| Fitness Proportionate Selection |
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In fitness proportionate selection, as in all selection methods, possible solutions or Chromosome s are assigned a fitness by the Fitness Function . In fitness proportionate selection, this fitness level is used to associate a Probability of selection with each individual chromosome. While candidate solutions with a higher fitness will be less likely to be eliminated, there is still a chance that they may be. Contrast this with a less sophisticated selection algorithm, such as Truncation Selection , which will eliminate a fixed percentage of the weakest candidates. With fitness proportionate selection there is a chance some weaker solutions may survive the selection process; this is an advantage, as though a solution may be weak, it may include some component which could prove useful following the recombination process. The analogy to a roulette wheel can be envisaged by imagining a roulette wheel in which each candidate solution represents a pocket on the wheel; the size of the pockets are proportionate to the probability of selection of the solution. Selecting N chromosomes from the population is equivalent to playing N games on the roulette wheel, as each candidate is drawn independently. Others selection techniques, such as Stochastic Universal Sampling 1996, page 120 or Tournament Selection , are often used in practice. This is because they have less stochastic noise, or are fast, easy to implement and have a constant selection pressure 1996 . Note performance gains can be achieved by using a Binary Chop rather than a linear search to find the right pocket. EXTERNAL LINKS
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