Discrete Fourier transform.
FFT(X) is the discrete Fourier transform of vector X. If the
length of X is a power of two, a fast radix-2 fast-Fourier
transform algorithm is used. If the length of X is not a
power of two, a slower non-power-of-two algorithm is employed.
FFT(X,N) is the N-point FFT, padded with zeros if X has less
than N points and truncated if it has more.
If X is a matrix, the FFT operation is applied to each column.
See also IFFT1XY3SAB, FFT2 , IFFT2 , FFTSHIFT .