Compute radical and idempotents of a quotient algebra

edit

In the meantime I have learned that these things can be done for admissible quotients of path algebras with the aid of the GAP package QPA. This also works in Sage via letting GAP be the intermediator.

It works as follows:

gap> LoadPackage("qpa");;
gap> k:=Rationals;
Rationals
gap> Q:=Quiver(1,[[1,1,"a"],[1,1,"b"]]);
<quiver with 1 vertices and 2 arrows>
gap> kQ:=PathAlgebra(k,Q);
<Rationals[<quiver with 1 vertices and 2 arrows>]>
gap> AssignGeneratorVariables(kQ);
\#I  Assigned the global variables [ v1, a, b ]
gap> rels:=[a^2,b^2, a*b-b*a];
[ (1)*a^2, (1)*b^2, (1)*a*b+(-1)*b*a ]
gap> A:=kQ/rels;
<Rationals[<quiver with 1 vertices and 2 arrows>]/
<two-sided ideal in <Rationals[<quiver with 1 vertices and 2 arrows>]>, 
  (3 generators)>>
gap> IsAdmissibleQuotientOfPathAlgebra(A);
true
gap> RAD:=RadicalOfAlgebra(A);
<algebra of dimension 3 over Rationals>
gap> Display(RAD);
Algebra( Rationals, [ [(1)*a], [(1)*b], [(1)*a*b] ] )
gap> Dimension(RAD);
3
gap>

If we let $k$ be a finite field, then the command

IdempotentsForDecomposition(A);

works, but I don't have a computational solution for the case $k=\mathbb{Q}$. I do not yet have a solution for the non-commutative case.