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Circular Shift That Centers a Discrete Fourier Transform
Syntax fftshift(z)
See Also dft , fft

circularly shifts the elements of the matrix z so that the first row corresponds to the center row of that result, and the first column of z corresponds to the center column of the result.

Fourier Transforms
If z is a vector and the result of a one dimensional discrete transform or if it is a matrix and the result of a two dimension discrete transform, fftshift shifts the zero frequency to the center of the grid.

If you enter
     z = 1 :: 4
O-Matrix will reply

In O-Matrix mode, the routine dft performs the discrete transform and the routine fft does this shifting automatically. In Mlmode , fft is the discrete transform.