Seminars and Colloquia by Series

Friday, April 20, 2018 - 10:00 , Location: Skiles 006 , Jose Acevedo , Georgia Tech , Organizer: Kisun Lee
In this talk we show how to obtain some (sometimes sharp) inequalities between subgraph densities which are valid asymptotically on any sequence of finite simple graphs with an increasing number of vertices. In order to do this we codify a simple graph with its edge monomial and establish a nice graphical notation that will allow us to play around with these densities.  
Friday, April 13, 2018 - 10:00 , Location: Skiles 006 , Tim Duff , Georgia Tech , Organizer: Kisun Lee
The fundamental data structures for numerical methods in algebraic geometry are called "witness sets." The term "trace test" refers to certain numerical methods which verify the completeness of such witness sets. It is natural to ask questions about the complexity of such a test and in what sense its output may be regarded as "proof." I will give a basic exposition of the trace test(s) with a view towards these questions
Friday, April 6, 2018 - 10:00 , Location: Skiles 006 , Jaewoo Jung , Georgia Tech , jaewoojung@gatech.edu , Organizer: Kisun Lee
H. Dao, C. Huneke, and J. Schweig provided a bound of the regularity of edge-ideals in their paper “Bounds on the regularity and projective dimension of ideals associated to graphs”. In this talk, we introduced their result briefly and talk about a bound of the regularity of Stanley-Reisner ideals using similar approach.
Friday, March 30, 2018 - 10:00 , Location: Skiles 006 , Jaewoo Jung , Georgia Tech , Organizer: Kisun Lee
One way to analyze a module is to consider its minimal free resolution and take a look its Betti numbers. In general, computing minimal free resolution is not so easy, but in case of some certain modules, computing the Betti numbers become relatively easy by using a Hochster's formula (with the associated simplicial complex. Besides, Mumford introduced Castelnuovo-Mumford regularity. The regularity controls when the Hilbert function of the variety becomes a polynomial. (In other words, the regularity represents how much the module is irregular). We can define the regularity in terms of Betti numbers and we may see some properties for some certain ideals using its associated simplicial complex and homology. In this talk, I will review the Stanley-Reisner ideals, the (graded) betti-numbers, and Hochster's formula. Also, I am going to introduce the Castelnuovo-Mumford regularity in terms of Betti numbers and then talk about a useful technics to analyze the Betti-table (using the Hochster's formula and Mayer-Vietories sequence).
Friday, March 16, 2018 - 10:00 , Location: Skiles 006 , Kisun Lee , Georgia Tech , klee669@gatech.edu , Organizer: Kisun Lee
Expanding the topic we discussed on last week, we consider the way to certify roots for system of equations with D-finite functions. In order to do this, we will first introduce the notion of D-finite functions, and observe the property of them. We also suggest two different ways to certify this, that is, alpha-theory and the Krawczyk method. We use the concept of majorant series for D-finite functions to apply above two methods for certification. After considering concepts about alpha-theory and the Krawczyk method, we finish the talk with suggesting some open problems about these.
Friday, March 9, 2018 - 10:00 , Location: Skiles 006 , Kisun Lee , Georgia Tech , klee669@gatech.edu , Organizer: Kisun Lee
This is an intoductory talk for the currently using methods for certifying roots for system of equations. First we discuss about alpha-theory which was constructed by Smale and Shub, and explain how this theory could be modified in order to apply in actual problems. In this step, we point out that alpha theory is still restricted only into polynomial systems and polynomial-exponential systems. After that as a remedy for this problem, we will introduce an interval arithmetic, and the Krawczyk method. We will end the talk with a discussion about how these current methods could be used in more general setting.
Friday, March 2, 2018 - 10:00 , Location: Skiles 254 , Marcel Celaya , Georgia Tech , mcelaya@gatech.edu , Organizer: Kisun Lee
In this talk we will discuss the paper of Adiprasito, Huh, and Katz titled "Hodge Theory for Combinatorial Geometries," which establishes the log-concavity of the characteristic polynomial of a matroid.
Friday, February 23, 2018 - 10:00 , Location: Skiles 006 , Tim Duff , Georgia Tech , tduff3@gatech.edu , Organizer: Kisun Lee
Polyhedral homotopy methods solve a sparse, square polynomial system by deforming it into a collection of square "binomial start systems." Computing a complete set of start systems is generally a difficult combinatorial problem, despite the successes of several software packages. On the other hand, computing a single start system is a special case of the matroid intersection problem, which may be solved by a simple combinatorial algorithm. I will give an introduction to polyhedral homotopy and the matroid intersection algorithm, with a view towards possible heuristics that may be useful for polynomial system solving in practice.
Friday, February 23, 2018 - 10:00 , Location: Skiles 006 , Tim Duff , Georgia Tech , tduff3@gatech.edu , Organizer: Kisun Lee
TBA
Friday, February 16, 2018 - 10:10 , Location: Skiles 006 , Libby Taylor , Georgia Tech , libbyrtaylor@gmail.com , Organizer: Kisun Lee
Algebraic geometry has a plethora of cohomology theories, including the derived functor, de Rham, Cech, Galois, and étale cohomologies.  We will give a brief overview of some of these theories and explain how they are unified by the theory of motives.  A motive is constructed to be a “universal object” through which all cohomology theories factor.  We will motivate the theory using the more familiar examples of Jacobians of curves and Eilenberg-Maclane spaces, and describe how motives generalize these constructions to give categories which encode all the cohomology of various algebro-geometric objects.  The emphasis of this talk will be on the motivation and intuition behind these objects, rather than on formal constructions.

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