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Matching statistic: St001911
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St001911: Permutations ⟶ ℤResult quality: 100% ●values known / values provided: 100%●distinct values known / distinct values provided: 100%
Values
[1] => 0
[1,2] => 0
[2,1] => 0
[1,2,3] => 0
[1,3,2] => 1
[2,1,3] => 1
[2,3,1] => 0
[3,1,2] => 0
[3,2,1] => 1
[1,2,3,4] => 0
[1,2,4,3] => 2
[1,3,2,4] => 3
[1,3,4,2] => 1
[1,4,2,3] => 2
[1,4,3,2] => 4
[2,1,3,4] => 2
[2,1,4,3] => 4
[2,3,1,4] => 2
[2,3,4,1] => 0
[2,4,1,3] => 1
[2,4,3,1] => 3
[3,1,2,4] => 1
[3,1,4,2] => 3
[3,2,1,4] => 4
[3,2,4,1] => 2
[3,4,1,2] => 0
[3,4,2,1] => 2
[4,1,2,3] => 0
[4,1,3,2] => 2
[4,2,1,3] => 3
[4,2,3,1] => 1
[4,3,1,2] => 2
[4,3,2,1] => 4
[1,2,3,4,5] => 0
[1,2,3,5,4] => 3
[1,2,4,3,5] => 5
[1,2,4,5,3] => 2
[1,2,5,3,4] => 4
[1,2,5,4,3] => 7
[1,3,2,4,5] => 5
[1,3,2,5,4] => 8
[1,3,4,2,5] => 4
[1,3,4,5,2] => 1
[1,3,5,2,4] => 3
[1,3,5,4,2] => 6
[1,4,2,3,5] => 4
[1,4,2,5,3] => 7
[1,4,3,2,5] => 9
[1,4,3,5,2] => 6
[1,4,5,2,3] => 2
Description
A descent variant minus the number of inversions.
This statistic is defined for general finite crystallographic root system Φ with Weyl group W as follows: Let 2ρ=∑β∈Φ+β=∑α∈Δbαα be the sum of the positive roots expressed in the simple roots.
For w∈W this statistic is then
stat(w)=∑α∈Δ:w(α)∈Φ−bα−ℓ(w),
where the sum ranges over all descents of w and ℓ(w) is the Coxeter length.
It was shown in [1], that for irreducible groups, it holds that
∑w∈Wqstat(w)=f∏α∈Δ1−qbα1−qeα,
where {eα∣α∈Δ} are the exponents of the group and f is its index of connection, i.e., the index of the root lattice inside the weight lattice.
For a permutation σ∈Sn, this becomes
stat(σ)=∑i∈Des(σ)i⋅(n−i)−inv(σ).
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