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Title: Type II Matrices
Speaker: Ada Chan Affiliation: York University Room: MC 5479Abstract:
In 1867, Sylvester defined an {\sl inverse orthogonal matrix} as an $n\times n$ complex matrix $W$ satisfying
Title: Discrete diffusion on graphs and real hyperplane arrangements
Speaker: David Wagner Affiliation: University of Waterloo Room: MC 6483Abstract:
In 2016, Duffy et al. introduced the following process on a graph. Initially, each vertex has some integer number of ``chips'' placed there (possibly negative).
Title:
Speaker: Lise Turner Affiliation: University of Waterloo Room: MC 5501Abstract:
There are several different notions of what it means for a graph to converge. One popular notion for sparse graphs is BenjaminiSchramm convergence which focuses on local properties of the graphs.
Title: Greedy Heuristic for Maximizing Submodular Set Functions
Speaker: Ishan Bansal Affiliation: University of Waterloo Room: MC 5417Abstract:
Several hard combinatorial optimization problems can be posed in the following framework: maximize a submodular function over its domain subject to a cardinality constraint.
Title: Extending drawings of K(n) to pseudolines and pseudocircles
Speaker: Bruce Richter Affiliation: University of Waterloo Room: MC 5501Abstract:
In the early part of the 21st century, it was shown that the number of crossings in a straightline drawing of K(n) is at least the number H(n), which is conjectured to be the crossing number of K(n). In fact, it is now known that, for n at least 10, the inequality is strict.
Title: Quantum Colouring and Derangements
Speaker: Chris Godsil Affiliation: University of Waterloo Room: MC 5479Abstract:
Work in quantum information has lead to the introduction of quantum colourings.
Title: Scattering amplitudes and associahedra
Speaker: Hugh Thomas Affiliation: UQAM Room: MC 5417Abstract:
The classic approach to scattering amplitudes sums a contribution from a (potentially very large) number of Feynman diagrams.
Title: A Pseudoforest Analogue of the Strong Nine Dragon Tree Conjecture
Speaker: Logan Grout Affiliation: University of Waterloo Room: MC 5501Abstract:
In 2016, Jiang and Yang proved the Nine Dragon Tree Conjecture, a strengthening of the classical arboricity result of NashWilliams (1964). On the way to developing this proof, Fan, Lim Song, and Yang proved an analogous result for decomposing graphs into pseudoforests, which is a strengthening of Hakimi’s Theorem.
Title: Maximizing a Monotone Submodular Function subject to a Matroid Constraint
Speaker: Justin Toth Affiliation: University of Waterloo Room: MC 5417Abstract:
Based on the paper by Calinescu, Chekuri, Pál, and Vondrák of the same title. We will study a randomized $(1\frac{1}{e})$approximation algorithm for the titular problem.
Title: On the depth of cutting planesOn the depth of cutting planes
Speaker: Laurent Poirrier Affiliation: University of Waterloo Room: MC 5501Abstract:
We tackle one of the most important open problems in computational integer programming: cut selection.
For four decades, cutting planes were believed to be useful only for structured combinatorial problems. This changed in 1995 when Balas, Ceria and Cornuéjols showed that Gomory cuts could helpfully strengthen the formulation of general integer programming problems. Since then, many other cut generation techniques have been developed, but their practical success has been moderate at best.
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