function energy = potential_energy_param ( theta, n, s, R )
% ƒ|ƒeƒ“ƒVƒƒƒ‹ƒGƒlƒ‹ƒM�[
    energy = 0;
    for k=1:n-1
        energy = energy + (1/2)*R*(theta(k+1)-theta(k))^2/(s(k+1)-s(k));
    end
end
