Kron for Fun and UniformScaling (#499)

* define types in \otimes, and kron for Fun and I

* version bump to v0.8.40

* don't restrict \otimes

* Add tests

* Add test for I ⊗ x

Author: jishnub

Project.toml

@@ -1,6 +1,6 @@
 name = "ApproxFunBase"
 uuid = "fbd15aa5-315a-5a7d-a8a4-24992e37be05"
-version = "0.8.39"
+version = "0.8.40"
 
 [deps]
 AbstractFFTs = "621f4979-c628-5d54-868e-fcf4e3e8185c"

src/Multivariate/Multivariate.jl

@@ -110,3 +110,5 @@ function Base.kron(f::Fun,g::Fun)
 end
 Base.kron(f::Fun,g::Number) = kron(f,Fun(g))
 Base.kron(f::Number,g::Fun) = kron(Fun(f),g)
+Base.kron(f::Fun,g::UniformScaling) = kron(f,Operator(g))
+Base.kron(f::UniformScaling,g::Fun) = kron(Operator(f),g)

test/PolynomialSpacesTests.jl

@@ -203,7 +203,7 @@ Base.:(==)(a::UniqueInterval, b::UniqueInterval) = (@assert a.parentinterval ==
         @test f(0.5)*g(0.5) ≈ (f*g)(0.5)
     end
 
-    @testset "Multivariate" begin
+    @testset "ArraySpace" begin
         @testset for S in Any[Chebyshev(), Legendre()]
             f = Fun(x->ones(2,2), S)
             @test (f+1) * f ≈ (1+f) * f ≈ f^2 + f
@@ -213,6 +213,16 @@ Base.:(==)(a::UniqueInterval, b::UniqueInterval) = (@assert a.parentinterval ==
         end
     end
 
+    @testset "Multivariate" begin
+        @testset "kron" begin
+            x = Fun()
+            O = x ⊗ I
+            @test O * Fun((x,y)->x^2 * y^2, Chebyshev()^2) ≈ Fun((x,y)->x^3 * y^2, Chebyshev()^2)
+            O = I ⊗ x
+            @test O * Fun((x,y)->x^2 * y^2, Chebyshev()^2) ≈ Fun((x,y)->x^2 * y^3, Chebyshev()^2)
+        end
+    end
+
     @testset "static coeffs" begin
         f = Fun(Chebyshev(), SA[1,2,3])
         g = Fun(Chebyshev(), [1,2,3])