MATLAB Function Reference 
Multidimensional discrete Fourier transform
Syntax
Description
Y = fftn(X)
returns the discrete Fourier transform (DFT) of X
, computed with a multidimensional fast Fourier transform (FFT) algorithm. The result Y
is the same size as X.
Y = fftn(X,siz)
pads X
with zeros, or truncates X
, to create a multidimensional array of size siz
before performing the transform. The size of the result Y
is siz
.
Algorithm
This computes inplace the onedimensional 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 how MATLAB optimizes the algorithm used to compute an FFT of a particular size and dimension.

Data Type Support
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
.
See Also
fft2  fftshift 
© 19942005 The MathWorks, Inc.