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Distance-2 Domatic Numbers of Graphs Derek Kiser East Tennessee State University

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Distance-2 Domatic Numbers of Graphs Derek Kiser East Tennessee State University East Tennessee State University Digital Commons @ East Tennessee State University Electronic Theses and Dissertations Student Works 5-2015 Distance-2 Domatic Numbers of Graphs Derek Kiser East Tennessee State University Follow this and additional works at: https://dc.etsu.edu/etd Part of the Discrete Mathematics and Combinatorics Commons Recommended Citation Kiser, Derek, "Distance-2 Domatic Numbers of Graphs" (2015). Electronic Theses and Dissertations. Paper 2505. https://dc.etsu.edu/ etd/2505 This Thesis - Open Access is brought to you for free and open access by the Student Works at Digital Commons @ East Tennessee State University. It has been accepted for inclusion in Electronic Theses and Dissertations by an authorized administrator of Digital Commons @ East Tennessee State University. For more information, please contact [email protected]. Distance-2 Domatic Numbers of Graphs A thesis presented to the faculty of the Department of Mathematics East Tennessee State University In partial fulfillment of the requirements for the degree Master of Science in Mathematical Sciences by Derek Kiser May 2015 Teresa W. Haynes, Ph.D., Chair Robert A. Beeler, Ph.D. Robert B. Gardner, Ph.D. Keywords: distance-2 domination, distance-2 domatic number ABSTRACT Distance-2 Domatic Numbers of Graphs by Derek Kiser The distance d(u; v) between two vertices u and v in a graph G equals the length of a shortest path from u to v. A set S of vertices is called a distance-2 dominating set if every vertex in V n S is within distance-2 of at least one vertex in S. The distance-2 domatic number is the maximum number of sets in a partition of the vertices of G into distance-2 dominating sets. We give bounds on the distance-2 domatic number of a graph and determine the distance-2 domatic number of selected classes of graphs. 2 Copyright by Derek Kiser 2015 3 DEDICATION I would like to dedicate this thesis to my late grandfather, Nelson Kiser. Through the observation of his life I learned to love well and to appreciate the uniqueness of all those around us. 4 ACKNOWLEDGMENTS I want to thank Dr. Robert Beeler and Dr. Robert Gardner for taking the time to read and make corrections to the original draft of my theis as well as Dr. Hedetniemi for proposing the topic. And I want to thank Dr. Teresa Haynes. Not for being an amazing instructor or adviser, but an amazing person. Twenty years from now I will not remember her for her love of graph theory or the wonderful energy she brought to the classroom. I will not remember her for how she introduced me to the subject of graph theory or how she sent me to a conference for the first time with confidence. I will not remember the time spent working on this thesis or her responses to my many homework questions. I will not remember her for her love of dogs or her hatred for ticks, but I will always remember her for her advice on life and faith, in which I was blessed to hear and witness. 5 TABLE OF CONTENTS ABSTRACT . .2 ACKNOWLEDGMENTS . .5 LIST OF FIGURES . .7 1 INTRODUCTION . .8 1.1 Introduction to Graph Theory . .8 2 DOMINATION . 11 2.1 Introduction to Domination . 11 2.2 Domination and Domatic Number Background . 12 2.3 Total Domatic Number Background . 15 3 DISTANCE-2 DOMINATION . 18 3.1 Distance-2 Domination . 18 4 DISTANCE-2 DOMATIC NUMBER RESULTS . 21 4.1 Bounds on the Distance-2 Domatic Number . 21 4.2 Specific Families . 24 5 CONCLUDING REMARKS . 36 BIBLIOGRAPHY . 38 VITA ...................................... 39 6 LIST OF FIGURES 1 G4;5 = P4 × P5 ............................... 10 2 Modified Houses . 12 3 Counterexample to the c ≤ d conjecture . 16 4 Modified Houses 2 . 19 5 Cycles . 26 6 d≤2(G11;13) ≥ 6 .............................. 33 7 Graph G . 