code: def vi_scale_score(self,x):
          
          return np.exp(-2.0*np.log(self.sigma0))*(x-self.mu0)**2 - 1.0
docs: 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