The following code produces an expected array of equations in LaTeX output, but doesn't do so for docx output:
```
---
title: A Document
...
## Math Equations
An array of equations:
\begin{eqnarray}
\nabla \cdot \vec{B} &=& 0 \nonumber \\
\nabla \times \vec{E} &=& - \frac{\partial B}{\partial t} \nonumber \\
\end{eqnarray}
```
If we surround the `eqnarray` environment with double dollar signs we get the expected docx output, but specifying latex as output yields a `! Missing \endgroup inserted` error.
```
---
title: A Document
...
## Math Equations
An array of equations:
$$
\begin{eqnarray}
\nabla \cdot \vec{B} &=& 0 \nonumber \\
\nabla \times \vec{E} &=& - \frac{\partial B}{\partial t} \nonumber \\
\end{eqnarray}
$$
```
Cheers,
Paul