# How can I get the explanation borders with pmatrix?

I have asked this question in chat. How can I add the explanation borders to the below matrix?

\begin{align*}
C_{D_{1\succ 2}, \mathrm{increasing}}    &= \underbrace{\begin{pmatrix} 1   &   -1  &   1 & -1  &   1   &   -1 &    1 & -1  \\ \end{pmatrix}}_{1\times 8\text{ matrix}}  \\
A_{D_{1\succ 2}, \mathrm{increasing}}    &=
\underbrace{\begin{pmatrix}
1   &   0   &   1   &   0   &   1   &   0   &   1   &   0   \\
0   &   1   &   0   &   1   &   0   &   1   &   0   &   1   \\
1   &   1   &   0   &   0   &   1   &   1   &   0   &   0   \\
0   &   0   &   1   &   1   &   0   &   0   &   1   &   1   \\
1   &   1   &   1   &   1   &   0   &   0   &   0   &   0   \\
1   &   1   &   1   &   1   &   0   &   0   &   0   &   0   \\
0   &   0   &   0   &   0   &   1   &   1   &   1   &   1   \\
\end{pmatrix}}_{7\times 8 \text{ matrix}}.
\end{align*}

I want this kind of $p_1, p_2, ...$ borders to the matrix above. I have been able to add them with blockarray and block here but now I need to add them to the existing pmatrix data-structure. How can I get it with the pmatrix?

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Consider the kbordermatrix package: hss.caltech.edu/~kcb/TeX/kbordermatrix.pdf (you may need to get the .sty file yourself: mirrors.ustc.edu.cn/CTAN/macros/generic)/misc/kbordermatrix.sty. – Ethan Bolker Aug 26 '13 at 14:11

You can use the kbordermatrix package which is for some reason not CTAN but you can download it from http://www.hss.caltech.edu/~kcb/LaTeX.shtml and there is a short documentation there too. Just save the .sty file to the same folder with your actual document.

\documentclass{article}
\usepackage{mathtools,kbordematrix}

\begin{document}

% Change the default brackets to parentheses
\renewcommand{\kbldelim}{(}
\renewcommand{\kbrdelim}{)}
$\underbrace{\kbordermatrix{ & t_1& t_2 &\cdots & t_n & \cdots & t_h &\cdots & t_{2^n}\\ p_1 & 1 & 0 & 1 & 0 & 1 & 0 & 1 & 0 \\ p_2 & 0 & 1 & 0 & 1 & 0 & 1 & 0 & 1 \\ p_3 & 1 & 1 & 0 & 0 & 1 & 1 & 0 & 0 \\ p_4 & 0 & 0 & 1 & 1 & 0 & 0 & 1 & 1 \\ \hline p_5 & 1 & 1 & 1 & 1 & 0 & 0 & 0 & 0 \\ p_6 & 1 & 1 & 1 & 1 & 0 & 0 & 0 & 0 \\ p_7 & 0 & 0 & 0 & 0 & 1 & 1 & 1 & 1 \\ }}_{7\times 8 \text{ matrix}}$
\end{document}

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Do you know whether there is any easy way to get the underbrace only under the matrix not under the explanation column $p_1,p_2,...,p_7$? – hhh Aug 26 '13 at 15:56
@hhh You can use \cline{2-12} starting from the second column – percusse Aug 27 '13 at 14:38

I'm sorry but I don't understand which one you are referring to. So, I've added both.

\documentclass{article}
\usepackage{amsmath}
\usepackage{blkarray,multirow}

\begin{document}

\begin{align*}
I_{D_{1\succ 2}, \mathrm{increasing}} &= \{53, 54, 57, 58, 69, 70, 73, 74\}_{\mathrm{DEC}} \\
C_{D_{1\succ 2}, \mathrm{increasing}} &= \underbrace{\begin{pmatrix} 1 & -1 & 1 & -1 & 1 & -1 & 1 & -1 \\ \end{pmatrix}}_{1\times 8\text{ matrix}} \\
A_{D_{1\succ 2}, \mathrm{increasing}} &=
\underbrace{\begin{blockarray}{ccccccccc}
\begin{block}{c(cccccccc)}
p_1 & 1 & 0 & 1 & 0 & 1 & 0 & 1 & 0 \\
p_2 & 0 & 1 & 0 & 1 & 0 & 1 & 0 & 1 \\
p_3 & 1 & 1 & 0 & 0 & 1 & 1 & 0 & 0 \\
p_4 & 0 & 0 & 1 & 1 & 0 & 0 & 1 & 1 \\
p_5 & 1 & 1 & 1 & 1 & 0 & 0 & 0 & 0 \\
p_6 & 1 & 1 & 1 & 1 & 0 & 0 & 0 & 0 \\
p_7 & 0 & 0 & 0 & 0 & 1 & 1 & 1 & 1 \\
\end{block}
\end{blockarray}}_{7\times 8 \text{ matrix}}.
\end{align*}

$A= \underbrace{\begin{blockarray}{ccc|cccc|c|cccc} & t_1& t_2 & ... & ... & ... & ... & t_n & ... & t_h & ... & t_{2^n} \\ \begin{block}{c(cc|cccc|c|cccc@{\hspace*{5pt}})} p_1 &1&0& \BAmulticolumn{4}{c|}{\multirow{4}{*}{B_1}}& 0 &...&1&...&1\\ p_2 &0&1& &&&&0&...&0&...&1\\ p_3 &0&0& &&&&0&...&1&...&1\\ p_4 &0&0& &&&&0&...&0&...&1\\ \cline{1-12}% don't use \hline p_5 &0&0& \BAmulticolumn{4}{c|}{\multirow{4}{*}{B_2}}& 0 &...&0&...&1\\ p_6 &0&0 &&&&&0&...&0&... &1\\ ... &...&... &&&&&...&...&...&... &...\\ p_{n-1} &0&0 &&&&&0&...&0&... &1\\ p_n &0&0 &&&&&1&...&0&... &1\\ \end{block} \end{blockarray}}_{7\times 8 \text{ matrix}}.$

\end{document}

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It is slightly misleading to have the underbrace under the explanation borders because the matrix is just the thing inside the brackets. How to get it only under the brackets (not having the $p_1,p_2, ...,p_n$ column)? – hhh Aug 26 '13 at 15:44