Fix kron ambiguity for triangular/hermitian matrices (#54413)

stdlib/LinearAlgebra/src/symmetric.jl

@@ -525,28 +525,26 @@ for (T, trans, real) in [(:Symmetric, :transpose, :identity), (:(Hermitian{<:Uni
     end
 end
 
-function kron(A::Hermitian{T}, B::Hermitian{S}) where {T<:Union{Real,Complex},S<:Union{Real,Complex}}
+function kron(A::Hermitian{<:Union{Real,Complex},<:StridedMatrix}, B::Hermitian{<:Union{Real,Complex},<:StridedMatrix})
     resultuplo = A.uplo == 'U' || B.uplo == 'U' ? :U : :L
-    C = Hermitian(Matrix{promote_op(*, T, S)}(undef, _kronsize(A, B)), resultuplo)
+    C = Hermitian(Matrix{promote_op(*, eltype(A), eltype(B))}(undef, _kronsize(A, B)), resultuplo)
     return kron!(C, A, B)
 end
-
-function kron(A::Symmetric{T}, B::Symmetric{S}) where {T<:Number,S<:Number}
+function kron(A::Symmetric{<:Number,<:StridedMatrix}, B::Symmetric{<:Number,<:StridedMatrix})
     resultuplo = A.uplo == 'U' || B.uplo == 'U' ? :U : :L
-    C = Symmetric(Matrix{promote_op(*, T, S)}(undef, _kronsize(A, B)), resultuplo)
+    C = Symmetric(Matrix{promote_op(*, eltype(A), eltype(B))}(undef, _kronsize(A, B)), resultuplo)
     return kron!(C, A, B)
 end
 
-function kron!(C::Hermitian{<:Union{Real,Complex}}, A::Hermitian{<:Union{Real,Complex}}, B::Hermitian{<:Union{Real,Complex}})
+function kron!(C::Hermitian{<:Union{Real,Complex},<:StridedMatrix}, A::Hermitian{<:Union{Real,Complex},<:StridedMatrix}, B::Hermitian{<:Union{Real,Complex},<:StridedMatrix})
     size(C) == _kronsize(A, B) || throw(DimensionMismatch("kron!"))
     if ((A.uplo == 'U' || B.uplo == 'U') && C.uplo != 'U') || ((A.uplo == 'L' && B.uplo == 'L') && C.uplo != 'L')
         throw(ArgumentError("C.uplo must match A.uplo and B.uplo, got $(C.uplo) $(A.uplo) $(B.uplo)"))
     end
     _hermkron!(C.data, A.data, B.data, conj, real, A.uplo, B.uplo)
     return C
 end
-
-function kron!(C::Symmetric{<:Number}, A::Symmetric{<:Number}, B::Symmetric{<:Number})
+function kron!(C::Symmetric{<:Number,<:StridedMatrix}, A::Symmetric{<:Number,<:StridedMatrix}, B::Symmetric{<:Number,<:StridedMatrix})
     size(C) == _kronsize(A, B) || throw(DimensionMismatch("kron!"))
     if ((A.uplo == 'U' || B.uplo == 'U') && C.uplo != 'U') || ((A.uplo == 'L' && B.uplo == 'L') && C.uplo != 'L')
         throw(ArgumentError("C.uplo must match A.uplo and B.uplo, got $(C.uplo) $(A.uplo) $(B.uplo)"))
@@ -555,7 +553,7 @@ function kron!(C::Symmetric{<:Number}, A::Symmetric{<:Number}, B::Symmetric{<:Nu
     return C
 end
 
