docs: def Zstar(self):
          """ predict the value of the fixed effect """
          RV = self.Ystar().copy()
          for term_i in range(self.n_terms):
              if self.identity_trick and self.A_identity[term_i]:
                  RV-=np.dot(self.Fstar()[term_i],self.B_hat()[term_i])
              else:
                  RV-=np.dot(self.Fstar()[term_i],np.dot(self.B_hat()[term_i],self.Astar()[term_i]))
          self.clear_cache('DLZ')
          return RV