Second function by Schaffer. The defintion is given by the formula
$$f(\mathbf{x}) = 0.5 + \frac{\cos^2(sin(|\mathbf{x}_1^2 - \mathbf{x}_2^2|)) - 0.5}{(1 + 0.001(\mathbf{x}_1^2 + \mathbf{x}_2^2))^2}$$
subject to \(\mathbf{x}_i \in [-100, 100], i = 1, 2\).