Three kinds of models x(m)）=-2ax(n-k)+之bw(n-ka=l k=0 (3)Autoregressive moving average (ARMA) model,denoted by ARMA(p,q). Both ak and bk are not equal to zeros, h H2)= X( 、 k=0 W(z) k=0Three kinds of models (3) Autoregressive moving average (ARMA) model, denoted by ARMA(p , q). Both a k and b k are not equal to zeros, 0 0 ( ) ( ) ( ) q k k k p k k k b z X z H z W z a z − = − = = = ∑ ∑