MATLAB Function Reference    

Inverse discrete Fourier transform



y = ifft(X) returns the inverse discrete Fourier transform (DFT) of vector X, computed with a fast Fourier transform (FFT) algorithm.

If X is a matrix, ifft returns the inverse DFT of each column of the matrix.

If X is a multidimensional array, ifft operates on the first non-singleton dimension.

y = ifft(X,n) returns the n-point inverse DFT of vector X.

y = ifft(X,[],dim) and y = ifft(X,n,dim) return the inverse DFT of X across the dimension dim.

For any X, ifft(fft(X)) equals X to within roundoff error. If X is real, ifft(fft(X)) may have small imaginary parts.


The algorithm for ifft(X) is the same as the algorithm for fft(X), except for a sign change and a scale factor of n = length(X). As for fft, the execution time for ifft 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.

See Also

fft, ifft2, ifftn, ifftshift

dftmtx and freqz, in the Signal Processing Toolbox

  if ifft2