Graph Theory
Total Page:16
File Type:pdf, Size:1020Kb

Load more
Recommended publications
-
COMP 761: Lecture 9 – Graph Theory I
COMP 761: Lecture 9 – Graph Theory I David Rolnick September 23, 2020 David Rolnick COMP 761: Graph Theory I Sep 23, 2020 1 / 27 Problem In Königsberg (now called Kaliningrad) there are some bridges (shown below). Is it possible to cross over all of them in some order, without crossing any bridge more than once? (Please don’t post your ideas in the chat just yet, we’ll discuss the problem soon in class.) David Rolnick COMP 761: Graph Theory I Sep 23, 2020 2 / 27 Problem Set 2 will be due on Oct. 9 Vincent’s optional list of practice problems available soon on Slack (we can give feedback on your solutions, but they will not count towards a grade) Course Announcements David Rolnick COMP 761: Graph Theory I Sep 23, 2020 3 / 27 Vincent’s optional list of practice problems available soon on Slack (we can give feedback on your solutions, but they will not count towards a grade) Course Announcements Problem Set 2 will be due on Oct. 9 David Rolnick COMP 761: Graph Theory I Sep 23, 2020 3 / 27 Course Announcements Problem Set 2 will be due on Oct. 9 Vincent’s optional list of practice problems available soon on Slack (we can give feedback on your solutions, but they will not count towards a grade) David Rolnick COMP 761: Graph Theory I Sep 23, 2020 3 / 27 A graph G is defined by a set V of vertices and a set E of edges, where the edges are (unordered) pairs of vertices fv; wg. -
Q(A) - Balance Super Edge Magic Graphs Results
International Journal of Pure and Applied Mathematical Sciences. ISSN 0972-9828 Volume 10, Number 2 (2017), pp. 157-170 © Research India Publications http://www.ripublication.com Q(A) - Balance Super Edge Magic Graphs Results M. Rameshpandi and S. Vimala 1Assistant Professor, Department of Mathematics, Pasumpon Muthuramalinga Thevar College, Usilampatti, Madurai. 2Assistant Professor, Department of Mathematics, Mother Teresa Women’s University, Kodaikanal. Abstract Let G be (p,q)-graph in which the edges are labeled 1,2,3,4,…q so that the vertex sums are constant, mod p, then G is called an edge magic graph. Magic labeling on Q(a) balance super edge–magic graphs introduced [5]. In this paper extend my discussion of Q(a)- balance super edge magic labeling(BSEM) to few types of special graphs. AMS 2010: 05C Keywords: edge magic graph, super edge magic graph, Q(a) balance edge- magic graph. 1.INTRODUCTION Magic graphs are related to the well-known magic squares, but are not quite as famous. Magic squares are an arrangement of numbers in a square in such a way that the sum of the rows, columns and diagonals is always the same. All graphs in this paper are connected, (multi-)graphs without loop. The graph G has vertex – set V(G) and edge – set E(G). A labeling (or valuation) of a graph is a map that carries graph elements to numbers(usually to the positive or non- negative integers). Edge magic graph introduced by Sin Min Lee, Eric Seah and S.K Tan in 1992. Various author discussed in edge magic graphs like Edge magic(p,3p-1)- graphs, Zykov sums of graphs, cubic multigraphs, Edge-magicness of the composition of a cycle with a null graph. -
On the Group-Theoretic Properties of the Automorphism Groups of Various Graphs
ON THE GROUP-THEORETIC PROPERTIES OF THE AUTOMORPHISM GROUPS OF VARIOUS GRAPHS CHARLES HOMANS Abstract. In this paper we provide an introduction to the properties of one important connection between the theories of groups and graphs, that of the group formed by the automorphisms of a given graph. We provide examples of important results in graph theory that can be understood through group theory and vice versa, and conclude with a treatment of Frucht's theorem. Contents 1. Introduction 1 2. Fundamental Definitions, Concepts, and Theorems 2 3. Example 1: The Orbit-Stabilizer Theorem and its Application to Graph Automorphisms 4 4. Example 2: On the Automorphism Groups of the Platonic Solid Skeleton Graphs 4 5. Example 3: A Tight Bound on the Product of the Chromatic Number and Independence Number of