add issparse and sparsearray

Author: huanglangwen

src/ArrayInterface.jl

@@ -20,11 +20,23 @@ ismutable(x) = ismutable(typeof(x))
 ismutable(::Type{<:Array}) = true
 ismutable(::Type{<:Number}) = false
 
+"""
+    ArrayInterface.issparse(x::AbstractArray)
+
+determine whether `findstructralnz` accepts the parameter `x`
+"""
+ArrayInterface.issparse(x::AbstractArray)=false
+ArrayInterface.issparse(x::SparseMatrixCSC)=true
+ArrayInterface.issparse(x::Diagonal)=true
+ArrayInterface.issparse(x::Bidiagonal)=true
+ArrayInterface.issparse(x::Tridiagonal)=true
+ArrayInterface.issparse(x::SymTridiagonal)=true
+
 """
     findstructralnz(x::AbstractArray)
 
 Return: (I,J) #indexable objects
-Find sparsity pattern of special matrices, similar to first two elements of findnz(::SparseCSCMatrix)
+Find sparsity pattern of special matrices, similar to first two elements of findnz(::SparseMatrixCSC)
 """
 function findstructralnz(x::Diagonal)
   n=size(x,1)
@@ -84,6 +96,11 @@ function findstructralnz(x::Union{Tridiagonal,SymTridiagonal})
   (rowind,colind)
 end
 
+function findstructralnz(x::SparseMatrixCSC)
+  rowind,colind,_=findnz(x)
+  (rowind,colind)
+end
+
 function __init__()
 
   @require StaticArrays="90137ffa-7385-5640-81b9-e52037218182" begin

test/runtests.jl

@@ -6,21 +6,31 @@ using StaticArrays
 @test ArrayInterface.ismutable(@SVector [1,2,3]) == false
 @test ArrayInterface.ismutable(@MVector [1,2,3]) == true
 
-using LinearAlgebra
+using LinearAlgebra, SparseArrays
 D=Diagonal([1,2,3,4])
+@test ArrayInterface.issparse(D)
 rowind,colind=findstructralnz(D)
 @test [D[rowind[i],colind[i]] for i in 1:4]==[1,2,3,4]
 
 Bu = Bidiagonal([1,2,3,4], [7,8,9], :U)
+@test ArrayInterface.issparse(Bu)
 rowind,colind=findstructralnz(Bu)
 @test [Bu[rowind[i],colind[i]] for i in 1:7]==[1,7,2,8,3,9,4]
 Bl = Bidiagonal([1,2,3,4], [7,8,9], :L)
+@test ArrayInterface.issparse(Bl)
 rowind,colind=findstructralnz(Bl)
 @test [Bl[rowind[i],colind[i]] for i in 1:7]==[1,7,2,8,3,9,4]
 
 Tri=Tridiagonal([1,2,3],[1,2,3,4],[4,5,6])
+@test ArrayInterface.issparse(Tri)
 rowind,colind=findstructralnz(Tri)
 @test [Tri[rowind[i],colind[i]] for i in 1:10]==[1,2,3,4,4,5,6,1,2,3]
 STri=SymTridiagonal([1,2,3,4],[5,6,7])
+@test ArrayInterface.issparse(STri)
 rowind,colind=findstructralnz(STri)
 @test [STri[rowind[i],colind[i]] for i in 1:10]==[1,2,3,4,5,6,7,5,6,7]
+
+Sp=sparse([1,2,3],[1,2,3],[1,2,3])
+@test ArrayInterface.issparse(Sp)
+rowind,colind=findstructralnz(Sp)
+@test [Tri[rowind[i],colind[i]] for i in 1:3]==[1,2,3]