English

Eccentricities in the flip-graphs of convex polygons

Combinatorics 2019-08-12 v2

Abstract

The flip-graph of a convex polygon π\pi is the graph whose vertices are the triangulations of π\pi and whose edges correspond to flips between them. The eccentricity of a triangulation TT of π\pi is the largest possible distance in this graph from TT to any triangulation of π\pi. It is well known that, when all n3n-3 interior edges of TT are incident to the same vertex, the eccentricity of TT in the flip-graph of π\pi is exactly n3n-3, where nn denotes the number of vertices of π\pi. Here, this statement is generalized to arbitrary triangulations. Denoting by n3kn-3-k the largest number of interior edges of TT incident to a vertex, it is shown that the eccentricity of TT in the flip-graph of π\pi is exactly n3+kn-3+k, provided kn/22k\leq{n/2-2}. Inversely, the eccentricity of a triangulation, when small enough, allows to recover the value of kk. More precisely, if kn/85/2k\leq{n/8-5/2}, it is also shown that TT has eccentricity n3+kn-3+k if and only if exactly n3kn-3-k of its interior edges are incident to a given vertex. When k>n/22k>n/2-2, bounds on the eccentricity of TT are also given and discussed.

Keywords

Cite

@article{arxiv.1706.06456,
  title  = {Eccentricities in the flip-graphs of convex polygons},
  author = {Lionel Pournin},
  journal= {arXiv preprint arXiv:1706.06456},
  year   = {2019}
}

Comments

16 pages, 4 figures