NP-Completeness of List Coloring and Precoloring Extension on the Edges of Planar Graphs
Total Page:16
File Type:pdf, Size:1020Kb
Load more
Recommended publications
-
A Brief History of Edge-Colorings — with Personal Reminiscences
Discrete Mathematics Letters Discrete Math. Lett. 6 (2021) 38–46 www.dmlett.com DOI: 10.47443/dml.2021.s105 Review Article A brief history of edge-colorings – with personal reminiscences∗ Bjarne Toft1;y, Robin Wilson2;3 1Department of Mathematics and Computer Science, University of Southern Denmark, Odense, Denmark 2Department of Mathematics and Statistics, Open University, Walton Hall, Milton Keynes, UK 3Department of Mathematics, London School of Economics and Political Science, London, UK (Received: 9 June 2020. Accepted: 27 June 2020. Published online: 11 March 2021.) c 2021 the authors. This is an open access article under the CC BY (International 4.0) license (www.creativecommons.org/licenses/by/4.0/). Abstract In this article we survey some important milestones in the history of edge-colorings of graphs, from the earliest contributions of Peter Guthrie Tait and Denes´ Konig¨ to very recent work. Keywords: edge-coloring; graph theory history; Frank Harary. 2020 Mathematics Subject Classification: 01A60, 05-03, 05C15. 1. Introduction We begin with some basic remarks. If G is a graph, then its chromatic index or edge-chromatic number χ0(G) is the smallest number of colors needed to color its edges so that adjacent edges (those with a vertex in common) are colored differently; for 0 0 0 example, if G is an even cycle then χ (G) = 2, and if G is an odd cycle then χ (G) = 3. For complete graphs, χ (Kn) = n−1 if 0 0 n is even and χ (Kn) = n if n is odd, and for complete bipartite graphs, χ (Kr;s) = max(r; s). -
When the Vertex Coloring of a Graph Is an Edge Coloring of Its Line Graph — a Rare Coincidence
View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Repository of the Academy's Library When the vertex coloring of a graph is an edge coloring of its line graph | a rare coincidence Csilla Bujt¶as 1;¤ E. Sampathkumar 2 Zsolt Tuza 1;3 Charles Dominic 2 L. Pushpalatha 4 1 Department of Computer Science and Systems Technology, University of Pannonia, Veszpr¶em,Hungary 2 Department of Mathematics, University of Mysore, Mysore, India 3 Alfr¶edR¶enyi Institute of Mathematics, Hungarian Academy of Sciences, Budapest, Hungary 4 Department of Mathematics, Yuvaraja's College, Mysore, India Abstract The 3-consecutive vertex coloring number Ã3c(G) of a graph G is the maximum number of colors permitted in a coloring of the vertices of G such that the middle vertex of any path P3 ½ G has the same color as one of the ends of that P3. This coloring constraint exactly means that no P3 subgraph of G is properly colored in the classical sense. 0 The 3-consecutive edge coloring number Ã3c(G) is the maximum number of colors permitted in a coloring of the edges of G such that the middle edge of any sequence of three edges (in a path P4 or cycle C3) has the same color as one of the other two edges. For graphs G of minimum degree at least 2, denoting by L(G) the line graph of G, we prove that there is a bijection between the 3-consecutive vertex colorings of G and the 3-consecutive edge col- orings of L(G), which keeps the number of colors unchanged, too. -
K-Outerplanar Graphs, Planar Duality, and Low Stretch Spanning Trees
k-Outerplanar Graphs, Planar Duality, and Low Stretch Spanning Trees Yuval Emek∗ Abstract Low distortion probabilistic embedding of graphs into approximating trees is an extensively studied topic. Of particular interest is the case where the approximating trees are required to be (subgraph) spanning trees of the given graph (or multigraph), in which case, the focus is usually on the equivalent problem of finding a (single) tree with low average stretch. Among the classes of graphs that received special attention in this context are k-outerplanar graphs (for a fixed k): Chekuri, Gupta, Newman, Rabinovich, and Sinclair show that every k-outerplanar graph can be probabilistically embedded into approximating trees with constant distortion regardless of the size of the graph. The approximating trees in the technique of Chekuri et al. are not necessarily spanning trees, though. In this paper it is shown that every k-outerplanar multigraph admits a spanning tree with constant average stretch. This immediately translates to a constant bound on the distortion of probabilistically embedding k-outerplanar graphs into their spanning trees. Moreover, an efficient randomized algorithm is presented for constructing such a low average stretch spanning tree. This algorithm relies on some new insights regarding the connection between low average stretch spanning trees and planar duality. Keywords: planar graphs, outerplanarity, average stretch, planar dual. ∗Microsoft Israel R&D Center, Herzelia, Israel and School of Electrical Engineering, Tel Aviv University, Tel Aviv, Israel. E-mail: [email protected]. Supported in part by the Israel Science Foundation, grants 221/07 and 664/05. 1 Introduction The problem. -
