... FFTW - Tutorial . ... This chapter describes the basic usage of FFTW, i.e., how to compute the Fourier transform of a single array. ... Section Words of Wisdom shows how you can save FFTW's plans for future use. ... The transform itself is computed by passing the plan along with the input and output arrays to fftw_one : void fftw_one(fftw_plan plan, fftw_complex *in, fftw_complex *out); . ... We access the complex outputs of the in-place transforms by casting each real array to a fftw_complex...