Information Technology Reference
In-Depth Information
The mutation operator was extended to all the domains and it continues to
be the most important genetic operator, single-handedly allowing an effi-
cient evolution. However, different mutation operators were implemented
(head/tail mutation, Dw mutation, and Dt mutation) so that their roles could
be understood in more detail but, for practical matters, one usually uses the
same mutation rate for all of them, which is obviously equivalent to having
just one operator controlling the mutation rate.
Inversion was also extended to GEP-nets, with the usual operator working
in the heads of genes and two others working in Dw and Dt to further en-
hance the circulation of weights and thresholds in the genetic pool (see their
description in section 10.2.1).
The IS and RIS transposition operators were also transposed to GEP-nets
and their action is obviously restricted to the heads and tails of genes. How-
ever, special transposition operators were created that operate within Dw
and Dt in order to help in the circulation of weights and thresholds in the
population (see their description in section 10.2.2).
The extension of both recombination and gene transposition to GEP-nets
is straightforward as their actions never result in mixed domains or alpha-
bets. However, for them to work properly (i.e., to allow an efficient evolu-
tion), one must be careful in determining which weights and/or thresholds
go to which region after the splitting of the chromosomes, otherwise the
system is incapable of evolving efficiently. In the case of gene recombina-
tion and gene transposition, to keep track of a gene's weights and thresholds
is not difficult and, in fact, these operators are easily implemented and work
very well in GEP-nets. But in the case of one-point and two-point recombi-
nation, chromosomes are split anywhere and, therefore, it is impossible to
keep track of the weights and thresholds that are attached to each neuron. In
fact, if applied straightforwardly, these operators produce such evolutionary
monsters that they are of little use in multigenic systems. Therefore, for
multigenic systems, a special intragenic two-point recombination was cre-
ated in order to restrict the exchange of sequences to a particular gene (see
its description in section 10.2.3).
And finally, in addition to all these operators that work exclusively on the
chromosome sequence, special mutation operators - direct mutation of
weights and direct mutation of thresholds - were also created in order to
introduce modification in the set of available weights and thresholds (see
their description in section 10.2.4).
