Mitchell, T. J. (2010) An exploration of evolutionary computation ...

problems with unknown characteristics. In rugged problem spaces comprising multiple
peaks and flat plateaus, recombination and mutation are still beneficial to evolution;
however, their benefits cannot be explained by the genetic repair hypothesis alone.
2.3.2.3 Mutation
In contrast to both the GA (in which recombination is widely regarded to be the primary
variation operator) and EP (relying upon mutation alone), the ES takes an intermediate
position: mutation and recombination are applied with equal importance (Beyer, 2001).
However, the mutation operator does provide the primary source of variation, and thus
exploration. Recombination works synergistically with mutation, reducing variation error
and accelerating progress rates.
Object Parameter Mutation
Mutation is applied to the object parameters of each recombinant with the addition of
the mutation vector :
This delivers the mutated object parameters . Each element of the mutation vector is
drawn randomly from the standard normal distribution and scaled according to
the mutation strength specified by the strategy parameters of the recombinant individual.
This mutation scheme ensures that mutative jumps through the search space are:
ordinal, favouring small jumps through the search space over large jumps.
scalable, according to the mutation strength , such that any point within the space
may be reached.
unbiased, ensuring that, on average, mutants deviate from their point of origin
isotropically.
The lack of bias in the mutation operator ensures that that there is no deterministic drift
without selection.
Variations
In its most rudimentary form, the mutation normal distribution is isotropic, i.e., only one
step-size parameter is required for the mutation of all object parameters . With an
isotropic mutation scheme, the surface of mutation probability isodensity forms a circle,
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