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Math-Fi seminar on 21 May.

2026.05.21 Thu up

Date: 21 May. (Thu.)
Place: West Wing, 6th floor, Colloquium Room and on the Web (zoom)
Time: 16:50-18:20
Speaker : Naoki Masuda (University of Michigan)
Title: 高次ネットワーク上の意見形成確率モデル
Abstract:

本講演では、まず、ネットワーク科学という研究分野の簡単な紹介を行う。次に、いくつかの種類の高次ネットワーク上の進化ダイナミクスの研究について紹介する。進化ダイナミクスは、本研究の範囲で言えば、平たく言うと、集団意見形成ダイナミクスを表す確率過程である。高次ネットワークとしては、近年のネットワーク科学で盛んに研究されている構造でもあるハイパーグラフ、多層ネットワーク、テンポラル（＝ネットワーク自体が時間変化する）・ネットワークを考える。（逆に、高次でないネットワークは、典型的なネットワーク、すなわち数学で言う「グラフ」のことを表す。）これらの高次ネットワーク上での上記確率過程の振る舞いは、典型的なネットワークの上での同じ確率過程と比べてかなり異なる。具体的には、ネットワークが進化の「増幅器」でありやすいか、「抑制器」でありやすいか、が異なる。このことを、マルチンゲール解析、数値計算などによって示す。

Math-Fi seminar on 14 May.

2026.05.14 Thu up

Date: 14 May. (Thu.)
Place: West Wing, 6th floor, Colloquium Room and on the Web (zoom)
Time: 16:50-18:20
Speaker : Alessio Rondelli ((University of Bologna)
Title: McKean-Vlasov SDEs and particle systems: What, Why and How.
Abstract:

McKean-Vlasov SDEs are a class of Stochastic Differential Equations

where the coefficients depend upon the marginals of the solution. Their

study is justified by their usefulness in modeling the evolution of

multi-agent systems using the mean-field approximation. Both classical

and modern techniques are presented for strong and weak well-posedness

and the concept of propagation of chaos gets explored.

Math-Fi seminar on 23 Apr. (Co-organized as a Quantum Walk Seminar)

2026.04.23 Thu up

Date: 23 Apr. (Thu.)
Place: West Wing, 6th floor, Colloquium Room and on the Web (zoom)
Time: 16:50-17:50
Speaker : Hiromichi OHNO (Shinshu University)
Title: Maze solving by quantum walk
Abstract:

本講演では，グラフを迷路に見立て，スタートとゴールを設定し，グローバーウォークを用いてスタートからゴールまでの経路を発見するアルゴリズムについて解説する．このアルゴリズムでは，量子ウォークの収束することは示せているが，収束先の確率分布から経路を発見できるかどうかは部分的な解答しか得られていない．これらの内容について数学的な証明を与えながら，具体的ないくつかの例を紹介する．

Math-Fi seminar on 17 Apr.

2026.04.16 Thu up

Date: 17 Apr. (Thu.)
Place: West Wing, 6th floor, Colloquium Room and on the Web (zoom)
Time: 16:20-17:50
Speaker : Antoine Jacquier (Imperial College)
Title: Quantum Computing, a new toolbox for Stochastic Analysis & Machine Learning?
Abstract:

We are interested here in recent developments in Quantum Computing from an algorithmic standpoint and with a view towards applications (with an emphasis on Mathematical Finance and Stochastic Analysis). We shall in particular focus on Universal Approximations theorems for Parameterised Quantum Circuits as well as on the links between (partial) measurements of Quantum systems and Stochastic diffusions.

Math-Fi seminar on 9 Apr. (Co-organized as a Quantum Walk Seminar)

2026.04.09 Thu up

Date: 9 Apr. (Thu.)
Place: West Wing, 6th floor, Colloquium Room and on the Web (zoom)
Time: 16:50-17:50
Speaker : Yohei Tanaka (Ritsumeikan University)
Title: On understanding chiral unitaries via real parts
Abstract:

We study unitary operators with chiral symmetry, that is, unitary operators associated with a fixed involution. Such operators naturally arise in the study of quantum walks and related areas. A standard approach is to decompose the underlying Hilbert space according to this symmetry, which leads to a convenient block representation. In this framework, we focus on the real part of the unitary and use it as a useful tool to understand its spectral structure. Based on this viewpoint, we present several related topics and results, illustrating how the real-part perspective provides a simple and unified way to analyze chiral unitaries.

Ritsumeikan University Seminar

2026.04.07 Tue up

Date: 14 Sep-18 Sep
Place: West Wing, 6th floor, Colloquium Room or 7th floor seminar room and on the Web (zoom)
Time:

14 Sep-17 Sep
(1) 13:30～15:00
(2) 15:15～16:45
18 Sep
13:30～15:00

Speaker : Fumio Hiai (Tohoku University)
Title: Matrix analysis and applications to quantum information
Abstract:

In this intensive seminar, we begin by reviewing operator means and operator perspectives,

followed by explanations of operator inequalities, majorization, and trace inequalities for operators

and matrices. Next, we explain various quantum f-divergences that are important in

quantum information, including the recently developed hockey-stick f-divergence. Furthermore,

we discuss several topics related to the Fisher information (the monotonic metric) that

is important in quantum information geometry.

