$$\left\{ \begin{array}{lll}\dot{x}_{1} & = & x_{2}\\\dot{x}_{2} & = & -(x_{1}+x_{2}^{3}-x_{2})+u\end{array}\right.$$
$u\in[-0.2,0.2]$
Search space: $[-2, 2]\times[-2,2]$