probability of choosing an individual for breeding of the next generation is proportional to its fitness, the better the fitness is, the higher chance for that individual to be chosen. Choosing individuals can be depicted as spinning a roulette that has as many pockets as there are individuals in the current generation, with sizes depending on their probability. Probability of choosing individual is equal to , where is the fitness of and is the size of current generation (note that in this method one individual can be drawn multiple times). Rank Selection In rank selection, the selection probability does not depend directly on the fitness, but on the fitness rank of an individual within the population. This puts large fitness differences into perspective; moreover, the exact fitness values themselves do not have to be available, but only a sorting of the individuals according to quality. Linear ranking, which goes back to Baker, is often used. It allows the selection pressure to be set by the parameter , which can take values between 1.0 (no selection pressure) and 2.0 (high selection pressure). The probability for rank positions is obtained as follows: In addition to the adjustable selection pressure, an advantage of rank-based selection can additionally be seen in the fact that it also gives worse individuals a chance to reproduce and thus to improve. This can be particularly helpful in applications with restrictions, since it facilitates the overcoming of a restriction in several intermediate steps, i.e. via a sequence of several individuals rated poorly due to restriction violations. Steady State Selection In every generation few are selected (good - with high fitness) chromosomes for creating a new offspring. Then some (bad - with low fitness) chromosomes are removed and the new offspring is placed in their place. The rest of population survives to new generation. Tournament Selection Tournament Selection is a method of choosing the individual from the set of individuals. The winner of each tournament is selected to perform crossover. Elitist Selection Often to get better parameters, strategies with partial reproduction are used. One of them is elitism, in which a small portion of the best individuals from the last generation is carried over (without any changes) to the next one. Boltzmann Selection In Boltzmann selection, a continuously varying temperature controls the rate of selection according to a preset schedule. The temperature starts out high, which means that the selection