function d = fastEuclideanDistance(a,b)

% DISTANCE - computes Euclidean distance matrix

%

% E = distance(A,B)

%

%    A - (DxM) matrix 

%    B - (DxN) matrix

%

% Returns:

%    E - (MxN) Euclidean distances between vectors in A and B

%

%

% Description : 

%    This fully vectorized (VERY FAST!) m-file computes the 

%    Euclidean distance between two vectors by:

%

%                 ||A-B|| = sqrt ( ||A||^2 + ||B||^2 - 2*A.B )

%

% Example : 

%    A = rand(400,100); B = rand(400,200);

%    d = distance(A,B);

% Author   : Roland Bunschoten

%            University of Amsterdam

%            Intelligent Autonomous Systems (IAS) group

%            Kruislaan 403  1098 SJ Amsterdam

%            tel.(+31)20-5257524

%            bunschot@wins.uva.nl

% Last Rev : Oct 29 16:35:48 MET DST 1999

% Tested   : PC Matlab v5.2 and Solaris Matlab v5.3

% Thanx    : Nikos Vlassis

% Copyright notice: You are free to modify, extend and distribute 

%    this code granted that the author of the original code is 

%    mentioned as the original author of the code.

if (nargin ~= 2)

   error('Not enough input arguments');

end

if (size(a,1) ~= size(b,1))

   error('A and B should be of same dimensionality');

end

aa=sum(a.*a,1); bb=sum(b.*b,1); ab=a'*b; 

d = sqrt(abs(repmat(aa',[1 size(bb,2)]) + repmat(bb,[size(aa,2) 1]) - 2*ab));