Two-dimensional test function based on the defintion
$$f(\mathbf{x}) = \frac{\sin^2(\mathbf{x}_1 - \mathbf{x}_2)\sin^2(\mathbf{x}_1 + \mathbf{x}_2)}{\sqrt{\mathbf{x}_1^2 + \mathbf{x}_2^2}}.$$
The domain of definition is bounded by the box constraints
\(\mathbf{x}_i \in [0, 10], i = 1, 2\).