1. The problem statement, all variables and given/known data Is there a good way to do a fit. The fft looks simple: I am trying to fit data from my experiment to the very nonlinear nested sine function given as equation 3 here: http://www.physics.umd.edu/courses/Phys375/HillSpring10/Labs/Lab5Diffraction.pdf 2. Relevant equations see above 3. The attempt at a solution I am using matlab, the model function is crazy! Though the data looks good in fourier space.