function corr = correlation(X, Y, ranking) 
%Compute the correlations between columns of matrices 

if (nargin < 2)
    fprintf('%s\n', help(sprintf('%s', mfilename)));
    error('Incorrect number of inputs - see above usage instructions.');
end

corr = sum(X.*Y, 1) ./ (sqrt(sum(X.^2, 1)) .* sqrt(sum(Y.^2, 1)));