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X-ORIGINAL-URL:https://aarms.math.ca
X-WR-CALDESC:Events for 
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DTSTART:20230101T000000
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BEGIN:VEVENT
DTSTART;TZID=UTC:20240117T153000
DTEND;TZID=UTC:20240117T163000
DTSTAMP:20260612T034916
CREATED:20240110T181847Z
LAST-MODIFIED:20240110T182517Z
UID:7474-1705505400-1705509000@aarms.math.ca
SUMMARY:Atlantic Graph Theory Seminar
DESCRIPTION:Speaker:  Leslie Hogben\, Iowa State University\nTitle:         Forts\, (fractional) zero forcing\, and Cartesian products of graphs\n\nAbstract: 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 quantum systems and as an upper bound for  maximum multiplicity of an eigenvalue (or maximum nullity) among matrices having off-diagonal nonzero pattern described by the edges of the graph $G$\, and rediscovered later both as part of power domination and as fast-mixed graph searching.\n\nWhether a set is a zero forcing set can be tested using a certain type of set called a fort\, which obstructs zero forcing.   The maximum number of disjoint forts (fort number)  provides another  lower bound for the zero forcing number; results about fort number will be discussed.  Forts can be used in integer programs to determine the zero forcing number and fort number.  The relaxation of these integer programs leads to dual linear programs that define the fractional zero forcing number\, or equivalently\, the fractional fort number\, and results about these parameters will be discussed.\n\nThere is a well-known upper bound for the zero forcing number of a Cartesian product in terms of the zero forcing numbers and orders of the constituent graphs.  The question of a lower bound for the zero forcing number of a Cartesian product has recently been studied.  It is easy to see that there is a Vizing-like lower bound when the constituent graphs of the Cartesian product both have maximum nullity equal to zero forcing number.  Fractional zero forcing and fort number provide additional lower bounds on the the zero forcing number of a Cartesian product in terms of parameters of the constituent graphs.\n\n______________________________________________________________________________\nJeannette Janssen is inviting you to a scheduled Zoom meeting.\n\nTopic: Atlantic Graph Theory Seminar\nJoin Zoom Meeting\nhttps://us02web.zoom.us/j/86415230827?pwd=QUxLUnlMdWYzL05zSUJ4bnBCOUJnZz09\n\nMeeting ID: 864 1523 0827\nPasscode: 835547
URL:https://aarms.math.ca/event/atlantic-graph-theory-seminar-leslie-hogben/
LOCATION:Online via Zoom
CATEGORIES:AARMS Atlantic Graph Theory Seminar
ORGANIZER;CN="jeannette Janssen":MAILTO:jeannette.janssen@dal.ca
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=UTC:20240124T153000
DTEND;TZID=UTC:20240124T163000
DTSTAMP:20260612T034916
CREATED:20240118T184108Z
LAST-MODIFIED:20240118T184230Z
UID:7478-1706110200-1706113800@aarms.math.ca
SUMMARY:Atlantic Graph Theory Seminar
DESCRIPTION:Speaker: Torsten Mütze\, Un. Warwick\nTitle: Kneser graphs are Hamiltonian\n  \nAbstract: 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 n=2k+1. The main contribution of our work is to prove the conjecture in full generality. We also extend this Hamiltonicity result to all connected generalized Johnson graphs (except the Petersen graph). The generalized Johnson graph J(n\,k\,s) has as vertices all k-element subsets of an n-element ground set\, and an edge between any two sets whose intersection has size exactly s. Clearly\, we have K(n\,k)=J(n\,k\,0)\, i.e.\, generalized Johnson graphs include Kneser graphs as a special case. Our results imply that all known families of vertex-transitive graphs defined by intersecting set systems have a Hamilton cycle\, which settles an interesting special case of Lovász’ conjecture on Hamilton cycles in vertex-transitive graphs from 1970. Our main technical innovation is to study cycles in Kneser graphs by a kinetic system of multiple gliders that move at different speeds and that interact over time\, reminiscent of the gliders in Conway’s Game of Life\, and to analyze this system combinatorially and via linear algebra.\n  \nThis is joint work with my students Arturo Merino (TU Berlin) and Namrata (Warwick).\n\n———————————————————\nJoin Zoom Meeting\nhttps://us02web.zoom.us/j/86415230827?pwd=QUxLUnlMdWYzL05zSUJ4bnBCOUJnZz09\n\nMeeting ID: 864 1523 0827\nPasscode: 835547
URL:https://aarms.math.ca/event/atlantic-graph-theory-seminar-8/
LOCATION:Online via Zoom
CATEGORIES:AARMS Atlantic Graph Theory Seminar
ORGANIZER;CN="jeannette Janssen":MAILTO:jeannette.janssen@dal.ca
END:VEVENT
BEGIN:VEVENT
DTSTART;VALUE=DATE:20240126
DTEND;VALUE=DATE:20240129
DTSTAMP:20260612T034916
CREATED:20230922T154105Z
LAST-MODIFIED:20230925T101319Z
UID:7318-1706227200-1706486399@aarms.math.ca
SUMMARY:Combinatorial Algebra Meets Algebraic Combinatorics
DESCRIPTION:Combinatorial Algebra Meets Algebraic Combinatorics (CAAC) is a two-day workshop bringing together researchers working at the intersection of combinatorics and algebra. It examines the role of combinatorial structures\, such as permutations\, matroids and polytopes\, arising from problems in Schubert calculus\, commutative algebra\, and other branches of algebra\, representation theory and geometry.
URL:https://aarms.math.ca/event/combinatorial-algebra-meets-algebraic-combinatorics/
LOCATION:Montreal\, Montreal\, Quebec\, Canada
CATEGORIES:AARMS sponsored events
ORGANIZER;CN="Jake Levinson":MAILTO:jake.levinson@umontreal.ca
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BEGIN:VEVENT
DTSTART;TZID=UTC:20240131T153000
DTEND;TZID=UTC:20240131T163000
DTSTAMP:20260612T034916
CREATED:20240127T122401Z
LAST-MODIFIED:20240127T122513Z
UID:7485-1706715000-1706718600@aarms.math.ca
SUMMARY:Atlantic Graph Theory Seminar
DESCRIPTION:Speaker: Thiago de Holleben\, Dalhousie University\nTitle: Homological invariants of graphs with no induced cycles of length divisible by 3\n \nAbstract:  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.\nIn an attempt to better understand the structure of the induced subgraphs of a graph with bounded chromatic number\, Kalai and Meshulam posed questions relating topological invariants of the independence complex\, and the chromatic number of a graph. Since then\, there have been several results bounding chromatic numbers of graphs using topology. In 2022\, Jinha Kim showed a conjecture of Engström stating the exact topological structure of the independence complex of a ternary graph. In this talk\, we describe a graph theoretic way of computing this structure. As an application\, we show that -1 is a root of the independence polynomial of a forest F if and only if the induced matching number of F is not equal to the domination number of F.\n \nJoin Zoom Meeting\nhttps://us02web.zoom.us/j/86415230827?pwd=QUxLUnlMdWYzL05zSUJ4bnBCOUJnZz09\n\n\nMeeting ID: 864 1523 0827\nPasscode: 835547
URL:https://aarms.math.ca/event/atlantic-graph-theory-seminar-9/
LOCATION:Online via Zoom
CATEGORIES:AARMS Atlantic Graph Theory Seminar
ORGANIZER;CN="jeannette Janssen":MAILTO:jeannette.janssen@dal.ca
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