I am using this solution here to make long dashes within a matrix, and it is working well. The code is:
\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{matrix}
% possible to customize here the dash aspect
\newcommand{\mydash}{
\draw(0.3,0.5ex)--(-0.3,0.5ex);
}
\begin{document}
\[P=
\begin{tikzpicture}[baseline=-0.5ex]
\matrix(m)[matrix of math nodes,left delimiter=(,right delimiter=),ampersand replacement=\&]
{
\mydash \& y_1 \& \mydash \\
\mydash \& y_2+z_2 \& \mydash \\
\mydash \& y_3 \& \mydash \\
};
\end{tikzpicture}
\]
\end{document}
However, I am now sure how to start writing full blown equations with it. I have not had much luck. The above makes a nice matrix with lines along the rows.
1) What I want is something like P = X Y Z, where X, Y , and Z, are all shown with the lines along its rows as in the prior example given. I cannot seem to concatenate them for whatever reason though...
2) I would like the matrix brackets to also be square, and not curvy.

[. – kan Apr 10 '13 at 21:00