Vertex-Transitive Graphs 6 6. Frucht's Theorem 7 7. Acknowledgements 9 8. References 9 1. Introduction Groups and graphs are two highly important kinds of structures studied in math- ematics. Interestingly, the theory of groups and the theory of graphs are deeply connected. In this paper, we examine one particular such connection: that which emerges from the observation that the automorphisms of any given graph form a group under composition. In section 2, we provide a framework for understanding the material discussed in the paper. In sections 3, 4, and 5, we demonstrate how important results in group theory illuminate some properties of automorphism groups, how the geo- metric properties of particular embeddings of graphs can be used to determine the structure of the automorphism groups of all embeddings of those graphs, and how the automorphism group can be used to determine fundamental truths about the structure of the graph. -
MTH 304: General Topology Semester 2, 2017-2018
MTH 304: General Topology Semester 2, 2017-2018 Dr. Prahlad Vaidyanathan Contents I. Continuous Functions3 1. First Definitions................................3 2. Open Sets...................................4 3. Continuity by Open Sets...........................6 II. Topological Spaces8 1. Definition and Examples...........................8 2. Metric Spaces................................. 11 3. Basis for a topology.............................. 16 4. The Product Topology on X × Y ...................... 18 Q 5. The Product Topology on Xα ....................... 20 6. Closed Sets.................................. 22 7. Continuous Functions............................. 27 8. The Quotient Topology............................ 30 III.Properties of Topological Spaces 36 1. The Hausdorff property............................ 36 2. Connectedness................................. 37 3. Path Connectedness............................. 41 4. Local Connectedness............................. 44 5. Compactness................................. 46 6. Compact Subsets of Rn ............................ 50 7. Continuous Functions on Compact Sets................... 52 8. Compactness in Metric Spaces........................ 56 9. Local Compactness.............................. 59 IV.Separation Axioms 62 1. Regular Spaces................................ 62 2. Normal Spaces................................ 64 3. Tietze's extension Theorem......................... 67 4. Urysohn Metrization Theorem........................ 71 5. Imbedding of Manifolds.......................... -
General Topology
General Topology Tom Leinster 2014{15 Contents A Topological spaces2 A1 Review of metric spaces.......................2 A2 The definition of topological space.................8 A3 Metrics versus topologies....................... 13 A4 Continuous maps........................... 17 A5 When are two spaces homeomorphic?................ 22 A6 Topological properties........................ 26 A7 Bases................................. 28 A8 Closure and interior......................... 31 A9 Subspaces (new spaces from old, 1)................. 35 A10 Products (new spaces from old, 2)................. 39 A11 Quotients (new spaces from old, 3)................. 43 A12 Review of ChapterA......................... 48 B Compactness 51 B1 The definition of compactness.................... 51 B2 Closed bounded intervals are compact............... 55 B3 Compactness and subspaces..................... 56 B4 Compactness and products..................... 58 B5 The compact subsets of Rn ..................... 59 B6 Compactness and quotients (and images)............. 61 B7 Compact metric spaces........................ 64 C Connectedness 68 C1 The definition of connectedness................... 68 C2 Connected subsets of the real line.................. 72 C3 Path-connectedness.......................... 76 C4 Connected-components and path-components........... 80 1 Chapter A Topological spaces A1 Review of metric spaces For the lecture of Thursday, 18 September 2014 Almost everything in this section should have been covered in Honours Analysis, with the possible exception of some of the examples. For that reason, this lecture is longer than usual. Definition A1.1 Let X be a set. A metric on X is a function d: X × X ! [0; 1) with the following three properties: • d(x; y) = 0 () x = y, for x; y 2 X; • d(x; y) + d(y; z) ≥ d(x; z) for all x; y; z 2 X (triangle inequality); • d(x; y) = d(y; x) for all x; y 2 X (symmetry). -
