random permutation with no matches to the position

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Valeria 2016-2-25

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评论： Valeria 2016-2-25

Hello everyone,

I have a question. When using randperm function I would like to get only those permutations where no i number appears on the position i in the vector. Does anybody have a suggestion on how to do so?

Example: 1 2 3 4 5

acceptable permutation: 3 1 5 2 4

non-acceptable permutation: 1 3 5 2 4

Thanks a lot in advance!

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Stephen23 2016-2-25

编辑：Stephen23 2016-2-25

在 MATLAB Online 中打开

Brute force derangement:

N = 9;
out = randperm(N);
while any(out==(1:N))
    out = randperm(N);
end

Valeria 2016-2-25

great, thanks!

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Answer 1

Torsten 2016-2-25

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编辑：Torsten 2016-2-25

An answer is provided under

http://stackoverflow.com/questions/28051975/generating-random-derangements-in-matlab-permutations-without-any-fixed-Point

Best wishes

Torsten.

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Answer 2

Jos (10584) 2016-2-25

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编辑：Jos (10584) 2016-2-25

This specific type of permutation is called a derangement, and there are many methods to generate one. However, it is no so easy to come up with an elegant and fast algorithm.

Take a look at this old thread: http://www.mathworks.com/matlabcentral/newsreader/view_thread/302075#820677

There are several implementations on the file exchange. I will promote my own ;-) http://www.mathworks.com/matlabcentral/fileexchange/30189-randpermfull