Put a circle around elements in a matrix environment

Question

So I'm trying to put circles around 6,8,10,18 in row 1-4 respectively, however this does give me an error warning saying "missing $ inserted"

\documentclass{article}
\usepackage{mathtools}
\setlength\parindent{0pt}
\usepackage{tikz}



\begin{document}

$   
\text{M}=\begin{pmatrix}
4 & \tikz\node[draw,circle]{6} & 4 & 5 \\ 
3 & 8 & 1 & 6 \\ 
2 & 9 & 2 & 10 \\ 
1 & 2 & 3 & 18
\end{pmatrix}
$ 

\end{document}

How can I correct this error, because positioning various $ around the command hasn't helped so far.

This code is not compileable, you must give the entire code starting with \documentclass{} and ending with \end{document} which allows you to reproduce your error. — AndréC, Oct 28 '18 at 13:51
it's a fragment of the code, it's embedded in a article environment — Christian Singer, Oct 28 '18 at 13:53

CarLaTeX · Answer 1 · 2018-10-28T20:59:36.883

14

With a tikz matrix you can get a better alignment:

\documentclass{article}
\usepackage{mathtools}
\setlength\parindent{0pt}
\usepackage{tikz}
\usetikzlibrary{matrix}
\begin{document}
\[
\text{M}=
\begin{tikzpicture}[baseline]
\matrix[
    matrix of math nodes, 
    minimum size=16pt,
    row sep=2pt,
    column sep=2pt,
    left delimiter=(,
    right delimiter=), 
    inner xsep=0pt
    ]{
    4 & |[draw, circle]|6 & 4 & 5 \\ 
    3 & |[draw, circle]|8 & 1 & 6 \\ 
    2 & 9 & 2 & |[draw, circle]|10 \\ 
    1 & 2 & 3 & |[draw, circle]|18\\
    };
\end{tikzpicture}
\]
\end{document}

edited Oct 28 '18 at 20:59

answered Oct 28 '18 at 20:54

CarLaTeX

62,716

1

That looks alot nicer than my result with a regular matrix, thanks! – Christian Singer Oct 30 '18 at 08:41
Would there be a way to change the size of circle? – le4m Apr 11 '22 at 08:37
1

@Le4M Yes, of course, you can. Just write draw, circle, minimum size=<your_desired_size>. – CarLaTeX Apr 11 '22 at 18:58

score 6 · Accepted Answer · answered Oct 28 '18 at 14:02

6

The tikz code must always be ended with a semicolon.

4 & \tikz\node[draw,circle]{6}; & 4 & 5 \\

\documentclass{article}
\usepackage{mathtools}
\setlength\parindent{0pt}
\usepackage{tikz}

\begin{document}

$   
\text{M}=
\begin{pmatrix}
4 & \tikz\node[draw,circle]{6}; & 4 & 5 \\ 
3 & 8 & 1 & 6 \\ 
2 & 9 & 2 & 10 \\ 
1 & 2 & 3 & 18
\end{pmatrix}
$ 
\end{document}

answered Oct 28 '18 at 14:02

AndréC

24,137

@ChristianSinger It is not necessary to use mathtools, tikz has a native matrix management that simplifies syntax. – AndréC Oct 28 '18 at 14:13

score 2 · Answer 3 · answered Aug 26 '21 at 22:35

A simple solution with an ordinary matrix and pstricks:

\documentclass{article}
\usepackage{mathtools}
\setlength\parindent{0pt}
\usepackage{pstricks}
\begin{document}
$ \psset{framesep=1pt, linewidth=0.4pt}
\text{M}=\begin{pmatrix}
4 & \pscirclebox{6} & 4 & 5 \
3 & \pscirclebox{8} & 1 & 6 \
2 & 9 & 2 & \pscirclebox{10} \
1 & 2 & 3 & \pscirclebox{18}
\end{pmatrix}$
\end{document}

score 2 · Answer 4 · edited Feb 27 '23 at 10:59

Since longer numbers rather need to be highlighted by ellipses than by circles, and multicolored circles can be useful, here is another example of how to use F. Pantigny's answer to get different colored ellipses:

 \begin{equation}
A = 
\setlength{\extrarowheight}{1mm}
\begin{bNiceMatrix}
0.0    &0.86   &-1.91  &-0.51  & 1.14\\
-1.47  & 0.0   &-0.57  &-0.33  & 0.038\\
 2.20  &-1.93  & 0.0   &-0.36  &-2.04\\
-2.42  &-2.97  & 1.78  & 0.0   &-0.59\\
-2.55  &-0.61  &-0.58  & 0.85  & 0.0
\CodeAfter
%% uses self-defined colours (see default packages/newcommands.tex)
  \tikz \draw[color = red]    (1-3) ellipse (7mm and 3mm)
                                    (3-1) ellipse (7mm and 3mm);
  \tikz \draw[color = green] (1-5) ellipse (7mm and 3mm)
                                    (5-1) ellipse (7mm and 3mm);
  \tikz \draw[color = blue]     (3-4) ellipse (7mm and 3mm)
                                    (4-3) ellipse (7mm and 3mm);
  \tikz \draw[color = black](4-5) ellipse (7mm and 3mm)
                                    (5-4) ellipse (7mm and 3mm);
\end{bNiceMatrix}
\label{matrix: competition matrix oscillating}
\end{equation}

score 1 · Answer 5 · answered Aug 27 '21 at 17:41

With nicematrix and Tikz:

\documentclass{article}
\usepackage{nicematrix,tikz}
\begin{document}
$M = 
\setlength{\extrarowheight}{1mm}
\begin{pNiceMatrix}
4 & 6 & 4 & 5 \
3 & 8 & 1 & 6 \
2 & 9 & 2 & 10 \
1 & 2 & 3 & 18 
\CodeAfter
  \tikz \draw (1-2) circle (1.7mm) 
              (2-2) circle (1.7mm) 
              (3-4) circle (2.1mm) 
              (4-4) circle (2.1mm) ;
\end{pNiceMatrix}$
\end{document}

Put a circle around elements in a matrix environment

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