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22 Mart 2013 Cuma

PREMATURE CONVERGENCE IN GENETIC ALGORITHM


GA is a kind of hill-climbing search; more specifically it is very similar to a randomized beam search. As with all hill-climbing algorithms, there is a problem of local maxima. There is no absolute assurance that a genetic algorithm will find a global optimum. It happens very often when the populations have a lot of subjects. Local maxima in a genetic problem are those individuals that get stuck with a pretty good, but not optimal, fitness measure. [7]



When applying genetic algorithm for solving large-scale and complex real-world problems, premature convergence is the one of the most frequently encountered difficulties. In that situation  , the  solving  procedure  is  trapped  in  the suboptimal state and  most  of the operators can’t  produce offspring surpassing their parents any more . It has been proven that the genetic algorithm can't converge to the global optimal solution [8]

Any small mutation gives worse fitness. Fortunately, crossover can help them get out of a local maximum. Also, mutation is a random process, so it is possible that we may have a sudden large mutation to get these individuals out of this situation. (In fact, these individuals never get out. It's their offspring that get out of local maxima.) Overall, GAs have less problems with local maxima than back-propagation neural networks. [9]

Sources:

[7] [9]  C. R. Dyer, CS 540 Lecture Notes, University of Wisconsin – Madison
[8] Rudolph G., 1994, “Convergence Analysis of Canonical Genetic Algorithms”, IEEE Trans.  On Neural Networks, Vo1.5(1), p96-101.

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