function [affinity] = CalculateAffinity(data)

% set the parameters
sigma = 1;
data = full(data);
affinity = zeros(size(data,1), size(data,2));
for i=1:size(data,1)    
    for j=i:size(data,2)
        dist = sqrt(norm(data(i,:) - data(j,:)));
        %dist = sqrt((data(i,1) - data(j,1))^2 + (data(i,2) - data(j,2))^2); 
        affinity(i,j) = dist;
        affinity(j,i) = affinity(i,j);
    end
end
affinity = exp(-affinity./(2*sigma^2));
affinity = sparse(affinity);