Compute the inverse of fftn.
a : array
s : sequence (int)
axis : int
The n-dimensional ifft of a. s is a sequence giving the shape of the input an result along the transformed axes, as n for fft. Results are packed analogously to fft: the term for zero frequency in all axes is in the low-order corner, while the term for the Nyquist frequency in all axes is in the middle.
If neither s nor axes is specified, the transform is taken along all axes. If s is specified and axes is not, the last len(s) axes are used. If axes are specified and s is not, the input shape along the specified axes is used. If s and axes are both specified and are not the same length, an exception is raised.