English

Vertex Partitions and Maximum $\G$-free Subgraphs

Combinatorics 2023-09-06 v2

Abstract

We define a (V1,V2,,Vk)(V_1, V_2, \ldots, V_k)-partition for a given graph HH and graphical properties P1,P2,,PkP_1, P_2, \ldots, P_k as a partition where each ViV_i induces a subgraph of HH with property PiP_i. Matamala (2007) extended this result by showing that for any graph HH with Δ(H)=p+q\Delta(H)=p+q, there exists a (V1,V2)(V_1, V_2)-partition of V(H)V(H) where H[V1]H[V_1] is a maximum order (p1)(p-1)-degenerate induced subgraph and H[V2]H[V_2] is (q1)(q-1)-degenerate. Additionally, Catlin and Lai proved that if Δ(H)5\Delta(H)\geq 5, HH has a (V1,V2)(V_1, V_2)-partition such that H[V1]H[V_1] is a maximum order acyclic induced subgraph, ω(H[V2])Δ(H)2\omega(H[V_2])\leq \Delta(H)-2, and Δ(H[V2])Δ(H)2\Delta(H[V_2])\leq \Delta(H)-2. Rowshan and Taherkhani demonstrated that given a graph GG with a minimum degree δ(G)\delta(G) and for k=Δ(H)δ(G)k=\lceil \frac{\Delta(H)}{\delta(G)}\rceil, there exists a (V1,V2,,Vk)(V_1, V_2, \ldots, V_k)-partition of the vertex set of HH, such that each H[Vi]H[V_i] is GG-free, meaning it does not contain a subgraph isomorphic to GG, and H[V1]H[V_1] is a maximum order GG-free induced subgraph. In our paper, we present a novel result for a connected graph HH with Δ(H)5\Delta(H)\geq 5 and without KΔ(H)+1eK_{\Delta(H)+1}\setminus e as a subgraph. We establish that when p1p2pk12p_1\geq p_2\geq\cdots\geq p_{k-1}\geq 2, pk4p_k\geq 4, i=1kpi=Δ(H)1+k\sum_{i=1}^k p_i=\Delta(H)-1+k, and Gi\mathcal{G}_i represents a family of graphs with a minimum degree at least pi1p_i-1 for each i[k1]i\in [k-1], a (V1,V2,,Vk)(V_1, V_2, \ldots, V_k)-partition of V(H)V(H) exists. This partition guarantees that H[V1]H[V_1] is a maximum order G1\mathcal{G}_1-free induced subgraph, H[Vi]H[V_i] is Gi\mathcal{G}_i-free for each 2ik12\leq i\leq k-1, Δ(H[Vk])pk\Delta(H[V_k])\leq p_k, and either H[Vk]H[V_k] is KpkK_{p_k}-free or its pkp_k-cliques are disjoint.

Keywords

Cite

@article{arxiv.2207.04964,
  title  = {Vertex Partitions and Maximum $\G$-free Subgraphs},
  author = {Yaser Rowshan},
  journal= {arXiv preprint arXiv:2207.04964},
  year   = {2023}
}
R2 v1 2026-06-25T00:49:04.239Z