PlanetPhysics/Laplacian in Cylindrical Coordinates

The Laplacian operator in cylindrical coordinates is

$$ \nabla _{cyl}^{2} = \frac{1}{r} \frac{\partial}{\partial r}\left(r \frac{\partial}{\partial r}\right) + \frac{1}{r^2} \frac{\partial^2}{\partial \theta^2} + \frac{\partial^2}{\partial z^2} $$