\section{FFTSHIFT Shift FFT Output}

\subsection{Usage}

The \verb|fftshift| function shifts the DC component (zero-frequency)
of the output from an FFT to the center of the array.  For vectors
this means swapping the two halves of the vector.  For matrices,
the first and third quadrants are swapped.  So on for N-dimensional
arrays.  The syntax for its use is
\begin{verbatim}
     y = fftshift(x).
\end{verbatim}
Alternately, you can specify that only one dimension be shifted
\begin{verbatim}
     y = fftshift(x,dim).
\end{verbatim}
