Add diagonal branch to eigfact (#24550)

* Add diagonal branch to eigfact

* Promote to type S

Author: Evey

base/linalg/diagonal.jl

@@ -408,7 +408,12 @@ end
 eigvals(D::Diagonal{<:Number}) = D.diag
 eigvals(D::Diagonal) = [eigvals(x) for x in D.diag] #For block matrices, etc.
 eigvecs(D::Diagonal) = Matrix{eltype(D)}(I, size(D))
-eigfact(D::Diagonal) = Eigen(eigvals(D), eigvecs(D))
+function eigfact(D::Diagonal; permute::Bool=true, scale::Bool=true)
+    if any(!isfinite, D.diag)
+        throw(ArgumentError("matrix contains Infs or NaNs"))
+    end
+    Eigen(eigvals(D), eigvecs(D))
+end
 
 #Singular system
 svdvals(D::Diagonal{<:Number}) = sort!(abs.(D.diag), rev = true)

base/linalg/eigen.jl

@@ -99,7 +99,9 @@ julia> F[:vectors]
 """
 function eigfact(A::StridedMatrix{T}; permute::Bool=true, scale::Bool=true) where T
     S = promote_type(Float32, typeof(one(T)/norm(one(T))))
-    eigfact!(copy_oftype(A, S), permute = permute, scale = scale)
+    AA = copy_oftype(A, S)
+    isdiag(AA) && return eigfact(Diagonal(AA), permute = permute, scale = scale)
+    return eigfact!(AA, permute = permute, scale = scale)
 end
 eigfact(x::Number) = Eigen([x], fill(one(x), 1, 1))