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Population model (evolutionary algorithm)
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<p>The population model of an <a href="/facts/Evolutionary_algorithm/bo7eHlcA">evolutionary algorithm</a> (EA) describes the structural properties of its population to which its members are subject. A population is the set of all proposed solutions of an EA considered in one iteration, which are also called <i>individuals</i> according to the biological role model. The individuals of a population can generate further individuals as offspring with the help of the <a href="/facts/Genetic_operator/M0VhYIBW">genetic operators</a> of the procedure. </p><p>The simplest and widely used population model in EAs is the <i>global</i> or <i><a href="/facts/Panmixia/75y6jxdD">panmictic</a> model</i>, which corresponds to an unstructured population. It allows each individual to choose any other individual of the population as a partner for the production of offspring by <a href="/facts/Crossover_(genetic_algorithm)/fRBnRV7r">crossover</a>, whereby the details of the <a href="/facts/Selection_(genetic_algorithm)/YrIlmEBy">selection</a> are irrelevant as long as the <a href="/facts/Fitness_function/Xeoc1I3C">fitness</a> of the individuals plays a significant role. Due to global mate selection, the genetic information of even slightly better individuals can prevail in a population after a few generations (<a href="/facts/Iteration/AMc1p7BL">iteration</a> of an EA), provided that no better other offspring have emerged in this phase. If the solution found in this way is not the <a href="/facts/Mathematical_optimization/oRn8Iv5I">optimum</a> sought, that is called <i><a href="/facts/Premature_convergence/1qDpBNRS">premature convergence</a></i>. This effect can be observed more often in panmictic populations. </p><p>In nature global mating pools are rarely found. What prevails is a certain and limited isolation due to spatial distance. The resulting local neighbourhoods initially evolve independently and <a href="/facts/Mutant/sWgrsoFS">mutants</a> have a higher chance of persisting over several generations. As a result, <a href="/facts/Genotype/MlzK1Mfz">genotypic</a> diversity in the gene pool is preserved longer than in a panmictic population. </p><p>It is therefore obvious to divide the previously global population by substructures. Two basic models were introduced for this purpose, the <i>island models</i>, which are based on a division of the population into fixed subpopulations that exchange individuals from time to time, and the <i>neighbourhood models</i>, which assign individuals to overlapping neighbourhoods, also known as <i>cellular genetic</i> or <i>evolutionary algorithms</i> (cGA or cEA). The associated division of the population also suggests a corresponding parallelization of the procedure. For this reason, the topic of population models is also frequently discussed in the literature in connection with the parallelization of EAs. </p>