code: def _create_latent_variables(self):
          
  
          self.latent_variables.add_z('Constant', fam.Normal(0,3,transform=None), fam.Normal(0, 3))
  
          for ar_term in range(self.ar):
              self.latent_variables.add_z('AR(' + str(ar_term+1) + ')', fam.Normal(0,0.5,transform=None), fam.Normal(0, 3))
  
          for ma_term in range(self.ma):
              self.latent_variables.add_z('MA(' + str(ma_term+1) + ')', fam.Normal(0,0.5,transform=None), fam.Normal(0, 3))
docs: Creates the model's latent variables
  
          A latent variable addition requires:
  
          - Latent variable name - e.g Constant
          - Latent variable prior family - e.g. Normal(0, 1)
          - Variational approximation - e.g. Normal(0, 1)
  
          Returns
          ----------
          None (adds to self.latent_variables)