Extension of a radix-2 fast Fourier transform (FFT) program to include a prime factor

A simple procedure is presented to develop a fast Fourier transform (FFT) program for PQ points starting from a program for Q points, with emphasis on Q = 2
^M
. The transformation with respect to the factor P is followed by a transformation of P groups of Q points each using the existing subroutine, then the array is unscrambled with respect to P.