code: def update_ar_coefs(self):
          
          del self.ar_coefs
          for ar_order in range(1, self.effective_max_ar_order+1):
              self.calc_all_ar_coefs(ar_order, self.ma)
              if self._rel_rmse < self.max_rel_rmse:
                  break
          else:
              with hydpy.pub.options.reprdigits(12):
                  raise RuntimeError(
                      f'Method `update_ar_coefs` is not able to determine '
                      f'the AR coefficients of the ARMA model with the desired '
                      f'accuracy.  You can either set the tolerance value '
                      f'`max_rel_rmse` to a higher value or increase the '
                      f'allowed `max_ar_order`.  An accuracy of `'
                      f'{objecttools.repr_(self._rel_rmse)}` has been reached '
                      f'using `{self.effective_max_ar_order}` coefficients.')
docs: Determine the AR coefficients.
  
          The number of AR coefficients is subsequently increased until the
          required precision |ARMA.max_rel_rmse| is reached.  Otherwise,
          a |RuntimeError| is raised.