Identifier
- St000798: Permutations ⟶ ℤ
Values
[1,2] => 0
[2,1] => 1
[1,2,3] => 0
[1,3,2] => 2
[2,1,3] => 1
[2,3,1] => 1
[3,1,2] => 2
[3,2,1] => 3
[1,2,3,4] => 0
[1,2,4,3] => 3
[1,3,2,4] => 2
[1,3,4,2] => 2
[1,4,2,3] => 3
[1,4,3,2] => 5
[2,1,3,4] => 1
[2,1,4,3] => 4
[2,3,1,4] => 1
[2,3,4,1] => 1
[2,4,1,3] => 2
[2,4,3,1] => 4
[3,1,2,4] => 2
[3,1,4,2] => 4
[3,2,1,4] => 3
[3,2,4,1] => 3
[3,4,1,2] => 2
[3,4,2,1] => 3
[4,1,2,3] => 3
[4,1,3,2] => 5
[4,2,1,3] => 4
[4,2,3,1] => 4
[4,3,1,2] => 5
[4,3,2,1] => 6
[1,2,3,4,5] => 0
[1,2,3,5,4] => 4
[1,2,4,3,5] => 3
[1,2,4,5,3] => 3
[1,2,5,3,4] => 4
[1,2,5,4,3] => 7
[1,3,2,4,5] => 2
[1,3,2,5,4] => 6
[1,3,4,2,5] => 2
[1,3,4,5,2] => 2
[1,3,5,2,4] => 3
[1,3,5,4,2] => 6
[1,4,2,3,5] => 3
[1,4,2,5,3] => 6
[1,4,3,2,5] => 5
[1,4,3,5,2] => 5
[1,4,5,2,3] => 3
[1,4,5,3,2] => 5
[1,5,2,3,4] => 4
[1,5,2,4,3] => 7
[1,5,3,2,4] => 6
[1,5,3,4,2] => 6
[1,5,4,2,3] => 7
[1,5,4,3,2] => 9
[2,1,3,4,5] => 1
[2,1,3,5,4] => 5
[2,1,4,3,5] => 4
[2,1,4,5,3] => 4
[2,1,5,3,4] => 5
[2,1,5,4,3] => 8
[2,3,1,4,5] => 1
[2,3,1,5,4] => 5
[2,3,4,1,5] => 1
[2,3,4,5,1] => 1
[2,3,5,1,4] => 2
[2,3,5,4,1] => 5
[2,4,1,3,5] => 2
[2,4,1,5,3] => 5
[2,4,3,1,5] => 4
[2,4,3,5,1] => 4
[2,4,5,1,3] => 2
[2,4,5,3,1] => 4
[2,5,1,3,4] => 3
[2,5,1,4,3] => 6
[2,5,3,1,4] => 5
[2,5,3,4,1] => 5
[2,5,4,1,3] => 6
[2,5,4,3,1] => 8
[3,1,2,4,5] => 2
[3,1,2,5,4] => 6
[3,1,4,2,5] => 4
[3,1,4,5,2] => 4
[3,1,5,2,4] => 5
[3,1,5,4,2] => 8
[3,2,1,4,5] => 3
[3,2,1,5,4] => 7
[3,2,4,1,5] => 3
[3,2,4,5,1] => 3
[3,2,5,1,4] => 4
[3,2,5,4,1] => 7
[3,4,1,2,5] => 2
[3,4,1,5,2] => 4
[3,4,2,1,5] => 3
[3,4,2,5,1] => 3
[3,4,5,1,2] => 2
[3,4,5,2,1] => 3
[3,5,1,2,4] => 3
[3,5,1,4,2] => 5
[3,5,2,1,4] => 4
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Description
The makl of a permutation.
According to [1], this is the sum of the number of occurrences of the vincular patterns $(1\underline{32})$, $(\underline{31}2)$, $(\underline{32}1)$ and $(\underline{21})$, where matches of the underlined letters must be adjacent.
According to [1], this is the sum of the number of occurrences of the vincular patterns $(1\underline{32})$, $(\underline{31}2)$, $(\underline{32}1)$ and $(\underline{21})$, where matches of the underlined letters must be adjacent.
References
[1] Amini, N. Equidistributions of Mahonian statistics over pattern avoiding permutations arXiv:1705.05298
Code
def statistic(pi):
patterns = [([1,3,2],[2]), ([3,1,2],[1]), ([3,2,1],[1]), ([2,1],[1])]
return sum(vincular_occurrences(pi, p, c) for p, c in patterns)
def vincular_occurrences(perm, pat, columns):
n = len(pat)
R = [(c, i) for c in columns for i in range(n+1)]
return mesh_pattern_occurrences(perm, pat, R=R)
def G(w):
return [ (x+1,y) for (x,y) in enumerate(w) ]
def mesh_pattern_occurrences(perm, pat, R=[]):
occs = 0
k = len(pat)
n = len(perm)
pat = G(pat)
perm = G(perm)
for H in Subsets(perm, k):
H = sorted(H)
X = dict(G(sorted(i for (i,_) in H)))
Y = dict(G(sorted(j for (_,j) in H)))
if H == [ (X[i], Y[j]) for (i,j) in pat ]:
X[0], X[k+1] = 0, n+1
Y[0], Y[k+1] = 0, n+1
shady = ( X[i] < x < X[i+1] and Y[j] < y < Y[j+1]
for (i,j) in R
for (x,y) in perm
)
if not any(shady):
occs = occs + 1
return occs
Created
May 16, 2017 at 16:57 by Martin Rubey
Updated
Jan 10, 2018 at 20:36 by Martin Rubey
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