How to Emphasis/Highlight Specific Components of a Matrix (e. g. Bold or Color)

Question

I have the following matrix

\begin{pmatrix} 
  1 & 3 & 2 & 6 \\ 
  4 & 1 & 8 & 2 \\ 
  3 & 9 & 4 & 12 \\ 
  12 & 3 & 16 & 4 
\end{pmatrix}

And I want the '1' and '6' from the first row and '12' and '4' from the last row to be marked in some way. Either in bold lettering or inside a small 'box' or some other way (not a different color though). I want it to be clear to the reader, these are the Komponents to pay attention to. Does anyone know how to do this?

Answer 1

• I made the numbers bold - please see How can I get bold math symbols?.
• For colored numbers, please see Simpler way to add color to equations in math mode?.

Code

\documentclass[]{article}

\usepackage{amsmath}
\usepackage{bm}

\begin{document}

% https://tex.stackexchange.com/questions/595

\begin{equation}
\begin{pmatrix} 
  \bm{1} & 3 & 2 & \bm{6} \\ 
  4 & 1 & 8 & 2 \\ 
  3 & 9 & 4 & 12 \\ 
  \bm{12} & 3 & 16 & \bm{4} 
\end{pmatrix}
\end{equation}

\end{document}

Output

Answer 2

Three other possibilities:

\documentclass[]{article}
\usepackage[svgnames]{xcolor}
\usepackage{mathtools}
\usepackage{bm}
\newcommand\ub[1]{\underbracket[0.4pt][1.5pt]{\mkern1mu#1\mkern1mu}}
\newcommand\hl[1]{\color{DarkGrey}{\bm{#1}}}

\begin{document}

\begin{equation}\setlength\fboxsep{2pt}
  \begin{pmatrix}
    \boxed{1} & 3 & 2 & \boxed{6} \\
    4 & 1 & 8 & 2 \\
    3 & 9 & 4 & 12 \\
    \boxed{12} & 3 & 16 & \boxed{4}
  \end{pmatrix}
  \qquad
  \begin{pmatrix}
    \ub{1} & 3 & 2 & \ub{6} \\
    4 & 1 & 8 & 2 \\
    3 & 9 & 4 & 12 \\
    \ub{12} & 3 & 16 & \ub{4}
  \end{pmatrix}
  \qquad
  \begin{pmatrix}
    \hl{1} & 3 & 2 & \hl{6} \\
    4 & 1 & 8 & 2 \\
    3 & 9 & 4 & 12 \\
    \hl{12} & 3 & 16 & \hl{4}
  \end{pmatrix}
\end{equation}

\end{document}