## 過去の記録

### 2020年12月21日(月)

#### 複素解析幾何セミナー

10:30-12:00   オンライン開催
Martin Sera 氏 (京都先端科学大学)
On a mixed Monge-Ampère operator for quasiplurisubharmonic functions
[ 講演概要 ]
This reports on a joint work with R. Lärkäng and E. Wulcan. We consider mixed Monge-Ampère products of quasiplurisubharmonic functions with analytic singularities (introduced in a previous work with H. Raufi additionally). These products have the advantage that they preserve mass (a property which is missing for non-pluripolar products).
The main result of the work presented here is that such Monge-Ampère products can be regularized as explicit one parameter limits of mixed Monge-Ampère products of smooth functions, generalizing a result of Andersson-Błocki-Wulcan. We will explain how the theory of residue currents, going back to Coleff-Herrera, Passare and others, plays an important role in the proof.
As a consequence, we get an approximation of Chern and Segre currents of certain singular hermitian metrics on vector bundles by smooth forms in the corresponding Chern and Segre classes.
[ 参考URL ]
https://zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

### 2020年12月18日(金)

#### 談話会・数理科学講演会

15:30-16:30   オンライン開催

Hilbertの証明論 (JAPANESE)
[ 講演概要 ]

[ 参考URL ]
https://forms.gle/Nmi1KieFDjhchdU69

### 2020年12月17日(木)

#### 東京名古屋代数セミナー

16:00-17:30   オンライン開催
オンライン開催の詳細は下記URLをご覧ください。
Xiao-Wu Chen 氏 (University of Science and Technology of China)
The finite EI categories of Cartan type (English)
[ 講演概要 ]
We will recall the notion of a finite free EI category introduced by Li. To each Cartan triple, we associate a finite free EI category, called the finite EI category of Cartan type. The corresponding category algebra is isomorphic to the 1-Gorenstein algebra, introduced by Geiss-Leclerc-Schroer, that is associated to possibly another Cartan triple. The construction of the second Cartan triple is related to the well-known unfolding of valued graphs. We will apply the obtained algebra isomorphism to re-interpret some tau-locally free modules as induced modules over a certain skew group algebra. This project is joint with Ren Wang.
[ 参考URL ]
http://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html

#### 情報数学セミナー

14:55-18:35   オンライン開催
URLは高島克幸氏と藤原洋氏のご講演では異なります

[ 講演概要 ]

[ 参考URL ]

AIの機械学習における分類とクラスタリング (Japanese)
[ 講演概要 ]
今回は、教師あり学習の「分類」の中から、ロジスティック回帰と近傍法について述べる。ニューラルネットワークと共に、機械学習のアルゴリズムの基本が、ディープラーニングを究めるために重要であるため、その基礎について述べる。
次に、教師なし学習としてのクラスタリングを取り上げ、アルゴリズムの例をとしては、k平均法と混合ガウス分布を取り上げる。
さらに、次元の呪い、次元削減の1つの方法としての主成分分析について触れる。
最後に、ニューラルネットワークからディープラーニングへの手順について述べた後、AIの実用例として、メディア、医療、交通渋滞予測、介護現場の省力化の例を示す。
[ 参考URL ]
https://forms.gle/Uhy8uBujZatjNMsGA

### 2020年12月16日(水)

#### 代数学コロキウム

17:00-18:00   オンライン開催

Rigid analytic Hyodo--Kato theory with syntomic coefficients (Japanese)
[ 講演概要 ]
The Hyodo—Kato theory is the study of comparison between Hyodo—Kato cohomology and de Rham cohomology associated to semistable schemes over complete discrete valuation rings of mixed characteristic $(0,p)$.
In this talk, we will give a rigid analytic reconstruction of Hyodo—Kato theory and study coefficients of cohomology.
Our construction is useful for explicit computation and treatment of base extension, because it gives us a natural interpretation of the dependence of Hyodo—Kato theory on the choice of a branch of the $p$-adic logarithm.
The results of this talk are based on a joint work with Veronika Ertl, which deals with the case of trivial coefficient.

