How to make matrix elements which spans multiple columns/rows?

Question

I have a matrix which I would like to typeset. From the linked image, it can be seen that the bottom elements span 2 columns (and 2 rows but that's not as important), how do I typset it?

Right now I am trying this

\begin{gather}
    \begin{bmatrix}
        0 & 0 & 1 & 0\\
        0 & 0 & 0 & 1\\
        A^{-1} C & & -A^{-1} B
    \end{bmatrix}
\end{gather}

but it doesn't seem to work, as expected.

Answer 1

Just use a \multicolumn.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
    \begin{gather}
    \begin{bmatrix}
    0 & 0 & 1 & 0\\
    0 & 0 & 0 & 1\\
    \multicolumn{2}{c}{A^{-1} C} & \multicolumn{2}{c}{-A^{-1} B}
    \end{bmatrix}
    \end{gather}
\end{document}