Opened 6 years ago

Closed 6 years ago

# Group algebra of nonstandard symmetric groups broken

Reported by: Owned by: darij major sage-duplicate/invalid/wontfix combinatorics symmetric group, group algebra, permutations sage-combinat, tscrim, virmaux, nthiery Travis Scrimshaw N/A #16926

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)
```

### comment:1 Changed 6 years ago by darij

• Description modified (diff)

### comment:2 Changed 6 years ago by nthiery

I just implemented that in #16926; this ticket can probably be closed as duplicate.

### comment:3 Changed 6 years ago by darij

Great job! Can I ask you to review my doctests? (probably half a minute of work, thanks!)

### comment:4 Changed 6 years ago by tscrim

• Milestone changed from sage-6.6 to sage-duplicate/invalid/wontfix
• Reviewers set to Travis Scrimshaw
• Status changed from new to needs_review

Done.

### comment:5 Changed 6 years ago by tscrim

• Status changed from needs_review to positive_review

### comment:6 Changed 6 years ago by vbraun

• Resolution set to duplicate
• Status changed from positive_review to closed
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