同样,利用对称性 若 (n)=x1(n)x2(n) 则F(k)=DFS[(n)=∑(m)W N ∑X1(1)2(k-D A之2(D)X1(k-1)同样，利用对称性 1 1 2 0 1 ( ) ( ) N l X l X k l N        1 2 1 0 1 ( ) ( ) N l X l X k l N        1 2 若 y(n)  x (n)x (n) 1 0 ( ) [ ( )] ( ) N nk N n Y k DFS y n y n W   则      