In the paper https://arxiv.org/abs/1210.4699. How to solve this equation?
I've tried it, it's not same as in this paper. Even zero order still not the same.
This is what I try to do at zero order.
input
$$E=E_0\left(r_0\right)$$
$$H=H_0\left(r_0\right)$$
$$b=b\left(r_0\right)$$...