[gecode-users] question about channeling intvars<->set

[Guido Tack]

Marco Correia wrote:
> In the reference manual, 
> 
> http://www.gecode.org/doc-
> latest/reference/group__TaskModelSetConnect.html#ga1bde4fb2947a0b93cf248e75e078969e
> 
> it says that channel(IntVarArgs x, SetVar s) posts the propagator for
> 
> { x_1,...,x_{n-1} } = y and x_i < x_{i-1}
> 
> 1. I'm not sure I'm getting the correct meaning. This means that the 
> propagator also forces x to be sorted in increasing order, right?

Yes, that's correct.

> 2. If 1 is correct, then what is the most efficient way of enforcing a similar 
> constraint but without the requirement that x is sorted? Should I use the sort 
> global constraint on x to map it to an xsorted and then channel xsorted 
> instead?

That would be possible.  Be careful though that it will also force all x to be distinct.
Depending on the semantics you need, a more efficient version could be

   rel(home, SOT_UNION, x, y)

I changed the name of channel to channelSorted in the trunk, and added channel as an alias to rel in the minimodel.hh header.  I think it's more intuitive that way.

> 3. I guess there is a typo in the reference manual. In the latex expression it 
> refers to y, where the constraint says the SetVar arg is called s.

Thanks, I fixed it in the svn trunk.

Cheers,
	Guido

-- 
Guido Tack, http://people.cs.kuleuven.be/~guido.tack/