Interval Edge-Colorings of Graphs
University of Central Florida STARS Electronic Theses and Dissertations, 2004-2019 2016 Interval Edge-Colorings of Graphs Austin Foster University of Central Florida Part of the Mathematics Commons Find similar works at: https://stars.library.ucf.edu/etd University of Central Florida Libraries http://library.ucf.edu This Masters Thesis (Open Access) is brought to you for free and open access by STARS. It has been accepted for inclusion in Electronic Theses and Dissertations, 2004-2019 by an authorized administrator of STARS. For more information, please contact [email protected]. STARS Citation Foster, Austin, "Interval Edge-Colorings of Graphs" (2016). Electronic Theses and Dissertations, 2004-2019. 5133. https://stars.library.ucf.edu/etd/5133 INTERVAL EDGE-COLORINGS OF GRAPHS by AUSTIN JAMES FOSTER B.S. University of Central Florida, 2015 A thesis submitted in partial fulfilment of the requirements for the degree of Master of Science in the Department of Mathematics in the College of Sciences at the University of Central Florida Orlando, Florida Summer Term 2016 Major Professor: Zixia Song ABSTRACT A proper edge-coloring of a graph G by positive integers is called an interval edge-coloring if the colors assigned to the edges incident to any vertex in G are consecutive (i.e., those colors form an interval of integers). The notion of interval edge-colorings was first introduced by Asratian and Kamalian in 1987, motivated by the problem of finding compact school timetables. In 1992, Hansen described another scenario using interval edge-colorings to schedule parent-teacher con- ferences so that every person’s conferences occur in consecutive slots. -
Vizing's Theorem and Edge-Chromatic Graph
VIZING'S THEOREM AND EDGE-CHROMATIC GRAPH THEORY ROBERT GREEN Abstract. This paper is an expository piece on edge-chromatic graph theory. The central theorem in this subject is that of Vizing. We shall then explore the properties of graphs where Vizing's upper bound on the chromatic index is tight, and graphs where the lower bound is tight. Finally, we will look at a few generalizations of Vizing's Theorem, as well as some related conjectures. Contents 1. Introduction & Some Basic Definitions 1 2. Vizing's Theorem 2 3. General Properties of Class One and Class Two Graphs 3 4. The Petersen Graph and Other Snarks 4 5. Generalizations and Conjectures Regarding Vizing's Theorem 6 Acknowledgments 8 References 8 1. Introduction & Some Basic Definitions Definition 1.1. An edge colouring of a graph G = (V; E) is a map C : E ! S, where S is a set of colours, such that for all e; f 2 E, if e and f share a vertex, then C(e) 6= C(f). Definition 1.2. The chromatic index of a graph χ0(G) is the minimum number of colours needed for a proper colouring of G. Definition 1.3. The degree of a vertex v, denoted by d(v), is the number of edges of G which have v as a vertex. The maximum degree of a graph is denoted by ∆(G) and the minimum degree of a graph is denoted by δ(G). Vizing's Theorem is the central theorem of edge-chromatic graph theory, since it provides an upper and lower bound for the chromatic index χ0(G) of any graph G. -
Characterizations of Restricted Pairs of Planar Graphs Allowing Simultaneous Embedding with Fixed Edges
Characterizations of Restricted Pairs of Planar Graphs Allowing Simultaneous Embedding with Fixed Edges J. Joseph Fowler1, Michael J¨unger2, Stephen Kobourov1, and Michael Schulz2 1 University of Arizona, USA {jfowler,kobourov}@cs.arizona.edu ⋆ 2 University of Cologne, Germany {mjuenger,schulz}@informatik.uni-koeln.de ⋆⋆ Abstract. A set of planar graphs share a simultaneous embedding if they can be drawn on the same vertex set V in the Euclidean plane without crossings between edges of the same graph. Fixed edges are common edges between graphs that share the same simple curve in the simultaneous drawing. Determining in polynomial time which pairs of graphs share a simultaneous embedding with fixed edges (SEFE) has been open. We give a necessary and sufficient condition for when a pair of graphs whose union is homeomorphic to K5 or K3,3 can have an SEFE. This allows us to determine which (outer)planar graphs always an SEFE with any other (outer)planar graphs. In both cases, we provide efficient al- gorithms to compute the simultaneous drawings. Finally, we provide an linear-time decision algorithm for deciding whether a pair of biconnected outerplanar graphs has an SEFE. 1 Introduction In many practical applications including the visualization of large graphs and very-large-scale integration (VLSI) of circuits on the same chip, edge crossings are undesirable. A single vertex set can be used with multiple edge sets that each correspond to different edge colors or circuit layers. While the pairwise union of all edge sets may be nonplanar, a planar drawing of each layer may be possible, as crossings between edges of distinct edge sets are permitted. -