36 7 1 INTRODUCTION 1.1 Introduction to Graph Theory A graph G = (V; E) is made up of a finite nonempty set V and a possibly empty set E. The elements of V are referred to as vertices and the elements of E; two element subsets of V; are referred to as edges. The number of vertices, jV j, in a graph is known as the order of G, and the number of edges, jEj, is known as the size of G. The letters n and m are typically used to denote the order and size respectively of a graph. An edge denoted by uv, represents adjacent vertices u and v. The graphs we consider are finite, undirected, have edges that must join two vertices, and the maximum number of edges allowed to join two vertices is one. The open neighborhood of a vertex v 2 V is the set N(v) = fu j uv 2 V g of vertices adjacent to v. Each vertex in u 2 N(v) is called a neighbor of v. The degree of a vertex v is deg(v) = jN(v)j. The minimum and maximum degrees of any vertex in a graph G are denoted δ(G) and ∆(G), respectively. A vertex v 2 V is called an isolated vertex if it has no neighbors, that is, deg(v) = 0. A vertex with exactly one neighbor is called a leaf, and its neighbor is called a support vertex. The closed neighborhood of a vertex v 2 V is the set N[v] = N(v) [ fvg. The open neighborhood S of a set S ⊆ V of vertices is N(S) = v2S N(v), while the closed neighborhood of a S set S is the set N[S] = v2S N[v]. The S-private neighborhood of a vertex v 2 S is the set pn[v; S] = N[v] n N[S n fvg]; vertices in the set pn[v; S] are called private neighbors of v (with respect to S). A walk in a graph G is a sequence of vertices starting with a vertex u and ending 8 at a vertex v, where the consecutive vertices in the walk are adjacent in G. A walk in a graph G such that no vertex is repeated is referred to as a path. The distance d(u; v) between two vertices u and v in a graph G equals the length of a shortest path from u to v. Two vertices u and v in a graph are connected if the graph contains a path between u and v. A graph G itself is said to be connected if every two vertices of G are connected. A graph H is a subgraph of a graph G if V (H) ⊆ V (G) and E(H) ⊆ E(G). If H is a subgraph of a graph G and either V (H) is a proper subset of V (G) or E(H) is a proper subset of E(G), then H is a proper subgraph of G. For a nonempty subset S of V (G); the subgraph G[S] of G induced by S has S as its vertex set and two vertices u and v are adjacent in G[S] if and only if u and v are adjacent in G. A subgraph H of a graph G is called an induced subgraph if there is a nonempty subset S of V (G) such that H = G[S]. A connected subgraph H of a graph G is a component of G if H is not a proper subgraph of any connected subgraph of G. The complement G of a graph G is a graph with the vertex set V (G) where two vertices are adjacent in G if and only if they are not adjacent in G. The eccentricity of a vertex v of a connected graph G is the distance between v and the vertex farthest from v in G. The diameter of G denoted diam(G) is the largest eccentricity of the vertices of a graph G, while the radius of G is the smallest eccentricity of the vertices. A path Pn is a graph of order n and size n − 1 with vertices denoted v1; v2; :::; vn and edges vivi + 1 for i = 1; 2; :::; n − 1. A cycle Cn is a graph of order and size n with vertices denoted v1; v2; :::; vn and edges vivi+1 for i = 1; 2; :::; n − 1 and v1vn.A 9 Figure 1: G4;5 = P4 × P5 grid Gr;c is a cartesian product of two paths Pr × Pc (where the cartesian product K = G1 × G2 has vertex set V (K) = V (G1) × V (G2) and vertices (u1; v1) and (u2; v2) in V (K) are adjacent if and only if either u1 = u2 and v1v2 2 E(G2) or v1 = v2 and u1u2 2 E(G1). An example of a G3;4 is given in Figure 1. A complete graph Kn is a graph in which every two distinct vertices are adjacent. A graph G is a complete bipartite graph Km;n if V (G) can be partitioned into two sets U and W so that uw is an edge of G if and only if u 2 U and w 2 W . A vertex coloring of a graph G is an assignment of colors to the vertices of G where one color is assigned to each vertex. Vertex colorings in which adjacent vertices are colored differently are known as a proper vertex coloring.A k-coloring is a coloring in which each color used is one of k colors. A graph G is k-colorable if there exists a coloring of G from a set of k colors.
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