Abstract

An important problem in graph theory is that of determining the maximum number of edges in a given graph $G$ that contains no specific subgraphs. This problem has attracted the attention of many researchers. An example of such a problem is the determination of an upper bound on the number of edges of a graph that has no triangles. In this paper, we let $\mathcal{G}(n,V_{r,3})$ denote the class of graphs on $n$ vertices containing no $r$-vertex-disjoint cycles of length $3$. We show that for large $n$, $\mathcal{E}(G)\les \lfloor \frac{(n-r+1)^2}{4} \rfloor +(r-1)(n-r+1)$ for every $G\in\mathcal{G}(n,V_{r,3})$. Furthermore, equality holds if and only if $G=\Omega(n,r)=K_{r-1,\lfloor \frac{n-r+1}2\rfloor,\lceil \frac{n-r+1}2\rceil}$ where $\Omega(n,r)$ is a tripartite graph on $n$ vertices.

Highlights

  • In this paper, we only consider simple graphs with vertex set V(G) and edge set E(G)

  • An important problem in graph theory is that of determining the maximum number of edges in a given graph G that contains no specific subgraphs

  • The cycle on n vertices is denoted by Cn and the complete tripartite graph with partitioning sets of order m, n and k is denoted by Km,n,k

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Summary

Introduction

We only consider simple graphs with vertex set V(G) and edge set E(G). An important problem in extremal graph theory is the determination of maximum number of edges a graph has under a condition that the given graph has no specific subgraphs. Such an example is finding an upper bound for E(G) whenever G has no triangles (cycles of length 3) or, in general, G has no odd disjoint cycles. G ∈ G(n; V2k+1) where G(n; V2k+1) is the class of graphs on n vertices containing no vertex-disjoint cycles of length 2k + 1. M. M., 2012) in which we considered here no r vertex-disjoint cycles of length 3 instead of edge-disjoint cycles discussed in

Important Lemmas and Theorems
Main Result

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