Minor-Closed Graph Classes with Bounded Layered Pathwidth
Minor-Closed Graph Classes with Bounded Layered Pathwidth Vida Dujmovi´c z David Eppstein y Gwena¨elJoret x Pat Morin ∗ David R. Wood { 19th October 2018; revised 4th June 2020 Abstract We prove that a minor-closed class of graphs has bounded layered pathwidth if and only if some apex-forest is not in the class. This generalises a theorem of Robertson and Seymour, which says that a minor-closed class of graphs has bounded pathwidth if and only if some forest is not in the class. 1 Introduction Pathwidth and treewidth are graph parameters that respectively measure how similar a given graph is to a path or a tree. These parameters are of fundamental importance in structural graph theory, especially in Roberston and Seymour's graph minors series. They also have numerous applications in algorithmic graph theory. Indeed, many NP-complete problems are solvable in polynomial time on graphs of bounded treewidth [23]. Recently, Dujmovi´c,Morin, and Wood [19] introduced the notion of layered treewidth. Loosely speaking, a graph has bounded layered treewidth if it has a tree decomposition and a layering such that each bag of the tree decomposition contains a bounded number of vertices in each layer (defined formally below). This definition is interesting since several natural graph classes, such as planar graphs, that have unbounded treewidth have bounded layered treewidth. Bannister, Devanny, Dujmovi´c,Eppstein, and Wood [1] introduced layered pathwidth, which is analogous to layered treewidth where the tree decomposition is arXiv:1810.08314v2 [math.CO] 4 Jun 2020 required to be a path decomposition. -
Acyclic Edge-Coloring of Planar Graphs
Acyclic edge-coloring of planar graphs: ∆ colors suffice when ∆ is large Daniel W. Cranston∗ January 31, 2019 Abstract An acyclic edge-coloring of a graph G is a proper edge-coloring of G such that the subgraph ′ induced by any two color classes is acyclic. The acyclic chromatic index, χa(G), is the smallest ′ number of colors allowing an acyclic edge-coloring of G. Clearly χa(G) ∆(G) for every graph G. Cohen, Havet, and M¨uller conjectured that there exists a constant M≥such that every planar ′ graph with ∆(G) M has χa(G) = ∆(G). We prove this conjecture. ≥ 1 Introduction proper A proper edge-coloring of a graph G assigns colors to the edges of G such that two edges receive edge- distinct colors whenever they have an endpoint in common. An acyclic edge-coloring is a proper coloring acyclic edge-coloring such that the subgraph induced by any two color classes is acyclic (equivalently, the edge- ′ edges of each cycle receive at least three distinct colors). The acyclic chromatic index, χa(G), is coloring the smallest number of colors allowing an acyclic edge-coloring of G. In an edge-coloring ϕ, if a acyclic chro- color α is used incident to a vertex v, then α is seen by v. For the maximum degree of G, we write matic ∆(G), and simply ∆ when the context is clear. Note that χ′ (G) ∆(G) for every graph G. When index a ≥ we write graph, we forbid loops and multiple edges. A planar graph is one that can be drawn in seen by planar the plane with no edges crossing. -
31 Aug 2020 Injective Edge-Coloring of Sparse Graphs
Injective edge-coloring of sparse graphs Baya Ferdjallah1,4, Samia Kerdjoudj 1,5, and André Raspaud2 1LIFORCE, Faculty of Mathematics, USTHB, BP 32 El-Alia, Bab-Ezzouar 16111, Algiers, Algeria 2LaBRI, Université de Bordeaux, 351 cours de la Libération, 33405 Talence Cedex, France 4Université de Boumerdès, Avenue de l’indépendance, 35000, Boumerdès, Algeria 5Université de Blida 1, Route de Soumâa BP 270, Blida, Algeria September 1, 2020 Abstract An injective edge-coloring c of a graph G is an edge-coloring such that if e1, e2, and e3 are three consecutive edges in G (they are consecutive if they form a path or a cycle of length three), then e1 and e3 receive different colors. The minimum integer k such that, G has an injective edge-coloring with k ′ colors, is called the injective chromatic index of G (χinj(G)). This parameter was introduced by Cardoso et al. [12] motivated by the Packet Radio Network ′ problem. They proved that computing χinj(G) of a graph G is NP-hard. We give new upper bounds for this parameter and we present the rela- tionships of the injective edge-coloring with other colorings of graphs. The obtained general bound gives 8 for the injective chromatic index of a subcubic graph. If the graph is subcubic bipartite we improve this last bound. We prove that a subcubic bipartite graph has an injective chromatic index bounded by arXiv:1907.09838v2 [math.CO] 31 Aug 2020 6. We also prove that if G is a subcubic graph with maximum average degree 7 8 less than 3 (resp. -
