The defintion of this two-dimensional function is given by $$f(\mathbf{x}) = \prod_{i = 1}^{2} \left(\sum_{j = 1}^{5} \cos((j + 1)\mathbf{x}_i + j\right)$$ subject to \(\mathbf{x}_i \in [-10, 10], i = 1, 2\).
makeShubertFunction()[smoof_single_objective_function]
J. P. Hennart (ed.), Numerical Analysis, Proc. 3rd AS Workshop, Lecture Notes in Mathematics, vol. 90, Springer, 1982.