答案1
举个例子,我已经通过编辑创建了图像的最后一个矩阵非常好的用户@egreg:
%% Compile and read me!
\documentclass[a4paper,12pt]{article}
\usepackage{mathtools}
\usepackage{newtxtext,newtxmath}
\begin{document}
\[\mathrel{\underset{\sim}{R}}\begin{bmatrix}
1 & 0 & 0 \\
0 & 1 & 0 \\
0 & 0 & 0
\end{bmatrix}
\begin{matrix}
\\
\,\text{by }\,\mathsf{R}_{1}+\mathsf{R}_{3}\text{ and }\,\mathsf{R}_{2}-\mathsf{2R}_{3}\\
\\
\end{matrix}\]
\end{document}