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Log-concavity of the independence polynomials of $\mathbf{W}_{p}$ graphs

Combinatorics 2025-09-04 v2 Discrete Mathematics

Abstract

Let GG be a graph of order nn. For a positive integer pp, GG is said to be a Wp\mathbf{W}_{p} graph if npn\geq p and every pp pairwise disjoint independent sets of GG are contained within pp pairwise disjoint maximum independent sets. In this paper, we establish that every connected Wp\mathbf{W}_{p} graph GG is pp-quasi-regularizable if and only if n(p+1)αn\geq(p+1)\cdot\alpha, where α\alpha is the independence number of GG and p2p\neq2. This finding ensures that the independence polynomial of a connected Wp\mathbf{W}_{p} graph GG is log-concave whenever (p+1)αnpα+2pα+p(p+1)\cdot\alpha\leq n\leq p\cdot\alpha+2\sqrt{p\cdot\alpha+p} and α24(α+1)p\frac{\alpha^{2}}{4\left( \alpha+1\right) }\leq p, or pα+2pα+p<n(α2+1)p+(α1)2α1p\cdot\alpha+2\sqrt{p\cdot\alpha+p}<n\leq \frac{\left( \alpha^{2}+1\right) \cdot p+\left( \alpha-1\right) ^{2}}{\alpha-1} and α(α1)α+1p\frac{\alpha\left( \alpha-1\right) }{\alpha+1}\leq p. Moreover, the clique corona graph GKpG\circ K_{p} serves as an example of the Wp\mathbf{W}_{p} graph class. We further demonstrate that the independence polynomial of GKpG\circ K_{p} is always log-concave for sufficiently large pp. Keywords: very well-covered graph; quasi-regularizable graph; corona graph; Wp\mathbf{W}_{p} graph; independence polynomial; log-concavity.

Keywords

Cite

@article{arxiv.2409.00827,
  title  = {Log-concavity of the independence polynomials of $\mathbf{W}_{p}$ graphs},
  author = {Do Trong Hoang and Vadim E. Levit and Eugen Mandrescu and My Hanh Pham},
  journal= {arXiv preprint arXiv:2409.00827},
  year   = {2025}
}

Comments

16 pages, 2 figures