Creates the negative log marginal likelihood of the model

        Parameters
        ----------

        data : np.array
            Data to be smoothed

        beta : np.array
            Contains untransformed starting values for latent variables

        Returns
        ----------
        - Smoothed states

def smoothed_state(self,data,beta):
        """ Creates the negative log marginal likelihood of the model

        Parameters
        ----------

        data : np.array
            Data to be smoothed

        beta : np.array
            Contains untransformed starting values for latent variables

        Returns
        ----------
        - Smoothed states
        """         

        T, Z, R, Q, H = self._ss_matrices(beta)
        alpha, V = univariate_KFS(data,Z,H,T,Q,R,0.0)
        return alpha, V