c i2 Uj 2 Z U(5)=-kk:-1(5) 1(s) U2S）=-kk,Z(s)       22 2 1 1 1 1 0 0 i u k k iu ( ) ( ) ( ) ( ) ( ) 1 2 22 1 2 11 1 k k Z s I s U s k k I s U s Z   L     u1 i2 u2 i1 Z L