Public function to access the uplo for Symmetric/Hermitian

src/LinearAlgebra.jl

@@ -181,7 +181,8 @@ public AbstractTriangular,
         zeroslike,
         matprod_dest,
         fillstored!,
-        fillband!
+        fillband!,
+        uplo
 
 const BlasFloat = Union{Float64,Float32,ComplexF64,ComplexF32}
 const BlasReal = Union{Float64,Float32}

src/bidiag.jl

@@ -115,6 +115,13 @@ Bidiagonal(A::Bidiagonal) = A
 Bidiagonal{T}(A::Bidiagonal{T}) where {T} = A
 Bidiagonal{T}(A::Bidiagonal) where {T} = Bidiagonal{T}(A.dv, A.ev, A.uplo)
 
+"""
+    LinearAlgebra.uplo(S::Bidiagonal)::Symbol
+
+Return a `Symbol` corresponding to whether the upper or lower off-diagonal band is stored.
+"""
+uplo(::Bidiagonal) = sym_uplo(B.uplo)
+
 _offdiagind(uplo) = uplo == 'U' ? 1 : -1
 
 @inline function Base.isassigned(A::Bidiagonal, i::Int, j::Int)

src/symmetric.jl

@@ -237,6 +237,33 @@ nonhermitianwrappertype(::SymSymTri{<:Real}) = Symmetric
 nonhermitianwrappertype(::Hermitian{<:Real}) = Symmetric
 nonhermitianwrappertype(::Hermitian) = identity
 
+"""
+    LinearAlgebra.uplo(S::Union{Symmetric, Hermitian})::Symbol
+
+Return a `Symbol` corresponding to the stored triangular half in the matrix `S`,
+that is, the elements are common between `S` and `parent(S)` for that triangular half.
+
+# Example
+```jldoctest
+julia> S = Symmetric([1 2; 3 4], :U)
+2×2 Symmetric{Int64, Matrix{Int64}}:
+ 1  2
+ 2  4
+
+julia> LinearAlgebra.uplo(S)
+:U
+
+julia> H = Hermitian([1 2; 3 4], :L)
+2×2 Hermitian{Int64, Matrix{Int64}}:
+ 1  3
+ 3  4
+
+julia> LinearAlgebra.uplo(H)
+:L
+```
+"""
+uplo(S::HermOrSym) = sym_uplo(S.uplo)
+
 size(A::HermOrSym) = size(A.data)
 axes(A::HermOrSym) = axes(A.data)
 @inline function Base.isassigned(A::HermOrSym, i::Int, j::Int)

test/bidiag.jl

@@ -47,6 +47,8 @@ Random.seed!(1)
             # from vectors
             ubd = Bidiagonal(x, y, :U)
             lbd = Bidiagonal(x, y, :L)
+            @test LinearAlgebra.uplo(ubd) == :U
+            @test LinearAlgebra.uplo(lbd) == :L
             @test ubd != lbd || x === dv0
             @test ubd.dv === x
             @test lbd.ev === y

test/symmetric.jl

@@ -1343,4 +1343,11 @@ end
     @test_throws msg LinearAlgebra.fillband!(Symmetric(A), 2, 0, 1)
 end
 
+@testset "uplo" begin
+    S = Symmetric([1 2; 3 4], :U)
+    @test LinearAlgebra.uplo(S) == :U
+    H = Hermitian([1 2; 3 4], :L)
+    @test LinearAlgebra.uplo(H) == :L
+end
+
 end # module TestSymmetric