Matrix in a matrix
Something like this ?
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\[
\left[
\begin{array}{c@{}c@{}c}
\left[\begin{array}{cc}
a_{11} & a_{12} \\
a_{21} & a_{22} \\
\end{array}\right] & \mathbf{0} & \mathbf{0} \\
\mathbf{0} & \left[\begin{array}{ccc}
b_{11} & b_{12} & b_{13}\\
b_{21} & b_{22} & b_{23}\\
b_{31} & b_{32} & b_{33}\\
\end{array}\right] & \mathbf{0}\\
\mathbf{0} & \mathbf{0} & \left[ \begin{array}{cc}
c_{11} & c_{12} \\
c_{21} & c_{22} \\
\end{array}\right] \\
\end{array}\right]
\]
\end{document}
After seven years ... with use of bmatrix
from the amsmath
package:
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\[
\begin{bmatrix}
\begin{bmatrix}
a_{11} & a_{12}\\
a_{21} & a_{22}\\
\end{bmatrix} & \mathbf{0} & \mathbf{0} \\
\mathbf{0} & \begin{bmatrix}
b_{11} & b_{12} & b_{13}\\
b_{21} & b_{22} & b_{23}\\
b_{31} & b_{32} & b_{33}\\
\end{bmatrix} & \mathbf{0} \\
\mathbf{0} & \mathbf{0} & \begin{bmatrix}
c_{11} & c_{12}\\
c_{21} & c_{22}\\
\end{bmatrix} \\
\end{bmatrix}
\]
\end{document}