Star Coloring Outerplanar Bipartite Graphs
Discussiones Mathematicae Graph Theory 39 (2019) 899–908 doi:10.7151/dmgt.2109 STAR COLORING OUTERPLANAR BIPARTITE GRAPHS Radhika Ramamurthi and Gina Sanders Department of Mathematics California State University San Marcos San Marcos, CA 92096-0001 USA e-mail: [email protected] Abstract A proper coloring of the vertices of a graph is called a star coloring if at least three colors are used on every 4-vertex path. We show that all outerplanar bipartite graphs can be star colored using only five colors and construct the smallest known example that requires five colors. Keywords: chromatic number, star coloring, outerplanar bipartite graph. 2010 Mathematics Subject Classification: 05C15. 1. Introduction A proper r-coloring of a graph G is an assignment of labels from {1, 2,...,r} to the vertices of G so that adjacent vertices receive distinct colors. The minimum r so that G has a proper r-coloring is called the chromatic number of G, denoted by χ(G). The chromatic number is one of the most studied parameters in graph theory, and by convention, the term coloring of a graph is usually used instead of proper coloring. In 1973, Gr¨unbaum [5] considered proper colorings with the additional constraint that the subgraph induced by every pair of color classes is acyclic, i.e., contains no cycles. He called such colorings acyclic colorings, and the minimum r such that G has an acyclic r-coloring is called the acyclic chromatic number of G, denoted by a(G). In introducing the notion of an acyclic coloring, Gr¨unbaum noted that the condition that the union of any two color classes induces a forest can be generalized to other bipartite graphs. -
Surviving Rates of Trees and Outerplanar Graphs for the Firefighter Problem
Surviving rates of trees and outerplanar graphs for the ¯re¯ghter problem Leizhen Cai¤ Yongxi Chengy Elad Verbinz Yuan Zhouz Abstract The ¯re¯ghter problem is a discrete-time game on graphs introduced by Hartnell in an attempt to model the spread of ¯re, diseases, computer viruses and suchlike in a macro-control level. To measure the defence ability of a graph as a whole, Cai and Wang de¯ned the surviving rate of a graph G for the ¯re¯ghter problem to be the average percentage of vertices that can be saved when a ¯re starts randomly at one vertex of G. In this paper, we prove that the surviving rate of every n-vertex outerplanar graph log n is at least 1 ¡ £( n ), which is asymptotically tight. We also show that the greedy log n strategy of Hartnell and Li for trees saves at least 1 ¡ £( n ) percentage of vertices on average for an n-vertex tree. Key words: ¯re¯ghter problem, surviving rate, tree, outerplanar graph 1 Introduction The study of a discrete-time game, the ¯re¯ghter problem, was initiated by Hartnell [7] in 1995 in an attempt to model the spread of ¯re, diseases, computer viruses and suchlike in a macro-control level. At time 0, a ¯re breaks out at a vertex v of a graph G = (V; E). At each subsequent time, a ¯re¯ghter protects one vertex not yet on ¯re, and the ¯re then spreads from all burning vertices to all their unprotected neighbors. The process ends when the ¯re can no longer spread. -
Fractional and Circular Separation Dimension of Graphs
Fractional and Circular Separation Dimension of Graphs Sarah J. Loeb∗and Douglas B. West† Revised June 2017 Abstract The separation dimension of a graph G, written π(G), is the minimum number of linear orderings of V (G) such that every two nonincident edges are “separated” in some ordering, meaning that both endpoints of one edge appear before both endpoints of the other. We introduce the fractional separation dimension πf (G), which is the minimum of a/b such that some a linear orderings (repetition allowed) separate every two nonincident edges at least b times. In contrast to separation dimension, fractional separation dimension is bounded: always πf (G) 3, with equality if and only if G contains K4. There is no stronger ≤ 3m bound even for bipartite graphs, since πf (Km,m) = πf (Km+1,m) = m+1 . We also compute πf (G) for cycles and some complete tripartite graphs. We show that πf (G) < √2 when G is a tree and present a sequence of trees on which the value tends to 4/3. Finally, we consider analogous problems for circular orderings, where pairs of non- incident edges are separated unless their endpoints alternate. Let π◦(G) be the number of circular orderings needed to separate all pairs and πf◦(G) be the fractional version. Among our results: (1) π◦(G) = 1 if and only G is outerplanar. (2) π◦(G) 2 when 3 ≤ G is bipartite. (3) π◦(Kn) log2 log3(n 1). (4) πf◦(G) 2 for every graph G, with ≥ − 3m 3 ≤ equality if and only if K4 G.