设 Vn+ (n+1) y(n+2) n+ y= 0=|,"b n+N 5(m+N) n y(2)a(n+2)…al(2) ①= y(n+N-1)…-y(N)l(n+N)…(N)❖ 设             + + + =                     =             + + + = ( ) ( 2) ( 1) , , ( ) ( 2) ( 1) 0 1 n N n n b b a a y n N y n y n y n n                      − + − − + − + − + − − +  = ( 1) ( ) ( ) ( ) ( 1) (2) ( 2) (2) ( ) (1) ( 1) (1) y n N y N u n N u N y n y u n u y n y u n u          