#18005: Group algebra of nonstandard symmetric groups broken
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Reporter: darij | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.6
Component: combinatorics | Resolution:
Keywords: symmetric group, group | Merged in:
algebra, permutations | Reviewers:
Authors: | Work issues:
Report Upstream: N/A | Commit:
Branch: | Stopgaps:
Dependencies: #16926 |
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Description changed by darij:
Old description:
> I have recorded the problem in #16926. Quoting
> src/sage/groups/perm_gps/permgroup_named.py:
>
> {{{
> def algebra(self, base_ring):
> """
> Return the symmetric group algebra associated to ``self``.
>
> .. WARNING::
>
> This is broken!
>
> sage: S = SymmetricGroup([2,3,5])
> sage: S.an_element()
> (2,3,5)
> sage: S.algebra(QQ)(_)
> Traceback (most recent call last):
> ...
> ValueError: The permutation has length 3 but its maximal
> element is 5. Some
> element may be repeated, or an element is missing, but
> there is something
> wrong with its length.
>
> Best make it a usual group algebra with none of the bells and
> whistles
> of the SGA but with functioning methods.
>
> EXAMPLES::
>
> sage: S4 = SymmetricGroup(4)
> sage: S4.algebra(QQ)
> Symmetric group algebra of order 4 over Rational Field
> """
> from sage.combinat.symmetric_group_algebra import
> SymmetricGroupAlgebra
> return SymmetricGroupAlgebra(base_ring, self)
> }}}
New description:
I have found and recorded the problem in #16926, although it predates said
ticket. Quoting src/sage/groups/perm_gps/permgroup_named.py:
{{{
def algebra(self, base_ring):
"""
Return the symmetric group algebra associated to ``self``.
.. WARNING::
This is broken!
sage: S = SymmetricGroup([2,3,5])
sage: S.an_element()
(2,3,5)
sage: S.algebra(QQ)(_)
Traceback (most recent call last):
...
ValueError: The permutation has length 3 but its maximal
element is 5. Some
element may be repeated, or an element is missing, but
there is something
wrong with its length.
Best make it a usual group algebra with none of the bells and
whistles
of the SGA but with functioning methods.
EXAMPLES::
sage: S4 = SymmetricGroup(4)
sage: S4.algebra(QQ)
Symmetric group algebra of order 4 over Rational Field
"""
from sage.combinat.symmetric_group_algebra import
SymmetricGroupAlgebra
return SymmetricGroupAlgebra(base_ring, self)
}}}
--
--
Ticket URL: <http://trac.sagemath.org/ticket/18005#comment:1>
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