This two-dimensional multimodal test function follows the formula $$f(\mathbf{x}) = \cos(\mathbf{x}_1)\sin(\mathbf{x}_2) - \frac{\mathbf{x}_1}{(\mathbf{x}_2^2 + 1)}$$ with \(\mathbf{x}_1 \in [-1, 2], \mathbf{x}_2 \in [2, 1]\).
makeAdjimanFunction()[smoof_single_objective_function]
C. S. Adjiman, S. Sallwig, C. A. Flouda, A. Neumaier, A Global Optimization Method, aBB for General Twice-Differentiable NLPs-1, Theoretical Advances, Computers Chemical Engineering, vol. 22, no. 9, pp. 1137-1158, 1998.