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Please note: The University of Waterloo is closed for all events until further notice.

# Events by month

## February 2019

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### Combinatorial Optimization Reading Group- Rose McCarty

Friday, February 1, 2019 — 1:00 PM EST

Title: 2-approximation of chromatic number on graph classes excluding a minor

Speaker: Rose McCarty Affiliation: University of Waterloo Room: MC 5479

Abstract: In this talk we will see a 2-approximation of the chromatic number of graphs excluding a fixed minor.

### Tutte Colloquium - Gabriel Coutinho

Friday, February 1, 2019 — 3:30 PM EST

Title: Eigenvalue bounds to the (co)clique and chromatic numbers

Speaker: Gabriel Coutinho Affiliation: Federal University of Minas Gerais, Brazil Room: MC 5501

Abstract:

This is perhaps one of the oldest topics of interest in spectral graph theory, dating back to the works of Hoffman, Haemers, Delsarte and others, in the 70s.

### Reading Group on Entropy and Counting- Jorn van der Pol

Tuesday, February 5, 2019 — 2:00 PM EST

Title: Applications of the entropy method: Brégman's theorem

Speaker: Jorn van der Pol Affiliation: University of Waterloo Room: MC 6486

Abstract: Following Section 5 of Galvin's notes on Entropy and Counting,

### Algebraic Graph Theory Seminar- Caelan Wang

Thursday, February 7, 2019 — 1:30 PM EST

Title: Permutation Problems, Chessboards, and Rook Equivalence

Speaker: Caelan Wang Affiliation: University of Waterloo Room: MC 6486

Abstract: We discuss the motivation and development of the theory around rook polynomials.

### Combinatorial Optimization Reading Group- Tom Kelly

Friday, February 8, 2019 — 1:00 PM EST

Title:‘Coloring 3-colorable graphs with o(n^1⁄5) colors’ by Kawarabayashi and Thorup

Speaker: Tom Kelly Affiliation: University of Waterloo Room: MC 5479

Abstract: Much attention has been devoted to nding polynomial time algorithms for coloring three-
colorable graphs with the fewest possible colors.

### Tutte Colloquium - Jane Gao

Friday, February 8, 2019 — 3:30 PM EST

Title: The rank of random matrices over finite fields

Speaker: Jane Gao Affiliation: University of Waterloo Room: MC 5501

Abstract:

We determine the rank of a random matrix over a finite field with prescribed numbers of non-zero entries in each row and column. As an application we obtain a formula for the rate of low-density parity check codes.

### Graphs and Matroids Seminar- James Davies ** Rescheduled**

Wednesday, February 13, 2019 — 3:30 PM EST

Title: Circle graphs are quadratically x-bounded

Speaker: James Davies Affiliation: University of Waterloo Room: **New Room** MC 5501

Abstract: A circle graph $G$ is an intersection graph of a set of chords on a circle.

### Algebraic Graph Theory Seminar- Christopher van Bommel

Thursday, February 14, 2019 — 1:30 PM EST

Title: Quantum Walks, State Transfer, and Entanglement

Speaker: Christopher van Bommel Affiliation: University of Waterloo Room: MC 6486

Abstract: Quantum walks are the quantum analogues of classical random walks and can be used to model quantum computations.

### Combinatorial Optimization Reading Group- Sharat Imbrahimpur

Friday, February 15, 2019 — 1:00 PM EST

Title: Coloring 3-colorable graphs with o(n^1/5) colors

Speaker: Sharat Ibrahimpur Affiliation: University of Waterloo Room: MC 5479

Abstract: This is the second part of the seminar on recent results obtained by Kawarabayashi and Thorup

### **Rescheduled** Reading Group on Entropy and Counting- Jane Gao

Tuesday, February 19, 2019 — 2:00 PM EST

Title: Applications of the entropy method: Counting proper colorings of a regular graph

Speaker: Jane Gao Affiliation: University of Waterloo Room: MC 6486

Abstract: Following Section 6 of Galvin's notes on Entropy and Counting, we will explore Galvin and Tetali’s tight upper bound

### Reading Group on Entropy and Counting- John Schanck

Tuesday, February 26, 2019 — 2:00 PM EST

Title: Bounding Dedekind numbers with entropy

Speaker: John Schanck Affiliation: University of Waterloo Room: MC 6486

Abstract: The Dedekind numbers (sequence A000372 in the OEIS)

### Graphs and Matroids Seminar- Ahmed Ashraf

Wednesday, February 27, 2019 — 3:30 PM EST

Title: Cyclic flat approach to matroid base polytopes

Speaker: Ahmed Ashraf Affiliation: Western University Room: MC 5501

Abstract: Ardila, Benedetti and Doker realised matroid polytopes as generalized permutohedra, and using the work of Postnikov,

### Special Seminar - Yi-Shuai Niu

Thursday, February 28, 2019 — 3:30 PM EST

Title: Difference-of-SOS and Difference-of-Convex-SOS Decomposition Techniques for Polynomials

Speaker: Yi-Shuai Niu Affiliation:

SJTU-Paristech & Maths department Shanghai Jiao Tong University

Room: MC 5501

Abstract:

We are interested in polynomial decomposition techniques for reformulating any multivariate polynomial into difference-of-sums-of-squares (DSOS) and difference-of-convex-sums-of-squares (DCSOS) polynomials.

### February 2019

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