On Wed, Mar 06, 2013 at 04:27:57AM -0800, Travis Scrimshaw wrote:
> I'd throw a type error if the group W was infinite since this does not
> exist. Also I would think it would be (relatively) easy to check if
> subgroup the group is finite since there are only 3 infinitely families
> and would be easy to detect when it does not fall into these types
> (basically if the Coxeter matrix has something off the sub/super diagonals
> or is type D), the rest are exceptional and could just be a big case check
> by equality. Of course this would only be after it has been broken up into
> connected components. Perhaps I'm over simplifying things...
Yes, we will definitely want some automatic type recognition at some
point (like GAP does); as a side effect this will give finite type
detection.
Now, for the problem at hand, I guess that's overkill. Let's write in
the specs, as a big fat warning, that the function will only terminate
if the (parabolic sub) group is finite. And add some simple and fast
sanity checks in the easy to handle cases. Something like:
def longest_element(index_set=None):
if index_set is None:
if self in CoxeterGroups().Infinite():
raise ...
...
Cheers,
Nicolas
--
Nicolas M. Thiéry "Isil" <nthi...@users.sf.net>
http://Nicolas.Thiery.name/
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