Are there any built-in way to calculate inversions?

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.

Answer 1

[David Goodmanson]

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