id summary reporter owner description type status priority milestone component resolution keywords cc merged author reviewer upstream work_issues branch commit dependencies stopgaps
18700 Have GroupAlgebra(Q, R) and G.algebra(R) return the same standard class for group algebras tscrim sage-combinat "Consider the following situation:
{{{
sage: P = RootSystem(['A',2,1]).weight_lattice()
sage: W = RootSystem(['A',2,1]).weight_space()
sage: W.has_coerce_map_from(P)
True
sage: PA = P.algebra(QQ)
sage: WA = W.algebra(QQ)
sage: WA.has_coerce_map_from(PA)
False
}}}
The last line should be `True`. This comes from the fact that `GroupAlgebra` implements some extra coercion logic and `G.algebra(R)` does not return an instance of this class.
To remedy this, we lift a good portion of the `GroupAlgebra` code to the appropriate categories, where we impose the restriction that a `(Semi)Group.Algebra` must have a basis indexed by elements of the (semi)group, and have all group algebras redirect to the now (lightweight) class `GroupAlgebra_class` in order to implement coercions." enhancement closed major sage-8.0 coercion fixed group algebras sage-combinat aschilling nthiery bsalisbury1 chapoton Travis Scrimshaw, Nicolas M. Thiéry Ben Salisbury N/A 3160e26eb25eb09fc7164f020783da2122b18ffd 3160e26eb25eb09fc7164f020783da2122b18ffd #23000 #23211