Crossoverincludesnonotionofaschemaonlyofthechromosomes

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Unformatted text preview: 11****00 is the set of all solutions encoded in 8 bits, beginning with two ones and ending with two zeros Solutions in this set all share the same variants of the properties encoded at these loci Schema qualifiers Length The inclusive distance between the two bits in a schema which are furthest apart (the defining length of the previous example is 8) Order The number of fixed bits in a schema (the order of the previous example is 4) Not just sum of the parts GAs explicitly evaluate and operate on whole solutions GAs implicitly evaluate and operate on building blocks Existing schemas may be destroyed or weakened by crossover New schemas may be spliced together from existing schema Crossover includes no notion of a schema – only of the chromosomes Why do they work Schemas can be destroyed or conserved So how are good schemas propagated through generations? Conserved – good – schemas confer higher fitness on the offspring inheriting them Fitter offspring are probabilistically more likely to be chosen to reproduce Approximating schema dynamics Let H be a schema with at least one instance present in the population at time t Let m(H, t) be the number of instances of H at time t Let x be an instance of H and f(x) be its fitness The expected number of offspring of x is f(x)/f(pop) (by fitness proportionate selection) To know E(m(H, t +1)) (the expected number of instances of schema H at the next time unit), sum f(x)/f(pop) for all x in H GA never explicitly calcula...
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