Matrix in matrix: how to adjust vertical space?

Question

Normally, I'm kind of a Latex guru and I find solutions to problems easily with sites like this, but now I encountered something I cannot find an appropriate solution for: I have matrices within a matrix and the bows seem to be glued to each other, look:

My code looks like this:

\begin{pmatrix}
\begin{pmatrix}
 0 & 1\\
 0 & 0\\
\end{pmatrix} & 
\begin{pmatrix}
 1\\
 1\\
\end{pmatrix}
& \begin{pmatrix}
0\\
2\\
\end{pmatrix}\\
 \begin{pmatrix}
0 & 2\\
\end{pmatrix} & \begin{pmatrix}
 0\\
\end{pmatrix} & \begin{pmatrix}
 0\\
\end{pmatrix}\\
\begin{pmatrix}
 0 & 0\\
\end{pmatrix} & \begin{pmatrix}
 0\\
\end{pmatrix} & \begin{pmatrix}
 1\\
\end{pmatrix}\\
\end{pmatrix} 

How can I add just a little vertical space between the submatrices?

Answer 1

Here I added a stacking gap (default 3pt, settable with optional argument) to one of the matrices on row 2. It adds the gap above and below the item. Note, though, that if there are other matrix or vector terms in the same equation (not shown), you may need to add gap to those as well, in order to keep rows on the same vertical level.

\documentclass{article}
\usepackage{stackengine,amsmath}
\stackMath
\begin{document}
\[
\begin{pmatrix}
\begin{pmatrix}
 0 & 1\\
 0 & 0\\
\end{pmatrix} & 
\begin{pmatrix}
 1\\
 1\\
\end{pmatrix}
& \begin{pmatrix}
0\\
2\\
\end{pmatrix}\\
\addstackgap{
\begin{pmatrix}
0 & 2\\
\end{pmatrix}} & \begin{pmatrix}
 0\\
\end{pmatrix} & \begin{pmatrix}
 0\\
\end{pmatrix}\\
\begin{pmatrix}
 0 & 0\\
\end{pmatrix} & \begin{pmatrix}
 0\\
\end{pmatrix} & \begin{pmatrix}
 1\\
\end{pmatrix}\\
\end{pmatrix} 
\]
\end{document}

Answer 2

Vertical spacing is inconsistent in mathmode and behaves differently from that of textmode, that is why simply adding \\[length] wouldn't work. I suggest adding a zero-length \rule of a chosen height can solve the problem. Of course, adding a zero-length \rule inevitably adds a space of {}, so I also put an equal negative space length \! to compensate for this.

\documentclass{article}
\usepackage{amsmath}
\begin{document}

\begin{equation}
\begin{pmatrix}
\begin{pmatrix}
 0 & 1\\
 0 & 0\\
\end{pmatrix} & 
\begin{pmatrix}
 1\\
 1\\
\end{pmatrix}
& \begin{pmatrix}
0\\
2\\
\end{pmatrix}\\\!\rule{0in}{.16in}
\begin{pmatrix}
0 & 2\\
\end{pmatrix} & \begin{pmatrix}
 0\\
\end{pmatrix} & \begin{pmatrix}
 0\\
\end{pmatrix}\\\!\rule{0in}{.16in}
\begin{pmatrix}
 0 & 0\\
\end{pmatrix} & \begin{pmatrix}
 0\\
\end{pmatrix} & \begin{pmatrix}
 1\\
\end{pmatrix}\\
\end{pmatrix} 
\end{equation}

\end{document}