# Matrix within matrix with numbering

What is the best way to create the below matrix in LaTeX? I tried two ways

1) using gather, pmatrix and vmatrix inside but cannot get the desired formatting

\begin{gather}
\begin{pmatrix}
\begin{vmatrix} x_{11} & x_{12} \\  x_{21} & x_{22}\\ \end{vmatrix}
\\ y \\ z\\
\end{pmatrix}
\end{gather}


2) I get the right format using two arrays but the numbering (gather) doesn't work

\begin{gather}
$\left( \begin{array}{cr} \left| \begin{array}{cr} x_{11} & x_{12} \\ x_{21} & x_{22} \end{array}\right| \\ y \\ z \\ \end{array} \right)$
\end{gather}


You shouldn't be using gather for a single equation. Anyway, the second example is wrong because you must not have $...$ inside a math display.

The image shows too wide spaces around the fences; it was probably obtained with array.

I'll present three possibilities, in order of preference. Here I use three consecutive equation environment just because they're independent examples; for groups of consecutive equations, gather or align should obviously be used in a real document.

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{equation}
\begin{pmatrix}
\begin{vmatrix} x_{11} & x_{12} \\  x_{21} & x_{22} \end{vmatrix}
\\ y \\ z
\end{pmatrix}
\end{equation}

\begin{equation}
\begin{pmatrix}
\;\begin{vmatrix} x_{11} & x_{12} \\  x_{21} & x_{22} \end{vmatrix}\;
\\ y \\ z
\end{pmatrix}
\end{equation}

\begin{equation}
\left(
\begin{array}{c}
\left|\begin{array}{cc}
x_{11} & x_{12} \\  x_{21} & x_{22}
\end{array}\right|
\\ y \\ z
\end{array}
\right)
\end{equation}

\end{document} 