Create a copy while evaluating eigvals(::Diagonal) (#45048)

JuliaLang · May 2, 2022 · b9d8280 · b9d8280
1 parent ef1c9ce
commit b9d8280
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diff --git a/stdlib/LinearAlgebra/src/diagonal.jl b/stdlib/LinearAlgebra/src/diagonal.jl
@@ -704,7 +704,7 @@ function pinv(D::Diagonal{T}, tol::Real) where T
 end
 
 #Eigensystem
-eigvals(D::Diagonal{<:Number}; permute::Bool=true, scale::Bool=true) = D.diag
+eigvals(D::Diagonal{<:Number}; permute::Bool=true, scale::Bool=true) = copy(D.diag)
 eigvals(D::Diagonal; permute::Bool=true, scale::Bool=true) =
     [eigvals(x) for x in D.diag] #For block matrices, etc.
 eigvecs(D::Diagonal) = Matrix{eltype(D)}(I, size(D))

diff --git a/stdlib/LinearAlgebra/test/diagonal.jl b/stdlib/LinearAlgebra/test/diagonal.jl
@@ -465,6 +465,13 @@ end
     @test sort([eigvals(D)...;], by=LinearAlgebra.eigsortby) ≈ eigvals([D.diag[1] zeros(3,2); zeros(2,3) D.diag[2]])
 end
 
+@testset "eigvals should return a copy of the diagonal" begin
+    D = Diagonal([1, 2, 3])
+    lam = eigvals(D)
+    D[3,3] = 4 # should not affect lam
+    @test lam == [1, 2, 3]
+end
+
 @testset "eigmin (#27847)" begin
     for _ in 1:100
         d = randn(rand(1:10))