支撑矩阵

Question

如何才能让它看起来不错？请帮忙！

Answer 1

你可以调整我的答案https://tex.stackexchange.com/a/145718/4427

\documentclass{article}
\usepackage{amsmath}

\newcommand{\underbracedmatrix}[2]{%
  \left(\;
  \smash[b]{\underbrace{
    \begin{matrix}#1\end{matrix}
  }_{#2}}
  \;\right)
  \vphantom{\underbrace{\begin{matrix}#1\end{matrix}}_{#2}}
}

\begin{document}
\[
\Delta_n=\det
  \underbracedmatrix{
    A & B \\
    B & A & B \\
      & B & \ddots & \ddots \\
      &   & \ddots & \ddots & B \\
      &   &        & B      & A
  }{n\times n}
\]
\end{document}