[gecode-users] missing doc for element constraint

[Guido Tack]

Denys Duchier wrote:

> Guido Tack <tack at gecode.org> writes:
> 
>> These element constraints are for 2d matrices of width w and height h encoded in the IntVarArgs a.
> 
> that's the missing information. the constraint is then actually:
> 	a(x,y) = z
> or is it:
> 	a(y,x) = z
> for a matrix a or width w and height h.  It would be really nice to make
> this clear.

The constraint is a[x+w*y] = z, and w*h must be a.size(), just as the documentation says.

I don't want to discuss whether that's a(x,y) or a(y,x) because there's been enough confusion about the Matrix class already... In programming terms (as opposed to mathematics), a is a 2d array in row-major order, and z is constrained to be the element in row y and column x.  I'll add that to the documentation.

The minimodel library contains element constraints on Matrix objects, which of course internally use these post functions.

Cheers,
	Guido

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