Many large computational problems depend on solutions to systems of linear equations. One widely used method of solving systems of linear equations is the Conjugate Gradient method (CG). Terminating CG after only a few iterations can save computational resources but can also cause an error in the solution to the system of linear equations, and…
Nonlinear preconditioning refers to transforming a nonlinear algebraic system to a form for which Newton-type algorithms have improved success through quicker advance to the domain of quadratic convergence. We place these methods, which go back at least as far as the Additive Schwarz Preconditioned Inexact Newton (ASPIN, 2002) in the context of a proliferation distinguished…
Using a definition of Euler characteristic for fractionally-graded complexes based on roots of unity, we show that the Euler characteristics of Dowlin’s “sl(n)-like” Heegaard Floer knot invariants HFK_n recover both Alexander polynomial evaluations and sl(n) polynomial evaluations at certain roots of unity for links in S^3. We show that the equality of these evaluations can…
In this joint ongoing work with Nicolas Forcadel (INSA Rouen) we study traffic flows models with a bifurcation. The model consists in a single incoming road divided after a junction into several outgoing ones. There are basically two classes of models to describe this situation: microscopic models, which explain how each vehicle behaves in function…
Affine Lie algebras, also sometimes called current algebras, are infinite-dimensional analogs of finite-dimensional semisimple Lie algebras. The representation theory of affine Lie algebras has applications in many areas of mathematics (number theory, combinatorics, group theory, geometry, topology, etc.) and physics (conformal field theory, integrable systems, statistical mechanics, etc.). To study the combinatorial properties of affine Lie algebra…
First, I will make a general introduction to vertex algebras. Then, I will mention some results of recent work with Bojko Bakalov on Logarithmic vertex algebras. Jointly in person in SAS 4201 or virtually on Zoom. The Zoom link is sent out to the Algebra and Combinatorics mailing list, please contact Corey Jones at cmjones6@ncsu.edu to…
A rank-revealing QR factorization (RRQR) of an mxn matrix A can be an efficient alternative to the singular value decomposition. Given 1≤k<n, the problem of computing an RRQR is selecting k linearly independent columns of A. In this talk, we discuss the RRQR and present an efficient two-staged randomized algorithm to compute one. We analyze…
A linear compartmental model is a linear ODE model which can be visualized by a directed graph. Identifiability is the study of determining whether a model's parameter values can be inferred from the defining "input-output equation" under perfect conditions. In this talk, I present a novel combinatorial formula for the computation of the coefficients of these…
We propose novel numerical methods for solving a class of high-order hyperbolic PDEs on general geometries, which involve 2nd-order derivatives in time and up-to 4th-order derivatives in space. These PDEs are widely used in modeling thin-walled elastic structures such as beams, plates and shells, etc. High-order spatial derivatives together with general geometries bring a number…
I will overview some important milestones in the development of the Invariant Theory from its classical times to modern days, leading into a discussion of the current progress in theory, computation, and applications. The highlights include Hilbert's basis theorem, geometric invariant theory, differential algebra of invariants, the moving frame approach, Lie's work on symmetries of…
In this talk we propose a model for the simulation of retinal prostheses based on the use of organic polymer nanoparticles (NP). The model consists of a nonlinearly coupled system of elliptic partial differential equations accounting for: (1) light photoconversion into free charged carriers in the NP bulk; (2) charge transport in the NP bulk…
We will prove lower bounds for the p-energies of mappings of real, complex and quaternionic projective spaces to arbitrary Riemannian manifolds. The equality cases of the results for real and complex projective space give strong characterizations of some families of energy-minimizing harmonic mappings of these spaces. If we have enough time, we will also describe…
We improve Cheeger's lower bound for the first nonzero eigenvalue of the Laplacian on compact Riemannian manifolds with Ricci curvature bounded from below. Zoom link: https://ncsu.zoom.us/j/8027642791?pwd=d1lNaWZyUW4zeUFvaTA5VmlsTWtjdz09
Are you a math undergrad or grad student and interested in doing an internship related to math? This event is for you! The Graduate Training Module for Friday, October 8th is titled, "What is an Internship?" and consists of a panel of current graduate students who have done several different types of internships, and are ready and…
We review randomized algorithms for the numerical solution of least squares/regression problems, with a focus on algorithms that row-sketch from the left, or column-sketch from the right. These algorithms tend to be efficient and accurate on matrices that have many more rows than columns. We present probabilistic bounds for the amount of sampling required to…
I will tell you about my dissertation work on two variants of stable Grothendieck polynomials and their combinatorics. Relevant combinatorial objects include crystals (edge-labelled directed digraphs from representation theory), tableaux (numbers in boxes with rules), decreasing factorizations (numbers in parentheses), and insertion algorithms (how to put numbers in boxes). Background in algebraic combinatorics is helpful…
We consider an optimal control problem subject to a poro-visco-elastic model with applications to fluid flows through biological tissues. Our goal is to optimize the fluid pressure and solid displacement using distributed or boundary control. We discuss an application of this problem to a tissue in the human eye. Previous literature on well- posedness of…
In this talk, I will present our recent numerical methodology studies for unsteady moving interface problems and applications to dynamic fluid-structure interaction (FSI) problems. Our numerical methodologies include the body-fitted mesh method (arbitrary Lagrangian−Eulerian (ALE) method), the body-unfitted mesh method (fictitious domain (FD) method), combining with the mixed finite element approximation, as well as the…
Broadly speaking, there are two classes of inverse problems — those that are concerned with the analysis of PDEs, and those that are geometric in nature. In this talk, I will introduce the audience to these classes by highlighting two classical examples: Calderón’s problem for the PDE setting, and the boundary rigidity problem in the…