Splitting a large matrix into two arrays with horizontal dots

Question

I've been reading a book that had the following equation:

And I was wondering how to copy that into a TeX code, I'm not sure how to split this matrix properly while including the name of it and having it numbered as one equation (the exact entries are not necessary).

Answer 1

I suggest you embed an aligned[b] environment in an equation environment, so that the equation number gets placed on the bottom row. Then use a

\left( \begin{matrix} ... \end{matrix} \right.

construct in the upper row and a

\right. \begin{matrix} ... \end{matrix} \left)

construct in the lower row.

\documentclass{article} % or some other suitable document class
\usepackage{amsmath}    % for 'aligned' environment

\begin{document}

\begin{equation}
\begin{aligned}[b]
\mathbf{Y}_{\ell}(r) 
&= \left(
  \begin{matrix}
  a & b & 0 \\
  c & d & 0 \\
  e & f & \rho_0 r^l \\
  g & h & 0  \\
  0 & 0 & r^l\\
  i & j & k 
  \end{matrix}
  \right.  \ \cdots \\
&\qquad \cdots \ \left. 
  \begin{matrix}
  l & m & 0 \\
  n & o & 0 \\
  p & q & r \\
  s & t & 0 \\
  0 & 0 & u \\
  v & w & 0
  \end{matrix}
  \right)
\end{aligned}
\end{equation}

\end{document}