Lower Bounds and Fixed-Parameter Tractability of Drawing Graphs
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The Circle Packing Theorem
Alma Mater Studiorum · Università di Bologna SCUOLA DI SCIENZE Corso di Laurea in Matematica THE CIRCLE PACKING THEOREM Tesi di Laurea in Analisi Relatore: Pesentata da: Chiar.mo Prof. Georgian Sarghi Nicola Arcozzi Sessione Unica Anno Accademico 2018/2019 Introduction The study of tangent circles has a rich history that dates back to antiquity. Already in the third century BC, Apollonius of Perga, in his exstensive study of conics, introduced problems concerning tangency. A famous result attributed to Apollonius is the following. Theorem 0.1 (Apollonius - 250 BC). Given three mutually tangent circles C1, C2, 1 C3 with disjoint interiors , there are precisely two circles tangent to all the three initial circles (see Figure1). A simple proof of this fact can be found here [Sar11] and employs the use of Möbius transformations. The topic of circle packings as presented here, is sur- prisingly recent and originates from William Thurston's famous lecture notes on 3-manifolds [Thu78] in which he proves the theorem now known as the Koebe-Andreev- Thurston Theorem or Circle Packing Theorem. He proves it as a consequence of previous work of E. M. Figure 1 Andreev and establishes uniqueness from Mostov's rigid- ity theorem, an imporant result in Hyperbolic Geometry. A few years later Reiner Kuhnau pointed out a 1936 proof by german mathematician Paul Koebe. 1We dene the interior of a circle to be one of the connected components of its complement (see the colored regions in Figure1 as an example). i ii A circle packing is a nite set of circles in the plane, or equivalently in the Riemann sphere, with disjoint interiors and whose union is connected. -
[Cs.CG] 1 Nov 2019 Forbidden (See [11,24,36,38] for Surveys and Reports)
An Experimental Study of a 1-planarity Testing and Embedding Algorithm ? Carla Binucci, Walter Didimo, and Fabrizio Montecchiani Universit`adegli Studi di Perugia, Italy fcarla.binucci,walter.didimo,[email protected] Abstract. The definition of 1-planar graphs naturally extends graph planarity, namely a graph is 1-planar if it can be drawn in the plane with at most one crossing per edge. Unfortunately, while testing graph planarity is solvable in linear time, deciding whether a graph is 1-planar is NP-complete, even for restricted classes of graphs. Although several polynomial-time algorithms have been described for recognizing specific subfamilies of 1-planar graphs, no implementations of general algorithms are available to date. We investigate the feasibility of a 1-planarity test- ing and embedding algorithm based on a backtracking strategy. While the experiments show that our approach can be successfully applied to graphs with up to 30 vertices, they also suggest the need of more sophis- ticated techniques to attack larger graphs. Our contribution provides initial indications that may stimulate further research on the design of practical approaches for the 1-planarity testing problem. 1 Introduction The study of sparse nonplanar graphs is receiving increasing attention in the last years. One objective of this research stream is to extend the rich set of results about planar graphs to wider families of graphs that can better model real-world problems (see, e.g., [27,28,29,30,31]). Another objective is to create readable visualizations of nonplanar networks arising in various application scenarios (see, e.g., [23,39]). -
On Dynamical Gaskets Generated by Rational Maps, Kleinian Groups, and Schwarz Reflections
