From 222ab12ef74f8cba26f9251d61dfae9c9c8812ec Mon Sep 17 00:00:00 2001
From: Nuwan Yapa <yapanuwan@gmail.com>
Date: Mon, 29 Apr 2024 10:58:24 -0400
Subject: [PATCH] Kronecker sum implemented

---
 helper.jl | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/helper.jl b/helper.jl
index 019871f..96e42e3 100644
--- a/helper.jl
+++ b/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]
@@ -15,4 +17,10 @@ better_sum(arr::Array{ComplexF64}) = better_sum(real.(arr)) + 1im * better_sum(i
 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))]
\ No newline at end of file
+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
\ No newline at end of file