[texhax] Dividing a matrix into sub-matrices

[Wolfgang Lorenz]

Hello list readers,


I'd like to create a matrix, that's subdivided into several
sub-matrices. The elements of all matrices still should be aligned. I
have found the package blkarray, which is does the placing of the
elements and also produces the sub-matrix brackets. Unfortunately, when
I put the brackets around the whole matrix there seems to be an empty
line below the sub-matrices (see quite minimal example below). Using
nested bmatrix environments produces the right brackets, but doesn't
align the elements of the sub-matrices. Is there a way to get the best
out of both methods?


Thanks,
  Wolfgang


%%% Example file: submatrix.tex %%%

\documentclass{scrreprt}
\usepackage{amsmath}
\usepackage{blkarray}

\newcommand{\xy}[2]{\ensuremath{\frac{x_{#1}}{y_{#2}}}}

\begin{document}

\begin{equation}
	\begin{bmatrix}
		\begin{bmatrix}
			\xy{1,1}{1,1} & 0 \\
			\xy{1,2}{1,1} & 0
		\end{bmatrix} &
		\begin{bmatrix}
			\xy{1,1}{2,1} & \xy{1,1}{2,2} \\
			\xy{1,2}{2,1} & \xy{1,2}{2,2}
		\end{bmatrix} \\
		\begin{bmatrix}
			\xy{2,1}{1,1} & \xy{2,1}{1,2} \\
			\xy{2,2}{1,1} & \xy{2,2}{1,2}
		\end{bmatrix} &
		\begin{bmatrix}
			\xy{2,1}{2,1} & \xy{2,1}{2,2} \\
			\xy{2,2}{2,1} & \xy{2,2}{2,2}
		\end{bmatrix}
	\end{matrix}
\end{equation}

\begin{equation}
	\left[\begin{blockarray}{cccc}
		\begin{block}{[cc][cc]}
			\xy{1,1}{1,1} & 0 & \xy{1,1}{2,1} & \xy{1,1}{2,2} \\
			\xy{1,2}{1,1} & 0 & \xy{1,2}{2,1} & \xy{1,2}{2,2} \\
		\end{block}
		\begin{block}{[cc][cc]}
			\xy{2,1}{1,1} & \xy{2,1}{1,2} & \xy{2,1}{2,1} & \xy{2,1}{2,2} \\
			\xy{2,2}{1,1} & \xy{2,2}{1,2} & \xy{2,2}{2,1} & \xy{2,2}{2,2} \\
		\end{block}
	\end{blockarray}\right]
\end{equation}

\end{document}

%%% End of example file %%%