CanaDAM 2015 University of Saskatchewan, June 1 - 4, 2015 www.cms.math.ca//2015
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# Schedule - Contributed Minisymposia

Please note that schedules are subject to change without notice, particularly changes within a given session.

 Algorithmic construction of combinatorial objects (CM6) Organizer and Chair: Jan Goedgebeur (Ghent University) Computers are often used in combinatorics to determine if combinatorial objects with given structural or extremal properties exist as these existence problems are often too complex to solve by hand. This is done by designing and implementing generation algorithms which construct combinatorial objects from a given class (typically avoiding the generation of isomorphic copies). In this minisymposium we will give an overview of specialized generation algorithms which have been applied to solve various combinatorial problems. Tuesday June 2 10:20 - 10:45 Aaron Williams (Bard College at Simon's Rock), Recent Results on Necklaces, Lyndon Words, and Universal Cycles, ARTS 106 10:50 - 11:15 Veronika Irvine (University of Victoria), A Mathematical Model for Lace: Its use in enumerating and generating lace patterns, ARTS 106 11:20 - 11:45 Jan Goedgebeur (Ghent University), Minimal obstructions to graph coloring, ARTS 106 11:50 - 12:15 Geoffrey Exoo (Indiana State University), Finding Combinatorial Structures with Simple Heuristics, ARTS 106 12:20 - 12:45 Stanislaw Radziszowski (Rochester Institute of Technology), Some computational and theoretical problems for Ramsey numbers, ARTS 106 Automated analysis of combinatorial structures (CM1) Organizer and Chair: Stephen Melczer (University of Waterloo and ENS Lyon) Over the last several decades, techniques coming from pure mathematics, computer science, combinatorics, and probability theory have been combined in novel ways to permit automatic yet rigorous analysis of combinatorial structures and their underlying properties. This minisymposium will give a broad view of these approaches, including talks on the theoretical tools developed for this purpose — such as Analytic Combinatorics in Several Variables — along with recent applications to the study of lattice walks and polymer models. By combining both theory and practice, the session aims to strengthen old collaborations and foster new ones. Monday June 1 10:20 - 10:45 Marni Mishna (Simon Fraser University), A Baxter class of a different kind, and other walks on Young's Lattice, ARTS 211 10:50 - 11:15 Mark Wilson (University of Auckland), Analytic Combinatorics in Several Variables, ARTS 211 11:20 - 11:45 Torin Greenwood (University of Pennsylvania), Asymptotics of the Coefficients of Bivariate Analytic Functions with Algebraic Singularities, ARTS 211 11:50 - 12:15 Thomas Wong (University of British Columbia), Two Friendly Walks in a Sticky Slab, ARTS 211 12:20 - 12:45 Hui Huang (RISC - Linz), An Improved Abramov-Petkovsek Reduction and Creative Telescoping for Hypergeometric Terms, ARTS 211 Colourings, colour graphs, and homomorphisms (CM2) Organizer and Chair: Gary MacGillivray (University of Victoria) This collection of talks begins by discussing when it is possible to generate all $k$-colourings of a complete multipartite graph in minimal change order, that is, when the graph of vertex colourings has a Hamilton cycle. The next topic to be discussed is the structure of graphs which are the graph of the vertex colourings of some other graph. We then move on to connectivity questions for the graph of circular colourings. The final two talks in the minisymposium address colourings of mixed graphs, that is, graphs with several edge sets and several arc sets, and homomorphisms of oriented graphs. Wednesday June 3 15:30 - 15:55 Stefan Bard (University of Victoria), Hamiltonicity of SDR graphs and colouring graphs, ARTS 211 16:00 - 16:25 Richard Brewster (Thompson Rivers University), The complexity of graph recoloring and reconfigurations, ARTS 211 16:30 - 16:55 Christopher Duffy (University of Victoria), Dropping Proper" in Vertex Colourings of Mixed Graphs., ARTS 211 17:00 - 17:25 Gary MacGillivray (University of Victoria), Locally-injective homomorphisms