Second function by Schaffer. The defintion is given by the formula $$f(\mathbf{x}) = 0.5 + \frac{\sin^2(\mathbf{x}_1^2 - \mathbf{x}_2^2) - 0.5}{(1 + 0.001(\mathbf{x}_1^2 + \mathbf{x}_2^2))^2}$$ subject to \(\mathbf{x}_i \in [-100, 100], i = 1, 2\).
makeSchafferN2Function()[smoof_single_objective_function]
S. K. Mishra, Some New Test Functions For Global Optimization And Performance of Repulsive Particle Swarm Method.