An important derivative operation in many applications is called the Laplacian; in Cartesian coordinates, for z = f(x,y), the Laplacian is Zxx + Zyy. In Polar coordinates the Laplacian is Zxx + Zyy = Zrr + Zr/(r) + Zθθ/(r^2), as derived above for my Calculus 3 class.