Reset the instance to its initial state

def reset(self):
        """Reset the instance to its initial state"""
        self.alpha_ = np.zeros(self._size, dtype=int)
        self.beta_ = np.zeros(self._size, dtype=int)
        self.theta_ = np.empty(self._size, dtype=float)
        if self.store_variance:
            self.var_theta_ = np.empty(self._size, dtype=float)
        if self.store_wp:
            self.theta_wp_ = np.empty(self._size, dtype=float)

        self._calc_theta()
        if self.store_variance:
            self._calc_var_theta()