立命館大学数理科学科

Math-Fi seminar on 17 Apr.

horie — Thu, 16 Apr 2026 07:41:03 +0000

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)

horie — Thu, 09 Apr 2026 06:15:09 +0000

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.

立命館大学集中セミナー

horie — Tue, 07 Apr 2026 02:34:38 +0000

Date: 9月14日－18日
Place: ウエストウィング6階談話会室あるいは７階のセミナー室　対面およびオンライン
Time:

9月14日(月)～17日 (木)

2コマ:

(1) 13:30～15:00

(2) 15:15～16:45

9月18日 (金)

1コマ13:30～15:00

Speaker : 日合文雄（東北大学名誉教授）
Title: 行列解析と量子情報への応用
Abstract:

この集中セミナーでは，最初に作用素平均と作用素パースペクティブを復習してから，作用素・

行列の作用素不等式，マジョリゼーション，トレース不等式などを解説する．次に，量子情報

で重要な種々の量子f-ダイバージェンスを説明する．特に最近発展しているホッケースチック

f-ダイバージェンスを取り上げる．さらに，量子情報幾何で重要なFisher 情報量（単調計量）

と関連するいくつかの話題を解説する．

Math-Fi seminar on 2 Apr.

horie — Tue, 07 Apr 2026 01:51:01 +0000

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.

horie — Tue, 07 Apr 2026 01:17:58 +0000

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.

horie — Fri, 27 Feb 2026 07:14:01 +0000

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- (modified on March 1)

15:20-16:20 Steven Hurder (University of Illinois at Chicago)

The dynamics of commensurators

16:30-17:30 Olga Lukina (Leiden University)

Cantor actions in dynamical systems

-Abstract-

Speaker 1: Steven 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.

horie — Tue, 10 Feb 2026 07:33:23 +0000

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].

立命館大学幾何学セミナー（2026年1月20日（火））

mathstaff — Fri, 16 Jan 2026 04:09:46 +0000

<<立命館大学幾何学セミナー>>

日時：2026年1月20日（火）16:45-20:00

プログラム：

16:45-18:00 講演

18:00-20:00 ディスカッション

講演者：松添博（名古屋工業大学）

題目：

推定関数の幾何学

概要：

情報幾何学は，確率測度の族を多様体とみなし，測度間の識別可能性などを計量や接続を用いて微分幾何学的に記述する理論である。

Fisher情報行列は自然な計量を与えるとともに，双対接続の導入により，最尤推定法をはじめとするさまざまな推定原理が幾何学的に記述される。

この枠組みを推定関数の立場から捉えると，推定関数は多様体上の接ベクトルに対応し，その選び方によって異なる推定方法が構成される。

本講演では，情報幾何学の基本的な考え方を概観したのち，推定関数の視点から情報幾何学における双対性などの構造について考察する。

開催方法：立命館大学びわこ・くさつキャンパス，ウェストウィング6階談話会室での対面開催．

講演の模様をZoomミーティングで配信する予定です．

講演へのオンライン参加をご希望の方は以下のリンクよりお申し込みください：

https://ritsumei-ac-jp.zoom.us/meeting/register/xaIT9RLfSymLnzxPx0Ig5g

登録された方にメールにてZoomミーティングに関する情報が届きます．

Math-Fi seminar on 15 January. (Co-organized as a Quantum Walk Seminar)

horie — Tue, 13 Jan 2026 04:03:00 +0000

Date: 15 Jan. (Thu.)

Place: West Wing, 6th floor, Colloquium Room and on the Web (zoom)

Time: 17:00-19:15

Speaker 1: Yuma Tamura（Ritsumeikan University）
Time:17:00-18:00
Title: Affine過程の表現公式と部分積分公式
Abstract:

本講演では，次の確率微分方程式で定義される拡散型のAffine processを扱う：

dX^x_t = \sqrt{ \alpha X^x_t } \,dW_t + ( \beta X^x_t + b )dt,\quad X^x_0=x.

ここで，$W$は$1$次元Brown運動であり，$ \alpha > 0 $, $ \beta \in \mathbf{R} $, $ b \ge 0 $は定数のパラメータである．Affine processのクラスは，代表的な金利モデルであるCox–Ingersoll–Ross (CIR)モデルを含むため，数理ファイナンスにおいて重要である．

本研究では，テスト関数$f$に対し，期待値の初期値$x$による微分

\partial_x E[ f(X^x_T) ]

の表現公式および部分積分公式を導出する．特に前者は，数理ファイナンスにおける「オプションのデルタ」に対応し，実務的な応用可能性を持つ．

また，本講演ではこれらの公式の発見の端緒となったsquared Bessel processに関する考察についても述べる．

さらに，学生に向けて，最初にsquared Bessel processの基本事項の解説も行う予定である．

なお，本講演の内容はArturo Kohatsu-Higa氏（立命館大学）との共同研究に基づく．

Speaker 2: Takuya Nakagawa (Ritsumeikan University)
Time:18:15-19:15
Title: $L^{\alpha-1}$ distance between two one-dimensional stochastic differential equations with drift terms driven by a symmetric $\alpha$-stable process
Abstract:

This paper develops a quantitative stability theory for one-dimensional SDEs with non-zero drift and time-dependent coefficients, driven by a symmetric $\alpha$-stable process for $\alpha\in(1,2)$. We establish the first explicit convergence rates for this broad class. Our main result is a H\”older-type estimate for the $L^{\alpha-1}(\Omega)$ distance between two solution paths, which quantifies stability with respect to the initial values and coefficients. In this estimate, the distance between coefficients is measured by a weighted integral norm constructed from the transition probability density of one of the solutions. The proof is based on a refined analysis of a mollified auxiliary function, for which we establish a new, sharper derivative estimate to control the drift terms.

Random topics on Teichmüller theory

horie — Thu, 08 Jan 2026 05:45:59 +0000

“Random topics on Teichmüller theory”

日時：2026年1月28日(水)～ 2026年1月29日(木)

場所：立命館大学びわこくさつキャンパス　ウエストウイング6階　談話会室

詳細はこちら

https://sites.google.com/view/rtt4-2026/home