-function _hermkron!(C, A, B, conj::TC, real::TR, Auplo, Buplo) where {TC,TR}
+function _hermkron!(C, A, B, conj, real, Auplo, Buplo)
     n_A = size(A, 1)
     n_B = size(B, 1)
     @inbounds if Auplo == 'U' && Buplo == 'U'

stdlib/LinearAlgebra/src/triangular.jl

@@ -763,23 +763,21 @@ for op in (:+, :-)
     end
 end
 
-function kron(A::UpperTriangular{T}, B::UpperTriangular{S}) where {T<:Number,S<:Number}
-    C = UpperTriangular(Matrix{promote_op(*, T, S)}(undef, _kronsize(A, B)))
+function kron(A::UpperTriangular{<:Number,<:StridedMaybeAdjOrTransMat}, B::UpperTriangular{<:Number,<:StridedMaybeAdjOrTransMat})
+    C = UpperTriangular(Matrix{promote_op(*, eltype(A), eltype(B))}(undef, _kronsize(A, B)))
     return kron!(C, A, B)
 end
-
-function kron(A::LowerTriangular{T}, B::LowerTriangular{S}) where {T<:Number,S<:Number}
-    C = LowerTriangular(Matrix{promote_op(*, T, S)}(undef, _kronsize(A, B)))
+function kron(A::LowerTriangular{<:Number,<:StridedMaybeAdjOrTransMat}, B::LowerTriangular{<:Number,<:StridedMaybeAdjOrTransMat})
+    C = LowerTriangular(Matrix{promote_op(*, eltype(A), eltype(B))}(undef, _kronsize(A, B)))
     return kron!(C, A, B)
 end
 
-function kron!(C::UpperTriangular{<:Number}, A::UpperTriangular{<:Number}, B::UpperTriangular{<:Number})
+function kron!(C::UpperTriangular{<:Number,<:StridedMaybeAdjOrTransMat}, A::UpperTriangular{<:Number,<:StridedMaybeAdjOrTransMat}, B::UpperTriangular{<:Number,<:StridedMaybeAdjOrTransMat})
     size(C) == _kronsize(A, B) || throw(DimensionMismatch("kron!"))
     _triukron!(C.data, A.data, B.data)
     return C
 end
-
-function kron!(C::LowerTriangular{<:Number}, A::LowerTriangular{<:Number}, B::LowerTriangular{<:Number})
+function kron!(C::LowerTriangular{<:Number,<:StridedMaybeAdjOrTransMat}, A::LowerTriangular{<:Number,<:StridedMaybeAdjOrTransMat}, B::LowerTriangular{<:Number,<:StridedMaybeAdjOrTransMat})
     size(C) == _kronsize(A, B) || throw(DimensionMismatch("kron!"))
     _trilkron!(C.data, A.data, B.data)
     return C

stdlib/LinearAlgebra/test/symmetric.jl

@@ -580,6 +580,15 @@ end
     @test kron(A, B) ≈ kron(Symmetric(A), Symmetric(B))
 end
 
+@testset "kron with symmetric/hermitian matrices of matrices" begin
+    M = fill(ones(2,2), 2, 2)
+    for W in (Symmetric, Hermitian)
+        for (t1, t2) in ((W(M, :U), W(M, :U)), (W(M, :U), W(M, :L)), (W(M, :L), W(M, :L)))
+            @test kron(t1, t2) ≈ kron(Matrix(t1), Matrix(t2))
+        end
+    end
+end
+
 #Issue #7647: test xsyevr, xheevr, xstevr drivers.
 @testset "Eigenvalues in interval for $(typeof(Mi7647))" for Mi7647 in
         (Symmetric(diagm(0 => 1.0:3.0)),

stdlib/LinearAlgebra/test/triangular.jl

@@ -1052,6 +1052,14 @@ end
     end
 end
 
+@testset "kron with triangular matrices of matrices" begin
+    for T in (UpperTriangular, LowerTriangular)
+        t = T(fill(ones(2,2), 2, 2))
+        m = Matrix(t)
+        @test kron(t, t) ≈ kron(m, m)
+    end
+end
+
 @testset "copyto! with aliasing (#39460)" begin
     M = Matrix(reshape(1:36, 6, 6))
     @testset for T in (UpperTriangular, LowerTriangular)