On Sun, Dec 19, 2010 at 9:04 AM, Francois Maltey <fmal...@nerim.fr> wrote:
> Hello,
>
> I try to work with all the subsets of a cartesian product.
>
> So I begin with
>
> S = Set([1..4])
> P = CartesianProduct (S)
> Subsets (S) # is right
> Subsets (P) # fails
>
> Am I wrong ? (CartesianProduct isn't a Set) or is it a bug in Sage ?
Not a bug. If you type CartesianProduct? you will see it is an
interator, designed to be used in a for-loop. These are much faster
than set constructors. Here is an example:
sage: cp = CartesianProduct([1,2], [3,4]); cp
Cartesian product of [1, 2], [3, 4]
sage: cp.list()
[[1, 3], [1, 4], [2, 3], [2, 4]]
sage: cp.list()
[[1, 3], [1, 4], [2, 3], [2, 4]]
sage: for x in cp:
if 1 in x:
print x
....:
[1, 3]
[1, 4]
>
> Many thanks for your tips.
>
> Francois
>
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