# Past Events › AARMS Atlantic Graph Theory Seminar

## November 2023

### Atlantic Graph Theory Seminar

Speaker:  Santiago Guzman-Pro, TU Dresden Title:          Forbidden Tournaments and the Orientation (Completion) Problem Abstract:   For a fixed finite set of  oriented graphs F,  the F-free  orientation problem asks whether a given finite undirected graph G has an F-free orientation, i.e., whether the edges of  G  can be  oriented so that the  resulting  oriented  graph does not contain  any oriented graph from F as an oriented (induced) subgraph. It was first noted by Bang-Jensen, Huang, and Prisner that when F…

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### Atlantic Graph Theory Seminar

Speaker: Jordan Barrett, Toronto Metropolitan University Title: Graph burning, the burning number conjecture, and burning density Abstract: Graph burning is a discrete time process on a graph that acts as a simple model for the spread of social contagion in a network. Graph burning was introduced by Bonato, Janssen and Roshanbin in 2014, and with this introduction came the now famous "burning number conjecture". In the first half of my talk, I will introduce graph burning and give a brief overview of…

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## January 2024

### Atlantic Graph Theory Seminar

Speaker:  Leslie Hogben, Iowa State University Title:         Forts, (fractional) zero forcing, and Cartesian products of graphs Abstract: Zero forcing is an iterative process that repeatedly applies a rule to change the color of vertices of a graph $G$ from white to blue. The  zero forcing number is the minimum number of initially blue vertices that are needed to color all vertices blue through this process.  Standard zero forcing was introduced about fifteen years ago  in the control of…

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### Atlantic Graph Theory Seminar

Speaker: Torsten Mütze, Un. Warwick Title: Kneser graphs are Hamiltonian   Abstract: For integers k>=1 and n>=2k+1, the Kneser graph K(n,k) has as vertices all k-element subsets of an n-element ground set, and an edge between any two disjoint sets. It has been conjectured since the 1970s that all Kneser graphs admit a Hamilton cycle, with one notable exception, namely the Petersen graph K(5,2). This problem received considerable attention in the literature, including a recent solution for the sparsest case…

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### Atlantic Graph Theory Seminar

Speaker: Thiago de Holleben, Dalhousie University Title: Homological invariants of graphs with no induced cycles of length divisible by 3 Abstract:  If G is a graph with large chromatic number, what can we say about its induced subgraphs? In 2014, Bonamy et al. showed that if a graph has no induced cycles of length divisible by three, then its chromatic number is bounded. Such graphs are called ternary. In an attempt to better understand the structure of the induced subgraphs…

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## February 2024

### Atlantic Graph Theory Seminar

Zoom link below. Live viewing for local participants in Chase 227 (tea-drinkers are encouraged to bring their own mug). Speaker: Evelyn Smith-Roberge, Georgia Tech Title:Correspondence Packings of Planar Graphs Abstract: Suppose a graph G has list chromatic number k. It is easy to see that if L is a (k+1)-list assignment for G, then G admits two L-colourings f and g where f(v) =/= g(v) for every vertex v in the graph. But what if we want still more disjoint…

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### Atlantic Graph Theory Seminar

Speaker: Andrew Beveridge, Macalester College Title: Approval Ballot Triangles Time: Wednesday, February 14, 3.30pm Atlantic time Live viewing for local participants in Chase 227, Dalhousie University Bertrand's Ballot Problem enumerates the number of ways to count ballots so that candidate 1 never trails candidate 2. We generalize this problem by considering an approval ballot election between $n$ candidates. In an approval ballot election, each voter endorses a subset of candidates, rather than voting for just one person. The general approval…

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### Atlantic Graph Theory Seminar

Speaker: Ada Chan, York University Title: Polygamy in state transferAbstract:Let $X$ be a graph and $H$ be a Hermitian matrix associated with $X$.   The continuous-time quantum walk with Hamiltonian $H$ isdefined by the time-dependent unitary matrix\begin{equation*}U(t)=e^{i t H}.\end{equation*}Perfect state transfer occurs from vertex $a$ to vertex $b$ at time $\tau$ is $\vert U(\tau)_{b,a}\vert = 1$.   This phenomenon is relevant for information transmission in a quantum spin network.   For real and symmetric Hamiltonians, it is known that perfect state transfer can…

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### Atlantic Graph Theory Seminar

Pursuit-evasion on Graphs Trent Marbach, Toronto Metropolitan University The study of pursuit-evasion on graphs looks at games played between two adversaries, with one player tasked with alluding capture from the other on the graph. We will describe these types of games in general, although we will take a particular focus on two games: the Cops and Robber game, and the Localization game. A famous open conjecture for the Cops and Robber game has spurred recent work in the area, and…

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## March 2024

### Atlantic Graph Theory Seminar

Induced subgraphs and treewidth Speaker: Sophie Spirkl, University of Waterloo Abstract: Treewidth is a measure of the complexity of a graph and has both structural and algorithmic consequences. While results of Robertson and Seymour characterize which minors appear in graphs of large treewidth, the same question is still open for induced subgraphs. I will present some recent results towards an answer to this question, in particular, about when excluding a finite set of induced subgraphs leads to the answer being…

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