How to create a simple partitioned matrix

Question

I wish to create a matrix as displayed in the encircled region on the right (taken from here)

However, the code on the left does not seem to be generating the vertical through the matrix. Instead I am only getting one horizontal bar through the matrix.

Can someone please provide a simple code that generates the block/partitioned matrix on the right?

Thanks!

Answer 1

Use a vertical bar in the format specification: c|c. A complete example:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\[
C=
\left[
\begin{array}{c|c}
M & N \\
\hline
R & S
\end{array}
\right]
\]

\end{document}

As a side note, don't use $$...$$ in modern LaTeX documents; use \[...\]. See Why is \[ ... \] preferable to $$ ... $$?.