差分

$$\therefore~\mathrm{Re}~z\cdot(G_n-G'_n)=|z|^2G_2\cdot G_{n-1}~\begin{cases}G_n&=G'_n+\frac{|z|^2}{\mathrm{Re}~z}\cdot G_{n-1}\\G'_n&=G_n-\frac{|z|^2}{\mathrm{Re}~z}\cdot G_{n-1}\end{cases}$$