Writing a custom Selection Function for a Genetic Algorithm problem
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Hey guys, I am a bit lost on this. Any help would be appreciated. Essentially my problem is this: I want to write a custom SelectionFcn for my GA to select the 25 best parents and then select 2 at random to create 25 children. And the children should be the arithmetic mean between the parents.
I have olny gotten as far as this:
function parents = parents(expectation, nParents, options, state)
nParents = 25
parents = zeros(1,nParents);
% get the scores of the current population
curPopScores = state.Score;
% get the 25 best parents
if length(curPopScores)>25
% created matrix with scores and indices for each parent
if iscolumn(curPopScores)
data = [curPopScores'; 1:length(curPopScores)];
else
data = [curPopScores'; 1:length(curPopScores)];
end
% now sort the data on the column that corresponds to the scores
% (-1 means sort the first column in descending order)
sortedData = sortrows(data',-1);
% get the sorted parent indices from the first 25 elements
parents = sortedData(1:25,2);
That should work except I am unable to access the scores with "state.Score"
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Accepted Answer
Alan Weiss
on 20 Apr 2015
I am sorry that the documentation is not clear on this point. I will try to improve it.
function parents = myfun(expectation, nParents, options)
The question is what does the expectation argument mean? In fact, it is the vector of scaled fitness functions associated with the members of the population. So if you want the best 25 members, just sort expectation and take the top 25.
Alan Weiss
MATLAB mathematical toolbox documentation
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More Answers (2)
Geoff Hayes
on 4 Apr 2015
Renovatio - I don't have the Global Optimization Toolbox, but I suspect that you have to do something like the following (note that expectation and nParents are inputs to your function so you may not want to overwrite them)
function parents = parents(expectation, nParents, options)
nParents = 25
parents = zeros(1,nParents);
% get the current state of the GA
state = gaoptimget(options, 'state');
% get the scores of the current population
curPopScores = state.Score;
% get the 25 best parents
if length(curPopScores)>25
% created matrix with scores and indices for each parent
if iscolumn(curPopScores)
data = [curPopScores'; 1:length(curPopScores)];
else
data = [curPopScores'; 1:length(curPopScores)];
end
% now sort the data on the column that corresponds to the scores
% (-1 means sort the first column in descending order)
sortedData = sortrows(data',-1);
% get the sorted parent indices from the first 25 elements
parents = sortedData(1:25,2);
else
parents = 1:25;
end
The above should allow you to select the best 25 parents from the current generation. For more details on the state structure, see GA options.
yuan feng
on 10 Dec 2017
hello,i want to write a custom mutation function, but i don't know how to write, i would appreciate it if you can help me.
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