On Mon, Jun 14, 2010 at 05:33:58AM -0700, Frédéric Chapoton wrote:
> Ooops,
> This is because I did not use the root lattice.. This works :
>
> sage: A3=RootSystem(['A',3]).root_lattice()
> sage: t=A3.simple_root(1)+A3.simple_root(2)-A3.simple_root(3)
> sage: t.is_positive_root()
> False
>
> But anyway, I think the name is not correct, because it does not
> return true for positive roots, but for positve linear combinations of
> positive roots.. And the behaviour is not coherent, which was the
> cause of my initial problem.
+1!
I also have wanted a good name for this function for a while. The
precise spec of this function is: for f in the linear span of the
simple roots, tell whether f is in the cone spanned by the simple
roots.
Suggestions anyone?
Cheers,
Nicolas
--
Nicolas M. Thiéry "Isil" <nthi...@users.sf.net>
http://Nicolas.Thiery.name/
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