Matrix in a matrix

Question

I would like to draw a matrix with top left, top right, bottom left and bottom right blocks. The top left should be a 3x3 matrix with numerical entries, the top right is 0, the bottom left is 0 and the bottom right is just a "single" entry uJ. Here is my attempt.

$
\left[
\begin{array}{c|c}
[\begin{array{c|c|c}
0 & 0 & 2\mathrm tr(MM^{*}) \\
0 & 0 & -ua \\
u & -ua & 0 \end{array}]     &  0\\ \hline
0 & uJ 
\end{array}\right].
$

I would like to emphasize that the non-top-left entries are not just single entries, but blocks, so I do not want to just make a 4 by 4 matrix with vlines and hlines and additional 0's.

Welcome to TeX.SE. While code snippets are useful in explanations, it is always best to compose a fully compilable MWE that illustrates the problem including the \documentclass and the appropriate packages so that those trying to help don't have to recreate it. — Peter Grill, Apr 03 '12 at 17:51

score 34 · Accepted Answer · edited Jun 07 '17 at 17:48

34

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}

enter image description here

edited Jun 07 '17 at 17:48

Moriambar

11,466

answered Apr 03 '12 at 17:56

Alain Matthes

95,075

What does the @{} in the array definition mean? – amoebe Jan 10 '17 at 01:02
3

@amoebe @{} means nothing (no space) between those columns. If you want, you can have anything, by setting @{<anything>} – marsupilam Jun 07 '17 at 17:50

score 7 · Answer 2 · edited Apr 24 '19 at 03:40

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}

Matrix in a matrix

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