Clay Mathematics Institute 2005 James A
Contents Clay Mathematics Institute 2005 James A. Carlson Letter from the President 2 The Prize Problems The Millennium Prize Problems 3 Recognizing Achievement 2005 Clay Research Awards 4 CMI Researchers Summary of 2005 6 Workshops & Conferences CMI Programs & Research Activities Student Programs Collected Works James Arthur Archive 9 Raoul Bott Library CMI Profile Interview with Research Fellow 10 Maria Chudnovsky Feature Article Can Biology Lead to New Theorems? 13 by Bernd Sturmfels CMI Summer Schools Summary 14 Ricci Flow, 3–Manifolds, and Geometry 15 at MSRI Program Overview CMI Senior Scholars Program 17 Institute News Euclid and His Heritage Meeting 18 Appointments & Honors 20 CMI Publications Selected Articles by Research Fellows 27 Books & Videos 28 About CMI Profile of Bow Street Staff 30 CMI Activities 2006 Institute Calendar 32 2005 Euclid: www.claymath.org/euclid James Arthur Collected Works: www.claymath.org/cw/arthur Hanoi Institute of Mathematics: www.math.ac.vn Ramanujan Society: www.ramanujanmathsociety.org $.* $MBZ.BUIFNBUJDT*OTUJUVUF ".4 "NFSJDBO.BUIFNBUJDBM4PDJFUZ In addition to major,0O"VHVTU BUUIFTFDPOE*OUFSOBUJPOBM$POHSFTTPG.BUIFNBUJDJBOT ongoing activities such as JO1BSJT %BWJE)JMCFSUEFMJWFSFEIJTGBNPVTMFDUVSFJOXIJDIIFEFTDSJCFE the summer schools,UXFOUZUISFFQSPCMFNTUIBUXFSFUPQMBZBOJOnVFOUJBMSPMFJONBUIFNBUJDBM the Institute undertakes a 5IF.JMMFOOJVN1SJ[F1SPCMFNT SFTFBSDI"DFOUVSZMBUFS PO.BZ BUBNFFUJOHBUUIF$PMMÒHFEF number of smaller'SBODF UIF$MBZ.BUIFNBUJDT*OTUJUVUF $.* BOOPVODFEUIFDSFBUJPOPGB special projects -
HAMILTONICITY in CAYLEY GRAPHS and DIGRAPHS of FINITE ABELIAN GROUPS. Contents 1. Introduction. 1 2. Graph Theory: Introductory
HAMILTONICITY IN CAYLEY GRAPHS AND DIGRAPHS OF FINITE ABELIAN GROUPS. MARY STELOW Abstract. Cayley graphs and digraphs are introduced, and their importance and utility in group theory is formally shown. Several results are then pre- sented: firstly, it is shown that if G is an abelian group, then G has a Cayley digraph with a Hamiltonian cycle. It is then proven that every Cayley di- graph of a Dedekind group has a Hamiltonian path. Finally, we show that all Cayley graphs of Abelian groups have Hamiltonian cycles. Further results, applications, and significance of the study of Hamiltonicity of Cayley graphs and digraphs are then discussed. Contents 1. Introduction. 1 2. Graph Theory: Introductory Definitions. 2 3. Cayley Graphs and Digraphs. 2 4. Hamiltonian Cycles in Cayley Digraphs of Finite Abelian Groups 5 5. Hamiltonian Paths in Cayley Digraphs of Dedekind Groups. 7 6. Cayley Graphs of Finite Abelian Groups are Guaranteed a Hamiltonian Cycle. 8 7. Conclusion; Further Applications and Research. 9 8. Acknowledgements. 9 References 10 1. Introduction. The topic of Cayley digraphs and graphs exhibits an interesting and important intersection between the world of groups, group theory, and abstract algebra and the world of graph theory and combinatorics. In this paper, I aim to highlight this intersection and to introduce an area in the field for which many basic problems re- main open.The theorems presented are taken from various discrete math journals. Here, these theorems are analyzed and given lengthier treatment in order to be more accessible to those without much background in group or graph theory. -
Cayley Graphs of PSL(2) Over Finite Commutative Rings Kathleen Bell Western Kentucky University, [email protected]
