Help me please to apply a Laplace-like operator:$ \Delta f:= \frac{\partial^2 f}{\partial r^2} + \frac{\partial^2 f}{\partial z^2} + {1\over r}\,\frac{\partial f}{\partial r} - {f\over r^2} $ on the expression: $f:=\frac{r}{a}\rho^{-\alpha}\sin (\alpha\phi)$.
when $\rho=\sqrt{(r-a)^{2}+z^{2}} $
Thanks a lot!