Identifier
Values
[1,0] => [2,1] => [2,1] => [2,1] => 1
[1,0,1,0] => [3,1,2] => [1,3,2] => [1,3,2] => 2
[1,1,0,0] => [2,3,1] => [2,3,1] => [2,3,1] => 2
[1,0,1,0,1,0] => [4,1,2,3] => [1,2,4,3] => [1,2,4,3] => 3
[1,0,1,1,0,0] => [3,1,4,2] => [3,4,1,2] => [3,4,1,2] => 2
[1,1,0,0,1,0] => [2,4,1,3] => [2,1,4,3] => [2,1,4,3] => 2
[1,1,0,1,0,0] => [4,3,1,2] => [1,4,3,2] => [1,4,3,2] => 2
[1,1,1,0,0,0] => [2,3,4,1] => [2,3,4,1] => [2,3,4,1] => 3
[] => [1] => [1] => [1] => 1
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Description
The number of critical left to right maxima of the parking functions.
An entry $p$ in a parking function is critical, if there are exactly $p-1$ entries smaller than $p$ and $n-p$ entries larger than $p$. It is a left to right maximum, if there are no larger entries before it.
This statistic allows the computation of the Tutte polynomial of the complete graph $K_{n+1}$, via
$$ \sum_{P} x^{st(P)}y^{\binom{n+1}{2}-\sum P}, $$
where the sum is over all parking functions of length $n$, see [1, thm.13.5.16].
Map
Ringel
Description
The Ringel permutation of the LNakayama algebra corresponding to a Dyck path.
Map
parking function
Description
Interpret the permutation as a parking function.
Map
Foata bijection
Description
Sends a permutation to its image under the Foata bijection.
The Foata bijection $\phi$ is a bijection on the set of words with no two equal letters. It can be defined by induction on the size of the word:
Given a word $w_1 w_2 ... w_n$, compute the image inductively by starting with $\phi(w_1) = w_1$.
At the $i$-th step, if $\phi(w_1 w_2 ... w_i) = v_1 v_2 ... v_i$, define $\phi(w_1 w_2 ... w_i w_{i+1})$ by placing $w_{i+1}$ on the end of the word $v_1 v_2 ... v_i$ and breaking the word up into blocks as follows.
  • If $w_{i+1} \geq v_i$, place a vertical line to the right of each $v_k$ for which $w_{i+1} \geq v_k$.
  • If $w_{i+1} < v_i$, place a vertical line to the right of each $v_k$ for which $w_{i+1} < v_k$.
In either case, place a vertical line at the start of the word as well. Now, within each block between vertical lines, cyclically shift the entries one place to the right.
To compute $\phi([1,4,2,5,3])$, the sequence of words is
  • $1$
  • $|1|4 \to 14$
  • $|14|2 \to 412$
  • $|4|1|2|5 \to 4125$
  • $|4|125|3 \to 45123.$
In total, this gives $\phi([1,4,2,5,3]) = [4,5,1,2,3]$.
This bijection sends the major index (St000004The major index of a permutation.) to the number of inversions (St000018The number of inversions of a permutation.).