# Events by month

## November 2021

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### Algebraic Graph Theory Seminar - Allen Herman

Monday, November 1, 2021 — 11:30 to 11:30 AM EDT

Title: The results of a search for small association schemes with noncyclotomic eigenvalues

Speaker: Allen Herman Affiliation: University of Regina Zoom: Contact Soffia Arnadottir

Abstract:

### Tutte Colloquium - László Végh

Friday, November 5, 2021 — 3:30 PM EDT

Title: On complete classes of valuated matroids

Speaker: László Végh Affiliation: London School of Economics Zoom: Please email Emma Watson

Abstract:

Valuated matroids were introduced by Dress and Wenzel in 1992. They are a central object in discrete convex analysis, and play important roles in other areas such as mathematical economics and tropical geometry. Finding a constructive characterization, i.e., showing that all valuated matroids can be derived from a simple class by some basic operations has been a natural question proposed in various contexts.

### Tutte Colloquium - Greg Zaverucha

Friday, November 12, 2021 — 3:30 PM EST

Title: Shorter Zero-Knowledge Proofs from MPC

Speaker: Greg Zaverucha Affiliation: Microsoft Research Zoom: Please email Emma Watson

Abstract:

In this talk I will review the MPC-in-the-head approach to constructing zero-knowledge proofs, then talk about some recent research results to make the proofs shorter.

In a zero-knowledge proof system, a prover wants to convince a verifier that they know a secret value, without revealing it. A common case involves a one-way function, where the prover wants to convince a verifier that they know a secret input corresponding to a public output.

### Tutte Colloquium - Steph van Willigenburg

Friday, November 19, 2021 — 3:30 PM EST

Title: The (3+1)-free conjecture of chromatic symmetric functions

Speaker: Steph van Willigenburg Affiliation:

University of British Columbia

Abstract:

The chromatic symmetric function, dating from 1995, is a generalization of the chromatic polynomial. A famed conjecture on it, called the Stanley-Stembridge (3+1)-free conjecture, has been the focus of much research lately. In this talk we will be introduced to the chromatic symmetric function, the (3+1)-free conjecture, new cases and tools for resolving it, and answer another question of Stanley of whether the (3+1)-free conjecture can be widened. This talk requires no prior knowledge.

### Algebraic Graph Theory Seminar - Emily King

Monday, November 22, 2021 — 11:30 to 11:30 AM EST

Title: Switching Equivalence on the Grassmannian

Abstract:

When constructing configurations of subspaces with desirable properties, one might ask if the configuration is indeed "new.''  It has been known for about 50 years that Gram matrices of equiangular vectors in real Euclidean space correspond to finite simple graphs via the Seidel adjacency matrix, and the collections of such vectors which span the same lines correspond to switching equivalence classes of graphs.

### Tutte Colloquium - Ashwin Nayak

Friday, November 26, 2021 — 3:30 PM EST

Title: Quantum Distributed Complexity of Graph Diameter and Set Disjointness

Speaker: Ashwin Nayak Affiliation:

University of Waterloo

Abstract:

In the Congest model, a network of p processors cooperate to solve some distributed task. Initially, each processor knows only its unique label, the labels of its neighbours, and a polynomial upper bound on p, the size of the network. The processors communicate with their neighbours in rounds. In each round, a processor may perform local (quantum) computation, and send a short message to each of its neighbours. How many rounds of communication are required for some processor to compute the diameter of the network?

### Algebraic Graph Theory Seminar - Peter Dukes

Monday, November 29, 2021 — 11:30 to 11:30 AM EST

Title: Fractional decompositions and Latin square completion

Speaker: Peter Dukes Affiliation: University of Victoria Zoom: Contact Soffia Arnadottir

Abstract:

It was shown recently by Delcourt and Postle that any sufficiently large graph $G$ of order $n$ with minimum degree at least $0.827n$ has a fractional triangle decomposition, i.e. an assignment of weights to the triangles in $G$ such that for every edge $e$, the total of all weights of triangles containing $e$ is exactly one.

### November 2021

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