Backport: Fix kron product on sum spaces #640 (#641)

Author: jishnub

Project.toml

@@ -1,6 +1,6 @@
 name = "ApproxFunBase"
 uuid = "fbd15aa5-315a-5a7d-a8a4-24992e37be05"
-version = "0.8.65"
+version = "0.8.66"
 
 [deps]
 AbstractFFTs = "621f4979-c628-5d54-868e-fcf4e3e8185c"

src/Multivariate/Multivariate.jl

@@ -94,11 +94,12 @@ function Base.kron(f::Fun,g::Fun)
     sp=space(f)⊗space(g)
     it=tensorizer(sp)
     N=ncoefficients(f);M=ncoefficients(g)
+    n=ncomponents(f);m=ncomponents(g)
     cfs=Array{promote_type(cfstype(f),cfstype(g))}(undef,0)
     for (k,j) in it
-        # Tensor product is N x M, so if we are outside
-        # the (N+M)th diagonal we have no more entries
-        if k+j > N+M
+        # Tensor product is n*N x m*M, so if we are outside
+        # the (n*N+m*M)th diagonal we have no more entries
+        if k+j > N*n+M*m
             break
         elseif k ≤ N && j ≤ M
             push!(cfs,f.coefficients[k]*g.coefficients[j])