Math-Fi seminar on 2 Apr.

2026.04.07 Tue up

Date: 2 Apr. (Thu.)
Place: West Wing, 6th floor, Colloquium Room and on the Web (zoom)
Time: 12:00-13:30
Speaker : VU HUY HOANG (University of California, Santa Barbara)
Commentator : Ju-Yi Yen (University of Cincinnati)
Title: Molchanov’s Formula and Quantum Walks: A Probabilistic Approach
Abstract:

This paper establishes a robust link between quantum dynamics and classical ones by deriving a probabilistic representation for both continuous-time and discrete-time quantum walks. We first adapt the Molchanov formula, originally employed in the study of Schrodinger operators on multidimensional integer lattices, to characterize the evolution of continuous time quantum walks. Extending this framework, we develop a probabilistic method to represent discrete time quantum walks on an infinite integer line, bypassing the locality constraints that typically inhibit direct application of the Molchanov formula. The validity of our representation is empirically confirmed through a benchmark analysis of the Hadamard walk, demonstrating high fidelity with traditional unitary evolution. Our results suggest that this probabilistic lens offers a powerful alternative for learning multidimensional quantum walks and provides new analytical pathways for investigating quantum systems via classical stochastic processes.

Math-Fi seminar on 31 Mar.

2026.04.07 Tue up

Date: 31 Mar. (Tue.)
Place: West Wing, 6th floor, Colloquium Room and on the Web (zoom)
Time: 16:00–17:30
Speaker : Joseph Najnudel (University of Bristol)
Commentator : Ju-Yi Yen (University of Cincinnati)
Title: The Riemann zeta function and its connection with random matrix theory.
Abstract:

In this talk, we present some results and conjectures on the Riemann zeta function, its moments on the critical line, its extreme values, and its behaviour at the scale of the average spacing of the zeros. We then connect these results to similar properties satisfied by the characteristic polynomial of random unitary matrices.

Ritsumeikan Geometry Seminar on 13 Mar.

2026.02.27 Fri up

Date: March 13, Friday, 2026

Place: Colloquium room, West-Wing 6F, Biwako-Kusatsu Campus + Zoom meeting

Registration URL for Zoom:

https://ritsumei-ac-jp.zoom.us/meeting/register/A90nnMv0RNC7PFizhntG_w

-Program-

15:20-16:20 Olga Lukina (Leiden University)

Cantor actions in dynamical systems

16:30-17:30 Steven Hurder (University of Illinois at Chicago)

The dynamics of commensurators

-Abstract-

Speaker 1: Steve Hurder (University of Illinois at Chicago)
Title: The dynamics of commensurators
Abstract:

A commensurator of a countable group G is a virtual automorphism. That is, it is an isomorphism f : H -> K where H and K are subgroups of finite index of G. We associate to a commensurator f of G, a homeomorphism F : C -> C of a Cantor set C. In the general case the space C is the profinite completion of G, but our interest is in more general case where C is a quotient of the profinite completion of G. We study the dynamical properties of the map F : C -> C.

Speaker 2: Olga Lukina (Leiden University)
Title: Cantor actions in dynamical systems
Abstract:

In this talk, we consider dynamical systems on Cantor sets, given by group actions. Such systems arise as transverse dynamical systems in strange attractors and exceptional minimal sets of foliations. We present a few classification results.

Organizers:

Fukumoto Yoshihiro, Tarama Daisuke, Nozawa Hiraku

Contact:

hnozawa@fc.ritsumei.ac.jp

Math-Fi seminar on 12 Feb.

2026.02.10 Tue up

Date: 12 Feb. (Thu.)
Place: West Wing, 6th floor, Colloquium Room and on the Web (zoom)
Time: 16:00–17:30
Speaker : George Yin (University of Connecticut)
Title: Stochastic Approximation and Applications
Abstract:

We will give an introduction to stochastic approximation

methods. It will begin with a discussion on what stochastic approximation is and

what problems can be solved by using stochastic approximation methods. The RM and KW algorithms will be introduced. An overview of the analysis (including convergence, rates of convergence, weak convergence, efficiency, as well as time-varying parameter problems, and tracking algorithms etc.) is provided. Several application examples will be mentioned.

A reference for the talk is the book by H.J. Kushner and G. Yin,

Stochastic Approximation and Recursive Algorithms and Applications, 2nd Edition,

Springer-Verlag, New York, 2003, [Applications of Mathematics, Volume 35].