to tournaments, ARTS 211 Combinatorics, topology and statistical mechanics of polymer models I (CM7) Organizer and Chair: Nicholas Beaton (University of Saskatchewan) and Andrew Rechnitzer (University of British Columbia) This series of minisymposia will bring together researchers from a variety of fields, including combinatorics, topological knot theory and statistical mechanics, to discuss models of polymers such as DNA. This range of different perspectives and techniques has led a number of recent developments, and we hope that these sessions will foster further collaborations. Tuesday June 2 10:20 - 10:45 Aleks Owczarek (University of Melbourne), Three Interacting Friendly Directed walks; A Simple Model of Polymer Gelation, ARTS 211 10:50 - 11:15 Eric Rawdon (University of St. Thomas), What knots lurk inside other knots?, ARTS 211 11:20 - 11:45 EJ Janse van Rensburg (York University), Forces and Pressures in Models of Partially Directed Paths, ARTS 211 11:50 - 12:15 Javier Arsuaga (University of California, Davis), Topological analysis of chromosome conformation capture data., ARTS 211 12:20 - 12:45 Gerasim Iliev (University of Toronto), Order parameters for copolymers interacting with inhomogeneous surfaces, ARTS 211 Combinatorics, topology and statistical mechanics of polymer models II (CM8) Organizer and Chair: Nicholas Beaton (University of Saskatchewan) and Andrew Rechnitzer (University of British Columbia) This series of minisymposia will bring together researchers from a variety of fields, including combinatorics, topological knot theory and statistical mechanics, to discuss models of polymers such as DNA. This range of different perspectives and techniques has led a number of recent developments, and we hope that these sessions will foster further collaborations. Tuesday June 2 15:30 - 15:55 Nathan Clisby (University of Melbourne), Monte Carlo calculation of a new universal amplitude ratio for self-avoiding walks, ARTS 133 16:00 - 16:25 Koya Shimokawa (Saitama University), Unknotting operation and growth constant of knots in tube region, ARTS 133 16:30 - 16:55 Neal Madras (York University), Quenched Topology of Branched Polymers, ARTS 133 17:00 - 17:25 Mahshid Atapour (University of Saskatchewan), Entanglement of Dense Polymer Systems, ARTS 133 17:30 - 17:55 Steve Melczer (University of Waterloo), Enumerating Lattice Paths Through Multivariate Diagonals, ARTS 133 Combinatorics, topology and statistical mechanics of polymer models III (CM10) Organizer and Chair: Nicholas Beaton (University of Saskatchewan) and Andrew Rechnitzer (University of British Columbia) This series of minisymposia will bring together researchers from a variety of fields, including combinatorics, topological knot theory and statistical mechanics, to discuss models of polymers such as DNA. This range of different perspectives and techniques has led a number of recent developments, and we hope that these sessions will foster further collaborations. Wednesday June 3 10:20 - 10:45 Richard Brak (University of Melbourne), Coxeter Groups and Exactly Solvable Polymer Models, ARTS 133 10:50 - 11:15 Jason Cantarella (University of Georgia), Random Embedded Planar 4-Regular Graphs and Random Knot Diagrams, ARTS 133 11:20 - 11:45 Tetsuo Deguchi (Ochanomizu University), Topological polymers through the quaternionic algorithm, ARTS 133 11:50 - 12:15 Greg Buck (Saint Anselm College), What you can see from here: local recognition, ARTS 133 12:20 - 12:45 Nicholas Beaton (University of Saskatchewan), Solvable self-avoiding walk and polygon models with large growth rates, ARTS 133 Cycles in graphs I (CM11) Organizer and Chair: David Gunderson (University of Manitoba) and Ortrud Oellermann (University of Winnipeg) Dedicated to the memory of Ralph Faudree. Bondy’s meta conjecture states that almost any condition that guarantees that a graph is Hamiltonian guarantees much more about its cycle structure. In this context, a conjecture of Hendry states that hamiltonian chordal graphs are cycle extendable, i.e., for every non-spanning cycle $C$ there is a cycle $C’$ that contains the vertices of $C$ and one additional vertex. It's shown that this conjecture