM
To: users at gecode.org
Subject: [gecode-users] channel constraint posting not initially domain
consistent?

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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