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I've been trying several different approaches to place a box (a highlight red box) around equations in beamer. Though, I usually do not get the expected result, or a bunch of errors pops up and nothing compiles.

Below follows a MWE of three equations inside the align environment (ideally I want to keep this environment). I need a box that can go at each equation at a time (or more than one sometimes, but not all of them at once). Also, some methods I've tried could not place a box around the \sum correctly, usually cutting part of them out, or the iterators below them.

\documentclass{beamer} \usepackage[utf8]{inputenc} \usepackage{amsmath} \begin{document} \begin{align} & \left[ \omega \sum_{k \in K} y_k + \sum_{i \in V} \sum_{j \in V} \sum_{k \in K} c_{ij}x_{ijk}\right]\\ \notag\\ & \sum_{k \in K} \sum_{j \in V | j \ne i} x_{ijk} = 1 & & \forall i \in P\\ \notag\\ & \sum_{j \in V | j \ne i} x_{ijk} - \sum_{j \in V | j \ne i} x_{dev(i)jk} = 0 && \forall i \in P, k \in K \end{align} \end{document}

Thanks in advance,

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2 Answers 2

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I'd recommend the hf-tikz package; it requires hand adjustments, but is completely independent of align.

\documentclass{beamer} \usepackage[utf8]{inputenc} \usepackage{amsmath} \usepackage{hf-tikz} \begin{document} \begin{frame} \begin{align} \tikzmarkin{first}(0.2,0.75)(-0.2,-0.7) & \biggl[ \omega \sum_{k \in K} y_k + \sum_{i \in V} \sum_{j \in V} \sum_{k \in K} c_{ij}x_{ijk} \biggr] \tikzmarkend{first} \\[2ex] & \sum_{k \in K} \sum_{j \in V | j \ne i} x_{ijk} = 1 && \forall i \in P \\[2ex] \tikzmarkin{third}(0.2,0.6)(-0.2,-0.75) & \sum_{j \in V \mid j \ne i} x_{ijk} - \sum_{j \in V \mid j \ne i} x_{dev(i)jk} = 0 && \forall i \in P, k \in K \tikzmarkend{third} \end{align} \end{frame} \end{document}

enter image description here

If you just want the red border, with true corners,

\documentclass{beamer} \usepackage[utf8]{inputenc} \usepackage{amsmath} \usepackage[customcolors]{hf-tikz} \hfsetfillcolor{white} \hfsetbordercolor{red} \begin{document} \begin{frame} \begin{align} \tikzmarkin[disable rounded corners=true]{first}(0.2,0.75)(-0.2,-0.7) & \biggl[ \omega \sum_{k \in K} y_k + \sum_{i \in V} \sum_{j \in V} \sum_{k \in K} c_{ij}x_{ijk} \biggr] \tikzmarkend{first} \\[2ex] & \sum_{k \in K} \sum_{j \in V | j \ne i} x_{ijk} = 1 && \forall i \in P \\[2ex] \tikzmarkin[disable rounded corners=true]{third}(0.2,0.6)(-0.2,-0.75) & \sum_{j \in V \mid j \ne i} x_{ijk} - \sum_{j \in V \mid j \ne i} x_{dev(i)jk} = 0 && \forall i \in P, k \in K \tikzmarkend{third} \end{align} \end{frame} \end{document}

enter image description here

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  • This one seems to work exactly how I wanted it to work. Nice answer, thank you, egreg :) Commented Nov 29, 2016 at 22:52
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You can obtain it with the \Aboxed command from mathtools, but it can enclose a single &, so I had to remove the alignment of the ∀.

For colour, I patched the \boxed command from amsmath, which is used by \Aboxed (but be aware all math boxed equations will be red). Additionally, I used \smashoperator in case of large subscript, to improve the spacing with the following expression:

\documentclass{beamer} \usepackage[utf8]{inputenc} \usepackage{mathtools}} \usepackage{xpatch} \xpatchcmd{\boxed}{% \fbox}{% \fcolorbox{red}{white}}{}{} \begin{document} \begin{align} \Aboxed{& \Biggl[ \omega\sum_{k \in K} y_k + \sum_{i \in V} \sum_{j \in V} \sum_{k \in K} c_{ij}x_{ijk}\Biggr]}\\ \notag\\ &\sum_{k \in K} \smashoperator[r]{\sum_{j \in V | j \ne i}} x_{ijk}= 1 \qquad \forall i \in P\\ \notag\\ \Aboxed{&\smashoperator[r]{\sum_{j \in V | j \ne i}} x_{ijk} - \smashoperator{\sum_{j \in V | j \ne i}} x_{dev(i)jk}= 0\qquad \forall i \in P, k \in K} \end{align} \end{document}

enter image description here

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  • Thank you for the answer, Bernard. I really preferred that the \forall appeared in an extra &. There is no way to do that? Moreover, is there any way to make the box red? Commented Nov 29, 2016 at 1:48
  • For the rule colour I added a patch to \ boxed. For the other alignment, I don't how to do that: when I tried which & it gobbled the second column. Maybe a work-around using eqparbox? Commented Nov 29, 2016 at 2:14
  • Oh well, I guess I'll have to use this way then. Thanks again anyway, you have been very helpful :) (Edit: I'll wait a bit before voting for best answer, in case anyone appears with a magic answer) Commented Nov 29, 2016 at 2:37
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    if boxing can't handle &, then the \foralls can be aligned manually, by using \mathrlap of the first part of equation (2) over a phantom of the first part of equation (3), and setting the second part of equation (2) after that.. Commented Nov 29, 2016 at 18:35
  • Boxing accepts only one &, it seems. I was thinking of using eqparbox, but didn't have to test yet Commented Nov 29, 2016 at 20:05

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