I have the following rather large equation.
\begin{alignat*}{16}
1 &= &&b_m && &c_n + &b_m && &c_{n-1} &&R_L + &b_m && &c_{n-2} &R_L^2 + &\cdots + &b_m && &&c_1 &R_L^{n-1} \\
&+ &&b_{m-1} &&R_S^1 &c_n + &b_{m-1} &&R_S^1 &c_{n-1} &&R_L + &b_{m-1} &&R_S^1 &c_{n-2} &R_L^2 + &\cdots + &b_{m-1} &&R_S^1 &&c_1 &R_L^{n-1} \\
&+ &&b_{m-2} &&R_S^2 &c_n + &b_{m-2} &&R_S^2 &c_{n-1} &&R_L + &b_{m-2} &&R_S^2 &c_{n-2} &R_L^2 + &\cdots + &b_{m-2} &&R_S^2 &&c_1 &R_L^{n-1} \\
& && && & & && & && & \vdots \\
&+ &&b_1 &&R_S^{m-1} &c_n + &b_1 &&R_S^{m-1} &c_{n-1} &&R_L + &b_1 &&R_S^{m-1} &c_{n-2} &R_L^2 + &\cdots + &b_1 &&R_S^{m-1} &&c_1 &R_L^{n-1}
\end{alignat*}
I would like to use overbraces and underbraces to break things down, such as by using:
&+ &&b_1 &&R_S^{m-1} &c_n + &b_1 &&R_S^{m-1} &c_{n-1} &&R_L + &b_1 &&R_S^{m-1} &c_{n-2} &R_L^2 + &\cdots + \underbrace{&b_1 &&R_S^{m-1} &&c_1 &R_L^{n-1}}_{Explanation}
However, the align environment doesn't seem to like this; perhaps because alignment symbols get tucked inside of the underbrace call.
Is it possible to both align and over/underbrace my equation?