def __init__(self, Q, gamma, w, mu, T, Nk, tag=None):
        ck_plus, vk_plus = self._corr(gamma, w, mu, T, Nk, sigma=1.0)
        ck_minus, vk_minus = self._corr(gamma, w, mu, T, Nk, sigma=-1.0)

        super().__init__(