Number of variables: n variables.
  Definition:
f(x) = 20+e-20exp(-0.2(sqrt((1/n)sum(x(i)^2))-exp((1/n)sum(cos(2Pix(i)))
  Search domain: −15 ≤ x(i) ≤ 30, i = 1, 2, … , n.
  Number of local minima: several local minima.
  The global minimum: x =  (0, …, 0), f(x) = 0.