N-D fast Fourier transform
Y = fftn(X)
Y = fftn(X,siz)
fftn supports inputs of data types double and single. If you call fftn with the syntax y = fftn(X, ...), the output y has the same data type as the input X.
fftn(X) is equivalent to
Y = X; for p = 1:length(size(X)) Y = fft(Y,,p); end
This computes in-place the one-dimensional fast Fourier transform along each dimension of X. The execution time for fft depends on the length of the transform. It is fastest for powers of two. It is almost as fast for lengths that have only small prime factors. It is typically several times slower for lengths that are prime or which have large prime factors.
Note You might be able to increase the speed of fftn using the utility function fftw, which controls the optimization of the algorithm used to compute an FFT of a particular size and dimension.