% FFTSHIFT FFTSHIFT Shift FFT Output
% 
% Usage
% 
% The 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
% 
%      y = fftshift(x).
% 
% Alternately, you can specify that only one dimension be shifted
% 
%      y = fftshift(x,dim).
% 

% Copyright (c) 2002-2006 Samit Basu

function y = fftshift(x,dim)
if (nargin > 1)
  if (numel(dim) ~= 1 | dim ~= floor(dim(1)) | dim < 1)
    error('dim must be a positive scalar integer');
  end
  shiftvec = zeros(1,dim);
  shiftvec(dim) = floor(size(x,dim)/2);
else
  shiftvec = floor(size(x)/2);
end
y = circshift(x,shiftvec);