该函数ux=2x,uy=x^2;vx=y^2;vy=2xy,在原点满足柯西尼曼条件，在原点可导，导函数为ux-iuy=0
df/dz=(1/2)(d/dx-id/dy)(f(z))=0.5(0+0-i0-i0)=0
