In case it would help review this patch, let me try to explain it. The problem is to give a sort of classification of most maximal subgroups of Lie groups so that we can give branching rules.
The subgroups in question are of the type O(n) x O(m) in O(n+m) or Sp(n x m) in Sp(n) x Sp(m). Previously these were handled by "rule=extended". However this is not appropriate, and in some cases Sage would refuse to do a branching rule because the ranks did not match, even though these were cases where the branching rule was already programmed in. The problem is with odd orthogonal groups, where (for example) O(3)xO(3) --> O(6) embeds a rank 2 group in a rank 3 group. The extended rule is actually intended for maximal subgroups of the same rank. In these cases, you can recognize the subgroup by deleting one node from the extended Dynkin diagram. The solution in the patch is to create a new rule called orthogonal_sum. Programming in the branching rule basically amounts to describing the embedding of Cartan algebras, or its transpose, as a linear map. In the cases in question, the map is quite trivial, just the identity map embedding a direct sum of two vector spaces. Dan -- 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-de...@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.
