refactor: loop interchange for contiguous access

Author: Chaitanya Kumar

Benchmarks/ShallowWaterPDE/Solution.swift

@@ -43,8 +43,8 @@ struct Solution: Differentiable {
     func evolve() -> Self {
         var newWaterLevel = currentWaterLevel
 
-        for x in 1 ..< resolution - 1 {
-            for y in 1 ..< resolution - 1 {
+        for y in 1 ..< resolution - 1 {
+            for x in 1 ..< resolution - 1 {
                 // FIXME: Should be u2[x][y] = ...
                 let newValue: Float = 2 * currentWaterLevel[x, y] + (c * c * dt * dt + c * a * dt) * currentWaterLevel.laplace(x, y) * Float(resolution * resolution) - previousWaterLevel[x, y] - c * a * dt * previousWaterLevel.laplace(x, y) * Float(resolution * resolution)
                 newWaterLevel[x, y] = newValue

Benchmarks/ShallowWaterPDE/Storage+Float.swift

@@ -16,8 +16,8 @@ extension Array2DStorage where Element == Float {
     func meanSquaredError(to target: Array2DStorage<Float>) -> Float {
         var mse: Float = 0.0
 
-        for x in 0 ..< withoutDerivative(at: width) {
-            for y in 0 ..< withoutDerivative(at: height) {
+        for y in 0 ..< withoutDerivative(at: height) {
+            for x in 0 ..< withoutDerivative(at: width) {
                 let error = target[x, y] - self[x, y]
                 mse += error * error
             }