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Selection Methods

Selection Methods. Fitness Proportionate Selection Tournament Selection Rank Selection Linear Selection Exponential Selection Truncation Selection Selection methods are invoked each genetic operator. Fitness Proportionate Selection. Calculate the adjusted fitness for each individual.

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Selection Methods

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  1. Selection Methods • Fitness Proportionate Selection • Tournament Selection • Rank Selection • Linear Selection • Exponential Selection • Truncation Selection • Selection methods are invoked each genetic operator.

  2. Fitness Proportionate Selection • Calculate the adjusted fitness for each individual. • Create a mating pool. • Randomly select an individual from the mating pool.

  3. Fitness Proportionate Selection: Example Tree SF AF NF No. of Occs. (NF x Pop. Size) 0.3765 0  0 Tree1 15 0.0625 0.0753 Tree2 2 0.3333 0.4018 2.009  2 Tree3 4 0.2 0.2411 1.205  1 0.1429 Tree4 6 0.1723 0.8615  1 Tree5 10 0.0909 0.1096 0.548  1 Total 0.8296 Mating pool: Tree2 , Tree2, Tree3, Tree4, Tree5

  4. Tournament Selection • A tournament size is set as a GP parameter. • A group of individuals, equal to the tournament size is randomly selected from the population. • The raw fitness value is calculated for each individual. • The individual with the best fitness is chosen. • Selection is performed with replacement. • Selection pressure.

  5. Tournament Selection: Example Tournament size = 3 Tournament: Population: Chosen individual Tree2 2 Tree1 15 Tree5 10 Tree2 Tree2 2 Tree2 2 Tree2 2 Tree2 2 Tree3 4 Tree4 6 Potential Problems Tree5 10 Tree5 10

  6. Other Selection Methods • Rank Selection • Each individual is assigned a rank based on their fitness measure. • Two types of rank selection: linear ranking, exponential ranking. • Linear Selection and Exponential Selection • Similar to fitness proportionate selection. • Fitness of an individual is calculated relative to the entire population. • Truncation Selection • More than one offspring is created. • A subset of best individuals is chosen as parents for the next generation.

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