Popular 2-dimensional single-objective test function based on the formula:
$$f(\mathbf{x}) = a \left(\mathbf{x}_2 - b \mathbf{x}_1^2 + c \mathbf{x_1} - d\right)^2 + e\left(1 - f\right)\cos(\mathbf{x}_1) + e,$$
where \(a = 1, b = \frac{5.1}{4\pi^2}, c = \frac{5}{\pi}, d = 6, e = 10\) and
\(f = \frac{1}{8\pi}\). The box constraints are given by \(\mathbf{x}_1 \in [-5, 10]\)
and \(\mathbf{x}_2 \in [0, 15]\). The function has three global minima.