This module computes the Discrete Fourier Transform of a complex signal 
using the Fast Fourier Transform (FFT) algorithm of Cooley and Tukey
(see \cite{cooley.tukey:fft}, \cite{press.flannery.ea:numerical}).
It can also compute the Inverse Discrete Fourier Transform, by selecting 
the \verb+-i+ option.
Notice that, in this module, complex signals are represented by two fsignals: 
the first one contains the real part of the signal and the second one 
contains its imaginary part. 
\index{Fourier Transform}

