English

On the degree sequences of dual graphs on surfaces

Combinatorics 2020-08-04 v1 Discrete Mathematics

Abstract

Given two graphs GG and GG^* with a one-to-one correspondence between their edges, when do GG and GG^* form a pair of dual graphs realizing the vertices and countries of a map embedded in a surface? A criterion was obtained by Jack Edmonds in 1965. Furthermore, let d=(d1,,dn)\boldsymbol{d}=(d_1,\ldots,d_n) and t=(t1,,tm)\boldsymbol{t}=(t_1,\ldots,t_m) be their degree sequences. Then, clearly, i=1ndi=j=1mtj=2\sum_{i=1}^n d_i = \sum_{j=1}^m t_j = 2\ell, where \ell is the number of edges in each of the two graphs, and χ=n+m\chi = n - \ell + m is the Euler characteristic of the surface. Which sequences d\boldsymbol{d} and t\boldsymbol{t} satisfying these conditions still cannot be realized as the degree sequences? We make use of Edmonds' criterion to obtain several infinite series of exceptions for the sphere, χ=2\chi = 2, and projective plane, χ=1\chi = 1. We conjecture that there exist no exceptions for χ0\chi \leq 0.

Keywords

Cite

@article{arxiv.2008.00573,
  title  = {On the degree sequences of dual graphs on surfaces},
  author = {Endre Boros and Vladimir Gurvich and Martin Milanič and Jernej Vičič},
  journal= {arXiv preprint arXiv:2008.00573},
  year   = {2020}
}