ON DYNAMICAL GASKETS GENERATED BY RATIONAL MAPS, KLEINIAN GROUPS, AND SCHWARZ REFLECTIONS RUSSELL LODGE, MIKHAIL LYUBICH, SERGEI MERENKOV, AND SABYASACHI MUKHERJEE Abstract. According to the Circle Packing Theorem, any triangulation of the Riemann sphere can be realized as a nerve of a circle packing. Reflections in the dual circles generate a Kleinian group H whose limit set is an Apollonian- like gasket ΛH . We design a surgery that relates H to a rational map g whose Julia set Jg is (non-quasiconformally) homeomorphic to ΛH . We show for a large class of triangulations, however, the groups of quasisymmetries of ΛH and Jg are isomorphic and coincide with the corresponding groups of self- homeomorphisms. Moreover, in the case of H, this group is equal to the group of M¨obiussymmetries of ΛH , which is the semi-direct product of H itself and the group of M¨obiussymmetries of the underlying circle packing. In the case of the tetrahedral triangulation (when ΛH is the classical Apollonian gasket), we give a piecewise affine model for the above actions which is quasiconformally equivalent to g and produces H by a David surgery. We also construct a mating between the group and the map coexisting in the same dynamical plane and show that it can be generated by Schwarz reflections in the deltoid and the inscribed circle. Contents 1. Introduction 2 2. Round Gaskets from Triangulations 4 3. Round Gasket Symmetries 6 4. Nielsen Maps Induced by Reflection Groups 12 5. Topological Surgery: From Nielsen Map to a Branched Covering 16 6. Gasket Julia Sets 18 arXiv:1912.13438v1 [math.DS] 31 Dec 2019 7. -
Graph Planarity
Graph Planarity Alina Shaikhet Outline ▪ Definition. ▪ Motivation. ▪ Euler’s formula. ▪ Kuratowski’s theorems. ▪ Wagner’s theorem. ▪ Planarity algorithms. ▪ Properties. ▪ Crossing Number Definitions ▪ A graph is called planar if it can be drawn in a plane without any two edges intersecting. ▪ Such a drawing we call a planar embedding of the graph. ▪ A plane graph is a particular planar embedding of a planar graph. Motivation ▪ Circuit boards. Motivation ▪ Circuit boards. ▪ Connecting utilities (electricity, water, gas) to houses. Motivation ▪ Circuit boards. ▪ Connecting utilities (electricity, water, gas) to houses. Motivation ▪ Circuit boards. ▪ Connecting utilities (electricity, water, gas) to houses. ▪ Highway / Railroads / Subway design. self loops multi-edges Euler’s formula. Consider any plane embedding of a planar connected graph. Let V - be the number of vertices, E - be the number of edges and F - be the number of faces (including the single unbounded face), Then 푉 − 퐸 + 퐹 = 2. Euler formula gives the necessary condition for a graph to be planar. self loops multi-edges Euler’s formula. Consider any plane embedding of a planar connected graph. Let V - be the number of vertices, E - be the number of edges and F - be the number of faces (including the single unbounded face), Then 푉 − 퐸 + 퐹 = 2. Then 푉 − 퐸 + 퐹 = 퐶 + 1. C - is the number of connected components. 푉 − 퐸 + 퐹 = 2 Euler’s formula. 푉 = 6 퐸 = 12 퐹 = 8 푉 − 퐸 + 퐹 = 2 6 − 12 + 8 = 2 푉 − 퐸 + 퐹 = 2 Corollary 1 Let G be any plane embedding of a connected planar graph with 푉 ≥ 3 vertices. Then 1. -
Study on the Problem of the Number Ring Transformation
The Research on Circle Family and Sphere Family The Original Topic: The Research and Generalizations on Several Kinds of Partition Problems in Combinatorics The Affiliated High School of South China Normal University Yan Chen Zhuang Ziquan Faculty Adviser:Li Xinghuai 153 The Research on Circle Family and Sphere Family 【Abstract】 A circle family is a group of separate or tangent circles in the plane. In this paper, we study how many parts at most a plane can be divided by several circle families if the circles in a same family must be separate (resp. if the circles can be tangent). We also study the necessary conditions for the intersection of two circle families. Then we primarily discuss the similar problems in higher dimensional space and in the end, raise some conjectures. 【Key words】 Circle Family; Structure Graph; Sphere Family; Generalized Inversion 【Changes】 1. Part 5 ‘Some Conjectures and Unsolved Problems’ has been rewritten. 2. Lemma 4.2 has been restated. 3. Some small mistakes have been corrected. 154 1 The Definitions and Preliminaries To begin with, we introduce some newly definitions and related preliminaries. Definition 1.1 Circle Family A circle family of the first kind is a group of separate circles;A circle family of the second kind is a group of separate or tangent circles. The capacity of a circle family is the number of circles in a circle family,the intersection of circle families means there are several circle families and any two circles in different circle families intersect. Definition 1.2 Compaction If the capacity of a circle family is no less than 3,and it intersects with another circle family with capacity 2,we call such a circle family compact. -
