Identifier
- St000868: Permutations ⟶ ℤ
Values
[1] => 0
[1,2] => 0
[2,1] => 1
[1,2,3] => 0
[1,3,2] => 1
[2,1,3] => 2
[2,3,1] => 1
[3,1,2] => 3
[3,2,1] => 2
[1,2,3,4] => 0
[1,2,4,3] => 1
[1,3,2,4] => 2
[1,3,4,2] => 1
[1,4,2,3] => 3
[1,4,3,2] => 2
[2,1,3,4] => 2
[2,1,4,3] => 3
[2,3,1,4] => 3
[2,3,4,1] => 1
[2,4,1,3] => 4
[2,4,3,1] => 2
[3,1,2,4] => 3
[3,1,4,2] => 4
[3,2,1,4] => 4
[3,2,4,1] => 3
[3,4,1,2] => 5
[3,4,2,1] => 2
[4,1,2,3] => 4
[4,1,3,2] => 5
[4,2,1,3] => 5
[4,2,3,1] => 4
[4,3,1,2] => 6
[4,3,2,1] => 3
[1,2,3,4,5] => 0
[1,2,3,5,4] => 1
[1,2,4,3,5] => 2
[1,2,4,5,3] => 1
[1,2,5,3,4] => 3
[1,2,5,4,3] => 2
[1,3,2,4,5] => 2
[1,3,2,5,4] => 3
[1,3,4,2,5] => 3
[1,3,4,5,2] => 1
[1,3,5,2,4] => 4
[1,3,5,4,2] => 2
[1,4,2,3,5] => 3
[1,4,2,5,3] => 4
[1,4,3,2,5] => 4
[1,4,3,5,2] => 3
[1,4,5,2,3] => 5
[1,4,5,3,2] => 2
[1,5,2,3,4] => 4
[1,5,2,4,3] => 5
[1,5,3,2,4] => 5
[1,5,3,4,2] => 4
[1,5,4,2,3] => 6
[1,5,4,3,2] => 3
[2,1,3,4,5] => 2
[2,1,3,5,4] => 3
[2,1,4,3,5] => 4
[2,1,4,5,3] => 3
[2,1,5,3,4] => 5
[2,1,5,4,3] => 4
[2,3,1,4,5] => 3
[2,3,1,5,4] => 4
[2,3,4,1,5] => 4
[2,3,4,5,1] => 1
[2,3,5,1,4] => 5
[2,3,5,4,1] => 2
[2,4,1,3,5] => 4
[2,4,1,5,3] => 5
[2,4,3,1,5] => 5
[2,4,3,5,1] => 3
[2,4,5,1,3] => 6
[2,4,5,3,1] => 2
[2,5,1,3,4] => 5
[2,5,1,4,3] => 6
[2,5,3,1,4] => 6
[2,5,3,4,1] => 4
[2,5,4,1,3] => 7
[2,5,4,3,1] => 3
[3,1,2,4,5] => 3
[3,1,2,5,4] => 4
[3,1,4,2,5] => 5
[3,1,4,5,2] => 4
[3,1,5,2,4] => 6
[3,1,5,4,2] => 5
[3,2,1,4,5] => 4
[3,2,1,5,4] => 5
[3,2,4,1,5] => 6
[3,2,4,5,1] => 3
[3,2,5,1,4] => 7
[3,2,5,4,1] => 4
[3,4,1,2,5] => 5
[3,4,1,5,2] => 6
[3,4,2,1,5] => 5
[3,4,2,5,1] => 4
[3,4,5,1,2] => 7
[3,4,5,2,1] => 2
[3,5,1,2,4] => 6
[3,5,1,4,2] => 7
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Description
The aid statistic in the sense of Shareshian-Wachs.
This is the number of admissible inversions St000866The number of admissible inversions of a permutation in the sense of Shareshian-Wachs. plus the number of descents St000021The number of descents of a permutation.. This statistic was introduced by John Shareshian and Michelle L. Wachs in [1]. Theorem 4.1 states that the aid statistic together with the descent statistic is Euler-Mahonian.
This is the number of admissible inversions St000866The number of admissible inversions of a permutation in the sense of Shareshian-Wachs. plus the number of descents St000021The number of descents of a permutation.. This statistic was introduced by John Shareshian and Michelle L. Wachs in [1]. Theorem 4.1 states that the aid statistic together with the descent statistic is Euler-Mahonian.
References
[1] Shareshian, J., Wachs, M. L. $q$-Eulerian polynomials: excedance number and major index MathSciNet:2300004
Code
def statistic(pi):
return (sum(1 for i,j in pi.inversions()
if ((j < len(pi) and pi(j) < pi(j+1)) or
(i+1 < j and pi(j) > min(pi(k) for k in range(i+1,j)))))
+ pi.number_of_descents())
Created
Jun 27, 2017 at 08:53 by Christian Stump
Updated
Nov 03, 2017 at 00:15 by Martin Rubey
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