某处B不为零 A≠0 )yO=Ey( 力C v(x)=v0(x)( q A)(x)=0 文)=M一Jn某处B不为零  =  − = = −  − =   x A dl c i q x Me A x c iq x x x A x E x c iq A                  ( ) ( ) ( ) 0 ( ) ( ) ( ) ( ) ( ) ( ) 2 0 0 2 2        