15 BASIC PROPERTIES of CONVEX POLYTOPES Martin Henk, J¨Urgenrichter-Gebert, and G¨Unterm
15 BASIC PROPERTIES OF CONVEX POLYTOPES Martin Henk, J¨urgenRichter-Gebert, and G¨unterM. Ziegler INTRODUCTION Convex polytopes are fundamental geometric objects that have been investigated since antiquity. The beauty of their theory is nowadays complemented by their im- portance for many other mathematical subjects, ranging from integration theory, algebraic topology, and algebraic geometry to linear and combinatorial optimiza- tion. In this chapter we try to give a short introduction, provide a sketch of \what polytopes look like" and \how they behave," with many explicit examples, and briefly state some main results (where further details are given in subsequent chap- ters of this Handbook). We concentrate on two main topics: • Combinatorial properties: faces (vertices, edges, . , facets) of polytopes and their relations, with special treatments of the classes of low-dimensional poly- topes and of polytopes \with few vertices;" • Geometric properties: volume and surface area, mixed volumes, and quer- massintegrals, including explicit formulas for the cases of the regular simplices, cubes, and cross-polytopes. We refer to Gr¨unbaum [Gr¨u67]for a comprehensive view of polytope theory, and to Ziegler [Zie95] respectively to Gruber [Gru07] and Schneider [Sch14] for detailed treatments of the combinatorial and of the convex geometric aspects of polytope theory. 15.1 COMBINATORIAL STRUCTURE GLOSSARY d V-polytope: The convex hull of a finite set X = fx1; : : : ; xng of points in R , n n X i X P = conv(X) := λix λ1; : : : ; λn ≥ 0; λi = 1 : i=1 i=1 H-polytope: The solution set of a finite system of linear inequalities, d T P = P (A; b) := x 2 R j ai x ≤ bi for 1 ≤ i ≤ m ; with the extra condition that the set of solutions is bounded, that is, such that m×d there is a constant N such that jjxjj ≤ N holds for all x 2 P . -
Lombardi Drawings of Graphs 1 Introduction
Lombardi Drawings of Graphs Christian A. Duncan1, David Eppstein2, Michael T. Goodrich2, Stephen G. Kobourov3, and Martin Nollenburg¨ 2 1Department of Computer Science, Louisiana Tech. Univ., Ruston, Louisiana, USA 2Department of Computer Science, University of California, Irvine, California, USA 3Department of Computer Science, University of Arizona, Tucson, Arizona, USA Abstract. We introduce the notion of Lombardi graph drawings, named after the American abstract artist Mark Lombardi. In these drawings, edges are represented as circular arcs rather than as line segments or polylines, and the vertices have perfect angular resolution: the edges are equally spaced around each vertex. We describe algorithms for finding Lombardi drawings of regular graphs, graphs of bounded degeneracy, and certain families of planar graphs. 1 Introduction The American artist Mark Lombardi [24] was famous for his drawings of social net- works representing conspiracy theories. Lombardi used curved arcs to represent edges, leading to a strong aesthetic quality and high readability. Inspired by this work, we intro- duce the notion of a Lombardi drawing of a graph, in which edges are drawn as circular arcs with perfect angular resolution: consecutive edges are evenly spaced around each vertex. While not all vertices have perfect angular resolution in Lombardi’s work, the even spacing of edges around vertices is clearly one of his aesthetic criteria; see Fig. 1. Traditional graph drawing methods rarely guarantee perfect angular resolution, but poor edge distribution can nevertheless lead to unreadable drawings. Additionally, while some tools provide options to draw edges as curves, most rely on straight-line edges, and it is known that maintaining good angular resolution can result in exponential draw- ing area for straight-line drawings of planar graphs [17,25]. -
Planar Separator Theorem a Geometric Approach
