Identifier
- St000221: Permutations ⟶ ℤ
Values
[1] => 1
[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] => 0
[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] => 1
[1,4,3,2] => 1
[2,1,3,4] => 2
[2,1,4,3] => 0
[2,3,1,4] => 1
[2,3,4,1] => 0
[2,4,1,3] => 0
[2,4,3,1] => 0
[3,1,2,4] => 1
[3,1,4,2] => 0
[3,2,1,4] => 1
[3,2,4,1] => 0
[3,4,1,2] => 0
[3,4,2,1] => 0
[4,1,2,3] => 0
[4,1,3,2] => 0
[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] => 2
[1,2,5,4,3] => 2
[1,3,2,4,5] => 3
[1,3,2,5,4] => 1
[1,3,4,2,5] => 2
[1,3,4,5,2] => 1
[1,3,5,2,4] => 1
[1,3,5,4,2] => 1
[1,4,2,3,5] => 2
[1,4,2,5,3] => 1
[1,4,3,2,5] => 2
[1,4,3,5,2] => 1
[1,4,5,2,3] => 1
[1,4,5,3,2] => 1
[1,5,2,3,4] => 1
[1,5,2,4,3] => 1
[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] => 3
[2,1,3,5,4] => 1
[2,1,4,3,5] => 1
[2,1,4,5,3] => 0
[2,1,5,3,4] => 0
[2,1,5,4,3] => 0
[2,3,1,4,5] => 2
[2,3,1,5,4] => 0
[2,3,4,1,5] => 1
[2,3,4,5,1] => 0
[2,3,5,1,4] => 0
[2,3,5,4,1] => 0
[2,4,1,3,5] => 1
[2,4,1,5,3] => 0
[2,4,3,1,5] => 1
[2,4,3,5,1] => 0
[2,4,5,1,3] => 0
[2,4,5,3,1] => 0
[2,5,1,3,4] => 0
[2,5,1,4,3] => 0
[2,5,3,1,4] => 0
[2,5,3,4,1] => 0
[2,5,4,1,3] => 0
[2,5,4,3,1] => 0
[3,1,2,4,5] => 2
[3,1,2,5,4] => 0
[3,1,4,2,5] => 1
[3,1,4,5,2] => 0
[3,1,5,2,4] => 0
[3,1,5,4,2] => 0
[3,2,1,4,5] => 2
[3,2,1,5,4] => 0
[3,2,4,1,5] => 1
[3,2,4,5,1] => 0
[3,2,5,1,4] => 0
[3,2,5,4,1] => 0
[3,4,1,2,5] => 1
[3,4,1,5,2] => 0
[3,4,2,1,5] => 1
[3,4,2,5,1] => 0
[3,4,5,1,2] => 0
[3,4,5,2,1] => 0
[3,5,1,2,4] => 0
[3,5,1,4,2] => 0
>>> 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 number of strong fixed points of a permutation.
$i$ is called a strong fixed point of $\pi$ if
1. $j < i$ implies $\pi_j < \pi_i$, and
2. $j > i$ implies $\pi_j > \pi_i$
This can be described as an occurrence of the mesh pattern ([1], {(0,1),(1,0)}), i.e., the upper left and the lower right quadrants are shaded, see [3].
The generating function for the joint-distribution (RLmin, LRmax, strong fixed points) has a continued fraction expression as given in [4, Lemma 3.2], for LRmax see St000314The number of left-to-right-maxima of a permutation..
$i$ is called a strong fixed point of $\pi$ if
1. $j < i$ implies $\pi_j < \pi_i$, and
2. $j > i$ implies $\pi_j > \pi_i$
This can be described as an occurrence of the mesh pattern ([1], {(0,1),(1,0)}), i.e., the upper left and the lower right quadrants are shaded, see [3].
The generating function for the joint-distribution (RLmin, LRmax, strong fixed points) has a continued fraction expression as given in [4, Lemma 3.2], for LRmax see St000314The number of left-to-right-maxima of a permutation..
References
[1] Triangle read by rows: T(n,k) is the number of permutations of [n] having k strong fixed points (0<=k<=n). A permutation p of 1,2,...,n is said to have j as a strong fixed point (splitter) if p(k)<j for k<j and p(k)>j for k>j. OEIS:A145878
[2] Ex 1.128b Stanley, R. P. Enumerative combinatorics. Volume 1 MathSciNet:2868112
[3] Brändén, P., Claesson, A. Mesh patterns and the expansion of permutation statistics as sums of permutation patterns arXiv:1102.4226
[4] Kim, J. S., Stanton, D. The Combinatorics of Associated Laguerre Polynomials arXiv:1501.03880
[2] Ex 1.128b Stanley, R. P. Enumerative combinatorics. Volume 1 MathSciNet:2868112
[3] Brändén, P., Claesson, A. Mesh patterns and the expansion of permutation statistics as sums of permutation patterns arXiv:1102.4226
[4] Kim, J. S., Stanton, D. The Combinatorics of Associated Laguerre Polynomials arXiv:1501.03880
Code
def strong_fixed_point(x, i):
v = x[i]
for j in range(i):
if x[j] >= v:
return False
for j in range(i+1, len(x)):
if x[j] <= v:
return False
return True
def statistic(x):
return len([1 for i in range(len(x)) if strong_fixed_point(x, i)])
Created
Sep 22, 2014 at 16:58 by Martin Rubey
Updated
Oct 17, 2017 at 17:52 by Jang Soo Kim
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!