Seminars

Math-Fi seminar on 26 Mar.

2020.04.09 Thu up
  • Date: 26 Mar. (Thu.)
  • Place: On the Web
  • Time: 16:30-18:00
  • Speaker: Shin Harase (Ritsumeikan University)
  • Title: マルコフ連鎖モンテカルロ（MCMC）法の準モンテカルロ法化

Math-Fi seminar on 27 Feb.

2020.02.07 Fri up
  • Date: 27 Feb. (Thu.)
  • Place: W.W. 6th-floor, Colloquium Room
  • Time: 16:30-18:00
  • Speaker: Pierre Bras (École normale supérieure Paris)
  • Title: Bayesian inference and Metropolis-Hastings algorithms (provisional title)
  • Abstract:
​Markov chains Monte Carlo (MCMC) methods are simulation methods for sampling from a probability distribution from which direct sampling is difficult, and are particulary used in bayesian learning. The Metropolis-Hastings algorithm is one of the most popular. I will present the algorithm, then prove convergence results, and present the adaptation of the algorithm to stochastic optimization problems. Please come and join us.
 

Math-Fi seminar on 13 Feb.

2020.02.07 Fri up
  • Date: 13 Feb. (Thu.)
  • Place: W.W. 6th-floor, Colloquium Room
  • Time: 16:30-18:00
  • Speaker: Pierre Bras (École normale supérieure Paris)
  • Title: Stochastic optimization and neural networks
  • Abstract: 
Stochastic algorithms aim to solve optimization problems by randomly exploring the state space. They appear in machine learning and in financial mathematics, and are the main tool used for calibrating neural networks. I will demonstrate some convergence properties, and present the gradient descent in the framework of neural networks.
 

Math-Fi seminar on 17 Jan.

2020.01.14 Tue up
  • Date: 17 Jan. (Fri.)
  • Place: W.W. 6th-floor, Colloquium Room
  • Time: 16:30-18:40


  • First Speaker: Yushi Hamaguchi (Kyoto University)
  • Time: 16:30-17:30
  • Title: Time-inconsistent consumption-investment problems in incomplete markets
 
  • Second Speaker: Yuki Ueda (Hokkaido University) 
  • Time: 17:40-18:40
  • Title: Introduction to free probability theory and infinitely divisible distributions

Math-Fi seminar on 9 Jan.

2020.01.07 Tue up
  • Date: 9 Jan. (Thu.)
  • Place: W.W. 6th-floor, Colloquium Room
  • Time: 16:00-19:00


  • First Speaker: Katsushi Nakajima (Ritsumeikan Asia Pacific University)
  • Time: 16:00-17:30
  • Title: TBA

  • Second Speaker: Koya Sakakibara (Kyoto University)
  • Time: 17:30-19:00
  • Title: Numerical analysis of interface problem
  • Abstract:
​ The interface appears in several problems, such as fluid dynamics between two different liquids. To study its evolution and dynamics forms the basis of the research in natural science. Although there are several mathematical studies for interfacial phenomena, they are, in general, so difficult, and numerical study becomes an essential tool in this field.
 In this talk, I will talk about the numerical analysis of interface problem, and especially consider two issues: The Hele-Shaw problem and grain boundary. The Hele-Shaw problem describes the motion of viscous fluid in a quasi-two-dimensional space, which started from a short paper by Henry Selby Hele-Shaw (1854–1941). It is now recognized as a basic mathematical model to study the fingering phenomena (also known as the Saffman–Taylor instability), and several researchers have studied this problem; however, there are still several open questions. A problem on the grain boundary appears in the field of material science. A grain boundary is an interface between two grains, or crystallites, in a polycrystalline material. It is the two-dimensional defect in the crystal structure. The study of grain boundaries and their effects on the mechanical, electrical, and other properties of materials forms an essential topic in material science. My study aims to understand the mechanism of grain boundaries from mathematical and numerical points of view.
 In the first half of this talk, I will explain this problem and construct some efficient numerical scheme based on the method of fundamental solutions and the asymptotic uniform distribution method. I will also briefly survey the geometric numerical integration, which aims to construct a numerical scheme which inherits properties of the original problem in some discrete sense. In the second half of this talk, I will move on to the problem on grain boundaries and consider manifold-valued total variation flows. I will introduce spatially discretized total variation flow and construct a numerical scheme using the exponential map of the manifold. I will also present an energy dissipation property and convergence result.

