Hi Jesus,
On Wed, Oct 03, 2012 at 12:13:31PM +0200, Florent Hivert wrote:
> > When relabelling a Cartan type:
> >
> > sage: A3 = CartanType("A3")
> > sage: A3r = A3.relabel({1:2,2:3,3:1})
> >
> > one loses the cartan_matrix method, which is not implemented in
> > [...]/combinat/root_system/type_relabel.py.
> >
> > It would be trivial to create it: just calling the cartan_matrix method of
> > the CartanType parent and reordering columns and rows according to the
> > relabelling.
Good catch! Thanks for the feedback.
Actually, the problem is that ``cartan_matrix`` is implemented for
crystalographic cartan types (in the class
sage.combinat.root_system.cartan_type.CartanType_crystalographic).
However, when constructing a relabeled cartan type, that information
is lost; A3r is not put in the right class::
sage: A3.__class__.mro()
[<class 'sage.combinat.root_system.type_A.CartanType'>, ...
<class 'sage.combinat.root_system.cartan_type.CartanType_finite'>,
<class 'sage.combinat.root_system.cartan_type.CartanType_simply_laced'>,
<class 'sage.combinat.root_system.cartan_type.CartanType_crystalographic'>,
<class 'sage.combinat.root_system.cartan_type.CartanType_simple'>, ...
<class 'sage.combinat.root_system.cartan_type.CartanType_abstract'>, ...]
sage: A3r.__class__.mro()
[<class 'sage.combinat.root_system.type_relabel.CartanType'>, ...
<class 'sage.combinat.root_system.cartan_type.CartanType_abstract'>, ...]
There is already a hook in the constructor for relabelled cartan types
to handle this for affine cartan types. In
sage.combinat.root_system.type_relabel.CartanType.__init__, you will find:
if type.is_affine():
self._add_abstract_superclass(CartanType_affine)
And indeed this works::
sage: C = CartanType(["A",3,1])
sage: Cr = C.relabel({0:0,1:2,2:3,3:1})
sage: Cr.cartan_matrix()
[ 2 -1 -1 0]
[-1 2 0 -1]
[-1 0 2 -1]
[ 0 -1 -1 2]
So the right fix would be to add similar hooks for finite, simply
laced, crystalographic, and simple cartan types.
> > May I open a ticket in trac?
Please! I'd be happy to review a patch if you would be willing to
write one.
Cheers,
Nicolas
--
Nicolas M. Thiéry "Isil" <nthi...@users.sf.net>
http://Nicolas.Thiery.name/
--
You received this message because you are subscribed to the Google Groups
"sage-combinat-devel" group.
To post to this group, send email to sage-combinat-devel@googlegroups.com.
To unsubscribe from this group, send email to
sage-combinat-devel+unsubscr...@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/sage-combinat-devel?hl=en.