is false and interesting related results and new directions will be discussed. Ryjáček conjectured that locally connected graphs are weakly pancyclic, i.e., have a cycle of every length between their girth and circumference. Results supporting this conjecture for graphs with certain local conditions are presented and several open problems discussed. For graphs whose cycle spectrum is not continuous, structural properties are obtained; specifically if a given odd cycle length is forbidden and the graph has a maximum number of cycles. Wednesday June 3 15:30 - 15:55 Ben Seamone (Dawson College), Hendry's Conjecture: counterexamples and new open problems, ARTS 102 16:00 - 16:25 David Brown (Utah State University), Chordal Graphs aren’t Cycle Extendable … So What?, ARTS 102 16:30 - 16:55 Ortrud Oellermann (University of Winnipeg), Cycle Structure in Graphs with Certain Local Properties, ARTS 102 17:00 - 17:25 Sergei Tsaturian (University of Manitoba), Triangle-free graphs with the maximum number of cycles, ARTS 102 17:30 - 17:55 David Gunderson (University of Manitoba), Forbidding an odd cycle, extremal numbers and extremal graphs, ARTS 102 Cycles in graphs II (CM13) Organizer and Chair: David Gunderson (University of Manitoba) and Ortrud Oellermann (University of Winnipeg) Dedicated to the memory of Ralph Faudree. This session is devoted to properties of graphs with a large number of cycles. In particular a conjecture of Lovász and Plummer, which states that every 4-connected plane triangulation has a spanning Halin substructure, is shown to be false and properties of plane triangulations that have such substructures are discussed. Matching extension behaviour for families of graphs that are more general than plane triangulations are discussed and results for plane triangulations are compared with results for these more general structures. Graphs and hypergraphs defined using algebraic structures frequently have cyclic decompositions induced by the algebraic structure. Groups and graphs for which the colour-preserving or colour-permuting graph automorphisms all come from the group structure are discussed. Algebraic methods for constructing hypergraph decompositions related to the Payley graph constructions are presented. Thursday June 4 10:20 - 10:45 Michael Plummer (Vanderbilt University), Distance matching in punctured planar triangulations, ARTS 133 10:50 - 11:15 Joy Morris (Lethbridge University), Colour-preserving and colour-permuting automorphisms, ARTS 133 11:20 - 11:45 Shonda Gosselin (University of Winnipeg), Cyclic hypergraph decompositions, ARTS 133 11:50 - 12:15 Arthur S. Finbow (Saint Marys University), Well-Covered Pentagonalizations of the Plane, ARTS 133 Extremal combinatorics (CM12) Organizer and Chair: Deryk Osthus (University of Birmingham) Extremal Combinatorics is a vibrant area of Discrete Mathematics. Classical questions in Extremal Combinatorics often can be phrased in the following way: how does some (global) parameter force some (local) structure? An increasingly important trend in the area has been the use of probabilistic techniques and viewpoints. This approach has recently led to a number of major advances. The talks in this minisymposium will reflect this trend. Tuesday June 2 10:20 - 10:45 Roman Glebov (ETH Zurich), Comparable pairs in families of sets, ARTS 133 10:50 - 11:15 Diana Piguet (Czech Academy of Sciences), The Loebl-Komlós-Sós Conjecture, ARTS 133 11:20 - 11:45 Deryk Osthus (University of Birmingham), On the typical structure of triangle-free oriented graphs and digraphs, ARTS 133 11:50 - 12:15 Guillem Perarnau (McGill), Decomposition of bounded degree graphs into $C_4$-free subgraphs, ARTS 133 12:20 - 12:45 Yury Person (University of Frankfurt), Minimum degrees of minimal Ramsey graphs and hypergraphs, ARTS 133 Geometric representations of graphs (CM15) Organizer and Chair: Steven Chaplick (TU Berlin) Visualizations and representations of graphs by means of intersections or contacts of geometric objects have been widely investigated. Classical examples are interval graphs and Koebe circle representations. When representations are given they can sometimes be exploited in optimization