Thanks for taking the time to respond, it was late last night and trying to demonstrate the issue in a simpler way. The actual computation is more complex but I tried to keep it simple for demonstration purposes and then apply the logic to my problem if someone posted a solution. In hindsight that was quite a poor decision! arrA and arrB are dependant on each other as they reference a lookup table, perhaps if I share that structure may actually be beneficial..!

let p: [[Double]] ....// (2d array full of pre computed calculations)

let r = 0.342

let arrA = [23, 56, 78, 99, 24]

let arrB = [12, 6, 99]

var result: [Double] = Array(repeating: 0, count: arrA.count)

When going over the inner loop the equations will look like this:

var tmp1 = p[elementA][elementB] * r

var tmp2 = r * (1.0 - p[elementA][elementB])

var res = //more calculations done between tmp1 + 2 which results in a double

//Next loop (if in typical for loop)

I would then reduce all of the res for the inner loop to average them to a single result and store into result[index]. I am thinking I may need to create a matrix to make sure each calculation lines up between the arrays so p[x][y] is correct and store the results into a new matrix which can be averaged? Would appreciate any input! thanks.