[Tex/LaTex] How to make a box around an equation in align-environment

alignboxes

I would like to draw a frame around one equation to point it out. I used

\fbox{...}

but it didn't work out.
Here is a minimal example where I tried it. Any package suggestions?

\documentclass[
    german,
    paper=a4,
    ]{scrbook}              %KOMA-
\usepackage[latin1]{inputenc}
\usepackage[ngerman]{babel} 

\usepackage[babel,german=guillemets]{csquotes}
\usepackage[T1]{fontenc}    
\usepackage{amsmath}

\begin{document}

\begin{align}
Nu_\text{m}        &= \frac{\alpha_m \, L}{\lambda}    \text{ \quad .} \\ 
Nu_\text{m}        &= \frac{\alpha_m \, L}{\lambda}    \text{ \quad .}
\end{align}

\end{document}

Best Answer

The \Aboxed command from mathtools package does what you want.

MWE

\documentclass[
    german,
    paper=a4,
    ]{scrbook}              %KOMA-
\usepackage[latin1]{inputenc}
\usepackage[ngerman]{babel} 

\usepackage[babel,german=guillemets]{csquotes}
\usepackage[T1]{fontenc}    
\usepackage{amsmath,mathtools}

\begin{document}

\begin{align}
\Aboxed{Nu_\text{m}        &= \frac{\alpha_m \, L}{\lambda}    \text{ \quad .}} \\ 
\Aboxed{Nu_\text{m}        &= \frac{\alpha_m \, L}{\lambda}    \text{ \quad .}}
\end{align}

\end{document}

Output

enter image description here

Related Solutions

[Tex/LaTex] Left aligning equations without align character

Don't use align. Use gather instead.

\documentclass[fleqn]{article}
\usepackage{amsmath}
\begin{document}
\begin{gather}
b := (a \oplus s_1) \oplus s_2 \\ 
e := 0
\end{gather}
\end{document}

[Tex/LaTex] Box or [ around multiple lines inside align

An option using a \parbox inside a \fcolorbox inside a \makebox, and the whole construct inside \intertext; some changes to the original mark-up were done (in particular, the code was greatly simplified), but the original alignment of expressions before and after the box was preserved:

\documentclass{article}
\usepackage{mathtools}
\usepackage{tikzpagenodes}
\usetikzlibrary{tikzmark}

\begin{document}

Let:
\begin{align*}
G_{\delta_r}^{\beta} &= \frac{n_1 s + n_0}{s^2 + d_1 s + d_0} = \frac{0.01956 s + 7.01}{s^2 + 0.802 s + 6.489} \\
\text{step} \left(G_{\delta_r}^{\beta}(s) \right) = \frac{G_{\delta_r}^{\beta}(s)}{s} &= \frac{1}{s} \cdot \frac{n_1 s + n_0}{s^2 + d_1 s + d_0}
\intertext{%
\makebox[\linewidth][c]{\fcolorbox{blue}{white}{\parbox{\linewidth}{%
Expanding with partial fractions:
\[
\frac{x_1}{s} + \frac{x_{21}s + x_{20}}{s^2 + d_1 s + d_0} = 
\frac{1}{s} \cdot \frac{n_1 s + n_0}{s^2 + d_1 s + d_0}
\]
Removing denominator:
\[
x_1(s^2 + d_1 s + d_0) + s(x_{21} s + x_{20}) = n_1 s + n_0 
\]
Has solutions:
\[
x_{21} = \frac{-n_0}{d_0} = -1.08\qquad
x_1 = \frac{n_0}{d_0} = 1.08\qquad
x_{20} = n_1 - \frac{n_0 d_1}{d_0} = -0.847
\]
Hence:}}}
}
\frac{G_{\delta_r}^{\beta}(s)}{s} &= \frac{1.08}{s} - \frac{1.08s + 0.847}{s^2 + 0.8-2s + 6.489} \\
\shortintertext{Completing the square:}
\frac{G_{\delta_r}^{\beta}(s)}{s} &= \frac{1.08}{s} - \frac{1.08s + 0.847}{(s + 0.401)^2 + 6.328} \\
\shortintertext{Inverse Laplace:}
\mathcal{L}^{-1}\left\{ \frac{G_{\delta_r}^{\beta}(s)}{s} \right\} &=  1.08 - e^{-.401t} \left(1.08 \cos\alpha + \frac{0.847}{\sqrt{6.328}} \sin\alpha \right), 
\end{align*}
where $\alpha=t\sqrt{6.328}$.

\end{document}

enter image description here

Another option would be to use the tikzmark library; the idea is to use \tikzmark to place marks at the appropriate locations and then to use those marks to draw the blue rectangle. Below I show this approach and also illustrate another option for the mark-up (of course, this approach will also work with the above approach or with any other variation):

\documentclass{article}
\usepackage{mathtools}
\usepackage{tikzpagenodes}
\usetikzlibrary{tikzmark}

\begin{document}

Let:
\begin{align*}
G_{\delta_r}^{\beta} &= \frac{n_1 s + n_0}{s^2 + d_1 s + d_0} = \frac{0.01956 s + 7.01}{s^2 + 0.802 s + 6.489} \\
\text{step} \left(G_{\delta_r}^{\beta}(s) \right) = \frac{G_{\delta_r}^{\beta}(s)}{s} &= \frac{1}{s} \cdot \frac{n_1 s + n_0}{s^2 + d_1 s + d_0}
\end{align*}         
\tikzmark{start}Expanding with partial fractions:
\[
\frac{x_1}{s} + \frac{x_{21}s + x_{20}}{s^2 + d_1 s + d_0} = 
\frac{1}{s} \cdot \frac{n_1 s + n_0}{s^2 + d_1 s + d_0}
\]
Removing denominator:
\[
x_1(s^2 + d_1 s + d_0) + s(x_{21} s + x_{20}) = n_1 s + n_0 
\]
Has solutions:
\[
x_{21} = \frac{-n_0}{d_0} = -1.08\qquad
x_1 = \frac{n_0}{d_0} = 1.08\qquad
x_{20} = n_1 - \frac{n_0 d_1}{d_0} = -0.847\tikzmark{end}
\]
Hence:
\begin{align*} 
\frac{G_{\delta_r}^{\beta}(s)}{s} &= \frac{1.08}{s} - \frac{1.08s + 0.847}{s^2 + 0.8-2s + 6.489} \\
\shortintertext{Completing the square:}
\frac{G_{\delta_r}^{\beta}(s)}{s} &= \frac{1.08}{s} - \frac{1.08s + 0.847}{(s + 0.401)^2 + 6.328} \\
\shortintertext{Inverse Laplace:}
\mathcal{L}^{-1}\left\{ \frac{G_{\delta_r}^{\beta}(s)}{s} \right\} &=  1.08 - e^{-.401t} \left(1.08 \cos(t\sqrt{6.328}) + \frac{0.847}{\sqrt{6.328}} \sin(t\sqrt{6.328}) \right) 
\end{align*}

\begin{tikzpicture}[remember picture,overlay]
\draw[line width=1.5pt,blue]
  ([xshift=-1ex,yshift=2.5ex]current page text area.west|-{pic cs:start})
  rectangle
  ([yshift=-2.5ex]current page text area.east|-{pic cs:end});
\end{tikzpicture}

\end{document}

enter image description here

Best Answer

MWE

Output

Related Solutions

[Tex/LaTex] Left aligning equations without align character

[Tex/LaTex] Box or [ around multiple lines inside align

Related Question