Information Technology Reference
In-Depth Information
Generation N: 0
01234560123456
NaObaacOAbbcca-[0] = 4
AaNcbbaNcOaacc-[1] = 2
OONcbbbNcbcbca-[2] = 4
ANNcaacNcObaab-[3] = 2
AbObcbcOAacaac-[4] = 6
AcNbcbbAONbbcc-[5] = 4
NAcbcacNbOaaba-[6] = 2
NbNbbaaAacbacb-[7] = 3
NAAaccaONacbbb-[8] = 4
AAaccacNcaabab-[9] = 4
Figure 3.3.
The chromosomes of the individuals of the initial population and their
respective fitness (the value after the equal sign). The fitness corresponds to the
number of fitness cases (see Table 3.1) correctly solved by the program encoded in
each chromosome. The chromosomes encode sub-ETs linked by OR.
shown, but you shouldn't have any problems in drawing the programs they
encode and checking their fitnesses). Then, according to fitness, the indi-
viduals are selected to reproduce with modification. For instance, all the 10
individuals of the initial population shown in Figure 3.2 are viable (that is,
have non-zero fitness) and are therefore eligible to be selected to reproduce.
These viable individuals, among themselves, create as many new individu-
als as there are individuals in the population. As such, throughout a run, the
population size is kept unchanged. The descendants of the selected individu-
als consist of the new members of the next generation.
The expression of the best individuals of generation 0 (chromosome 4) is
shown in Figure 3.4. As you can easily check, this individual is able to solve
correctly six out of eight fitness cases, and thus has a fitness equal to six.
You have probably noticed that all the genes created randomly in the ini-
tial population have a function at position 0, which, as you already know,
corresponds to the root of the sub-ETs. Although I have chosen to have all
the genes in the initial population starting with a function, this is not very
important in multigenic systems. This feature of initial populations is a rem-
nant of the evolutionary process of GEP itself, for the first GEP implementa-
tion used chromosomes composed of only one gene. In those systems, genes
coding for one-element ETs were of little use and therefore were kept to a
minimum within populations. However, when multigenic chromosomes were
introduced, I did not change this feature of initial populations because