Western Kentucky University TopSCHOLAR® Masters Theses & Specialist Projects Graduate School Spring 2018 Cayley Graphs of PSL(2) over Finite Commutative Rings Kathleen Bell Western Kentucky University, [email protected] Follow this and additional works at: https://digitalcommons.wku.edu/theses Part of the Algebra Commons, and the Other Mathematics Commons Recommended Citation Bell, Kathleen, "Cayley Graphs of PSL(2) over Finite Commutative Rings" (2018). Masters Theses & Specialist Projects. Paper 2102. https://digitalcommons.wku.edu/theses/2102 This Thesis is brought to you for free and open access by TopSCHOLAR®. It has been accepted for inclusion in Masters Theses & Specialist Projects by an authorized administrator of TopSCHOLAR®. For more information, please contact [email protected]. CAYLEY GRAPHS OF P SL(2) OVER FINITE COMMUTATIVE RINGS A Thesis Presented to The Faculty of the Department of Mathematics Western Kentucky University Bowling Green, Kentucky In Partial Fulfillment Of the Requirements for the Degree Master of Science By Kathleen Bell May 2018 ACKNOWLEDGMENTS I have been blessed with the support of many people during my time in graduate school; without them, this thesis would not have been completed. To my parents: thank you for prioritizing my education from the beginning. It is because of you that I love learning. To my fianc´e,who has spent several \dates" making tea and dinner for me while I typed math: thank you for encouraging me and believing in me. To Matthew, who made grad school fun: thank you for truly being a best friend. I cannot imagine the past two years without you. To the math faculty at WKU: thank you for investing your time in me. -
Algorithms for Generating Star and Path of Graphs Using BFS Dr
Web Site: www.ijettcs.org Email: [email protected], [email protected] Volume 1, Issue 3, September – October 2012 ISSN 2278-6856 Algorithms for Generating Star and Path of Graphs using BFS Dr. H. B. Walikar2, Ravikumar H. Roogi1, Shreedevi V. Shindhe3, Ishwar. B4 2,4Prof. Dept of Computer Science, Karnatak University, Dharwad, 1,3Research Scholars, Dept of Computer Science, Karnatak University, Dharwad Abstract: In this paper we deal with BFS algorithm by 1.8 Diamond Graph: modifying it with some conditions and proper labeling of The diamond graph is the simple graph on nodes and vertices which results edges illustrated Fig.7. [2] and on applying it to some small basic 1.9 Paw Graph: class of graphs. The BFS algorithm has to modify The paw graph is the -pan graph, which is also accordingly. Some graphs will result in and by direct application of BFS where some need modifications isomorphic to the -tadpole graph. Fig.8 [2] in the algorithm. The BFS algorithm starts with a root vertex 1.10 Gem Graph: called start vertex. The resulted output tree structure will be The gem graph is the fan graph illustrated Fig.9 [2] in the form of Structure or in Structure. 1.11 Dart Graph: Keywords: BFS, Graph, Star, Path. The dart graph is the -vertex graph illustrated Fig.10.[2] 1.12 Tetrahedral Graph: 1. INTRODUCTION The tetrahedral graph is the Platonic graph that is the 1.1 Graph: unique polyhedral graph on four nodes which is also the A graph is a finite collection of objects called vertices complete graph and therefore also the wheel graph . -
The Monadic Second-Order Logic of Graphs Xvi: Canonical Graph Decompositions
Logical Methods in Computer Science Vol. 2 (2:2) 2006, pp. 1–46 Submitted Jun. 24, 2005 www.lmcs-online.org Published Mar. 23, 2006 THE MONADIC SECOND-ORDER LOGIC OF GRAPHS XVI: CANONICAL GRAPH DECOMPOSITIONS BRUNO COURCELLE LaBRI, Bordeaux 1 University, 33405 Talence, France e-mail address: [email protected] Abstract. This article establishes that the split decomposition of graphs introduced by Cunnigham, is definable in Monadic Second-Order Logic.This result is actually an instance of a more general result covering canonical graph decompositions like the modular decom- position and the Tutte decomposition of 2-connected graphs into 3-connected components. As an application, we prove that the set of graphs having the same cycle matroid as a given 2-connected graph can be defined from this graph by Monadic Second-Order formulas. 