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Missing hom method between WeylGroup and GAPGroup #4462

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TWiedemann opened this issue Jan 13, 2025 · 0 comments
Open

Missing hom method between WeylGroup and GAPGroup #4462

TWiedemann opened this issue Jan 13, 2025 · 0 comments
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enhancement New feature or request topic: groups

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@TWiedemann
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Similar to #4460, but for WeylGroup.

Setup:

julia> G = symmetric_group(3)
Sym(3)

julia> W = weyl_group(:A, 2)
Weyl group for root system defined by Cartan matrix [2 -1; -1 2]

julia> gen_G = [ cperm(G, [1,2]), cperm(G, [2,3]) ]
2-element Vector{PermGroupElem}:
 (1,2)
 (2,3)

julia> gen_W = gens(W)
2-element Vector{WeylGroupElem}:
 s1
 s2

It should be possible to define a homomorphism between G and W by lists of generators, but currently it is not:

julia> hom(W, G, gen_W, gen_G)
ERROR: MethodError: no method matching hom(::WeylGroup, ::PermGroup, ::Vector{WeylGroupElem}, ::Vector{PermGroupElem})
The function `hom` exists, but no method is defined for this combination of argument types.

Closest candidates are:
  hom(::Oscar.GAPGroup, ::Oscar.GAPGroup, ::Vector, ::Vector; check)
   @ Oscar ~/.julia/packages/Oscar/5kSAT/src/Groups/homomorphisms.jl:120
  hom(::AbstractVariety, ::AbstractVariety, ::Vector, ::Any; inclusion, symbol)
   @ Oscar ~/.julia/packages/Oscar/5kSAT/experimental/IntersectionTheory/src/Main.jl:278
  hom(::Oscar.MPolyLocRing, ::NCRing, ::Any, ::Vector; check)
   @ Oscar ~/.julia/packages/Oscar/5kSAT/src/AlgebraicGeometry/Schemes/AffineSchemes/Morphisms/Methods.jl:226
  ...

Stacktrace:
 [1] top-level scope
   @ REPL[7]:1

julia> hom(G, W, gen_G, gen_W)
ERROR: MethodError: no method matching hom(::PermGroup, ::WeylGroup, ::Vector{PermGroupElem}, ::Vector{WeylGroupElem})
The function `hom` exists, but no method is defined for this combination of argument types.

Closest candidates are:
  hom(::Oscar.GAPGroup, ::Oscar.GAPGroup, ::Vector, ::Vector; check)
   @ Oscar ~/.julia/packages/Oscar/5kSAT/src/Groups/homomorphisms.jl:120
  hom(::AbstractVariety, ::AbstractVariety, ::Vector, ::Any; inclusion, symbol)
   @ Oscar ~/.julia/packages/Oscar/5kSAT/experimental/IntersectionTheory/src/Main.jl:278
  hom(::Oscar.MPolyLocRing, ::NCRing, ::Any, ::Vector; check)
   @ Oscar ~/.julia/packages/Oscar/5kSAT/src/AlgebraicGeometry/Schemes/AffineSchemes/Morphisms/Methods.jl:226
  ...

Stacktrace:
 [1] top-level scope
   @ REPL[8]:1
@TWiedemann TWiedemann added the enhancement New feature or request label Jan 13, 2025
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Labels
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