Creates model latent variables

        Returns
        ----------
        None (changes model attributes)

def _create_latent_variables(self):
        """ Creates model latent variables

        Returns
        ----------
        None (changes model attributes)
        """

        # Create latent variables
        for no, i in enumerate(self.kernel.build_latent_variables()):
            self.latent_variables.add_z(i[0],i[1],i[2])
            self.latent_variables.z_list[no].start = i[3]

        self.z_no = len(self.kernel.build_latent_variables())

        # Use an ARIMA model to find starting point for the initial noise latent variable
        arma_start = arma.ARIMA(self.data, ar=self.ar, ma=0, integ=self.integ)
        x = arma_start.fit()
        arma_starting_values = arma_start.latent_variables.get_z_values()
        self.latent_variables.z_list[0].start = np.log(np.exp(np.power(arma_starting_values[-1],2)))