Are there any built-in way to calculate inversions?

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Ivor Horton
Ivor Horton 2020-6-15
回答： David Goodmanson 2020-6-16
In Mathematica, there is a built-in function
Inversions
which counts the number of inversions in permutation.
See the document for details at https://reference.wolfram.com/language/Combinatorica/ref/Inversions.html
Is there a similar function in Matlab?
Thanks.

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David Goodmanson
David Goodmanson 2020-6-16
Hi Ivor,
I do not know of one, but here is one way to accomplish it
p = [3 6 1 4 5 2]; % for example
inversions = 0;
for k = length(p):-1:2
f = find(k==p);
inversions = inversions + k -f;
p(f) = [];
end
inversions % the result

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