framedhighlightingmath-modematrices
I have a matrix and need to highlight some elements in the matrix. I have found how to highlight a single element (I want to put the cell in the square):
$$ A = \begin{bmatrix}
\fbox{0} & \fbox{0} & 0 \\
\fbox{0} & \fbox{0} & 0 \\
1 & 1 & 1 \\
\end{bmatrix}$$
But how can I outline elements of the submatrix like in the picture below? I need just a frame where some elements are located.
update
\documentclass{article}
\usepackage{tikz,amsmath}
\begin{document}
\newcommand\hlight[1]{\tikz[overlay, remember picture,baseline=-\the\dimexpr\fontdimen22\textfont2\relax]\node[rectangle,fill=blue!50,rounded corners,fill opacity = 0.2,draw,thick,text opacity =1] {$#1$};}
\begin{equation*}
\begin{pmatrix}
c & -a & 0 & \dots & \dots & \dots & 0 \\
-b & \hlight{a} & -a & \ddots & & & \vdots \\
0 & -b & c & \ddots & \ddots & & \vdots \\
\vdots & \ddots & \ddots & \ddots & \ddots & \ddots & \vdots \\
\vdots & & \ddots & \ddots & c & -a & 0 \\
\vdots & & & \ddots & -b & c & -a \\
0 & \dots & \dots & \dots & 0 & -b & c
\end{pmatrix}
\end{equation*}
\end{document}
One possibility is to set nodes and then do the highlighting with overlays.
\documentclass{beamer}
\usepackage{tikz}
\usetikzlibrary{calc,arrows,automata,positioning,fit}
\newcommand{\tikznode}[2]{\relax
\ifmmode%
\tikz[remember picture,baseline=(#1.base),inner sep=0pt] \node (#1) {$%\tikznodestyle
#2$};
\else
\tikz[remember picture,baseline=(#1.base),inner sep=0pt] \node (#1) {#2};%
\fi}
\usepackage{blkarray}
\begin{document}
\begin{frame}{Example}
\begin{figure}[H]
\centering
\begin{columns}
\begin{column}{.5\linewidth}
\scalebox{0.5}{
$
\renewcommand\arraystretch{1.3}
\begin{blockarray}{ccccccc}
& 1 & 2 & 3 & 4 & 5 & \tikznode{1}{6} \\
\begin{block}{@{}c\{[ccccc]c}
1 & 0 & 1 & 0 & 0 & 0 & 0 \\
2 & 0 & 0 & 1 & 0 & 1 & 0 \\
3 & 0 & 0 & 0 & 1 & 0 & 0 \\
4 & 0 & 0 & 0 & 0 & 0 & 0 \\
5 & 1 & 0 & 0 & 0 & 0 & 1 \\
6 & 0 & 1 & 0 & 0 & 0 & \tikznode{2}{0} \\
\end{block}
\tikznode{s}{s} & 1 & 2 & 2 & 2 & \tikznode{3}{2} \\
\end{blockarray}
$
\tikz[overlay,remember picture]{
\node[fill=blue,opacity=0.3,fit=(1) (2)]{};
\node[fill=blue,opacity=0.3,fit=(s) (3)]{}; }
}
\end{column}
\begin{column}{.5\linewidth}
\scalebox{0.5}{
$
\renewcommand\arraystretch{1.3}
\begin{blockarray}{ccccccc}
& 1 & 2 & 3 & 4 & 5 & \tikznode{5}{6} \\
\begin{block}{@{}c\{[ccccc]c}
1 & \tikznode{A}{0} & 1 & 0 & 0 & 0 & 0 \\
2 & 0 & 0 & 1 & 0 & 1 & 0 \\
3 & 0 & 0 & 0 & 1 & 0 & 0 \\
4 & 0 & 0 & 0 & 0 & 0 & 0 \\
5 & 1 & 0 & 0 & 0 & \tikznode{B}{0} & 1 \\
6 & 0 & 1 & 0 & 0 & 0 & \tikznode{6}{0} \\
\end{block}
\tikznode{7}{s} & 1 & 2 & 2 & 2 & \tikznode{8}{2} \\
\end{blockarray}
$
\tikz[overlay,remember picture]{
\node[fill=green,opacity=0.3,fit=(5) (6)]{};
\node[fill=green,opacity=0.3,fit=(7) (8)]{};
\path let \p1=(A), \p2=(B), \n1={atan2(\y2-\y1,\x2-\x1)} in
node[fill=red,opacity=0.3,rotate fit=\n1,fit=(A) (B)]{}; }
}
\end{column}
\end{columns}
\caption{Example}
\end{figure}
\end{frame}
\end{document}
Best Answer
You could use TikZ, and
fitlibrary for creating nodes fitting the desired area,overlayandremember picture, so you can later refer to those nodes, for example for drawing arrows and annotations later.To demonstrate why it's useful to have nodes for reference, I created an example, which shows transposing a matrix, highlights a submatrix both in the original matrix and the result, connected by an arrow and annotated: