Box around one or multiple equations using tcolorbox

Question

I want to put (1) a box around 1 equation inside an align environment, and also (2) a box around all equations in align environment. I'm already using tcolorbox and would like to use that. I have tried boxing all equations with tcolorbox but the problem is that it goes page-wide which I don't like, and also leaves a visible margin above the first equation. I want to keep equation numbers out of the box as well. Any suggestions?

Edit: Thanks for pointing me to a solution. The problem, however, is that all the solutions use another math environment (either within tcolorbox or empheq package). I am using a very specialized align environment and hence have to have a box without tcolorbox or empheq equation style.

So I want a box around align equations without leaving \begin{align} and \end{align} environment.

Edit2: Here is the MWE code.

\documentclass{article}

\usepackage{amsmath}


\begin{document}

\begin{flalign}

      \begin{gathered}

        A \quad  \vphantom{\sum \limits _{n=0} ^{N-1}} \\

        B \quad ~~ \vphantom{\sum \limits _{n=0} ^{N-1}}

      \end{gathered}

      &&

      \begin{aligned}\label{equationAB}

        A\: &= \sum \limits _{n=0} ^{N-1} a[n]\\

        B &= \sum \limits _{n=0} ^{N-1} b[n]

      \end{aligned}

      &&

    \end{flalign}

\end{document}

Please, show us your code. It is extremely unclear from your question what you have done and what you want to do. Any answer risk turning out to be useless. — cfr, Nov 18 '15 at 02:10
Does this help you? http://tex.stackexchange.com/a/237855/1952 or http://tex.stackexchange.com/a/240327/1952 — Ignasi, Nov 18 '15 at 08:46
The first link is really what I want, except that the box be around the actual equations and equations numbers be outside the box. — QMC, Nov 19 '15 at 02:24
@QasimChaudhari: The tcolorbox solution with tcbhighmath should be what you request, in my point of view. Any tcolorbox can be configured to match top etc. spacing, background colour, frame style etc. — , Dec 27 '15 at 08:53
@ChristianHupfer, how can I raise this question from dead after editing it? @ Ignasi, your solution helps but when using align equations, equation numbers are included. I want something like the first equation (number outside box) but with align environment. Thanks. — QMC, Apr 21 '16 at 15:29
@QasimChaudhari: Returning after such a long time? ;-) I've voted to reopen it — , Apr 21 '16 at 15:31
@QasimChaudhari In second link, there's an align example with numbers outside box (equations 7 and 8). — Ignasi, Apr 21 '16 at 16:55
@ChristianHupfer, Thanks :) @ Ignasi, Eq 7 and 8 use \begin and \end empheq, although I am using some particular settings with align, flalign, etc. and want to keep using actual align, flalign, etc. — QMC, Apr 23 '16 at 05:11
@QasimChaudhari: We reopened your question, now provide a compilable document, not just requests ;-) — , Apr 23 '16 at 05:14
@ChristianHupfer, I just added the MWE. I want a box around the equations such that A and B on the left and the number on the right are outside that box. Otherwise, A and B can be included if needed, but equation numbers must be outside. — QMC, Apr 27 '16 at 02:18
Note that you can only ping one person per comment. So you can't ping both Christian and Ignasi at the same time. The system tells you this if you try. — cfr, Apr 27 '16 at 03:00

score 4 · Accepted Answer · answered Apr 28 '16 at 10:57

4

I give a try with tcolorbox. Are you looking for the following?

The code puts a \tcbhighmath box around the aligned equations:

\documentclass{article}

\usepackage{amsmath}
\usepackage[many]{tcolorbox}

\begin{document}
  \begin{flalign}
    \begin{gathered}
      A \quad  \vphantom{\sum \limits _{n=0} ^{N-1}} \\
      B \quad ~~ \vphantom{\sum \limits _{n=0} ^{N-1}}
    \end{gathered}
    &&
    \tcbhighmath{\begin{aligned}\label{equationAB}
      A\: &= \sum \limits _{n=0} ^{N-1} a[n]\\
      B &= \sum \limits _{n=0} ^{N-1} b[n]
    \end{aligned}}
    &&
  \end{flalign}
\end{document}

answered Apr 28 '16 at 10:57

Thomas F. Sturm

25,210

@ThomasSturm. For some strange reason, it is producing a yellow background in my office computer but when I compile at home computer, it has a pink background. How can I have it yellow consistently? – QMC May 12 '16 at 03:24
@QasimChaudhari There should be no difference. But you can change the coloring locally like \tcbhighmath[colback=yellow]{... or setting highlight math style globally (page 335 of the documentation v3.91). – Thomas F. Sturm May 12 '16 at 10:44
@ThomasF.Sturm Is it possible to set \tcbhighmath[] globally in (the preamble)? I would love for all my equation and align environments to be shaded automatically or by default? – Raphael Jul 21 '21 at 08:11
@Raphael Yes, just adapt highlight math style or highlight math (page 373 of the documentation v4.51) for global effects, e.g. \tcbset{highlight math/.append style={enhanced, drop shadow}} – Thomas F. Sturm Jul 27 '21 at 05:46

score 2 · Answer 2 · answered Apr 28 '16 at 10:01

I think what you want is not possible with tcolorbox because you should change the environment, but you can always use tikzmark or hf-tikz which can draw boxes around any part of your text.

Next code shows how to use hf-tikz commands tikzmarkin and tikzmarkend. Both commands are defined like

\tikzmarkin{marker-id}(below right offset)(above left offset)
\tikzmarkend{marker-id}

marker-id is a label which is unique in every document and offsets are optional arguments to better adjust box size.

\documentclass{article}
\usepackage{amsmath}
\usepackage{hf-tikz}

\begin{document}

\begin{flalign}
      \begin{gathered}
        A \quad \vphantom{\sum \limits _{n=0} ^{N-1}} \\
        B \quad ~~ \vphantom{\sum \limits _{n=0} ^{N-1}}
      \end{gathered}
      &&
      \begin{aligned}\label{equationAB}
        \tikzmarkin{a}(1,-1)(-1,1) A\: &= \sum \limits _{n=0} ^{N-1} a[n]\\
        B &= \sum \limits _{n=0} ^{N-1} b[n]\tikzmarkend{a}
      \end{aligned}
      &&
    \end{flalign}
\end{document}

Box around one or multiple equations using tcolorbox

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