Nicolas, > > Is the following a bug? It seems so. > > > > sage: WeylGroup(CartanType(['B',2]).root_system().coweight_lattice()) > > Weyl Group of type ['C', 2] (as a matrix group acting on the coweight > > lattice) > > For good or bad, it's a corollary of the fact that the coweight > lattice is implemented as the weight lattice of the dual type.
Well, the lattice we started with was the coweight lattice of type B2, and that is isomorphic to the weight lattice of type C2. I don't like the description of the group. It should either say that it is the Weyl group of the coweight lattice of type B2 or the weight lattice of type C2. Maybe it should say Weyl Group of type ['C', 2] (as a matrix group acting on the coweight lattice of dual type). I had some code that checked whether a vector can be acted on by this group; it checked whether it was in the right lattice (coweight lattice of type B2) and couldn't tell that this was the same thing as the weight lattice of type C2, and failed. I can't see an easy way of having it check its input. --Mark -- You received this message because you are subscribed to the Google Groups "sage-combinat-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-combinat-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-combinat-devel@googlegroups.com. Visit this group at http://groups.google.com/group/sage-combinat-devel. For more options, visit https://groups.google.com/groups/opt_out.
