Dimensions: d

The Ackley function is widely used to test optimization algorithms. In its two-dimensional form, as shown in the preceding plot, it is characterized by a nearly flat outer region, and a large hole at the center. The function poses a risk for optimization algorithms, particularly hill-climbing algorithms, to be trapped in one of its many local minima. 

Recommended variable values are a = 20, b = 0.2, and c = 2π.