\frac{\partial p(\theta,z,\omega)}{\partial z}=-(A\theta^2+j \omega\frac{n}{2c}\theta^2}) p(\theta,z,\omega)   +\frac{D}{\theta}\frac{\partial p(\theta,z,\omega)}{\partial\theta}+D\frac{\partial^2p(\theta,z,\omega)}{\partial\theta^2}