Events by month

Title: Independence Polynomials and Their Roots

Abstract:

Independence polynomials are generating functions for the number of independent sets of each cardinality in a graph G.

Title: Signings and induced subgraphs of the Hypercube

Abstract:

Just over a month ago, Hao Haung resolved the sensitivity conjecture, a 30 year-old question about the complexity of boolean functions.

Title: Approximation Algorithms for Minimum-Norm Optimization Problems

Abstract:

In many optimization problems, a feasible solution induces a multidimensional cost vector. For example, in k-clustering, opening k facilities induces an assignment-cost vector indexed by the clients; in load-balancing, a schedule induces a load vector across the machines.

Title: Polynomial Spaces

Abstract:

We describe some simple machinery that enables us to derive upper bounds on the size of codes, and lower bounds on the size of designs in a quite general setting.

Title: Combinatorial questions motivated by Invariant Theory

Abstract:

We begin the talk by discussing a question in Invariant Theory: given a representation $V$ of a Lie group $G$, when if the invariant ring $k[V]^G$ a polynomial ring? We give a conjectural answer which we have verified for $SL_n$ and discuss some combinatorial questions motivated by the proof. This is joint work with Dan Edidin.

Title: Monochromatic cycle partitions

Abstract:

A classic result of Erdős, Gyárfás, and Pyber states that the vertex set of every complete graph, whose edges have been coloured with r colours, can be covered by r2 log r disjoint monochromatic cycles.

Title: Orthogonal Polynomials and the Addition Formula

Abstract:

Many questions about designs and codes in the unit sphere can be reduced to questions about members of a family of orthogonal polynomials, the so-called Gegenbauer polynomials.

Title: When are two Schur functions the same?

Abstract: 

A pair of skew shapes are said to be (skew) equivalent if they admit the same number of semistandard tableaux of any weight; i.e. if their associated skew Schur functions are equal.

Title: The sparsest matroids omitting an independent flat

Abstract:

Given integers $k,r \ge 1$, what is the smallest a rank-$r$ matroid can be that does not contain a $k$-element independent set that is also a flat? I will answer this question, characterize the extremal examples, and draw parallels with a problem in graph theory.

Title: Undermining key exchange

Abstract:

There are many ways to undermine systems that rely on cryptography. An attacker could of course try to find flaws in the hardware and software implementing the system, or find mathematical weaknesses in the cryptographic algorithms.

Title: Improving Implementations of CSIDH

Abstract: 

I will present on some papers related to implementations of CSIDH [1].

Title: LP bounds and the addition formula

Abstract:

I will show how we can derive useful bounds on the size of codes and designs, using linear programming and the addition formula.

Title: Chord diagrams, generating functions, and qft

Abstract:

I'll talk about some joint work with Julien Courtiel where some nice enumerative combinatorics tells us something about how gauge theories are such special quantum field theories.

Title: Submodular function maximization

Abstract:

I will give the introductory talk for this term's topic for the Combinatorial-Optimization Reading group, namely submodular function maximization. Submodular functions arise in diverse contexts in combinatorial optimization.

Title: Countable weighted graphs with no unfriendly partitions