function D = sqdist(X1, X2)
% Pairwise square Euclidean distance between two sample sets
% Input:
%   X1, X2: dxn1 dxn2 sample matrices
% Output:
%   D: n1 x n2 square Euclidean distance matrix
% Written by Mo Chen (sth4nth@gmail.com).
D = dot(X1,X1,1)'+dot(X2,X2,1)-2*(X1'*X2);