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%                                                                             %
% PAIRWISE VECTOR DIFFERENCE                                                  %
%  (c) 2009 Joseph Rushton Wakeling                                           %
%                                                                             %
%  Special thanks to Jaroslav Hajek for suggesting these implementations      %
%  for efficient pairwise vector diff calculation.                            %
%                                                                             %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
% This function calculates the pairwise differences between the columns of a
% given matrix X, returning a 3D matrix D such that
%
%     D(:,i,j) = X(:,i) - X(:,j)
%
function D = pairwisediff(X)

	if(exist('bsxfun')~=0)
		D = bsxfun( @minus, X, reshape(X,size(X,1),1,size(X,2)) );
	else
		XX = reshape(X,size(X,1),1,size(X,2));
		D = X(:, :, ones(1,size(X,2)) ) - XX(:, ones(1,size(X,2)), :);
	end

end