Thanks for the reply. There’s a lot to unpack there.
I was able to take the brute force approach and replicate the code on the CPU using a 256 x 256 grid. The results were accurate to within a few hundredths of a cm.
However, when I change the grid to 32 x 32 the results aren’t even close. The spectrum grid ends up a with much higher numbers due to the k^4 denominator. I could start reducing the PatchLength and/or Amplitudes to accommodate but that doesn’t seem like the right way to go about it.
Can you think of anything offhand that would need to be adjusted besides the GridSize, HalfGridSize, Ping Pong array length, and butterfly count constants when reducing the size from 256 to 32?