code: def effective_max_ar_order(self):
          
          return min(self.max_ar_order, self.ma.order-self.ma.turningpoint[0]-1)
docs: The maximum number of AR coefficients that shall or can be
          determined.
  
          It is the minimum of |ARMA.max_ar_order| and the number of
          coefficients of the pure |MA| after their turning point.