Opened 13 years ago

Closed 13 years ago

#8411 closed defect (fixed)

Branching rule fix and doc revision

Reported by: bump Owned by: sage-combinat
Priority: major Milestone: sage-4.4
Component: combinatorics Keywords: Branching rules
Cc: sage-combinat, brant@… Merged in: sage-4.4.alpha2
Authors: Daniel Bump Reviewers: Nicolas M. Thiéry, Brant Jones
Report Upstream: N/A Work issues:
Branch: Commit:
Dependencies: Stopgaps:

Status badges

Description (last modified by bump)

This corrects a minor problem with branching rules in weyl_characters.py.

Previously branching rules SO(m+n)->SO(m)xSO(n) were implemented using rule="extended", and similarly for symplectic groups. However there is one case where this does not meet the definition of the extended rule, namely SO(2n+2m+2)->SO(2n+1)xSO(2m+1). Indeed, the extended rule checks to see if the ranks are equal, which they are not in this case.

I thought the cleanest fix was to implement a new rule called "orthogonal_sum" for such cases.

I also took the chance to revise the documentation since what was said before about rule="symmetric" was misleading.

Minor bugfix in weightring: 0 in weight lattice should coerce to 1 not 0 in weight ring.

Attachments (1)

trac_8411_branching_rules.patch (4.9 KB) - added by bump 13 years ago.
Branching rule fix and revised doc in weyl_characters.py

Download all attachments as: .zip

Change History (10)

comment:1 Changed 13 years ago by bump

Status: newneeds_review

comment:2 Changed 13 years ago by bump

Description: modified (diff)

comment:3 Changed 13 years ago by nthiery

All test pass on 4.3.4 and, from a technical point of view, the patch looks good.

So it is good to go as soon as someone more knowledgeable with branching rules will have double check the mathematics? Well, of course, the expert is Dan :-) Maybe Brant?

comment:4 Changed 13 years ago by nthiery

Cc: brant@… added
Keywords: Branching rules added
Reviewers: Nicolas M. Thiéry, Brant Jones

comment:5 Changed 13 years ago by bump

jhpalmieri objected in #8414 to the fact that the patch there did not contain mercurial headers information.

I therefore remade this patch. There is no change to the content of the patch.

comment:6 Changed 13 years ago by nthiery

Please also include the ticket number in the patch title!

#8411: Branching rule fix and doc revision

Sorry for the extra bother ...

Changed 13 years ago by bump

Branching rule fix and revised doc in weyl_characters.py

comment:7 Changed 13 years ago by bump

Please also include the ticket number in the patch title!

#8411: Branching rule fix and doc revision

Sorry for the extra bother ...

OK, I changed the patch description to begin #8411.

comment:8 Changed 13 years ago by brant.c.jones

Status: needs_reviewpositive_review

This is a positive review for trac_8411.

Prior to this patch, sage would not branch e.g. SO(3) x SO(3) -> SO(6) because this would embed a rank 2 group in a rank 3 group, and the get_branching_rule() code required the ranks to be equal. After applying this patch, the "orthogonal_sum" rule will allow such branching (as the identity map) between types B/D, and within type C (only).

This patch correctly implements useful mathematics.

-- Brant Jones

comment:9 Changed 13 years ago by jhpalmieri

Merged in: sage-4.4.alpha2
Resolution: fixed
Status: positive_reviewclosed

Merged into 4.4.alpha2.

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