I want to produce equations with block matrices
\documentclass[a4paper,12pt,titlepage]{article} \usepackage[fleqn]{amsmath} \usepackage[pdftex]{graphicx} \usepackage{blkarray} \usepackage{mathtools} \usepackage{multirow} \newcommand{\rdots}{\hspace{.2ex}\raisebox{1ex}{\rotatebox{-12}{$\ddots$}}} \begin{document} \resizebox{0.9\textwidth}{!}{\begin{minipage}{\textwidth} \begin{align} \begin{blockarray}{(cccc|cccc)} 1 & & 0 & \cdots & \BAmulticolumn{4}{c}{\multirow{4}{*}{\huge$0$}}\\ & \rdots & & & & & &\\ 0 & & 1 & & & & &\\ \vdots & & & \rdots & & & &\\ \cline{1-8} & & & & 1 & & & \cdots \\ \BAmulticolumn{4}{c|}{\multirow{4}{*}{\huge$0$}} & & \rdots & \\ & & & & 0 & & 1 & \\ & & & & \vdots & & &\rdots \\ \end{blockarray}+ \begin{blockarray}{(cccc|cccc)} \BAmulticolumn{4}{c|}{\multirow{4}{*}{\huge$0$}} & \BAmulticolumn{4}{c}{\multirow{4}{*}{\huge$S-T$}} \\ & & & & & & & & \\ & & & & & & & & \\ & & & & & & & & \\ \cline{1-8} \BAmulticolumn{4}{c|}{\multirow{4}{*}{\huge$T-S$}} & \BAmulticolumn{4}{c}{\multirow{4}{*}{\huge$0$}} \\ & & & & & & & & \\ & & & & & & & & \\ & & & & & & & & \\ \end{blockarray} \end{align} \end{minipage}} \end{document} My code produces the correct matrices, but they are not the same size: 
the one on the lefthand size (with the S-T) is smaller! I don't get why, can anyone help?
\[ \huge \left( \begin{array}{c|c} I & 0 \\ \hline 0 & I \end{array} \right) + \left( \begin{array}{c|c} 0 & S-T \\ \hline T-S & 0 \end{array} \right) \](with a possible remark explaining thatIdenotes an identity matrix of the given size)? This is more concise and looks a lot better (in my opinion).