Glossary C - HHGT Evolutionary Computation

Evolutionary Computation Glossary

(biol) The dogma that nucleic acids act as templates for the synthesis of proteins, but never the reverse. More generally, the dogma that GENEs exert an influence over the form of a body, but the form of a body is never translated back into genetic code: acquired characteristics are not inherited. cf LAMARCKISM.

(GA) The dogma that the behaviour of the algorithm must be analysed using the SCHEMA THEOREM.

(life in general) The dogma that this all is useful in a way. "You guys have a dogma. A certain irrational set of believes. Well, here's my irrational set of beliefs. Something that works."

--- Rodney A. Brooks, [LEVY92]

CFS:

See CLASSIFIER SYSTEM.

CHROMOSOME:

(biol) One of the chains of DNA found in cells. CHROMOSOMEs contain GENEs, each encoded as a subsection of the DNA chain. Chromosomes are usually present in all cells in an organism, even though only a minority of them will be active in any one cell.

(EC) A datastructure which holds a `string' of task parameters, or genes. This may be stored, for example, as a binary bit-string, or an array of integers.

CLASSIFIER SYSTEM:

A system which takes a (set of) inputs, and produces a (set of) outputs which indicate some classification of the inputs. An example might take inputs from sensors in a chemical plant, and classify them in terms of: 'running ok', 'needs more water', 'needs less water', 'emergency'. See Q1.4 for more information.

COMBINATORIAL OPTIMIZATION:

Some tasks involve combining a set of entities in a specific way (e.g. the task of building a house). A general combinatorial task involves deciding (a) the specifications of those entities (e.g. what size, shape, material to make the bricks from), and (b) the way in which those entities are brought together (e.g. the number of bricks, and their relative positions). If the resulting combination of entities can in some way be given a FITNESS score, then COMBINATORIAL OPTIMIZATION is the task of designing a set of entities, and deciding how they must be configured, so as to give maximum fitness. cf ORDER-BASED PROBLEM.

COMMA STRATEGY:

Notation originally proposed in EVOLUTION STRATEGIEs, when a POPULATION of "mu" PARENTs generates "lambda" OFFSPRING and the mu parents are discarded, leving only the lambda INDIVIDUALs to compete directly. Such a process is written as a (mu,lambda) search. The process of only competing offspring then is a "comma strategy." cf. PLUS STRATEGY.

CONVERGED:

A GENE is said to have CONVERGED when 95% of the CHROMOSOMEs in the POPULATION all contain the same ALLELE for that gene. In some circumstances, a population can be said to have converged when all genes have converged. (However, this is not true of populations containing multiple SPECIES, for example.)

Most people use "convergence" fairly loosely, to mean "the GA has stopped finding new, better solutions". Of course, if you wait long enough, the GA will *eventually* find a better solution (unless you have already found the global optimum). What people really mean is "I'm not willing to wait for the GA to find a new, better solution, because I've already waited longer than I wanted to and it hasn't improved in ages."

An interesting discussion on convergence by Michael Vose can be found in GA-Digest v8n22, available from ftp://ftp.aic.nrl.navy.mil/pub/galist/digests/v8n22

CONVERGENCE VELOCITY:

The rate of error reduction.

COOPERATION:

The behavior of two or more INDIVIDUALs acting to increase the gains of all participating individuals.

CROSSOVER:

(EC) A REPRODUCTION OPERATOR which forms a new CHROMOSOME by combining parts of each of two `parent' chromosomes. The simplest form is single-point CROSSOVER, in which an arbitrary point in the chromosome is picked. All the information from PARENT A is copied from the start up to the crossover point, then all the information from parent B is copied from the crossover point to the end of the chromosome. The new chromosome thus gets the head of one parent's chromosome combined with the tail of the other. Variations exist which use more than one crossover point, or combine information from parents in other ways.

(biol) A complicated process which typically takes place as follows: chromosomes, while engaged in the production of GAMETEs, exchange portions of genetic material. The result is that an almost infinite variety of gametes may be produced. Subsequently, during sexual REPRODUCTION, male and female gametes (i.e. sperm and ova) fuse to produce a new DIPLOID cell with a pair of chromosomes.

In [HOLLAND92] the sentence "When sperm and ova fuse, matching chromosomes line up with one another and then cross their length, thus swapping genetic material" is thus wrong, since these two activities occur in different parts of the life cycle. [eds note: If sexual reproduction (the Real Thing) worked like in GAs, then Holland would be right, but as we all know, it's not the case. We just encountered a Freudian slip of a Grandmaster. BTW: even the German translation of this article has this "bug", although it's well-hidden by the translator.]

CS:

See CLASSIFIER SYSTEM.

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