zDistance

 zDistance(A,B) finds the Euclidean distances between the rows of A and of B

0001 % zDistance(A,B) finds the Euclidean distances between the rows of A and of B
0002 
0003 function [D] = zDistance(A,B)
0004 
0005 [M,t] = size(A);
0006 
0007 if nargin < 2,
0008 
0009   G = A * A';                        % inner products of rows of A
0010 
0011   a = diag(G);                       % sums of squares of each row of A
0012 
0013   X = repmat(a,1,M);                 % repeat a in each row
0014 
0015   D = sqrt(X + X' - 2*G);            % |u-v| = |u|^2 + |v|^2 - 2 u . v
0016 
0017 else
0018 
0019   a = sum((A.*A)');                  % sum of squares of each row of A
0020   b = sum((B.*B)');                  % sum of squares of each row of B
0021 
0022   M = length(a);                     % number of rows in A
0023   N = length(b);                     % number of rows in B
0024 
0025   X = repmat(b,M,1);                 % repeat a in each row
0026   Y = repmat(a',1,N);                % repeat b in each column
0027 
0028   G = A * B';                        % inner products of rows of A
0029 
0030   D = sqrt(X + Y - 2*G);             % |u-v| = |u|^2 + |v|^2 - 2 u . v
0031 
0032 end