[Tex/LaTex] How to adjust the width of a \hdashline inside a pmatrix

Question

I'm using \hdashline from the arydshln package to draw a horizontal line inside a pmatrix:

How can I reduce the width of this line to prevent it from touching the outer parentheses?

Answer 1

One way to do this is to use an array environment and make use of the @{} intercolumn specifiers to put in some negative space. Here is one piece of example code.

\documentclass{article}

\usepackage{amsmath,array,arydshln}

\begin{document}

\begin{equation*}
  \left(  
    \mkern4mu\begin{array}{@{\mkern-4mu}c@{\mkern-4mu}}
      \begin{pmatrix}
        r_{11}&r_{12}&r_{13}\\
        r_{21}&r_{22}&r_{23}\\
        r_{31}&r_{32}&r_{33}\\
      \end{pmatrix}
      \begin{pmatrix}
        x\\y\\z
      \end{pmatrix}
      \\
      \hdashline 1
    \end{array}\mkern4mu
  \right)
\end{equation*}

\end{document}