function d = l2_distance(X,Y)
% d = l2_distance(X)
% Compute pairwise l2 distances between column vectors in X
%
% Warning -- this implementation suffers from cancellation error.
%
% Author: David Ross, June 27, 2003.
%

if nargin == 1

    [D N] = size(X);

    lengths = sum(X.^2,1);
    d = repmat(lengths,[N 1]) + repmat(lengths',[1 N]);
    d = d - 2* X'*X;
    
elseif nargin == 2
    XX = sum(X.^2,1);
    YY = sum(Y.^2,1);
    d = repmat(XX', [1 size(Y,2)]) + repmat(YY, [size(X,2) 1]);
    d = d - 2*X'*Y;
    
else
    error('must have 1 or 2 arguments');
end