Kronecker sum implemented

helper.jl

@@ -1,3 +1,5 @@
+using LinearAlgebra
+
 "Sum over array while minimizing catastrophic cancellation as much as possible"
 function better_sum(arr::Array{Float64})
     pos_arr = arr[arr .> 0]
@@ -16,3 +18,9 @@ triangle_ineq(l1, l2, L) = abs(l1 - l2) ≤ L && L ≤ (l1 + l2)
 
 "Nearest value in a list to a given reference point"
 nearest(list::Array, ref) = list[argmin(norm.(list .- ref))]
+
+"Simple implementation of the Kronecker sum"
+function kron_sum(A::AbstractMatrix, B::AbstractMatrix)
+    @assert size(A, 1) == size(A, 2) && size(B, 1) == size(B, 2) "Matrices should be square"
+    return kron(A, I(size(B, 1))) + kron(B, I(size(A, 1)))
+end