Basic multimodal functions (CEC6–CEC20): These functions have numerous local optima but a single global optimum corresponding to each function. Generally, classical derivative based optimization techniques do not perform satisfactorily on such functions as they have the tendency to get stuck at a locally optimal solution. The fifteen functions in this category portray the following characteristics: being non-separable, asymmetrical, continuous everywhere but differentiable only on a set of points, continuous everywhere but differentiable nowhere, non-continuous, rotated, having a narrow valley from local optimum to global optimum, having a very large number of local optima and having the best and the second best optimal solutions far apart.