function t = divdiff(x, f)
    n = length(x);
    t=zeros(n);
    t(:,1)= f'
    for j = 2:n
      t(1:n-j+1,j) = (t(2:n-j+2,j-1) - t(1:n-j+1,j-1))./((x(j:n)-x(1:n-j+1))');
    endfor
end