Identifier
- St000873: Permutations ⟶ ℤ
Values
[1,2] => 2
[2,1] => 0
[1,2,3] => 3
[1,3,2] => 1
[2,1,3] => 1
[2,3,1] => 0
[3,1,2] => 1
[3,2,1] => 0
[1,2,3,4] => 4
[1,2,4,3] => 2
[1,3,2,4] => 2
[1,3,4,2] => 1
[1,4,2,3] => 2
[1,4,3,2] => 1
[2,1,3,4] => 1
[2,1,4,3] => 1
[2,3,1,4] => 2
[2,3,4,1] => 0
[2,4,1,3] => 2
[2,4,3,1] => 0
[3,1,2,4] => 1
[3,1,4,2] => 1
[3,2,1,4] => 0
[3,2,4,1] => 0
[3,4,1,2] => 2
[3,4,2,1] => 0
[4,1,2,3] => 1
[4,1,3,2] => 1
[4,2,1,3] => 0
[4,2,3,1] => 0
[4,3,1,2] => 0
[4,3,2,1] => 0
[1,2,3,4,5] => 5
[1,2,3,5,4] => 3
[1,2,4,3,5] => 3
[1,2,4,5,3] => 2
[1,2,5,3,4] => 3
[1,2,5,4,3] => 2
[1,3,2,4,5] => 2
[1,3,2,5,4] => 2
[1,3,4,2,5] => 3
[1,3,4,5,2] => 1
[1,3,5,2,4] => 3
[1,3,5,4,2] => 1
[1,4,2,3,5] => 2
[1,4,2,5,3] => 2
[1,4,3,2,5] => 1
[1,4,3,5,2] => 1
[1,4,5,2,3] => 3
[1,4,5,3,2] => 1
[1,5,2,3,4] => 2
[1,5,2,4,3] => 2
[1,5,3,2,4] => 1
[1,5,3,4,2] => 1
[1,5,4,2,3] => 1
[1,5,4,3,2] => 1
[2,1,3,4,5] => 1
[2,1,3,5,4] => 1
[2,1,4,3,5] => 1
[2,1,4,5,3] => 1
[2,1,5,3,4] => 1
[2,1,5,4,3] => 1
[2,3,1,4,5] => 2
[2,3,1,5,4] => 2
[2,3,4,1,5] => 3
[2,3,4,5,1] => 0
[2,3,5,1,4] => 3
[2,3,5,4,1] => 0
[2,4,1,3,5] => 2
[2,4,1,5,3] => 2
[2,4,3,1,5] => 1
[2,4,3,5,1] => 0
[2,4,5,1,3] => 3
[2,4,5,3,1] => 0
[2,5,1,3,4] => 2
[2,5,1,4,3] => 2
[2,5,3,1,4] => 1
[2,5,3,4,1] => 0
[2,5,4,1,3] => 1
[2,5,4,3,1] => 0
[3,1,2,4,5] => 1
[3,1,2,5,4] => 1
[3,1,4,2,5] => 1
[3,1,4,5,2] => 1
[3,1,5,2,4] => 1
[3,1,5,4,2] => 1
[3,2,1,4,5] => 0
[3,2,1,5,4] => 0
[3,2,4,1,5] => 1
[3,2,4,5,1] => 0
[3,2,5,1,4] => 1
[3,2,5,4,1] => 0
[3,4,1,2,5] => 2
[3,4,1,5,2] => 2
[3,4,2,1,5] => 0
[3,4,2,5,1] => 0
[3,4,5,1,2] => 3
[3,4,5,2,1] => 0
[3,5,1,2,4] => 2
[3,5,1,4,2] => 2
[3,5,2,1,4] => 0
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Description
The aix statistic of a permutation.
According to [1], this statistic on finite strings $\pi$ of integers is given as follows: let $m$ be the leftmost occurrence of the minimal entry and let $\pi = \alpha\ m\ \beta$. Then
$$ \operatorname{aix}\pi = \begin{cases} \operatorname{aix}\alpha & \text{ if } \alpha,\beta \neq \emptyset \\ 1 + \operatorname{aix}\beta & \text{ if } \alpha = \emptyset \\ 0 & \text{ if } \beta = \emptyset \end{cases}\ . $$
According to [1], this statistic on finite strings $\pi$ of integers is given as follows: let $m$ be the leftmost occurrence of the minimal entry and let $\pi = \alpha\ m\ \beta$. Then
$$ \operatorname{aix}\pi = \begin{cases} \operatorname{aix}\alpha & \text{ if } \alpha,\beta \neq \emptyset \\ 1 + \operatorname{aix}\beta & \text{ if } \alpha = \emptyset \\ 0 & \text{ if } \beta = \emptyset \end{cases}\ . $$
References
[1] Burstein, A. On the distribution of some Euler-Mahonian statistics MathSciNet:3357124
Code
def statistic(pi):
pi = list(pi)
if not pi:
return 0
i = min(pi)
j = pi.index(i)
alpha = pi[:j]
beta = pi[j+1:]
if alpha and beta:
return statistic(alpha)
elif alpha == []:
return 1 + statistic(beta)
else:
return 0
Created
Jun 27, 2017 at 11:42 by Christian Stump
Updated
Jun 27, 2017 at 11:42 by Christian Stump
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