3

What do I use to divide the matrix into a vertical line and a horizontal line?

\begin{equation*}
 A= 
\begin{bmatrix}
a & b & c & a & b & c & a & a & a & a \\
d & e & f & a & b & c & a & a & a & a \\
g & h & i & a & b & c & a & a & a & a \\
a & b & c & a & b & c & a & a & a & a \\
d & e & f & a & b & c & a & a & a & a \\
a & b & c & a & b & c & a & a & a & a \\
d & e & f & a & b & c & a & a & a & a \\
g & h & i & a & b & c & a & a & a & a \\
a & b & c & a & b & c & a & a & a & a \\
d & e & f & a & b & c & a & a & a & a \\
d & e & f & a & b & c & a & a & a & a \\
g & h & i & a & b & c & a & a & a & a 
\end{bmatrix}
\end{equation*}
Mico
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Tomais
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  • 1
    Please remember to post only code, which compiles when we copied it. Thank you – MS-SPO Jan 18 '24 at 03:44
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    does this help - https://tex.stackexchange.com/questions/459295/how-to-have-a-dotted-line-separate-a-matrix-into-upper-and-lower-part?rq=1 – js bibra Jan 18 '24 at 04:00
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    Where should the vertical and horizontal lines be placed? – Mico Jan 18 '24 at 04:18

1 Answers1

4

I suggest you switch from the bmatrix environment to an array environment. The third matrix in the following screenshot has vertical lines after columns 3 and 6, and horizontal lines after rows 3, 6, and 9.

enter image description here

\documentclass{article}
\usepackage{amsmath} % for 'align*' env.

\begin{document}
\begin{align}
A &= 
\begin{bmatrix}
a & b & c & a & b & c & a & a & a & a \
d & e & f & a & b & c & a & a & a & a \
g & h & i & a & b & c & a & a & a & a \
a & b & c & a & b & c & a & a & a & a \
d & e & f & a & b & c & a & a & a & a \
a & b & c & a & b & c & a & a & a & a \
d & e & f & a & b & c & a & a & a & a \
g & h & i & a & b & c & a & a & a & a \
a & b & c & a & b & c & a & a & a & a \
d & e & f & a & b & c & a & a & a & a \
d & e & f & a & b & c & a & a & a & a \
g & h & i & a & b & c & a & a & a & a 
\end{bmatrix} \
&= 
\left[ \begin{array}{@{} {10}{c} @{}} % switch to an 'array' setup
a & b & c & a & b & c & a & a & a & a \
d & e & f & a & b & c & a & a & a & a \
g & h & i & a & b & c & a & a & a & a \
a & b & c & a & b & c & a & a & a & a \
d & e & f & a & b & c & a & a & a & a \
a & b & c & a & b & c & a & a & a & a \
d & e & f & a & b & c & a & a & a & a \
g & h & i & a & b & c & a & a & a & a \
a & b & c & a & b & c & a & a & a & a \
d & e & f & a & b & c & a & a & a & a \
d & e & f & a & b & c & a & a & a & a \
g & h & i & a & b & c & a & a & a & a 
\end{array} \right] \
&\approx 
\left[ \begin{array}{@{} ccc | ccc | cccc @{}} % add vertical and horizontal lines
a & b & c & a & b & c & a & a & a & a \
d & e & f & a & b & c & a & a & a & a \
g & h & i & a & b & c & a & a & a & a \
\hline
a & b & c & a & b & c & a & a & a & a \
d & e & f & a & b & c & a & a & a & a \
a & b & c & a & b & c & a & a & a & a \
\hline
d & e & f & a & b & c & a & a & a & a \
g & h & i & a & b & c & a & a & a & a \
a & b & c & a & b & c & a & a & a & a \
\hline
d & e & f & a & b & c & a & a & a & a \
d & e & f & a & b & c & a & a & a & a \
g & h & i & a & b & c & a & a & a & a 
\end{array} \right]
\end{align*}


\end{document}
Mico
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