The score of the scale, where scale = exp(x) - used for variational inference

        Parameters
        ----------
        x : float
            A random variable

        Returns
        ----------
        The gradient of the scale latent variable at x

def vi_scale_score(self,x):
        """ The score of the scale, where scale = exp(x) - used for variational inference

        Parameters
        ----------
        x : float
            A random variable

        Returns
        ----------
        The gradient of the scale latent variable at x
        """
        return np.exp(-2.0*np.log(self.sigma0))*(x-self.mu0)**2 - 1.0