\section{FFTN N-Dimensional Forward FFT }

\subsection{Usage}

Computes the DFT of an N-dimensional numerical array along all
dimensions.  The general syntax for its use is
\begin{verbatim}
  y = fftn(x)
\end{verbatim}
which computes the same-size FFTs for each dimension of \verb|x|.
Alternately, you can specify the size vector
\begin{verbatim}
  y = fftn(x,dims)
\end{verbatim}
where \verb|dims| is a vector of sizes.  The array \verb|x| is zero padded
or truncated as necessary in each dimension so that the output
is of size \verb|dims|. The \verb|fftn| function is implemented by a sequence
of calls to \verb|fft|.
