Calculating Stream Function of Incompressible Fluid from Velocity

[Asies]

Hi everybody, I have been looking for a way to calculate the stream function if I know the velocity $$\vec{v}$$=(v_x,v_y,0) of a bidimentional flux.
From the formula given for $$\vec{v}$$, I know it is an incompressible fluid.

 

[arildno]

Well, the derivatives of the stream function $\phi$ are generally related to the velocity components as...?