我想要如下的效果
MWE如下:
\documentclass{article}
\usepackage{amsmath}% http://ctan.org/pkg/amsmath
\begin{document}
\[
\underbrace{\begin{pmatrix}x_1\\x_2\\x_3\end{pmatrix}}_\boldsymbol{x}
=\underbrace{\begin{pmatrix}1&-1&1\\0&1&-2\\0&0&1\end{pmatrix}}_{P}
\underbrace{\begin{pmatrix}y_1\\y_2\\y_3\end{pmatrix}}_\boldsymbol{y}
\implies\boldsymbol{x}=P\boldsymbol{y}
\]
\end{document}编译会报错
