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Artificial Intelligence and Soft Computing: Behavioral ... - Arteimi.info

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chromosomes. The performance of the strings, often called fitness, is then<br />

evaluated with the help of some functions, representing the constraints of the<br />

problem. Depending on the fitness of the chromosomes, they are selected for a<br />

subsequent genetic manipulation process. It should be noted that the selection<br />

process is mainly responsible for assuring survival of the best-fit individuals.<br />

After selection of the population strings is over, the genetic manipulation<br />

process consisting of two steps is carried out. In the first step, the crossover<br />

operation that recombines the bits (genes) of each two selected strings<br />

(chromosomes) is executed. Various types of crossover operators are found in<br />

the literature. The single point <strong>and</strong> two points crossover operations are<br />

illustrated in fig. 15.2 <strong>and</strong> 15.3 respectively. The crossover points of any two<br />

chromosomes are selected r<strong>and</strong>omly. The second step in the genetic<br />

manipulation process is termed mutation, where the bits at one or more<br />

r<strong>and</strong>omly selected positions of the chromosomes are altered. The mutation<br />

process helps to overcome trapping at local maxima. The offsprings produced<br />

by the genetic manipulation process are the next population to be evaluated.<br />

Crossover points<br />

11010 1010 10101 1001<br />

11010 1001 10101 1010<br />

Fig 15.2: A single point crossover after the 3-rd bit<br />

position from the L.S.B.<br />

Crossover points crossover points<br />

10101 1001 10011<br />

10101 1110 10011<br />

parents<br />

offsprings<br />

parents<br />

offsprings<br />

01101 1110 11101<br />

01101 10 01 11101<br />

Fig. 15.3: Two point crossover: one after the 4 th <strong>and</strong> the other after the 8 th<br />

bit positions from the L.S.B.

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