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Friday, August 3, 2018 — 3:30 PM EDT

Title: The geometry of matroids

Speaker:  Federico Ardila
Affiliation: San Francisco State University
Room: MC 5501

Abstract:

Matroid theory is a combinatorial theory of independence which has its origins in linear algebra and graph theory, and turns out to have deep connections with many other fields.

Friday, July 27, 2018 — 3:30 PM EDT

Title: Algorithms for Rank-1 Bimatrix Games

Speaker: Bernhard von Stengel
Affiliation: London School of Economics
Room: MC 5501

Abstract:

The rank of a bimatrix game is the matrix rank of the sum of the two payoff matrices.

Friday, July 20, 2018 — 3:30 PM EDT

Title: Claw-free matroids

Speaker: Peter Nelson
Affiliation: University of Waterloo
Room: MC 5501

Abstract: A simple binary matroid is claw-free if it has no independent rank-3 flat. I will discuss a structure theorem, obtained jointly with Kazuhiro Nomoto, that classifies these objects exactly.

Thursday, July 19, 2018 — 3:30 PM EDT

Title: Density and Structure of Homomorphism-Critical Graphs

Speaker: Evelyne Smith-Roberge
Affiliation: University of Waterloo
Room: MC 5417

Abstract: 

Let H be a graph. A graph G is H-critical if every proper subgraph of G admits a homomor-
phism to H, but G itself does not.

Tuesday, July 17, 2018 — 3:00 PM EDT

Title: Using Linear Algebra to do Matching Theory

Speaker: Justin Toth
Affiliation: University of Waterloo
Room: MC 5501

Abstract:

A matching in a graph is a set of edges with each vertex contained in at most one edge. A perfect matching is a matching in which each vertex is contained in some edge.

Thursday, July 12, 2018 — 3:30 PM EDT

Title: Gaps in the crossing numbers of drawings of the complete graph

Speaker: Bruce Richter
Affiliation: University of Waterloo
Room: MC 5479

Abstract: In the late 1990’s, a 5-author manuscript circulated proving the existence of intervals of integers that connot occur as the crossing number of a “good” drawing of the complete graph. 

Thursday, July 12, 2018 — 1:30 PM EDT

Title: Periodicity on Oriented Graphs by way of Transcendental Number Theory

Speaker: Sabrina Lato
Affiliation: University of Waterloo
Room: MC 6486

Abstract: Using the adjacency matrix of a graph, it is straightforward to show that perfect state transfer between two vertices at some time t implies that both vertices will be periodic at time 2t.

Friday, July 6, 2018 — 3:30 PM EDT

Title: The coloring problem for restricted graph classes

Speaker: Chinh T. Hoang
Affiliation: Wilfred Laurier University
Room: MC 5501

Abstract:

Let L be a set of graphs. Free(L) is the set of graphs that do not contain any graph in L as an induced subgraph.

Thursday, July 5, 2018 — 3:30 PM EDT

Title:Generalizing the problem of packing disjoint cycles

Speaker: Paul Wollan
Affiliation: University of Rome "La Sapienza"
Room: MC 5479

Abstract: A classic result of Erdos and Posa states that there exists a function f such that for all k,

Thursday, July 5, 2018 — 1:30 PM EDT

Title: Edge State Transfer

Speaker: Tina Chen
Affiliation: University of Waterloo
Room: MC 6486

Abstract: Most research about quantum state transfer on graphs use adjacency matrices as their Hamiltonians and investigate the transfers between single vertex states.

Friday, June 29, 2018 — 3:30 PM EDT

Title: The c2 invariant at p=2 by counting edge bipartitions

Speaker: Karen Yeats
Affiliation: University of Waterloo
Room: MC 5501

Abstract:

Since no one provided a visitor or volunteered for this week, I will explain how to prove a special case of a conjecture about the c2 invariant. 

Thursday, June 28, 2018 — 3:30 PM EDT

Title: Stretching drawings of graphs

Speaker: Alan Arroyo
Affiliation: University of Waterloo
Room: MC 5479

Abstract: Given a drawing D of a graph (where vertices are dots in the plane and edges are arbitrary curves connecting some pairs of dots),

Thursday, June 28, 2018 — 11:30 AM EDT

Title: The Many Faces of Circulation Algebras

Speaker: Nick Olson-Harris
Affiliation: University of Waterloo
Room: MC 6486

Abstract:  The circulation algebra is a commutative graded algebra associated to a graph, introduced by Wagner in 1998 to study flows.

