W = − ∑ 1 ≤ ℓ < j ≤ n ln ⁡ | e i ⁢ θ ℓ − e i ⁢ θ j | W=-\sum _{1\leq \ell <j\leq n}\ln |e^{i\theta _{\ell }}-e^{i\theta _{j}}|