Planar Separator Theorem A Geometric Approach based on A Framework for ETH-Tight Algorithms and Lower Bounds in Geometric Intersection Graphs by Mark de Berg, Hans L. Bodlaender, S´andor Kisfaludi-Bak, D´anielMarx and Tom C. van der Zanden Unit Disk Graphs • represent vertices as unit disks, i.e., disks with diameter 1 • disks intersect iff corresponding vertices are adjacent a d a b d b f $ e f e g g h h c c Unit Disk Graphs • represent vertices as unit disks, i.e., disks with diameter 1 • disks intersect iff corresponding vertices are adjacent • some unit disk graphs are planar a d a b d b f $ e f e g g h h c c Unit Disk Graphs • represent vertices as unit disks, i.e., disks with diameter 1 • disks intersect iff corresponding vertices are adjacent • some unit disk graphs are planar • some planar graphs are not unit disk graphs c c d b a d a 6$ b e f e f Geometric Separators Geometric Separators Geometric Separators Geometric Separators H Observation: Disks intersecting the boundary of H separate disks strictly inside H from disks strictly outside H . Small Balanced Separators Let G = (V ; E) be a graph. H ⊆ V is • a separator if there is a partition H; V1; V2 of V so that no edge in E has onep endpoint in V1 and one endpoint in V2, • small if jHj 2 O( n), • balanced if jV1j; jV2j ≤ βn for some constant β Small Balanced Geometric Separators H p Claim: There exists an H intersecting O( n) disks with ≤ 36=37n disks strictly inside H and ≤ 36=37n disks strictly outside H , i.e., H is a small balanced separator. -
Fixed Points, Koebe Uniformization and Circle Packings
Annals of Mathematics, 137 (1993), 369-406 Fixed points, Koebe uniformization and circle packings By ZHENG-XU HE and ODED SCHRAMM* Contents Introduction 1. The space of boundary components 2. The fixed-point index 3. The Uniqueness Theorem 4. The Schwarz-Pick lemma 5. Extension to the boundary 6. Maximum modulus, normality and angles 7. Uniformization 8. Domains in Riemann surfaces 9. Uniformizations of circle packings Addendum Introduction A domain in the Riemann sphere C is called a circle domain if every connected component of its boundary is either a circle or a point. In 1908, P. Koebe [Kol] posed the following conjecture, known as Koebe's Kreisnormierungsproblem: A ny plane domain is conformally homeomorphic to a circle domain in C. When the domain is simply connected, this is the con tent of the Riemann mapping theorem. The conjecture was proved for finitely connected domains and certain symmetric domains by Koebe himself ([K02], [K03]); for domains with various conditions on the "limit boundary compo nents" by R. Denneberg [De], H. Grotzsch [Gr], L. Sario [Sa], H. Meschowski *The authors were supported by N.S.F. Grants DMS-9006954 and DMS-9112150, respectively. The authors express their thanks to Mike Freedman, Dennis Hejhal, Al Marden, Curt McMullen, Burt Rodin, Steffen Rohde and Bill Thurston for conversations relating to this work. Also thanks are due to the referee, and to Steffen Rohde, for their careful reading and subsequent corrections. The paper of Sibner [Si3l served as a very useful introduction to the subject. I. Benjamini, O. Häggström (eds.), Selected Works of Oded Schramm, Selected Works in Probability and Statistics, DOI 10.1007/978-1-4419-9675-6_6, C Springer Science+Business Media, LLC 2011 105 370 z.-x. -
Planarity Testing Revisited
Electronic Colloquium on Computational Complexity, Report No. 9 (2011) Planarity Testing Revisited Samir Datta, Gautam Prakriya Chennai Mathematical Institute India fsdatta,[email protected] Abstract. Planarity Testing is the problem of determining whether a given graph is planar while planar embedding is the corresponding construction problem. The bounded space complexity of these problems has been determined to be exactly Logspace by Allender and Mahajan [AM00] with the aid of Reingold's result [Rei08]. Unfortunately, the algorithm is quite daunting and generalizing it to say, the bounded genus case seems a tall order. In this work, we present a simple planar embedding algorithm running in logspace. We hope this algorithm will be more amenable to generalization. The algorithm is based on the fact that 3-connected planar graphs have a unique embedding, a variant of Tutte's criterion on conflict graphs of cycles and an explicit change of cycle basis. We also present a logspace algorithm to find obstacles to planarity, viz. a Kuratowski minor, if the graph is non-planar. To the best of our knowledge this is the first logspace algorithm for this problem. 