# Write elements above and right outside the matrix

I found writing matrix's code is a boring work. There is one, you can see in pic below.

Can anybody help?

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This would be a good start: Where is the \matrix command? –  Werner Feb 23 '12 at 3:27
Thanks. I found only the blkarray package may provide help (Was I wrong?) from your links. But there is a large warning in its PDF document's. Can I use it without leading to any incompatibility? –  may you Feb 23 '12 at 3:38

This is definitely possible when using the blkarray package. Here's a mock-up with some index styling (in \scriptsize):

\documentclass{article}
\usepackage{blkarray}% http://ctan.org/pkg/blkarray
\newcommand{\matindex}[1]{\mbox{\scriptsize#1}}% Matrix index
\begin{document}
$A=\begin{blockarray}{ccc} \matindex{1} & \matindex{2} & \\ \begin{block}{(cc)c} a & b & \matindex{3} \\ c & d & \matindex{4} \\ e & f & \\ \end{block} \end{blockarray}$
\end{document}


This would also be doable using a plain array, but would require additional vertical alignment/compensation, perhaps removing some of the code readability that exists via blkarray.

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Hi Werner. I found your answer helpful. How does one selectively adjust the spacing between the block and the elements exterior to the block? –  user001 Mar 21 '12 at 1:12
@user001: Just on one side, or both (right and above)? –  Werner Mar 25 '12 at 21:29
Preferably I would like to adjust the spacing between the top elements and the matrix and the right elements and the matrix to different extents. –  user001 Mar 26 '12 at 1:20