diff --git a/experimental/LieAlgebras/src/LieAlgebras.jl b/experimental/LieAlgebras/src/LieAlgebras.jl index d6cd094e36c..e866dfbd8e6 100644 --- a/experimental/LieAlgebras/src/LieAlgebras.jl +++ b/experimental/LieAlgebras/src/LieAlgebras.jl @@ -74,6 +74,7 @@ import ..Oscar: ngens, order, parent_type, + permutation_group, rank, root, roots, diff --git a/experimental/LieAlgebras/src/WeylGroup.jl b/experimental/LieAlgebras/src/WeylGroup.jl index 821fe43e161..e4d0fd98e02 100644 --- a/experimental/LieAlgebras/src/WeylGroup.jl +++ b/experimental/LieAlgebras/src/WeylGroup.jl @@ -474,6 +474,59 @@ function isomorphism(::Type{FPGroup}, W::WeylGroup; set_properties::Bool=true) return MapFromFunc(W, G, iso, isoinv) end +function permutation_group(W::WeylGroup; set_properties::Bool=true) + return codomain(isomorphism(PermGroup, W; set_properties)) +end + +function isomorphism(::Type{PermGroup}, W::WeylGroup; set_properties::Bool=true) + @req is_finite(W) "Weyl group is not finite" + R = root_system(W) + type, ordering = root_system_type_with_ordering(R) + + if length(type) != 1 + error("Not implemented (yet)") + end + if !issorted(ordering) + error("Not implemented (yet)") + end + coxeter_type, n = only(type) + if coxeter_type == :A + G = symmetric_group(n + 1) + + iso = function (w::WeylGroupElem) + reduce(*, [cperm(G, [i, i + 1]) for i in word(w)]; init=cperm(G)) + end + + isoinv = function (p::PermGroupElem) + word = UInt8[] + for cycle in cycles(p) + transpositions = [ + sort([c, cycle[i + 1]]) for (i, c) in enumerate(cycle) if i < length(cycle) + ] + for t in transpositions + word = reduce( + vcat, + [ + [i for i in t[1]:(t[2] - 1)], + [i for i in reverse(t[1]:(t[2] - 2))], + word, + ], + ) + end + end + return W(word) + end + else + error("Not implemented (yet)") + end + + if set_properties + set_order(G, order(W)) + end + + return MapFromFunc(W, G, iso, isoinv) +end + ############################################################################### # ReducedExpressionIterator diff --git a/experimental/LieAlgebras/test/WeylGroup-test.jl b/experimental/LieAlgebras/test/WeylGroup-test.jl index 76178206bce..e78ad3d73ad 100644 --- a/experimental/LieAlgebras/test/WeylGroup-test.jl +++ b/experimental/LieAlgebras/test/WeylGroup-test.jl @@ -52,6 +52,7 @@ include( @testset "WeylGroup Group conformace test for $(Wname)" for (Wname, W) in [ ("A1", weyl_group(:A, 1)), + ("A5", weyl_group(:A, 5)), ("B4", weyl_group(root_system(:B, 4))), ("D5", weyl_group(cartan_matrix(:D, 5))), ("F4+G2", weyl_group((:F, 4), (:G, 2))), @@ -111,9 +112,55 @@ include( if is_finite(W) # remove once rand(W) is implemented for infinite groups w = rand(W) @test w == inv(iso)(iso(w)) + v = rand(W) + @test iso(v * w) == iso(v) * iso(w) + @test v * w == inv(iso)(iso(v) * iso(w)) end g = rand_pseudo(G) @test g == iso(inv(iso)(g)) + h = rand_pseudo(G) + @test inv(iso)(h * g) == inv(iso)(h) * inv(iso)(g) + @test h * g == iso(inv(iso)(h) * inv(iso)(g)) + end + end + end + end + + if has_root_system_type(root_system(W)) + type, ordering = root_system_type_with_ordering(root_system(W)) + if length(type) == 1 && issorted(ordering) && only(type)[1] == :A # only implemented for A_n (yet) + @testset "isomorphism(PermGroup, ::WeylGroup; set_properties=$set_properties)" for set_properties in + [ + false, true + ] + G = permutation_group(W; set_properties) + if (is_finite(W) && ngens(W) < 6) || set_properties #= for sane runtime =# + @test is_finite(G) == is_finite(W) + is_finite(W) && @test order(G) == order(W) + end + + iso = isomorphism(PermGroup, W; set_properties) + @test W == domain(iso) + G = codomain(iso) + if (is_finite(W) && ngens(W) < 6) || set_properties #= for sane runtime =# + @test is_finite(G) == is_finite(W) + is_finite(W) && @test order(G) == order(W) + if ngens(W) < 10 #= for sane runtime =# + for _ in 1:5 + if is_finite(W) # remove once rand(W) is implemented for infinite groups + w = rand(W) + @test w == inv(iso)(iso(w)) + v = rand(W) + @test iso(v * w) == iso(v) * iso(w) + @test v * w == inv(iso)(iso(v) * iso(w)) + end + g = rand_pseudo(G) + @test g == iso(inv(iso)(g)) + h = rand_pseudo(G) + @test inv(iso)(h * g) == inv(iso)(h) * inv(iso)(g) + @test h * g == iso(inv(iso)(h) * inv(iso)(g)) + end + end end end end