Identifier
- St000616: Permutations ⟶ ℤ
Values
[1] => 0
[1,2] => 0
[2,1] => 2
[1,2,3] => 0
[1,3,2] => 3
[2,1,3] => 2
[2,3,1] => 5
[3,1,2] => 6
[3,2,1] => 8
[1,2,3,4] => 0
[1,2,4,3] => 4
[1,3,2,4] => 3
[1,3,4,2] => 7
[1,4,2,3] => 8
[1,4,3,2] => 11
[2,1,3,4] => 2
[2,1,4,3] => 6
[2,3,1,4] => 5
[2,3,4,1] => 9
[2,4,1,3] => 10
[2,4,3,1] => 13
[3,1,2,4] => 6
[3,1,4,2] => 10
[3,2,1,4] => 8
[3,2,4,1] => 12
[3,4,1,2] => 14
[3,4,2,1] => 16
[4,1,2,3] => 12
[4,1,3,2] => 15
[4,2,1,3] => 14
[4,2,3,1] => 17
[4,3,1,2] => 18
[4,3,2,1] => 20
[1,2,3,4,5] => 0
[1,2,3,5,4] => 5
[1,2,4,3,5] => 4
[1,2,4,5,3] => 9
[1,2,5,3,4] => 10
[1,2,5,4,3] => 14
[1,3,2,4,5] => 3
[1,3,2,5,4] => 8
[1,3,4,2,5] => 7
[1,3,4,5,2] => 12
[1,3,5,2,4] => 13
[1,3,5,4,2] => 17
[1,4,2,3,5] => 8
[1,4,2,5,3] => 13
[1,4,3,2,5] => 11
[1,4,3,5,2] => 16
[1,4,5,2,3] => 18
[1,4,5,3,2] => 21
[1,5,2,3,4] => 15
[1,5,2,4,3] => 19
[1,5,3,2,4] => 18
[1,5,3,4,2] => 22
[1,5,4,2,3] => 23
[1,5,4,3,2] => 26
[2,1,3,4,5] => 2
[2,1,3,5,4] => 7
[2,1,4,3,5] => 6
[2,1,4,5,3] => 11
[2,1,5,3,4] => 12
[2,1,5,4,3] => 16
[2,3,1,4,5] => 5
[2,3,1,5,4] => 10
[2,3,4,1,5] => 9
[2,3,4,5,1] => 14
[2,3,5,1,4] => 15
[2,3,5,4,1] => 19
[2,4,1,3,5] => 10
[2,4,1,5,3] => 15
[2,4,3,1,5] => 13
[2,4,3,5,1] => 18
[2,4,5,1,3] => 20
[2,4,5,3,1] => 23
[2,5,1,3,4] => 17
[2,5,1,4,3] => 21
[2,5,3,1,4] => 20
[2,5,3,4,1] => 24
[2,5,4,1,3] => 25
[2,5,4,3,1] => 28
[3,1,2,4,5] => 6
[3,1,2,5,4] => 11
[3,1,4,2,5] => 10
[3,1,4,5,2] => 15
[3,1,5,2,4] => 16
[3,1,5,4,2] => 20
[3,2,1,4,5] => 8
[3,2,1,5,4] => 13
[3,2,4,1,5] => 12
[3,2,4,5,1] => 17
[3,2,5,1,4] => 18
[3,2,5,4,1] => 22
[3,4,1,2,5] => 14
[3,4,1,5,2] => 19
[3,4,2,1,5] => 16
[3,4,2,5,1] => 21
[3,4,5,1,2] => 24
[3,4,5,2,1] => 26
[3,5,1,2,4] => 21
[3,5,1,4,2] => 25
>>> Load all 873 entries. <<<
search for individual values
searching the database for the individual values of this statistic
/
search for generating function
searching the database for statistics with the same generating function
Description
The inversion index of a permutation.
The inversion index of a permutation $\sigma=\sigma_1\sigma_2\ldots\sigma_n$ is defined as
$$ \sum_{\mbox{inversion pairs } (\sigma_i,\sigma_j)} \sigma_i $$
where $(\sigma_i,\sigma_j)$ is an inversion pair if i < j and $\sigma_i > \sigma_j$.
This equals the sum of the entries in the corresponding descending plane partition; see [1].
The inversion index of a permutation $\sigma=\sigma_1\sigma_2\ldots\sigma_n$ is defined as
$$ \sum_{\mbox{inversion pairs } (\sigma_i,\sigma_j)} \sigma_i $$
where $(\sigma_i,\sigma_j)$ is an inversion pair if i < j and $\sigma_i > \sigma_j$.
This equals the sum of the entries in the corresponding descending plane partition; see [1].
References
[1] Striker, J. A direct bijection between descending plane partitions with no special parts and permutation matrices arXiv:1002.3391
[2] Irregular triangle read by rows: row n gives expansion of g.f. for descending plane partitions of order n with weight equal to sum of the parts. OEIS:A198890
[2] Irregular triangle read by rows: row n gives expansion of g.f. for descending plane partitions of order n with weight equal to sum of the parts. OEIS:A198890
Code
def statistic(p):
return sum( p[i-1] for i,j in p.inversions() )
Created
Aug 22, 2016 at 17:56 by Jessica Striker
Updated
Dec 30, 2016 at 10:30 by Christian Stump
searching the database
Sorry, this statistic was not found in the database
or
add this statistic to the database – it's very simple and we need your support!