'Inverse of the Jones reparameterization'

def _invtransparams(self, start_params):

    (k_ar, k_ma) = (self.k_ar, self.k_ma)
    k = (self.k_exog + self.k_trend)
    newparams = start_params.copy()
    arcoefs = newparams[k:(k + k_ar)]
    macoefs = newparams[(k + k_ar):]
    if (k_ar != 0):
        newparams[k:(k + k_ar)] = _ar_invtransparams(arcoefs)
    if (k_ma != 0):
        newparams[(k + k_ar):((k + k_ar) + k_ma)] = _ma_invtransparams(macoefs)
    return newparams
