Cover more lu instance types

Author: ChrisRackauckas

Project.toml

@@ -1,6 +1,6 @@
 name = "ArrayInterface"
 uuid = "4fba245c-0d91-5ea0-9b3e-6abc04ee57a9"
-version = "7.5.1"
+version = "7.5.2"
 
 [deps]
 Adapt = "79e6a3ab-5dfb-504d-930d-738a2a938a0e"

src/ArrayInterface.jl

@@ -600,6 +600,28 @@ function lu_instance(jac_prototype::SparseMatrixCSC)
     end
 end
 
+function lu_instance(A::Symmetric{T}) where {T}
+    noUnitT = typeof(zero(T))
+    luT = LinearAlgebra.lutype(noUnitT)
+    ipiv = Vector{LinearAlgebra.BlasInt}(undef, 0)
+    info = zero(LinearAlgebra.BlasInt)
+    return LU{luT}(similar(A, 0, 0), ipiv, info)
+end
+
+noalloc_diag(A::Diagonal) = A.diag
+noalloc_diag(A::Tridiagonal) = A.d
+noalloc_diag(A::SymTridiagonal) = A.dv
+
+function lu_instance(A::Union{Tridiagonal{T},Diagonal{T},SymTridiagonal{T}}) where {T}
+    noUnitT = typeof(zero(T))
+    luT = LinearAlgebra.lutype(noUnitT)
+    ipiv = Vector{LinearAlgebra.BlasInt}(undef, 0)
+    info = zero(LinearAlgebra.BlasInt)
+    vectype = similar(noalloc_diag(A), 0)
+    newA = Tridiagonal(vectype, vectype, vectype)
+    return LU{luT}(newA, ipiv, info)
+end
+
 """
   lu_instance(a::Number) -> a
 

test/core.jl

@@ -71,6 +71,11 @@ end
     A = sprand(50, 50, 0.5)
     @test lu_instance(A) isa typeof(lu(A))
     @test lu_instance(1) === 1
+
+    @test lu_instance(Symmetric(rand(3,3))) isa typeof(lu(Symmetric(rand(4,4))))
+    @test lu_instance(Tridiagonal(rand(3),rand(4),rand(3))) isa typeof(lu(Tridiagonal(rand(3),rand(4),rand(3))))
+    @test lu_instance(SymTridiagonal(rand(4),rand(3))) isa typeof(lu(SymTridiagonal(rand(4),rand(3))))
+    @test lu_instance(Diagonal(rand(4))) isa typeof(lu(Diagonal(rand(4))))
 end
 
 @testset "ismutable" begin