#8411: Branching rule fix and doc revision
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Reporter: bump | Owner: sage-combinat
Type: defect | Status: needs_review
Priority: major | Milestone: sage-4.4
Component: combinatorics | Keywords:
Author: Daniel Bump | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
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Description changed by bump:
Old description:
> 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.
New description:
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.
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/8411#comment:2>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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