From fb2e0e070d24f7cf0c8687ca72ba84002f0f8f8e Mon Sep 17 00:00:00 2001
From: Jishnu Bhattacharya <jishnub.github@gmail.com>
Date: Wed, 28 Jun 2023 23:19:38 +0530
Subject: [PATCH] kron for AbstractFill

---
 Project.toml       |  2 +-
 src/FillArrays.jl  |  2 +-
 src/fillalgebra.jl | 19 +++++++++++++++++++
 test/runtests.jl   | 22 ++++++++++++++++++++++
 4 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/Project.toml b/Project.toml
index 44a5e5e8..c4182cfd 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,6 +1,6 @@
 name = "FillArrays"
 uuid = "1a297f60-69ca-5386-bcde-b61e274b549b"
-version = "1.2.1"
+version = "1.3.0"
 
 [deps]
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
diff --git a/src/FillArrays.jl b/src/FillArrays.jl
index af3ee9af..3d90f3bb 100644
--- a/src/FillArrays.jl
+++ b/src/FillArrays.jl
@@ -10,7 +10,7 @@ import Base: size, getindex, setindex!, IndexStyle, checkbounds, convert,
 
 import LinearAlgebra: rank, svdvals!, tril, triu, tril!, triu!, diag, transpose, adjoint, fill!,
     dot, norm2, norm1, normInf, normMinusInf, normp, lmul!, rmul!, diagzero, AdjointAbsVec, TransposeAbsVec,
-    issymmetric, ishermitian, AdjOrTransAbsVec, checksquare, mul!
+    issymmetric, ishermitian, AdjOrTransAbsVec, checksquare, mul!, kron
 
 
 import Base.Broadcast: broadcasted, DefaultArrayStyle, broadcast_shape
diff --git a/src/fillalgebra.jl b/src/fillalgebra.jl
index 3dd222c3..b11fa5a2 100644
--- a/src/fillalgebra.jl
+++ b/src/fillalgebra.jl
@@ -434,3 +434,22 @@ fillzero(::Type{Zeros{T,N,AXIS}}, n, m) where {T,N,AXIS} = Zeros{T,N,AXIS}((n, m
 fillzero(::Type{F}, n, m) where F = throw(ArgumentError("Cannot create a zero array of type $F"))
 
 diagzero(D::Diagonal{F}, i, j) where F<:AbstractFill = fillzero(F, axes(D.diag[i], 1), axes(D.diag[j], 2))
+
+# kron
+
+_kronsize(f::AbstractFillVector, g::AbstractFillVector) = (size(f,1)*size(g,1),)
+_kronsize(f::AbstractFillVecOrMat, g::AbstractFillVecOrMat) = (size(f,1)*size(g,1), size(f,2)*size(g,2))
+function _kron(f::AbstractFill, g::AbstractFill, sz)
+    v = getindex_value(f)*getindex_value(g)
+    Fill(v, sz)
+end
+function _kron(f::Zeros, g::Zeros, sz)
+    Zeros{promote_type(eltype(f), eltype(g))}(sz)
+end
+function _kron(f::Ones, g::Ones, sz)
+    Ones{promote_type(eltype(f), eltype(g))}(sz)
+end
+function kron(f::AbstractFillVecOrMat, g::AbstractFillVecOrMat)
+    sz = _kronsize(f, g)
+    _kron(f, g, sz)
+end
diff --git a/test/runtests.jl b/test/runtests.jl
index df8d25db..bd736745 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -1482,6 +1482,28 @@ end
     end
 end
 
+@testset "kron" begin
+    for T in (Fill, Zeros, Ones), sz in ((2,), (2,2))
+        f = T{Int}((T == Fill ? (3,sz...) : sz)...)
+        g = Ones{Int}(2)
+        fc = collect(f)
+        gc = collect(g)
+        @test kron(f, f) == kron(fc, fc)
+        @test kron(f, f) isa T{Int,length(sz)}
+        @test kron(f, g) == kron(fc, gc)
+        @test kron(f, g) isa AbstractFill{Int,length(sz)}
+        @test kron(g, f) == kron(gc, fc)
+        @test kron(g, f) isa AbstractFill{Int,length(sz)}
+        @test kron(f, f .+ 0.5) == kron(fc, fc .+ 0.5)
+        @test kron(f, f .+ 0.5) isa AbstractFill{Float64,length(sz)}
+        @test kron(f, g .+ 0.5) isa AbstractFill{Float64,length(sz)}
+    end
+
+    E = Eye(2)
+    @test kron(E, E) isa typeof(E)
+    @test kron(E, E) == kron(collect(E), collect(E))
+end
+
 @testset "dot products" begin
     n = 15
     o = Ones(1:n)