用線劃分矩陣

Question

我用什麼把矩陣分成垂直線和水平線？

\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*}

Answer 1

我建議你從一個bmatrix環境切換到另一個array環境。以下螢幕截圖中的第三個矩陣在第 3 和第 6 列之後有垂直線，在第 3、6 和 9 行之後有水平線。

\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}