We give an overview of the interplay between structural graph theory, first-order logic, and parameterized complexity. We focus on introducing the subject. Time permitting, one particular topic will be the neighborhood complexity of monadically stable graph classes.
Thompson links are links arising from elements of the Thompson group. They were introduced by Vaughan Jones as part of his effort to construct a conformal field theory for every finite index subfactor. In this talk I will first talk about Jones' construction of Thompson links. Then I will talk about grid diagrams and introduce a notion of half grid diagrams to give an equivalent construction of Thompson links and further associate with each Thompson link a canonical Legendrian type. Lastly, I will talk about some applications about the maximal Thurston-Bennequin number and presentation of link group. This is joint work with Yangxiao Luo.
In this talk, I will give an introduction to the implicit boundary integral method based on the co-area formula and it provides a simple quadrature rule for boundary integral on general surfaces. Then, I will focus on the application of solving the linearized Poisson Boltzmann equation, which is used to model the electric potential of protein molecules in a solvent. Near the singularity, I will briefly discuss the choices of regularization/correction and illustrate the effect of both cases. In the end, I will show the numerical analysis for the error estimate.
I will briefly survey the theory of matroids with coefficients, which was introduced by Andreas Dress and Walter Wenzel in the 1980s and refined by the speaker and Nathan Bowler in 2016. This theory provides a unification of vector subspaces, matroids, valuated matroids, and oriented matroids. Then I will outline an intriguing connection between Lorentzian polynomials, as defined by Petter Brändén and June Huh, and matroids with coefficients. The second part of the talk represents ongoing joint work with June Huh, Mario Kummer, and Oliver Lorscheid.
A Latin square is an nxn grid filled with n symbols such that each symbol appears exactly once in each row and column. A transversal in a Latin square is a collection of n cells such that each row, column and symbol appears exactly once in the collection.
Latin squares were introduced by Euler in the 1700s and he was interested in the question of when a Latin square decomposes fully into transversals. Equivalently, when does a Latin square have an 'orthogonal mate'?
We'll discuss the history of this question, and some upcoming joint work with Richard Montgomery.
Motivated by applications to group synchronization and quadratic assignment on random data, we study a general problem of Bayesian inference of an unknown “signal” belonging to a high-dimensional compact group, given noisy pairwise observations of a featurization of this signal.
We establish a quantitative comparison between the signal-observation mutual information in any such problem with that in a simpler model with linear observations, using interpolation methods. For group synchronization, our result proves a replica formula for the asymptotic mutual information and Bayes-optimal mean-squared error. Via analyses of this replica formula, we show that the conjectural phase transition threshold for computationally-efficient weak recovery of the signal is determined by a classification of the real-irreducible components of the observed group representation(s), and we fully characterize the information-theoretic limits of estimation in the example of angular/phase synchronization over SO(2)/U(1). For quadratic assignment, we study observations given by a kernel matrix of pairwise similarities and a randomly permuted and noisy counterpart, and we show in a bounded signal-to-noise regime that the asymptotic mutual information coincides with that in a Bayesian spiked model with i.i.d. signal prior.
This is based on joint work with Kaylee Yang and Zhou Fan.
Over the last 40 years there have been great advances in computer hardware, solvers (methods for solving Ax=b and F(x)=0), meshing algorithms, time stepping methods, adaptivity and so on. Yet accurate prediction of fluid motion (for settings where this is needed) is still elusive. This talk will review three major hurdles that remain: ensemble simulations, time accuracy and model stagnation. Three recent ideas where numerical analysis can help push forward the boundary between what can be done and what can't be done will be described. This talk is based on joint work with many. It should be completely understandable by grad students with a basic PDE class.
A matroid $M$ is a pair $(E, \mathcal{I})$ where $E$ is a finite set, called the {\em ground set} of $M$, and $\mathcal{I}$ is a non-empty collection of subsets of $E$, called {\em independent sets} of $M$, such that (1) a subset of an independent set is independent; and (2) if $I$ and $J$ are independent sets with $|I| < |J|$, then exists $x \in J \backslash I$ such that $I \cup \{x\}$ is independent.
A graph $G$ gives rise to a matroid $M(G)$ where the ground set is $E(G)$ and a subset of $E(G)$ is independent if it spans a forest. Another example is a matroid that comes from a matrix over a field $F$: the ground set $E$ is the set of all columns and a subset of $E$ is independent if it is linearly independent over $F$.
Tutte's Wheel and Whirl Theorem and Seymour's Splitter Theorem are two well-known inductive tools for proving results for 3-connected graphs and matroids. In this talk, we will give a survey on induction theorems for various versions of 4-connected matroids and graphs.
A fundamental result in 3-dimensional contact topology due to Ding-Geiges tells us that any contact 3-manifold can be obtained via doing a surgery on a Legendrian link in the standard contact 3-sphere. So it's natural to ask how simple or complicated a surgery diagram could be for a given contact manifold? Contact surgery number is a measure of this complexity. In this talk, I will discuss this notion of complexity along with some examples. This is joint work with Marc Kegel.
The annual School of Math REU summer poster session will take place 11-2 on Thursday July 18th in the Skiles Atrium. We have a group of more than 20 students presenting projects on a variety of subjects (info for most of the projects available here). There will also be some light snacks and coffee etc. Come by and see the hard work that the students have done this summer; the students will certainly appreciate your interest!