1. Introduction Hierarchical graph decompositions are useful for the construction of efficient algorithms, and also because they give structural descriptions of the considered graphs. Cunningham and Edmonds have proposed in [18] a general framework for defining decompositions of graphs, hypergraphs and matroids. This framework covers many types of decompositions. Of particular interest is the split decomposition of directed and undirected graphs defined by Cunningham in [17]. A hierarchical decomposition of a certain type is canonical if, up to technical details like vertex labellings, there is a unique decomposition of a given graph (or hypergraph, or matroid) of this type. To take well-known examples concerning graphs, the modular decom- position is canonical, whereas, except in particular cases, there is no useful canonical notion of tree-decomposition of minimal tree-width. -
Tree-Decomposition Graph Minor Theory and Algorithmic Implications
DIPLOMARBEIT Tree-Decomposition Graph Minor Theory and Algorithmic Implications Ausgeführt am Institut für Diskrete Mathematik und Geometrie der Technischen Universität Wien unter Anleitung von Univ.Prof. Dipl.-Ing. Dr.techn. Michael Drmota durch Miriam Heinz, B.Sc. Matrikelnummer: 0625661 Baumgartenstraße 53 1140 Wien Datum Unterschrift Preface The focus of this thesis is the concept of tree-decomposition. A tree-decomposition of a graph G is a representation of G in a tree-like structure. From this structure it is possible to deduce certain connectivity properties of G. Such information can be used to construct efficient algorithms to solve problems on G. Sometimes problems which are NP-hard in general are solvable in polynomial or even linear time when restricted to trees. Employing the tree-like structure of tree-decompositions these algorithms for trees can be adapted to graphs of bounded tree-width. This results in many important algorithmic applications of tree-decomposition. The concept of tree-decomposition also proves to be useful in the study of fundamental questions in graph theory. It was used extensively by Robertson and Seymour in their seminal work on Wagner’s conjecture. Their Graph Minors series of papers spans more than 500 pages and results in a proof of the graph minor theorem, settling Wagner’s conjecture in 2004. However, it is not only the proof of this deep and powerful theorem which merits mention. Also the concepts and tools developed for the proof have had a major impact on the field of graph theory. Tree-decomposition is one of these spin-offs. Therefore, we will study both its use in the context of graph minor theory and its several algorithmic implications. -
The Spectrum of Platonic Graphs Over Finite Fields
View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector Discrete Mathematics 307 (2007) 1074–1081 www.elsevier.com/locate/disc The spectrum of Platonic graphs over finite fields Michelle DeDeoa, Dominic Lanphierb,∗, Marvin Mineic aDepartment of Mathematics, University of North Florida, Jacksonville, FL 32224, USA bDepartment of Mathematics, Western Kentucky University, Bowling Green, KY 42101, USA cDepartment of Mathematics, University of California, Irvine, CA 92697, USA Received 15 September 2005; received in revised form 26 June 2006; accepted 20 July 2006 Available online 13 October 2006 Abstract We give a decomposition theorem for Platonic graphs over finite fields and use this to determine the spectrum of these graphs. We also derive estimates for the isoperimetric numbers of the graphs. © 2006 Elsevier B.V. All rights reserved. Keywords: Cayley graph; Ramanujan graph; Isoperimetric number 1. Introduction r Let p be an odd prime, let r 1, and let Fq be the finite field with q = p elements. We consider a generalization of the Platonic graphs studied in [2,7–9]. In particular, using the notation from [7], we define our graphs G∗(q) as follows. Definition 1. Let the vertex set of G∗(q) be ∗ V(G (q)) ={()|, ∈ Fq ,() = (00)}/±1, and let () be adjacent to () if and only if det =±1. For q = p, the graph G∗(q) is called the qth Platonic graph. The name comes from the fact that when p = 3or 5, the graphs G∗(p) correspond to 1-skeletons of two of the Platonic solids, in other words, the tetrahedron and the icosahedron as in [2].