StretchingPairs

Pairs i < j with p(i) < i < j < p(j).

✓ checked against that system · ! checked, with disagreements (hover a chip)FindStatSt000516via Permutation✓↗

StretchingPairs(p)Pairs i < j with p(i) < i < j < p(j).

Typed signatures

Type	Package	Applies
(permutation) -> number	combinatorics	always

Domain: Permutation statistics

Details

• Defined over Permutation as an expression in _x, evaluated by compute-engine — the definition IS the implementation.
• Takes a Permutation and nothing else — it reads values against their positions, or walks the orbits, so it needs the bijection. Applying it to a bare list is a type error, not a wrong answer.

Definition

Epsil, as the implementation runs it.

on Permutation, over _x

0 if Length(_x) < 2 else Sum(Map(Function(Sum(Map(
                                                   Function(1, j),
                                                   Filter(
                                                           Range(
                                                                  i + 1,
                                                                  Length(_x),
                                                                ),
                                                           Function(_x[i] < i &&
                                                                    j < _x[j], j),
                                                         ),
                                                 )), i), Range(1, Length(_x) - 1)))

Examples

Basic #

the one-line word $312$

live ↗

In$\mathrm{StretchingPairs}({\operatorname{Permutation}}([3, 1, 2]))$Out$0$

the one-line word $2413$

live ↗

In$\mathrm{StretchingPairs}({\operatorname{Permutation}}([2, 4, 1, 3]))$Out$0$

Properties #

FindStat's value for [1,2]

live ↗

In$\mathrm{CombinatorialStat}({\operatorname{Permutation}}([1, 2]), \text{StretchingPairs})$Out$0$

Known value · FindStat St000516

FindStat's value for [2,1]

live ↗

In$\mathrm{CombinatorialStat}({\operatorname{Permutation}}([2, 1]), \text{StretchingPairs})$Out$0$

Known value · FindStat St000516

FindStat's value for [1,2,3]

live ↗

In$\mathrm{CombinatorialStat}({\operatorname{Permutation}}([1, 2, 3]), \text{StretchingPairs})$Out$0$

Known value · FindStat St000516

About

Examples	5
Crosswalk	FindStat