MATLAB Function Reference
ifftn

Multidimensional inverse discrete Fourier transform

Syntax

• ```Y = ifftn(X)
Y = ifftn(X`,`siz)
```

Description

```Y = ifftn(X) ``` returns the n-dimensional 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.`

```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`.

Remarks

For any `X`, `ifftn(fftn(X))` equals `X` within roundoff error. If `X` is real, `ifftn(fftn(X))` may have small imaginary parts.

Algorithm

`ifftn(X)` is equivalent to

• ```Y = X;
for p = 1:length(size(X))
Y = ifft(Y,[],p);
end
```

This computes in-place the one-dimensional inverse DFT along each dimension of `X`.

The execution time for i`fftn` 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.

`fftn`, `ifft`, `ifft2`, i`fftshift`