code: def update(self):
          
          pars = self.subpars.pars
          coefs = pars.control.responses.ar_coefs
          self.shape = coefs.shape
          self(coefs)
          pars.model.sequences.logs.logout.shape = self.shape
docs: Determine all AR coefficients.
  
          >>> from hydpy.models.arma import *
          >>> parameterstep('1d')
          >>> responses(((1., 2.), (1.,)), th_3=((1.,), (1., 2., 3.)))
          >>> derived.ar_coefs.update()
          >>> derived.ar_coefs
          ar_coefs([[1.0, 2.0],
                    [1.0, nan]])
  
          Note that updating parameter `ar_coefs` sets the shape of the log
          sequence |LogOut| automatically.
  
          >>> logs.logout
          logout([[nan, nan],
                  [nan, nan]])