Computational Intelligence

Evolution Strategies 75

φ

p

i

is the fitness score for p

i

β

j

is a constant of proportinality to scale φ

p

i

z

j

represents an offset

For the function used in the example, it has been shown that the optimum rate of

convergence is represented by

σ =

1.224

√

f(x)

n

,wheren is the number of dimensions

(B

¨

ack and Schwefel 1993).

Another way to perform mutation involves a process known as self-adaptation.

In this variation, the standard deviations (and rotation angles, if used) are modified

based on their current values. As a result, the search adapts to the er ror surface

contours (Fogel 1995).

Fitness, however, is sometimes not used directly by itself to decide which half ...