# How to draw this particular block matrix

by Subhajit Paul   Last Updated August 13, 2019 20:23 PM - source

I need to draw the following block matrix

The closest I have got is by using the following code:

\begin{pmatrix}
\lambda_1 & * & \dots & *\\
0 &  \lceil &  & \rceil \\
\vdots  & \mid & A_{n-1} & \mid \\
0 & \lfloor & & \rfloor
\end{pmatrix}


which produces .

I am open for a tikz based solution; but in that case, it needs to fit properly with the following alignat* environment:

\begin{alignat*}{3}
A\begin{pmatrix}
u_1 & \tilde{u}_{2} & \dots & \tilde{u}_{n}
\ lambda_1 u_1 & A\tilde{u}_{2} & \dots & A\tilde{u}_{n}
\end{pmatrix}\\
u_1 & \tilde{u}_{2} & \dots & \tilde{u}_{n}
\end{pmatrix}\begin{pmatrix}
lambda_1 & * & \dots & *\\
0 &  \lceil &  & \rceil \\
\vdots  & \mid & A_{n-1} & \mid \\
0 & \lfloor & & \rfloor
\end{pmatrix}
\end{alignat*}

Tags :

Two solutions: one based on blkarray, another based on pstricks:

\documentclass{article}
\usepackage{mathtools}
\usepackage{blkarray}
\usepackage{bigdelim}
\usepackage{pst-node, auto-pst-pdf}

\begin{document}

\begin{alignat*}{3}
A\begin{pmatrix}
u_1 & \tilde{u}_{2} & \dots & \tilde{u}_{n}
\lambda_1 u_1 & A\tilde{u}_{2} & \dots & A\tilde{u}_{n}
\end{pmatrix}\\
u_1 & \tilde{u}_{2} & \dots & \tilde{u}_{n}
\end{pmatrix}\begin{pmatrix}
\begin{blockarray}{@{}[email protected]{\;}}
\lambda_1 & * & \dots & *\\
\begin{block}{c|@{}[email protected]{\;}|}
\BAhhline{~|---|}
0 & & & \\
\vdots & & A_{n-1} & \\
0 & & & \\
\end{block}
\BAhhline{~|---|}
\end{blockarray}
\end{pmatrix}
\end{alignat*}

\begin{alignat*}{3}
A\begin{pmatrix}
u_1 & \tilde{u}_{2} & \dots & \tilde{u}_{n}
\lambda_1 u_1 & A\tilde{u}_{2} & \dots & A\tilde{u}_{n}
\end{pmatrix}\\
u_1 & \tilde{u}_{2} & \dots & \tilde{u}_{n}
\end{pmatrix}\begin{pmatrix}
\lambda_1 & * & \dots & *\\
0 & \pnode[-1ex, 2ex]{A} & & \\
\vdots & & A_{n-1} &\\
0 & & & \phantom{*}\pnode[0.4ex, -0.4ex]{B}\,\\
\end{pmatrix}
\psframe[linewidth=0.4pt](A)(B)
\end{alignat*}

\end{document}


Bernard
August 13, 2019 19:52 PM