'Inverse of the Jones reparameterization'

def _invtransparams(self, start_params):

    p = self.k_ar
    k = self.k_trend
    newparams = start_params.copy()
    newparams[k:(k + p)] = _ar_invtransparams(start_params[k:(k + p)].copy())
    return newparams
