This code is building from the solutions posted .  I am trying the approach suggested from the .  I am having two issues:   I am not sure how to get the arrow to point to the text "free variable" with this new approach, and The brackets seem to be shorter and closer to the numbers as compared to the original matrix.   Can you help me fix these issues of drawing the arrow to point to the text and also fix the way how the brackets appear?    This is how I would like my end result to look, Thanks!:    Here is the code:  \documentclass[11pt]{book}  \usepackage{amsmath,amsfonts,amssymb,amsthm} \usepackage{xcolor} \definecolor{ocre}{RGB}{0,173,239}  \usepackage{blkarray}  \makeatletter \renewcommand*\env@matrix[1][*\c@MaxMatrixCols c]{%   \hskip -\arraycolsep   \let\@ifnextchar\new@ifnextchar   \array{#1}} \makeatother  \usepackage{tikz}  \usetikzlibrary{arrows,matrix,positioning,fit} \tikzset{%   highlight/.style={rectangle,rounded corners,fill=ocre!50,draw,     fill opacity=0.5,thick,inner sep=0pt} } \newcommand{\tikzmark}[2]{\tikz[overlay,remember picture,   baseline=(#1.base)] \node (#1) {#2};} % \newcommand{\Highlight}[1][submatrix]{%     \tikz[overlay,remember picture]{     \node[highlight,fit=(left.north west) (right.south east)] (#1) {};} }  \begin{document}  \[ \begin{blockarray}{ccccc} x_{1} &amp; x_{2} &amp; x_{3} &amp; x_{4} &amp;  \\ \begin{block}{[cccc|c]}   1 &amp; 0 &amp; \tikzmark{left}{-1} &amp; 0 &amp; 0 \\   0 &amp; 1 &amp; 2 &amp; 0 &amp; 0 \\   0 &amp; 0 &amp; \tikzmark{right}{0} &amp; 1 &amp; 0 \\ \end{block} \end{blockarray}  \]  \Highlight[new1]   \tikz[overlay,remember picture] {   \draw[-&gt;,thick,red,dashed] (new1)  node [pos=0.66,above,text width = 2cm] {\emph{free \\ variable}; }}  \end{document}
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):  $$ A = \begin{bmatrix} \fbox{0} &amp; \fbox{0} &amp; 0 \\  \fbox{0} &amp; \fbox{0} &amp; 0 \\ 1 &amp; 1 &amp; 1 \\  \end{bmatrix}$$   But how can I outline elements of the submatrix like in the picture below? I need just a frame where some elements are located.
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Now I'm trying to add a table with notes right underneath it, like in this table for instance:    Since the \caption{} is used as a title above the table, I have to add an extra row for the notes that goes over the whole table width. The problem is that the notes won't fit into one line so I need multi-line cell. How can I accomplish that? Or am I doing it totally wrong and there is a much easier way? I guess footnotes don't work here.  \documentclass{apa6e}  \begin{document} \shorttitle{} \begin{table} \caption{title} \begin{tabular}{cc} foo &amp; bar\\ \hline \multicolumn{2}{l}{Notes. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Cras lacus orci, porttitor et posuere sit amet, tempor non justo. Ut quis aliquet turpis. Ut dictum nulla eget purus elementum a lacinia libero varius. Donec malesuada nulla ut odio rhoncus convallis. Aenean faucibus sollicitudin sapien, a vestibulum ante rhoncus sit amet. In vitae mi justo. In arcu metus, porta et lacinia ut, ultricies sed eros.} \end{tabular}  \end{table} \end{document} Vertical spaces between lines in cases environment \documentclass{article} \usepackage{amsmath} \begin{document} \begin{equation*}   X_i =    \begin{cases}     \left[\begin{smallmatrix}       0 \\ 1 \\ 2     \end{smallmatrix}\right]     &amp;     \text{if $i$ is even;}     \\     \left[\begin{smallmatrix}       2 \\ 1 \\ 0     \end{smallmatrix}\right]     &amp;     \text{otherwise.}   \end{cases} \end{equation*} \end{document}   This is the LaTeX code that I wrote based on a cases environment. There's no space between the matrices on the right. What's the best way to add some vertical spaces to separate them?    p.s. This is a simplified form of my original writing, so I cannot just accept suggestions like 'use a matrix transpose to transform the column vector into a row vector.' Wouldn't it be a good idea to be able to vote for questions to be moved to any Stack Exchange site? For example, I just voted  as off topic, but that was all I could do. I wish I could've voted it be moved to .  It's OK to have the predefined list of sites that is now when voting to move, but it would be nice to have a more link, where we could pick any Stack Exchange site.  Here's a quick mockup of how I see this implemented:    When the more link is clicked, a list of all the Stack Exchange sites should appear. Integral of the square of the normal distribution. Using Virtual Box, how can I install an OS to a secondary, physical disk, and boot it in both (at separate times) Virtual Box, and as a typical secondary OS install? Given that the sequence $(v,Av,A^2v,...,A^nv)$ is linearly dependent (1), $A_{n \times n}$, over $\mathbb{F^n}$ prove that scalars $c_0,c_1,..,c_n$ exist (such that not all of them are zeroes) such that the matrix $M=c_0I+c_1A+..+c_nA^n$ is singular.    First I'm not sure how (*) can be used here exactly. We can say that the sequence $(c_0I,c_1A,..,c_nA^n)$ resembles the sequence (1) where $v=I$. But here we have scalar $c_i$ so it's not exactly the same sequence.   Maybe I could say that the sequence $(c_0I,c_1A,..,c_nA^n)$ is linearly dependent because it has $n+1$ elements while over $dim\mathbb{F^n}=n$ $\quad$(2).  Intuitively I understand that suppose we sum all the matrices $c_iA^i$ and then in the last sum operation we get to some $c_jA^j$ and if it's a linear combination of other matrices then we can have such a $c_j$ that: $$ c_oI+\sum_{i=1}^{n-1} c_iA^i+c_jA^j=0 $$ But I don't think this is enough to prove. How do I remove "Ubuntu" in the bios boot menu? (UEFI) What can I do with .chk files in FOUND.000 folders? Just discovered I have gotten a FOUND.000 folder on my usb drive. I guess from running chkdsk once. It has three files in it:   FILE0000.CHK FILE0001.CHK FILE0002.CHK   What exactly can I do with these files? What are my options? Are they lost files? Are they garbage? 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