Packings and Coverings for Four Particular Graphs Each with Six Vertices and Nine Edges \(\lambda = 1\)

Qingde Kang1, Xiaoshan Liu2, Huixian Jia3
1Hebei Normal University,
2Shijiazhuang University Of Economics
3Shijiazhuang Post & Telecommunications High School

Abstract

Let \(\lambda K_v\) be the complete multigraph with \(v\) vertices. Let \(G\) be a finite simple graph. A \(G\)-design (\(G-GD_\lambda)(v)\) (\(G\)-packing (\(G-PD_\lambda)(v)\), \(G\)-covering (\(G-CD_\lambda)(v)\)) of \(K_v\) is a pair \((X, \mathcal{B})\), where \(X\) is the vertex set of \(K_v\), and \(\mathcal{B}\) is a collection of subgraphs of \(K_v\), called blocks, such that each block is isomorphic to \(G\) and any two distinct vertices in \(K_v\) are joined exactly (at most, at least) in \(\lambda\) blocks. In this paper, we will discuss the maximum packing designs and the minimum covering designs for four particular graphs each with six vertices and nine edges.