def neg_logposterior(self, beta):
        """ Returns negative log posterior

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

        alpha : np.array
            State matrix

        Returns
        ----------
        - Negative log posterior
        """
        post = self.neg_loglik(beta)
        for k in range(0,self.z_no):
            post += -self.latent_variables.z_list[k].prior.logpdf(beta[k])
        return post