# tikz matrix : centering cells

I have what's below and I do not know why the term m_{n+1,k} is not horizontally centered in its cell?

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{tikz}
\usetikzlibrary{matrix,positioning}
\begin{document}
\begin{tikzpicture}[baseline=(current  bounding  box.center)]
\tikzset{square matrix/.style={outer sep=-6pt,matrix of nodes,
nodes={draw,
minimum height=0.7cm,
anchor=center,
text width=0.7cm,
align=center,
outer sep=-6pt}}}
\matrix(mymatrix)[square matrix,left delimiter={[},right delimiter={]}]{
1 & 0\\
0 & $-m_{n+1,k}$\\};
\end{tikzpicture}
\end{document}

-
Because you specified text width, so the cell can't become large enough to accommodate the whole text. Try minimum width instead. Side question: Do you actually want the node borders to be drawn, or is this just for testing purposes? –  Jake Feb 9 '12 at 22:01
borders are here for testing purposes. I'll give the minimum width option a try. Thank you –  pluton Feb 10 '12 at 1:53
Just remove the text width=0.7cm and it will center automatically anyway or reduce the font size with \scriptscriptstyle. Otherwise you will be overprinting. –  percusse Feb 10 '12 at 15:29

ok, the minimum width option helps but I am now using a \makebox[0pt][c]{$-m_{k+1,n}$} to get the desired matrix.

-