MATLAB Function Reference 
Multidimensional inverse discrete Fourier transform
Syntax
Description
Y = ifftn(X)
returns the ndimensional inverse discrete Fourier transform (DFT) of X
, computed with a multidimensional fast Fourier transform (FFT) algorithm. The result Y
is the same size as X.
ifftn
tests X
to see whether it is conjugate symmetric. If so, the computation is faster and the output is real. An N1
byN2
by ... Nk
array X
is conjugate symmetric if
Y = ifftn(X,siz)
pads X
with zeros, or truncates X
, to create a multidimensional array of size siz
before performing the inverse transform. The size of the result Y
is siz
.
y = ifftn(..., 'symmetric')
causes ifftn
to treat X
as conjugate symmetric. This option is useful when X
is not exactly conjugate symmetric, merely because of roundoff error.
y = ifftn(..., 'nonsymmetric')
is the same as calling ifftn(...)
without the argument 'nonsymmetric'
.
Remarks
For any X
, ifftn(fftn(X))
equals X
within roundoff error.
Algorithm
This computes inplace the onedimensional inverse DFT along each dimension of X
.
The execution time for ifftn
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 ifftn 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
ifftn
supports inputs of data types double
and single
. If you call ifftn
with the syntax y = ifftn(X, ...)
, the output y
has the same data type as the input X
.
See Also
fftn
, fftw
, ifft
, ifft2
, ifftshift
ifft2  ifftshift 
© 19942005 The MathWorks, Inc.