Inline formula $E = m c^2$.
Out of line formula :
```formula
\begin{eqnarray*}
\dfrac{\partial u}{\partial t} & = & r_u \nabla^2 u - uv^2 + f_r \times \left(1 - u\right) \\
\dfrac{\partial v}{\partial t} & = & r_v \nabla^2 v + uv^2 - \left(f_r + k_r\right) \times v
\end{eqnarray*}
```