1 Introduction Planarity Testing, the problem of determining whether a given graph is planar (i.e. the vertices and edges can be drawn on a plane with no edge intersections except at their end- points) is a fundamental problem in algorithmic graph theory. Along with the problem of actually obtaining a planar embedding, it is a prerequisite for many an algorithm designed to work specifically for planar graphs. Our focus is on the bounded space complexity of the planarity embedding problem be- cause we know that many graph theoretic problems like reachability [BTV09], perfect match- ing [DKR10,DKT10], and even isomorphism [DLN08,DLN+09] have efficient bounded space algorithms when provided graphs embedded on the plane. -
Peter Hoek Thesis
Visual Encoding Approaches for Temporal Social Networks Peter John Hoek BIT (Distinction) CQU, MSc (IT) UNSW A thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Information Technology at the School of Engineering and Information Technology The University of New South Wales at the Australian Defence Force Academy 2013 Abstract Visualisations have become an inseparable part of social network analysis methodologies. However, despite the large amount of work in the field of social network visualisation there are still a number of areas in which current visualisation methods can be improved. The current dynamic network visualisation approaches consisting of aggregation or animated movies suffer from various limitations, such as introducing artefacts that could obscure interesting micro-level patterns or disrupting the users’ internalised mental models. In addition, very few social network tools support the inclusion of semantic and contextual information or provide visual topological representations based on network node attributes. This thesis introduces novel approaches to the visualisation of social networks and assesses their effectiveness through the use of concept demonstrators and prototypes. These are the software artefacts of this thesis, which provide illustrations of complementary visualisation techniques that could be considered for inclusion into social network visualisation and analysis tools. The novel methods for visualising temporal networks introduced in this thesis consist of: i an Attribute-Based -
Local Page Numbers
Local Page Numbers Bachelor Thesis of Laura Merker At the Department of Informatics Institute of Theoretical Informatics Reviewers: Prof. Dr. Dorothea Wagner Prof. Dr. Peter Sanders Advisor: Dr. Torsten Ueckerdt Time Period: May 22, 2018 – September 21, 2018 KIT – University of the State of Baden-Wuerttemberg and National Laboratory of the Helmholtz Association www.kit.edu Statement of Authorship I hereby declare that this document has been composed by myself and describes my own work, unless otherwise acknowledged in the text. I declare that I have observed the Satzung des KIT zur Sicherung guter wissenschaftlicher Praxis, as amended. Ich versichere wahrheitsgemäß, die Arbeit selbstständig verfasst, alle benutzten Hilfsmittel vollständig und genau angegeben und alles kenntlich gemacht zu haben, was aus Arbeiten anderer unverändert oder mit Abänderungen entnommen wurde, sowie die Satzung des KIT zur Sicherung guter wissenschaftlicher Praxis in der jeweils gültigen Fassung beachtet zu haben. Karlsruhe, September 21, 2018 iii Abstract A k-local book embedding consists of a linear ordering of the vertices of a graph and a partition of its edges into sets of edges, called pages, such that any two edges on the same page do not cross and every vertex has incident edges on at most k pages. Here, two edges cross if their endpoints alternate in the linear ordering. The local page number pl(G) of a graph G is the minimum k such that there exists a k-local book embedding for G. Given a graph G and a vertex ordering, we prove that it is NP-complete to decide whether there exists a k-local book embedding for G with respect to the given vertex ordering for any fixed k ≥ 3.