Ritsumeikan University Geometry Seminar (16/December/2019)

2019.12.10 Tue up
<<Ritsumeikan University Geometry Seminar>>

Date: 16/December/2019, Monday, 16:30-18:00

Title: Semitoric systems in geometry and dynamics

Speaker: Sonja Hohloch (University of Antwerp)

Abstract: PDF-file

Room: Ritsumeikan University, Biwako-Kusatsu Campus, Westwing, 6th floor, Colloquium Room

Ritsumeikan University Geometry Seminar (09/December/2019)

2019.12.04 Wed up
<<Ritsumeikan University Geometry Seminar>>

Date: 09/December/2019, Monday, 16:30-17:30

Title: BV structures on moduli spaces of flat connections

Speaker: Pavol Severa （University of Geneva）

Abstract:
Loops (or rather their homotopy classes) on an oriented surface form a Lie algebra, originally discovered by Goldman.The Lie bracket is given by a simple formula involving intersection points of two loops. This Lie algebra can be interpreted as the Poisson bracket on a moduli space of flat connections (given by the famous Atiyah-Bott symplectic form), if to each loop we assign the trace of the holonomy along the loop. Loops come also with another operation, a Lie cobracket discovered by Turaev, given by a very similar formula. I will explain what is the corresponding geometric structure on the moduli space. I will also try to explain why this structure is interesting and how it relates to the Kashiwara-Vergne problem in Lie theory. Based on a joint work in progress with Anton Alekseev, Florian Naef, and Jan Pulmann.

Room: Ritsumeikan University, Biwako-Kusatsu Campus, Westwing 6th floor, Colloquium Room.

Ritsumeikan Geometry Seminar

2019.10.24 Thu up
Date: 2 December (Mon) 16:20-17:50
Place: Colloquium Room, West-Wing 6th floor, Biwako-Kusatsu Campus, Ritsumeikan University
Speaker: Jesús Antonio Álvarez López (University of Santiago de Compostela)
Title: Topological Molino’s theory
Abstract: (joint work with Ramón Barral Lijó and Manuel Moreira Galicia) Molino’s description of Riemannian foliations on compact manifolds is generalized to the setting of compact equicontinuous foliated spaces, in the case where the leaves are dense. In particular, a structural local group is associated to such a foliated space. As applications, we obtain a partial generalization of results by Carrière and Breuillard-Gelander, relating the structural local group to the growth of the leaves, and a description of foliated homogeneous spaces.

Ritsumeikan Geometry Seminar

2019.10.23 Wed up
Place: Colloquium Room, West-Wing 6th floor, Biwako-Kusatsu Campus, Ritsumeikan University
Speaker: Olga Lukina (University of Vienna)

Talk 1

Date: 25 November (Mon) 16:20-17:50
Title: Introduction to group actions on Cantor sets
Abstract: In this talk, we consider basic tools and properties which we use in the subsequent talks to study minimal equicontinuous group actions on Cantor sets. The tools include chains of finite index subgroups. An important property is the local quasi-analyticity of an action, introduced by Alvarez Lopez and Candel. We illustrate the concepts and methods using examples.

Talk 2

Date: 28 November (Thu) 10:40-12:10
Title: Invariants of Cantor group actions
Abstract: In this talk, we consider two direct limit invariants which can be associated to a Cantor group action, introduced in a recent joint work with Steve Hurder, and the corresponding classification of Cantor group actions. It is recommended that the participants attend Talk 1 as a preparation for this talk.

Math-Fi seminar on 10 Oct.

2019.10.07 Mon up
  • Date: 10 Oct. (Thu.) 
  • Place: W.W. 6th-floor, Colloquium Room 
  • Time: 16:30-18:00 
  • Speaker: Dan Crisan (Imperial College London) 
  • Title: second lecture 

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