[Tex/LaTex] Highlight an equation within an align environment with color option

alignboxesequationshighlighting

I'd really like to do exactly what's being asked for in this question: Highlight an equation within an align environment, but with the ability to change the color when I call it, so that I could have one equation highlighted yellow, the next one highlighted lime, a third highlighted magenta, and a fourth highlighted yellow again, etc. (I'd also like the frame to be the same color as the highlight, but I'm pretty sure I can figure that part out. 🙂 ) I really like the first solution – the one with 15 votes – and would love to know how to tweak that one to do what I want – something like \alignedbox[yellow].

I'm not including a MWE since my question is just a follow-up to a previous one, but I can if it would be helpful.

I don't know if it's relevant or helpful, but what I'm doing right now is just using this that I found but don't really understand:

\newcommand{\highlight}[2][yellow]{\mathchoice%
    {\colorbox{#1}{$\displaystyle#2$}}% 
    {\colorbox{#1}{$\textstyle#2$}}%
    {\colorbox{#1}{$\scriptstyle#2$}}%
    {\colorbox{#1}{$\scriptscriptstyle#2$}}}%

and then using \phantom{} and \quad and such to try to get the horizontal spacing right so that things align the way I want. 🙂

Best Answer

You can just add one more parameter to the macro. Below I have made the first parameter to specify the color -- it is optional and defaults to yellow if not provided as in the first example:

enter image description here

Notes:

The main portion of this code is form Highlight an equation within an align environment, so please up vote that answer instead -- my addition here is just the addition of the first optional parameter.

Code:

\documentclass{article}
\usepackage{calc}
\usepackage{amsmath}
\usepackage{xcolor}

\newlength\dlf
\newcommand\alignedbox[3][yellow]{
  % #1 = color (optional, defaults to yellow)
  % #2 = before alignment
  % #3 = after alignment
  &
  \begingroup
  \settowidth\dlf{$\displaystyle #2$}
  \addtolength\dlf{\fboxsep+\fboxrule}
  \hspace{-\dlf}
  \fcolorbox{red}{#1}{$\displaystyle #2 #3$}
  \endgroup
}

\begin{document}
\begin{align*}
    \alignedbox{a}{=b} &                        c  &= d \\
                c &= d & \alignedbox[magenta!20]{i}{=k} \\
                e &= f &                        g  &= h  
\end{align*}
\end{document}

Related Solutions

[Tex/LaTex] Highlight an equation within an align environment

The mathtools package provides an Aboxed command, that allows one to make a box across an alignment. By redefining that slightly, you can get the desired effect:

\documentclass[11pt]{article}
\usepackage{color}
\usepackage{mathtools}
\usepackage{amssymb}
\usepackage{amsfonts}

\makeatletter
\def\@Aboxed#1&#2\ENDDNE{%
  \settowidth\@tempdima{$\displaystyle#1{}$}%
  \addtolength\@tempdima{\fboxsep}%
  \addtolength\@tempdima{\fboxrule}%
  \global\@tempdima=\@tempdima
  \kern\@tempdima
  &
  \kern-\@tempdima
  \fcolorbox{red}{yellow}{$\displaystyle #1#2$}
}
\makeatother

\begin{document}
\begin{align*}
              \Aboxed{a &= b}  &        c  &= d \\
                 c  &    = d   & \Aboxed{i &= k} \\
                 e  &    = f   &        g  &= h  
\end{align*}
\end{document}

I basically copied the definition of Aboxed from mathtools.dtx and changed the last line of the definition from \boxed to \fcolorbox{....

(I wasn't sure if the following should be added as a new answer or as an edit. Please advise if I should make it a new answer.)

When looking at some lecture notes I wrote a while ago, I found that I had a command for this purpose in my preamble, and it came to me that I had copied it from LaTeXcommunity.org, but never used it. So here is another solution, based on this post at LaTeX Community by daleif:

\documentclass{article}
\usepackage{calc}
\usepackage{amsmath}
\usepackage{xcolor}

\newlength\dlf
\newcommand\alignedbox[2]{
  % #1 = before alignment
  % #2 = after alignment
  &
  \begingroup
  \settowidth\dlf{$\displaystyle #1$}
  \addtolength\dlf{\fboxsep+\fboxrule}
  \hspace{-\dlf}
  \fcolorbox{red}{yellow}{$\displaystyle #1 #2$}
  \endgroup
}

\begin{document}
\begin{align*}
              \alignedbox{a}{=b}  &        c  &= d \\
                 c  &    = d   & \alignedbox{i}{=k} \\
                 e  &    = f   &        g  &= h  
\end{align*}
\end{document}

This yields:

enter image description here

This does not have the problem of overwriting an existing command, but requires the calc package.

[Tex/LaTex] equation labels inside a nested align and aligned environment

You can number each line using the alignat environment from the amsmath package.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{alignat}{2}
a &= b &\quad\Rightarrow\quad c &= d \\
e &= f &  g &= h
\end{alignat}
\end{document}

alignat

You can use \nonumber to suppress numbering on individual lines. I don't think it would be a good idea to separately number the equations in the left-hand column. Readers expecting to find the equation numbers at the edge of the page are likely to find this annoying.