Friday, June 22, 2018 — 3:30 PM EDT

Title: Two-level polytopes

Speaker: Kanstantsin Pashkovich
Affiliation: University of Waterloo
Room: MC 5501

Abstract:

This talk is dedicated to two-level polytopes. On one side, two-level polytopes form a well structured family of polytopes.

Thursday, June 21, 2018 — 3:30 PM EDT

Title: The price of connectivity for domination

Speaker: Paul Ouvrard
Affiliation: University of Bordeaux
Room: MC 5479

Abstract: The price of connectivity for dominating set in a graph G is the ratio between the minimum sizes of a connected dominating set and a dominating set of G.

Tuesday, June 19, 2018 — 3:00 PM EDT

Title: Minimization of convex compositions

Speaker: Courtney Paquette
Affiliation: Lehigh University
Room: MC 6486

Abstract:

Numerous optimization tasks can be posed as minimization of a finite convex function composed with a smooth map. Phase retrieval and matrix factorization problems are common examples.

Friday, June 15, 2018 — 3:30 PM EDT

Title: Distributed coloring in planar graphs

Speaker: Marthe Bonamy
Affiliation: University of Bordeaux
Room: MC 5501

Abstract:

We are concerned with efficiently coloring sparse graphs in the distributed setting with as few colors as possible. According to the celebrated Four Color Theorem, planar graphs can be colored with at most 4 colors, and the proof gives a (sequential) quadratic algorithm finding such a coloring.

Thursday, June 14, 2018 — 3:30 PM EDT

Title: Hamilton cycles in cubic planar graphs

Speaker: Frantisek Kardos
Affiliation: University of Bordeaux
Room: MC 5479

Abstract: Tait conjectured in 1884 that each cubic planar graph contains a Hamilton cycle. Had the conjecture been true,

Tuesday, June 12, 2018 — 1:00 PM EDT

Title: On isogeny graphs of supersingular elliptic curves over finite fields- Part 2

Speaker: Gora Adj
Affiliation: University of Waterloo
Room: MC 6486

 Abstract: After having defined the supersingular isogeny graph, in this second talk

Friday, June 8, 2018 — 3:30 PM EDT

Title: Online Learning of Quantum States

Speaker: Ashwin Nayak
Affiliation: University of Waterloo
Room: MC 5501

Abstract:

Suppose we have many copies of an unknown n-qubit state rho. We measure some copies of rho using a known two-outcome measurement E_1, then other copies using a measurement E_2, and so on.

Wednesday, June 6, 2018 — 3:30 PM EDT

Title: All Graphs are Beautiful

Speaker: Alan Arroyo
Affiliation: University of Waterloo
Room: MC 5417

Abstract: In this talk I will show that all graphs are beautiful. The proof is by induction on g

Tuesday, June 5, 2018 — 1:00 PM EDT

Title: On isogeny graphs of supersingular elliptic curves over finite fields

Speaker: Gora Adj
Affiliation: University of Waterloo
Room: MC 6486

Abstract: In this talk we will present some results on the isogeny graphs of supersingular elliptic curves

Friday, June 1, 2018 — 3:30 PM EDT

Title: Parameterized Approximation Algorithms for Steiner Network Problems 

Speaker: Andreas Feldmann
Affiliation: Charles University, Prague, Czech Republic
Room: MC 5501

Abstract:

Two standard approaches to handle NP-hard optimization problems are to develop approximation and parameterized algorithms.

Thursday, May 31, 2018 — 3:30 PM EDT

Title: Counting biased cliques

Speaker: Peter Nelson
Affiliation: University of Waterloo
Room: MC 5479

Abstract: A biased graph is a pair consisting of an undirected graph G,

Thursday, May 31, 2018 — 11:30 AM EDT

Title: A single pass bijection between certain quarter plane lattice walks and certain Motzkin-like paths.

Speaker: Karen Yeats
Affiliation: University of Waterloo
Room: MC 6486

Abstract: A p-tandem quarter plane walk is a walk starting at the origin and remaining in the first quadrant

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