diff --git a/src/orbitdata.jl b/src/orbitdata.jl index c51b3a1..d7bca32 100644 --- a/src/orbitdata.jl +++ b/src/orbitdata.jl @@ -165,3 +165,102 @@ function matrix_reps(preps::Dict{T,perm{I}}) where {T<:GroupElem, I<:Integer} end return Dict(kk[i] => mreps[i] for i in 1:length(kk)) end + +############################################################################### +# +# actions +# +############################################################################### + +function (p::perm)(A::GroupRingElem) + RG = parent(A) + result = zero(RG, eltype(A.coeffs)) + + for (idx, c) in enumerate(A.coeffs) + if c!= zero(eltype(A.coeffs)) + result[p(RG.basis[idx])] = c + end + end + return result +end + +############################################################################### +# +# Action of WreathProductElems on Nemo.MatElem +# +############################################################################### + +function matrix_emb(n::DirectPowerGroupElem, p::perm) + Id = parent(n.elts[1])() + elt = Diagonal([(-1)^(el == Id ? 0 : 1) for el in n.elts]) + return elt[:, p.d] +end + +function (g::WreathProductElem)(A::MatElem) + g_inv = inv(g) + G = matrix_emb(g.n, g_inv.p) + G_inv = matrix_emb(g_inv.n, g.p) + M = parent(A) + return M(G)*A*M(G_inv) +end + +import Base.* + +@doc doc""" + *(x::AbstractAlgebra.MatElem, P::Generic.perm) +> Apply the pemutation $P$ to the rows of the matrix $x$ and return the result. +""" +function *(x::AbstractAlgebra.MatElem, P::Generic.perm) + z = similar(x) + m = rows(x) + n = cols(x) + for i = 1:m + for j = 1:n + z[i, j] = x[i,P[j]] + end + end + return z +end + +function (p::perm)(A::MatElem) + length(p.d) == A.r == A.c || throw("Can't act via $p on matrix of size ($(A.r), $(A.c))") + return p*A*inv(p) +end + +############################################################################### +# +# Action of WreathProductElems on AutGroupElem +# +############################################################################### + +function AutFG_emb(A::AutGroup, g::WreathProductElem) + isa(A.objectGroup, FreeGroup) || throw("Not an Aut(Fₙ)") + parent(g).P.n == length(A.objectGroup.gens) || throw("No natural embedding of $(parent(g)) into $A") + elt = A() + Id = parent(g.n.elts[1])() + flips = Groups.AutSymbol[Groups.flip_autsymbol(i) for i in 1:length(g.p.d) if g.n.elts[i] != Id] + Groups.r_multiply!(elt, flips, reduced=false) + Groups.r_multiply!(elt, [Groups.perm_autsymbol(g.p)]) + return elt +end + +function AutFG_emb(A::AutGroup, p::perm) + isa(A.objectGroup, FreeGroup) || throw("Not an Aut(Fₙ)") + parent(p).n == length(A.objectGroup.gens) || throw("No natural embedding of $(parent(p)) into $A") + return A(Groups.perm_autsymbol(p)) +end + +function (g::WreathProductElem)(a::Groups.Automorphism) + A = parent(a) + g = AutFG_emb(A,g) + res = A() + Groups.r_multiply!(res, g.symbols, reduced=false) + Groups.r_multiply!(res, a.symbols, reduced=false) + Groups.r_multiply!(res, [inv(s) for s in reverse!(g.symbols)]) + return res +end + +function (p::perm)(a::Groups.Automorphism) + g = AutFG_emb(parent(a),p) + return g*a*inv(g) +end