3 RELATED WORKS
Several versions of genetic operators are described in
the literature and many studies have been done to im-
prove these operators’ performance, see for example
(J
´
ano
ˇ
s
´
ıkov
´
a et al., 2017; Xu et al., 2018; Das and
Pratihar, 2019). The problem of operator rates calcu-
lation is considered a challenging problem in the liter-
ature either for constant rates or dynamic approaches.
The optimal rates setting is likely to vary for differ-
ent problems (Pham and Karaboga, 2000), but it is a
time consuming task. For these reasons, some studies
focused on determining good control rates values for
the genetic operators.
For constants rates and binary individuals rep-
resentation, (De Jong, 1975) recommends a range
of [50,100] individuals in the population size, 60%
for crossover rate and 0.1% for mutation rate. The
(Schaffer et al., 1989) suggests a range of [20-30] in-
dividuals in the population, [75% - 95%] for crossover
rate and [0.5% - 1%] for mutation rate, while (Grefen-
stette, 1986) uses a population of 30 individual, 95%
for crossover and 1% for mutation. As it is possi-
ble to see, these ranges have large variations, being
inconclusive and strongly dependent on the research
knowledge and the problem variations.
On the other hand, some studies concentrate ef-
forts on adapting the control parameters during the
optimization process. These techniques involve ad-
justing the operators’ rates according to problems
characteristic as the search process, the trend of the
fitness, stability (Vannucci and Colla, 2015), fitness
value (Priya and Sivaraj, 2017; Pham and Karaboga,
2000), or based on experiments and domain expert
opinions (Li et al., 2006).
In order to adjust the mutation and crossover rates,
(Vannucci and Colla, 2015) uses a fuzzy inference
system to control the operators’ variation. Accord-
ing to the authors, this method also accelerates the at-
tainment of the optimal solution and avoid premature
stopping in a local optimum through a synergic effect
of mutation and crossover.
Another approach is presented in (Xu et al., 2018),
which uses the GA method to solve the traveling
salesman problem optimizing the mutation charac-
ters. In this case, a random cross mapping method and
a dynamic mutation probability are used to improve
the algorithm. In the approach, the crossover op-
eration varies according to the randomly determined
crossover point and the mutation rate is dynamically
changed according to population stability.
In (Das and Pratihar, 2019) the crossover operator
guided by the prior knowledge about the most promis-
ing areas in the search region is presented. In this
approach four parameters are defined to control the
crossover operator: crossover probability, variable-
wise crossover probability, multiplying factor, direc-
tional probability. It was noted the use of the direc-
tional information helps the algorithm to search in
more potential regions of the variable space.
In (Whitley and Hanson, 1989) is proposed an
adaptive mutation through monitoring the homogene-
ity of the solution population by measuring the Ham-
ming distance between the parents’ individuals during
the reproduction. Thereby, the more similar the par-
ents, the higher mutation probability.
In study of (Fogarty, 1989) adopts the same mu-
tation probability for all parts of an individual and
then decreased to a constant level after a given num-
ber of generations. Another strategy is presented in
(Pham and Karaboga, 2000), upper and lower limits
are chosen for the mutation rate and within those lim-
its the mutation rate is calculated for each individual,
according to the objective function value.
According to (Pham and Karaboga, 2000) in the
first 50 generations there are few good solutions in
the population, so in the initial stage high mutation
rate is preferable to accelerate the search. In contrast,
(Shimodaira, 1996) supports high mutation rates at
the end of the process, in order to come out from lo-
cal optima where the algorithm can be stuck. For the
references presented is possible to verify that there is
no consensus on the values of the rates. For this rea-
son, in this work the rates are dynamically established
by the analysis of population performance throughout
the evolutionary process.
4 DYNAMIC GENETIC
ALGORITHM
This study presents a dynamic Genetic Algorithm
with continuous variable individual representation
that is initially randomly generated (Haupt and Haupt,
2004). Through analysis of the GA behavior, it was
noted that the objective function standard deviation
of the beginning evolutionary process is higher, as ex-
pected because the generation of the initial population
is random. For this reason, the individuals are very
dispersed in the search region. For the same reason,
in the first iterations, the population amplitude is also
very higher. As the search process evolves, the popu-
lation tends to concentrate in specific feasible regions,
in which the chance to find the optimum solution is
higher (promising regions). This causes a decrease in
the standard deviation and amplitude of the objective
function value. At the end of the evolutionary pro-
cess, both amplitude and standard deviation tend to
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