code: def Ak(self, k, m_pred, P_pred):  # returns state iteration matrix
          
  
          return self.A[:, :, self.index[self.A_time_var_index, k]]
docs: function (k, m, P) return Jacobian of measurement function, it is
              passed into p_h.
              k (iteration number), starts at 0
              m: point where Jacobian is evaluated
              P: parameter for Jacobian, usually covariance matrix.