used by "fftfreq()".
Parameters:
      * input (Tensor) -- the tensor in FFT order
  * **dim** (*int**, **Tuple**[**int**]**, **optional*) -- The
    dimensions to rearrange. Only dimensions specified here will
    be rearranged, any other dimensions will be left in their
    original order. Default: All dimensions of "input".

-[ Example ]-



f = torch.fft.fftfreq(4)
f
   tensor([ 0.0000,  0.2500, -0.5000, -0.2500])
torch.fft.fftshift(f)
   tensor([-0.5000, -0.2500,  0.0000,  0.2500])



Also notice that the Nyquist frequency term at "f[2]" was moved to
   the beginning of the tensor.
This also works for multi-dimensional transforms:



x = torch.fft.fftfreq(5, d=1/5) + 0.1 * torch.fft.fftfreq(5, d=1/5).unsqueeze(1)
x
   tensor([[ 0.0000,  1.0000,  2.0000, -2.0000, -1.0000],
           [ 0.1000,  1.1000,  2.1000, -1.9000, -0.9000],
           [ 0.2000,  1.2000,  2.2000, -1.8000, -0.8000],


