[Tex/LaTex] Overbrace in amsmath align environment

alignamsmath

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?

Best Answer

Here is a solution using the array package. It is not ideal as you have to specify the width that the brace is supposed to span. There is a method to span columns using \extracolsep{\fill}, but I was not able to figure out where to place that so that the \hphantom span the entire column. But hopefully, this gets you going:

\documentclass{article}
\usepackage{amsmath}
\usepackage{array}

\newcolumntype{L}{l@{}}%

\begin{document}
\newcommand*{\WidthToSpan}{{R_L^2}{+}{\cdots +}b_{m-2} R_S^{m-1} c_1 R_L^{n-1}}%
\[
\begin{array}{LLLLLLLLLLLLLLLLLL}
1 &= &b_m     &          &c_n + &b_m     &          &c_{n-1} &R_L + &b_m     &          &c_{n-2} &R_L^2 + &\cdots + &b_m     &          &c_1 &R_L^{n-1} \\
  &+ &b_{m-1} &R_S^1     &c_n + &b_{m-1} &R_S^1     &c_{n-1} &R_L + &b_{m-1} &R_S^1     &c_{n-2} &R_L^2 + &\cdots + &b_{m-1} &R_S^1     &c_1 &R_L^{n-1} \\
  &+ &b_{m-2} &R_S^2     &c_n + &b_{m-2} &R_S^2     &c_{n-1} &R_L + &b_{m-2} &R_S^2     &c_{n-2} &R_L^2 + &\cdots + &b_{m-2} &R_S^2     &c_1 &R_L^{n-1} \\
  &  &        &          &      &        &          &        &      & \vdots \\
  &+ &b_1     &R_S^{m-1} &c_n + &b_1     &R_S^{m-1} &c_{n-1} &R_L + &b_1     &R_S^{m-1} &c_{n-2} &R_L^2 + &\cdots + &b_1     &R_S^{m-1} &c_1 &R_L^{n-1}\\
  &  &     & & & & & & & &  &  & \multicolumn{6}{@{}c}{\underbrace{\hphantom{\WidthToSpan}}_{\text{Explanation}}}
\end{array}
\]
\end{document}

enter image description here

Related Solutions

[Tex/LaTex] amsmath align environment: row spacing

You could add space manually like so:

\begin{align*}
X &= \frac{\textit{Some text here}}{\textit{And some text here}}\\[1em]
Y &= \frac{\textit{Will make everything}}{\textit{Look too close together}}
\end{align*}

change [1em] to suit how much space you want.

Thanks to Ian Thompson in the comments for pointing me to this slightly more elegant solution. If you want to add a little extra spacing to every row of an align:

\begingroup
\addtolength{\jot}{1em}
\begin{align*}
X &= \frac{\textit{Some text here}}{\textit{And some text here}}\\
Y &= \frac{\textit{Will make everything}}{\textit{Look too close together}}
\end{align*}
\endgroup

The \begingroup and \endgroup are to keep the extra alignment local to the environment. If you want all align environments to have the extra spacing, add \addtolength{\jot}{1em} to your preamble instead.

[Tex/LaTex] Using aligned and align without amsmath

To avoid needing to edit the existing doc you can defined a poor man's aligned as follows (but first try to get the rules changed)

enter image description here

\documentclass{article}   
\usepackage{mathptmx}       
\usepackage{helvet}         
\usepackage{courier}        
\usepackage{type1cm}        

\usepackage{graphicx}        

\usepackage[bottom]{footmisc}

\usepackage{amssymb}
\usepackage{amsfonts}
\usepackage{amsbsy}
\usepackage{amscd}
\usepackage{amstext}
\usepackage{dsfont}
\usepackage[english]{babel}
\usepackage{color}
\usepackage{graphics}
\usepackage{epsfig}
\usepackage{subfigure}
\usepackage{wrapfig}
\usepackage{psfrag}
\usepackage{color}
\usepackage{url}
\usepackage{verbatim}
\usepackage{algorithm}
\usepackage{algorithmic}


\begin{document}
\def\aligned{\vcenter\bgroup\let\\\cr
\halign\bgroup&\hfil${}##{}$&${}##{}$\hfil\cr}
\def\endaligned{\crcr\egroup\egroup}

\begin{equation}
\label{InitSystemNL}
\left\{
\begin{aligned}
\mathcal{R} \colon= -\Delta u &= f  \quad & &\text{in} \,\, \Omega \\ u &= 0 \quad & &\text{on} \,\, \partial\Omega, 
\end{aligned} 
\right.
\end{equation}

\end{document}

Best Answer

Related Solutions

[Tex/LaTex] amsmath align environment: row spacing

[Tex/LaTex] Using aligned and align without amsmath

Related Question