Test function with multiple global optima based on the definition $$f(\mathbf{x}) = \sum_{i = 1}^{4} (i + 1)\cos(i\mathbf{x}_1 + i - 1) \sum_{j = 1}^{4} (j + 1)\cos((j + 2) \mathbf{x}_2 + j + 1)$$ subject to \(\mathbf{x}_i \in [-10, 10], i = 1, 2\).
makeHansenFunction()[smoof_single_objective_function]
C. Fraley, Software Performances on Nonlinear lems, Technical Report no. STAN-CS-89-1244, Computer Science, Stanford University, 1989.