English

Resistance, oddness and colouring defect of snarks

Combinatorics 2024-07-15 v1

Abstract

Let GG be a bridgeless cubic graph. The \textit{resistance} of GG, denoted r(G)r(G), is the minimum number of edges which can be removed from GG in order to render 3-edge-colourability. The \textit{oddness} of GG, denoted ω(G)\omega(G), is the minimum number of odd components in a 2-factor of GG. The \textit{colouring defect} of GG (or simply, the \textit{defect} of GG), denoted μ3(G)\mu_3(G), is the minimum number of edges not contained in any set of three perfect matchings of GG. These three parameters are regarded as measurements of uncolourability of snarks, partly because any one of these parameters equal zero if and only if GG is 3-edge-colourable. It is also known that r(G)ω(G)r(G) \geq \omega(G) and that μ3(G)32ω(G)\mu_3(G) \geq \frac{3}{2}\omega(G) \cite{fiol,jinsteffen}. We have shown that the ratio of oddness to resistance can be arbitrarily large for non-trivial snarks \cite{allie1}. It has also been shown that the ratio of the defect to oddness can be arbitrarily large for non-trivial snarks, although this result was only shown for graphs with oddness equal to 2 \cite{karabasetal}. In the same paper, the question was posed whether there exists non-trivial snarks for given resistance rr or given oddness ω\omega, and arbitrarily large defect. In this paper, we prove a stronger result: For any positive integers r2r \geq 2, even ωr\omega \geq r, and d32ωd \geq \frac{3}{2}\omega, there exists a non-trivial snark GG with r(G)=rr(G)=r, ω(G)=ω\omega(G)=\omega and μ3(G)d\mu_3(G) \geq d.

Keywords

Cite

@article{arxiv.2407.09101,
  title  = {Resistance, oddness and colouring defect of snarks},
  author = {Imran Allie},
  journal= {arXiv preprint arXiv:2407.09101},
  year   = {2024}
}