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GA doesn't perform well

Started by January 02, 2002 05:01 PM
11 comments, last by edotorpedo 22 years, 10 months ago
Many researchs have shown that probably the best way to implement a GA is to use uniform crossove with a mutation rate of 0.05. This should be used with a steady-state GA meaning that the population of the GA should stay constant, while the worst genes are being replaced each time.

Uniform crossover means that given two parents, there is a 50% chance you''ll take a bit from a certain parent to use in a child. So, the code would go something like follow for crossover:

for (i = 0; i < gene_length; i++)
{
if (random() < 0.5)
{
child = parent1<br> }<br> else<br> {<br> child = parent2<br> }<br>}<br><br>This is used to generate one child, yet it is possible to use this to generate two off springs as well.<br><br>As for selection, I usually get the best results when I select the gene with the best fitness as one of the parents all the time. Then randomly select the second parent from the population. </i>
The above is NOT uniform crossover , at least not as it was originally implemented by Holland in his canonical Genetic Algorithm. Uniform crossover uses a uniform probability distribution to select a crossover site within the chromosome structure. For a chromosome of length L, there are L-1 crossover sites between genes. Therefore, each site will have a probability of 1/(L-1) of being selected. Every bit to the right of the crossover site is swapped between parents to create two children.

As for mutation rates, 5% is a commonly used number. However, having higher or lower mutation is permissable... it simply affects the likelihood that any given string will change schema.

Cheers,

Timkin
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Did greedy mutation and elitism work? Just a note about greedy mutation: I may not require less time, but rather less generations.

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