problems or to obtain deep structural results. For example, in many instances optimization problems are hard for general graphs but become polynomial-time solvable when restricted to intersection or contact graphs with a given representations. Another class of problems is to compute the representation or to decide whether it exists. In this minisymposium we highlight some recent developments in this active area at the intersection of graph theory and discrete geometry. Thursday June 4 10:20 - 10:45 Steven Chaplick (TU Berlin), Representing Planar Graphs By Homothets of Convex Sets, ARTS 211 10:50 - 11:15 George Mertzios (Durham University), New Geometric Representations and Domination Problems on Tolerance and Multitolerance Graphs, ARTS 211 11:20 - 11:45 Grzegorz Gutowski (Jagiellonian University), Extending Partial Bar Visibility Representations is Hard, ARTS 211 11:50 - 12:15 Jan Hubicka (University of Calgary), Ramsey lifts of classes of intersection graphs, ARTS 211 Graph packings and colorings (CM16) Organizer and Chair: Daniel Kral (University of Warwick) and Bojan Mohar (Simon Fraser University) Graph coloring problems are among the oldest problems in graph theory. The Four Color Theorem is one the most popular graph theory result known to the general public. Graph colorings appear in different scenarios and there have been many extensions of the classical notion of graph coloring proposed. More generally, it is possible to consider graph packings, i.e. partitioning graphs into subgraphs of a certain type. The aim of this minisymposium is to present several recent interesting results from this classical area of graph theory. Thursday June 4 15:30 - 15:55 Ross Churchley (Simon Fraser University), Packing odd edge-disjoint $(u,v)$-trails, ARTS 133 16:00 - 16:25 Hehui Wu (University of Mississippi), Triangle-free subgraph with large fractional chromatic number, ARTS 133 16:30 - 16:55 Ross Kang (Radboud University Nijmegen), Partition of random graphs into subgraphs of bounded component order, ARTS 133 17:00 - 17:25 Robert Samal (Charles University in Prague), Unique Vector Coloring and Cores, ARTS 133 17:30 - 17:55 Ping Hu (University of Warwick), Rainbow triangles in three-colored graphs, ARTS 133 Graph structure and algorithms (CM4) Organizer and Chair: Kathie Cameron (Wilfrid Laurier University) Often graphs arising in applications have special structure, which can sometimes be exploited to design efficient algorithms for problems that are hard in general. In this minisymposium we look at graph structure that results from excluding certain induced paths, cycles or small graphs, and instances where this allows for efficient algorithms for problems such as colouring and domination. Monday June 1 15:30 - 15:55 Kathie Cameron (Wilfrid Laurier University), Recognizing and Colouring Even-Hole-Free Apple-Free Graphs, ARTS 102 16:00 - 16:25 Murilo da Silva (Simon Fraser University), Decomposing (even-hole, bull)-free graphs, ARTS 102 16:30 - 16:55 Shenwei Huang (Simon Fraser University), Bounding Clique-width via Perfect Graphs, ARTS 102 17:00 - 17:25 Elaine Eschen (West Virginia University), Polynomial-time efficient domination on ($P_6, house)$-free graphs and $(P_6, bull)$-free graphs, ARTS 102 17:30 - 17:55 Jerry Spinrad (Vanderbilt University), Double Threshold Digraphs, ARTS 102 Graph theory of Brian Alspach I (CM3) Organizer and Chair: Joy Morris (University of Lethbridge) and Mateja Sajna (University of Ottawa) This minisymposium has been organised in honour of Brian Alspach. In person and through his work, Brian has been a major influence on the development of graph theory research in Canada. Since his retirement to Australia, his North American colleagues see him much less often than formerly. We welcome the opportunity of his attendance at this CanaDAM conference to share some of the research of his colleagues, collaborators, and former students, in areas of interest to him, including: Hamilton cycles, groups acting on graphs, tournaments, and cycle decompositions. Monday June 1 10:20 - 10:45 Brian Alspach (University of Newcastle), Pancyclicity and Cayley Graphs, ARTS 133 10:50 - 11:15 Barbara Maenhaut (University