Updown numbers and the initial monomials of the slope variety
The electronic journal of combinatorics, Tome 16 (2009) no. 1
Let $I_n$ be the ideal of all algebraic relations on the slopes of the ${n\choose2}$ lines formed by placing $n$ points in a plane and connecting each pair of points with a line. Under each of two natural term orders, the ideal of $I_n$ is generated by monomials corresponding to permutations satisfying a certain pattern-avoidance condition. We show bijectively that these permutations are enumerated by the updown (or Euler) numbers, thereby obtaining a formula for the number of generators of the initial ideal of $I_n$ in each degree.
DOI :
10.37236/171
Classification :
05A15, 05A05, 14N20
Mots-clés : permutations, pattern avoidance condition, enumeration, updown numbers, Euler numbers, number of generators, ideal
Mots-clés : permutations, pattern avoidance condition, enumeration, updown numbers, Euler numbers, number of generators, ideal
@article{10_37236_171,
author = {Jeremy L. Martin and Jennifer D. Wagner},
title = {Updown numbers and the initial monomials of the slope variety},
journal = {The electronic journal of combinatorics},
year = {2009},
volume = {16},
number = {1},
doi = {10.37236/171},
zbl = {1186.05014},
url = {http://geodesic.mathdoc.fr/articles/10.37236/171/}
}
Jeremy L. Martin; Jennifer D. Wagner. Updown numbers and the initial monomials of the slope variety. The electronic journal of combinatorics, Tome 16 (2009) no. 1. doi: 10.37236/171
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