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