of Queensland), Alspach's Cycle Decomposition Problem for Multigraphs, ARTS 133 11:20 - 11:45 Mateja Sajna (University of Ottawa), Alspach's Conjecture for complete equipartite multigraphs: the amalgamation-detachment approach, ARTS 133 11:50 - 12:15 Luis Goddyn (Simon Fraser University), Pairity thrackles on surfaces, ARTS 133 Graph theory of Brian Alspach II (CM5) Organizer and Chair: Joy Morris (University of Lethbridge) and Mateja Sajna (University of Ottawa) This minisymposium has been organised in honour of Brian Alspach. In person and through his work, Brian has been a major influence on the development of graph theory research in Canada. Since his retirement to Australia, his North American colleagues see him much less often than formerly. We welcome the opportunity of his attendance at this CanaDAM conference to share some of the research of his colleagues, collaborators, and former students, in areas of interest to him, including: Hamilton cycles, groups acting on graphs, tournaments, and cycle decompositions. Monday June 1 15:30 - 15:55 Dragan Marusic (University of Primorska, Slovenia), On the full automorphism group in vertex-transitive graphs, ARTS 133 16:00 - 16:25 Klavdija Kutnar (University of Primorska, Slovenia), HALF-ARC-TRANSITIVE GROUP ACTIONS WITH A SMALL NUMBER OF ALTERNETS, ARTS 133 16:30 - 16:55 Joy Morris (University of Lethbridge), The Cayley Isomorphism problem, ARTS 133 17:00 - 17:25 Dave Morris (University of Lethbridge), Hamiltonian cycles in some easy Cayley graphs, ARTS 133 Graph theory with applications in chemistry (CM9) Organizer and Chair: Patrick Fowler (University of Sheffield) and Wendy Myrvold (University of Victoria) Stability, structure and properties of carbon networks such as fullerenes and benzenoids are of theoretical and practical interest in chemistry and are often modelled using theories based on perfect matchings, graph adjacency matrices and graph spectra.This session explores ongoing applications of graph theory to carbon chemistry and physics. It includes contributions on models of benzenoid (and fullerene) stability based on the ideas proposed by Clar and Fries, on the construction and classification of carbon nanostructures, on the modelling of the currents induced in carbon structures by external magnetic fields (the ring currents used experimentally to characterise aromatic systems) and on their connections with the concepts of bond order introduced by Coulson and Pauling, both of which are essentially graph theoretical in nature. Tuesday June 2 15:30 - 15:55 Patrick Fowler (University of Sheffield), Graph Theory on the Edge of Chemistry: Perimeter Currents and Bond Orders, ARTS 102 16:00 - 16:25 Wendy Myrvold (University of Victoria), Graph Theoretic Models for Ring Currents, ARTS 102 16:30 - 16:55 Jack Graver (University of Syracuse), Fries chains in a fullerene, ARTS 102 17:00 - 17:25 Elizabeth Hartung (Massachusetts College of Liberal Arts), The Clar number and Kekule Count of Benzenoids, ARTS 102 17:30 - 17:55 Gunnar Brinkmann (University of Gent), Existence and Construction of Nanojoins, ARTS 102 Graphs and matrices (CM14) Organizer and Chair: Shaun Fallat and Karen Meagher (University of Regina) The study of graphs and matrices lies naturally at the intersection of linear algebra and combinatorics. The interplay of these two different areas has brought new revelations to each field. Often linear algebraic techniques provides insight into combinatorial constructions, objects, and patterns. Conversely, reasoning in combinatorics frequently sheds new light on properties of matrices. In this session, we will have speakers address how these two fields impact each other, present their new findings in these areas and introduce open problems. Thursday June 4 16:00 - 16:25 Wayne Barrett (Brigham Young University), The Fielder Vector and Tree Decompositions of Graphs, ARTS 102 17:00 - 17:25 Karen Meagher (University of Regina), Graphs that have a weighted adjacency matrix with spectrum $\{\lambda_1^{n-2}, \lambda_2^2\}$, ARTS 102 17:30 - 17:55 Jane Breen (University of Manitoba), Stationary vectors of stochastic matrices subject to combinatorial constraints, ARTS 102