How to write a block matrix in Latex in the following way:
I wrote the following code:
\[
Q=\left[
\begin{array}{c c c c}
\textbf{nI}& \vline & \textbf{J}\\
\hline
\textbf{J^T} &\vline &\textbf{K}
\end{array}
\right]
\]
I am getting the following error:
! Extra }, or forgotten $.\textdef@ ...th {#1}\let \f@size #2\selectfont #3}} \textbf{J^T}
and many more errors which are difficult to put here.
Can someone kindly help.
You can use a vertical line | within the column specification together with an \hline and only need 2 columns:
\documentclass{article}
\begin{document}
\[
X = \left[\begin{array}{ c | c }
A & B \\
\hline
C & D
\end{array}\right]
\]
\end{document}
It doesn't like the fact that you had the superscript inside the \textbf command.
\documentclass[10pt]{article}
\begin{document}
\begin{equation}
Q=\left[
\begin{array}{c c c c}
\textbf{nI}& \vline & \textbf{J}\\
\hline
\textbf{J}^\textbf{T} &\vline &\textbf{K}
\end{array}
\right]
\end{equation}
\end{document}
My proposal contains two examples. Obviously you can change the size of the characters inside the matrix using the usual commands that increase or decrease the size of a letter of text.
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\[
\renewcommand\arraystretch{1.5}
\left[\begin{array}{@{}c|c@{}}
\mbox{\Large A} & \mbox{\Large B} \\
\hline
\mbox{\Large C} & \mbox{\Large D}
\end{array}\right], \quad \left[\begin{array}{@{}c|c@{}}
\mbox{\Large $A$} & \mbox{\Large $B$} \\
\hline
\mbox{\Large $C$} & \mbox{\Large $D$}
\end{array}\right]
\]
\end{document}
\mathbf{A}. – Werner Aug 16 '19 at 05:15