get_D.m

function  S  = get_D(X)
    S = sqrt(L2_distance(X, X));
end

% compute squared Euclidean distance
% ||A-B||^2 = ||A||^2 + ||B||^2 - 2*A'*B
function d = L2_distance(a,b)
% a,b: two matrices. each column is a data
% d:   distance matrix of a and b
    if (size(a,1) == 1)
      a = [a; zeros(1,size(a,2))]; 
      b = [b; zeros(1,size(b,2))]; 
    end

    aa=sum(a.*a); bb=sum(b.*b); ab=a'*b; 
    d = repmat(aa',[1 size(bb,2)]) + repmat(bb,[size(aa,2) 1]) - 2*ab;

    d = real(d);
    d = max(d,0);
end