Generalize Bidiagonal/Tridiagonal constructors

Author: jishnub

src/bidiag.jl

@@ -109,8 +109,8 @@ julia> Bidiagonal(A, :L) # contains the main diagonal and first subdiagonal of A
  ⋅  ⋅  4  4
 ```
 """
-function Bidiagonal(A::AbstractMatrix, uplo::Symbol)
-    Bidiagonal(diag(A, 0), diag(A, uplo === :U ? 1 : -1), uplo)
+function (::Type{Bi})(A::AbstractMatrix, uplo::Symbol) where {Bi<:Bidiagonal}
+    Bi(diag(A, 0), diag(A, uplo === :U ? 1 : -1), uplo)
 end
 
 

src/diagonal.jl

@@ -99,9 +99,7 @@ julia> Diagonal(A)
  ⋅  5
 ```
 """
-Diagonal(A::AbstractMatrix) = Diagonal(diag(A))
-Diagonal{T}(A::AbstractMatrix) where T = Diagonal{T}(diag(A))
-Diagonal{T,V}(A::AbstractMatrix) where {T,V<:AbstractVector{T}} = Diagonal{T,V}(diag(A))
+(::Type{D})(A::AbstractMatrix) where {D<:Diagonal} = D(diag(A))
 function convert(::Type{T}, A::AbstractMatrix) where T<:Diagonal
     checksquare(A)
     isdiag(A) ? T(A) : throw(InexactError(:convert, T, A))

src/tridiag.jl

@@ -590,7 +590,7 @@ julia> Tridiagonal(A)
  ⋅  ⋅  3  4
 ```
 """
-Tridiagonal(A::AbstractMatrix) = Tridiagonal(diag(A,-1), diag(A,0), diag(A,1))
+(::Type{Tri})(A::AbstractMatrix) where {Tri<:Tridiagonal} = Tri(diag(A,-1), diag(A,0), diag(A,1))
 
 Tridiagonal(A::Tridiagonal) = A
 Tridiagonal{T}(A::Tridiagonal{T}) where {T} = A

test/bidiag.jl

@@ -1165,6 +1165,12 @@ end
     M = diagm(0 => [1,2,3], -1=>[4,5])
     B = convert(Bidiagonal, M)
     @test B == Bidiagonal(M, :L)
+    B = convert(Bidiagonal{Int8}, M)
+    @test B == M
+    @test B isa Bidiagonal{Int8, Vector{Int8}}
+    B = convert(Bidiagonal{Int8, OffsetVector{Int8, Vector{Int8}}}, M)
+    @test B == M
+    @test B isa Bidiagonal{Int8, OffsetVector{Int8, Vector{Int8}}}
     M = diagm(-1 => [1,2], 1=>[4,5])
     @test_throws InexactError convert(Bidiagonal, M)
 end

test/tridiag.jl

@@ -1106,6 +1106,12 @@ end
                 diagm(-1 => [1,2], 1=>[4,5])]
             B = convert(Tridiagonal, M)
             @test B == Tridiagonal(M)
+            B = convert(Tridiagonal{Int8}, M)
+            @test B == M
+            @test B isa Tridiagonal{Int8}
+            B = convert(Tridiagonal{Int8, OffsetVector{Int8, Vector{Int8}}}, M)
+            @test B == M
+            @test B isa Tridiagonal{Int8, OffsetVector{Int8, Vector{Int8}}}
         end
         @test_throws InexactError convert(Tridiagonal, fill(5, 4, 4))
     end