二、存在条件 J(=im∑f()A =stin. A==Ax +iAy 则f()=(5,)+(5,1)=l+mvn ∑++2 ∑uAx-V△)+0+4 Ax O k=1二、存在条件 ∵ 1 0 ( ) lim ( ) k n k k l n k z f z dz f z z ®¥ = D ® ò = D å 令 , k k k k k k z =x h+i Dz =Dx + Di y 则 ( ) ( , ) ( , ) k k k k k k k f z =u x h +in x h n = + u i [ ] 1 1 0 0 0 1 0 0 lim ( ) lim ( )( ) lim ( ) ( ) k k k k k n n k k k k k k n n k k z x y n k k k k k k k k n k x y f z u i x i y u x y i x u y x n n n ®¥ ®¥ = = ® D ® D ® ®¥ = D ® D ® D = + D + D = D - D + D + D å å å