Creates the negative log-likelihood of the model

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

        Returns
        ----------
        The negative logliklihood of the model

def neg_loglik(self, beta):
        """ Creates the negative log-likelihood of the model

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

        Returns
        ----------
        The negative logliklihood of the model
        """     

        sigma2, Y, __ = self._model(beta)
        parm = np.array([self.latent_variables.z_list[k].prior.transform(beta[k]) for k in range(beta.shape[0])])
        return -np.sum(ss.norm.logpdf(Y, loc=parm[-1]*np.ones(sigma2.shape[0]), scale=np.sqrt(sigma2)))