% compute PCA by centering and SVD
% included here since matlab's princomp
% is not available in all installations
function [X,V,D,mn] = pca(A)
    [m,n] = size(A);
    mn = mean(A);
    X = A - repmat(mn, m, 1);
    [U,S,V] = svd(X,'econ');
    X = X*V;
    D = diag(S);
    D = D.^2 / (m-1);
    D = diag(D);
end