Widen eltype in complex hermitian tridiagonal eigen (#52802)

Close #52801 by widening the `eltype` appropriately.
JuliaLang · Jan 9, 2024 · 17280b2 · 17280b2
1 parent bd3eab6
commit 17280b2
Show file tree

Hide file tree

Showing 2 changed files with 12 additions and 5 deletions.
diff --git a/stdlib/LinearAlgebra/src/symmetriceigen.jl b/stdlib/LinearAlgebra/src/symmetriceigen.jl
@@ -309,19 +309,19 @@ function eigen(A::Hermitian{Complex{T}, <:Tridiagonal}; kwargs...) where {T}
  E = dl
  Er = abs.(E)
  end
- S = Vector{Complex{T}}(undef, N)
+ S = Vector{eigtype(eltype(A))}(undef, N)
  S[1] = 1
  for i ∈ 1:N-1
- S[i+1] = iszero(Er[i]) ? one(Complex{T}) : S[i] * sign(E[i])
+ S[i+1] = iszero(Er[i]) ? oneunit(eltype(S)) : S[i] * sign(E[i])
  end
- B = SymTridiagonal(real(d), Er)
+ B = SymTridiagonal(float.(real.(d)), Er)
  Λ, Φ = eigen(B; kwargs...)
  return Eigen(Λ, Diagonal(S) * Φ)
  end
 end
 
 function eigvals(A::Hermitian{Complex{T}, <:Tridiagonal}; kwargs...) where {T}
  (; dl, d, du) = parent(A)
- E = A.uplo == 'U' ? abs.(du) : abs.(dl)
- eigvals(SymTridiagonal(real.(d), E); kwargs...)
+ Er = A.uplo == 'U' ? abs.(du) : abs.(dl)
+ eigvals(SymTridiagonal(float.(real.(d)), Er); kwargs...)
 end
diff --git a/stdlib/LinearAlgebra/test/symmetriceigen.jl b/stdlib/LinearAlgebra/test/symmetriceigen.jl
@@ -144,4 +144,11 @@ end
  @test e0 ≈ eu
 end
 
+@testset "Hermitian tridiagonal eigen with Complex{Int} elements (#52801)" begin
+ dv, ev = fill(complex(2), 4), fill(3-4im, 3)
+ HT = Hermitian(Tridiagonal(ev, dv, ev))
+ λ, V = eigen(HT)
+ @test HT * V ≈ V * Diagonal(λ)
+end
+
 end # module TestSymmetricEigen