English

Dual complementary polynomials of graphs and combinatorial interpretation on the values of the Tutte polynomial at positive integers

Combinatorics 2013-06-11 v2

Abstract

We introduce a modular (integral) complementary polynomial κ(G;x,y)\kappa(G;x,y) (κ\mathbbmz(G;x,y)\kappa_{\mathbbm z}(G;x,y)) of two variables of a graph GG by counting the number of modular (integral) complementary tension-flows (CTF) of GG with an orientation ϵ\epsilon. We study these polynomials by further introducing a cut-Eulerian equivalence relation on orientations and geometric structures such as the complementary open lattice polyhedron Δ\textscctf(G,ϵ)\Delta_\textsc{ctf}(G,\epsilon), the complementary open 0-1 polytope Δ\textsc+ctf(G,ϵ)\Delta^+_\textsc{ctf}(G,\epsilon), and the complementary open lattice polytopes Δ\textscρctf(G,ϵ)\Delta^\rho_\textsc{ctf}(G,\epsilon) with respect to orientations ρ\rho. The polynomial κ(G;x,y)\kappa(G;x,y) (κ\mathbbmz(G;x,y)\kappa_{\mathbbm z}(G;x,y)) is a common generalization of the modular (integral) tension polynomial τ(G,x)\tau(G,x) (τ\mathbbmz(G,x)\tau_\mathbbm{z}(G,x)) and the modular (integral) flow polynomial ϕ(G,y)\phi(G,y) (ϕ\mathbbmz(G,y)\phi_\mathbbm{z}(G,y)), and can be decomposed into a sum of product Ehrhart polynomials of complementary open 0-1 polytopes Δ\textsc+ctf(G,ρ)\Delta^+_\textsc{ctf}(G,\rho). There are dual complementary polynomials κˉ(G;x,y)\bar\kappa(G;x,y) and κˉ\mathbbmz(G;x,y)\bar\kappa_{\mathbbm z}(G;x,y), dual to κ\kappa and κ\mathbbmz\kappa_{\mathbbm z} respectively, in the sense that the lattice-point counting to the Ehrhart polynomials is taken inside a topological sum of the dilated closed polytopes Δˉ\textsc+ctf(G,ρ)\bar\Delta^+_\textsc{ctf}(G,\rho). It turns out that the polynomial κˉ(G;x,y)\bar\kappa(G;x,y) is Whitney's rank generating polynomial RG(x,y)R_G(x,y), which gives rise to a combinatorial interpretation on the values of the Tutte polynomial TG(x,y)T_G(x,y) at positive integers. In particular, some special values of κ\mathbbmz\kappa_\mathbbm{z} and κˉ\mathbbmz\bar\kappa_\mathbbm{z} (κ\kappa and κˉ\bar\kappa) count the number of certain special kinds (of equivalence classes) of orientations.

Keywords

Cite

@article{arxiv.1105.2675,
  title  = {Dual complementary polynomials of graphs and combinatorial interpretation on the values of the Tutte polynomial at positive integers},
  author = {Beifang Chen},
  journal= {arXiv preprint arXiv:1105.2675},
  year   = {2013}
}

Comments

28 pages, 3 figures