I use a pseudospectral DNS code for fluid simulations (a code I inherited) and I’m trying to boost performance by replacing the old FFT routines with equivalent FFTW routines. I have done this successfully in that I am getting the correct answers in my test cases, but I feel like I’m doing some things inefficiently, and I would appreciate tips on specific things that might improve my code. I will show a sample code snippet of the FFT routines and then ask specific questions based on what I’ve observed so far.