Talk:Selection (genetic algorithm)

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Sorting Population[edit]

What is gained by sorting the population by the value of the fitness function? Molinari 01:07, 29 July 2005 (UTC)[reply]

After sorting, binary search can be used, leading to a time complexity of O(n log n) for the whole selection process, whereas if you don´t you will have to search through all elemetns for each selection, leading to a time complexity of O(n^2). AB

I must be missing something. What does one search for (using binary search)? We need to find the individual whose _accumulated_ fitness function exceeds the random value. To do this there is no need to sort the individuals by fitness: just compute the accumulated values in linear time (go through the array) and the accumulated values are automatically in ascending order. Perhaps I do not understand step 5. Molinari 02:51, 31 October 2006 (UTC)[reply]

I also see no need to sort the individuals.

Me neither. Also, an alternative to accumulated sums and binary search is to first generate all the random numbers and sort them, and then go once through the population array, selecting individuals and advancing an index into the random number array as necessary. —Preceding unsigned comment added by 65.113.40.1 (talk) 20:28, 3 July 2008 (UTC)[reply]

Sorting individuals may be helpful when there exist noise or some other stochastic elements in the evaluation function.Birkan 18:16, 29 October 2007 (UTC)[reply]

How so? —Preceding unsigned comment added by 65.113.40.1 (talk) 20:30, 3 July 2008 (UTC)[reply]

Sorting not essential[edit]

Sorting is not essential to the roulette algorithm. It may be mentioned in a section about optimization. When many samples are get from the same probabilities, sorting is done once, reducing the search effort. But if probabilities are changed frequently, there is no significant advantage. Those technical issues should be addressed by the article. 179.236.82.100 (talk) 01:20, 10 August 2018 (UTC)[reply]

Merge[edit]

It seems to me that this should be merged in to the main article. -- Craigtalbert 05:13, 25 March 2007 (UTC)[reply]

I disagree since Tournament Selection is not specific just to Genetic Algorithm which such a merging would imply. —Preceding unsigned comment added by 82.47.155.12 (talk) 19:24, 21 September 2007 (UTC)[reply]

I disagree too. Tournament Selection can be used in many evolutionary techniques so it shouldn't be merged in the Genetic Algorithm article. And it also can't be merged to the Selection (genetic algorithm) article because tournament selection doesn't use neither sampling before selection nor ranking. DanceMacabre 07:17, 24 October 2007 (UTC)[reply]

Although I also do not see any significant difference in merging or not, it is a fact that tournament selection is applied in literature as a selection process in genetic algorithms; so can be a subcategory. A selection procedure does not necessarily need to have ranking to expedite individuals into mating pool. Birkan 18:12, 29 October 2007 (UTC)[reply]

Why is Roulette wheel selection redirected to Fitness proportionate selection? I would say that if we want to select individuals proportionaly to their fitness, it is not necessary to use Roulette wheel selection. DanceMacabre 11:35, 15 November 2007 (UTC)[reply]

Because they are the exact same thing. --Radu