# Partioned/block matrices with “empty” cells

I am trying to create a matrix like the following where notice that I envision it as a 4x4 matrix, with 4 blocks, one 1x1 block, one 3x1 block, one 1x3 block, and one 3x3 matrix. My confusion in writing this is in having the matrix by partitioned according to the above decomposition, BUT with only one element written in each block.

The only thing I know how to do is to write this as a 2x2 matrix which is not satisfying

\begin{align}
G^\mu{}_\nu &= \frac{\partial x ' {}^\mu}{\partial x^\nu} \\ \notag
&= \left(
\begin{array}{c|c}
\frac{\partial x ' {}^0}{\partial x^0}  & \frac{\partial x ' {}^0}{\partial x^i} \\
\hline
\frac{\partial x ' {}^i}{\partial x^0}  & \frac{\partial x ' {}^i}{\partial x^j}
\end{array}
\right) \\ \notag
&= \left(
\begin{array}{c|c}
1  & 0 \\
\hline
v^i  & R^i{}_j
\end{array}
\right)
\end{align} Any tips on how to create a 4x4 matrix with only one written element in a 3x3 (3x1, 1x3) block?

There is no problem. You create a matrix 4×4 and you put your coefficients at the right place:

\documentclass{article}
\usepackage{array}
\usepackage{amsmath}

\begin{document}
\begin{align}
G^\mu{}_\nu &= \frac{\partial x ' {}^\mu}{\partial x^\nu} \\ \notag
&= \left(
\begin{array}{c|ccc}
\frac{\partial x ' {}^0}{\partial x^0}  & & \frac{\partial x ' {}^0}{\partial x^i} & \\
\hline \\
\frac{\partial x ' {}^i}{\partial x^0}  & & \frac{\partial x ' {}^i}{\partial x^j} & \\
\\
\end{array}
\right) \\ \notag
&= \left(
\begin{array}{c|ccc}
1  & & 0 & \\
\hline
\\
v^i  & & R^i{}_j & \\
\\
\end{array}
\right)
\end{align}
\end{document} • If you don't want the collision between the first row (in the first matrix) with the horizontal rule, you should use cellspace. – F. Pantigny May 28 at 11:45
• Brilliant work! :D i will look into cellspace as well thank you – Lopey Tall May 28 at 12:37
• How exactly does cellspace work? After reading the manual, it seems the following in the preamble should be sufficient? It doesn't change anything though :/ \usepackage[math]{cellspace} \setlength\cellspacetoplimit{5pt} \setlength\cellspacebottomlimit{5pt} – Lopey Tall May 28 at 19:32
• You have to replace each c in the preamble of the array with >{$}Sc<{$} – F. Pantigny May 28 at 19:56
• ah cheers, not just Sc as I thought – Lopey Tall May 28 at 20:18