Problem with isolated vertices in RightModuleOverPathAlgebra

[erich-9]

For instance the following code does not work, but I think it should:

Q := Quiver(3, [ [1, 2, "a"] ]);
kQ := PathAlgebra(Rationals, Q);

AlgebraAsModuleOverEnvelopingAlgebra(kQ);

What goes wrong is that RightModuleOverPathAlgebra is not told what dimension the vector space at the isolated vertex 3 should have. Namely, running

Q := Quiver(3, [ [1, 2, "a"] ]);
kQ := PathAlgebra(Rationals, Q);

M := RightModuleOverPathAlgebra(kQ, [ ["a", [[1]]] ]);

raises the following error:

Error, Dimensions of element are incorrect called from
PathModuleElem( fam, base ) at .../lib/gap4r8/pkg/qpa-1.27/lib/module.gi:384 called from
CreateModuleBasis( Fam ) at .../lib/gap4r8/pkg/qpa-1.27/lib/module.gi:557 called from

[erich-9]

Here is a different but related problem. The code

Q := Quiver(3, [ [2, 3, "a"], [3, 2, "b"] ] );
kQ := PathAlgebra(Rationals, Q);

AssignGeneratorVariables(kQ);

A := kQ / [ b*a, a*b ];

IndecProjectiveModules(A);

leads to the error message:

Error, Record: '<rec>.vertices' must have an assigned value in
  vertices := fam!.vertices; at .../pkg/qpa-1.27/lib/module.gi:53 called from 
PathModuleElem( FamilyObj( Zero( indec_proj_list[i] )![1] ), list_of_min_gen[i] 
 ) at .../pkg/qpa-1.27/lib/modulespecial.gi:122 called from

Using here the quiver Q := Quiver(3, [ [1, 2, "a"], [2, 1, "b"] ] ) one gets not the same error message but instead the one reported in the first post.

[sunnyquiver]

Thank you very much for reporting this bug. It is now hopefully fixed.

Best regards, the QPA-team.