#### 統計数学セミナー

14:30-16:00   数理科学研究科棟(駒場) Zoom号室

Parthanil Roy 氏 (Indian Statistical Institute, Bangalore)
How to tell a tale of two tails? (ENGLISH)
[ 講演概要 ]
Asia-Pacific Seminar in Probability and Statistics https://sites.google.com/view/apsps/home

Branching random walk is a system of growing particles that starts with one particle. This particle branches into a random number of particles, and each new particle makes a random displacement independently of each other and of the branching mechanism. The same dynamics goes on and gives rise to a branching random walk. This model arises in statistical physics, and has connections to various probabilistic objects, mathematical biology, ecology, etc. In this overview talk, we shall discuss branching random walks and their long run behaviour. More precisely, we shall try to answer the following question: if we run a branching random walk for a very long time and take a snapshot of the particles, how would the system look like? We shall investigate how the tails of the progeny and displacement distributions change the answer to this question.
This talk is based on a series of joint papers with Ayan Bhattacharya, Rajat Subhra Hazra, Krishanu Maulik, Zbigniew Palmowski, Souvik Ray and Philippe Soulier.
[ 参考URL ]

### 2020年12月15日(火)

#### 数値解析セミナー

16:30-18:00   オンライン開催
Ming-Cheng Shiue 氏 (National Chiao Tung University)
Iterated pressure-correction projection methods for the 2d Navier-Stokes equations based on the scalar auxiliary variable approach (English)
[ 講演概要 ]
In this talk, the first-order iterated pressure-correction projection methods based on the scalar auxiliary variable approach is proposed and studied for the 2d Navier-Stokes equations and Boussinesq equations.
In the literature, enormous amounts of work have contributed to the study of numerical schemes for computing the Navier-Stokes equations. In general, two of the main numerical difficulties for solving Navier-Stokes equations are the incompressible condition and the nonlinear term. One of the approaches to deal with the incompressible condition is the so-called projection. The typical projection method only needs to solve the Poisson type of equations depending on the nonlinear term's treatment, which is efficient. However, the pressure-correction projection methods suffer from the splitting error, leading to spurious numerical boundary layers and the limitation of accuracy in time. In the literature, an iterated pressure-correction projection method has been proposed to overcome the difficulty.
As for the nonlinear term treatment, it is better to treat the nonlinear term explicitly so that one only requires to solve the corresponding linear system with constant coefficients at each time step. However, such treatment often results in a restricted time step due to the stable issue. Recently, the scalar auxiliary variable approach has been constructed to have an unconditional energy stable numerical scheme.
In this work, a new iterated pressure-correction projection method based on the scalar auxiliary variable's simple choice is proposed. We find that this new scheme can enjoy two properties, including reducing the splitting errors and having unconditional energy stability. The proofs of the energy stability and error convergence are provided and analyzed. Finally, numerical examples are provided to illustrate the theoretical work. This is joint work with Tony Chang.
[ 参考URL ]
https://forms.gle/y7w2nmaYtHNeoDSn8

#### トポロジー火曜セミナー

17:00-18:00   オンライン開催

Braids, triangles and Lissajous curve (JAPANESE)
[ 講演概要 ]
The purpose of this talk is to introduce Lissajous 3-braids. Suppose we have a closed curve on the plane, and we consider the periodic motion of n points along the closed curve. If the motion is collision-free, then we get a braid obtained from the trajectory of the set of n points in question. In this talk, we consider 3-braids coming from the periodic motion of 3 points on Lissajous curves. We classify Lissajous 3-braids and present a parametrization in terms of natural numbers together with slopes. We also discuss some properties of pseudo-Anosov stretch factors for Lissajous 3-braids. The main tool is the shape sphere --- the configuration space of the oriented similarity classes of triangles. This is a joint work with Hiroaki Nakamura and Hiroyuki Ogawa.
[ 参考URL ]
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html

### 2020年12月14日(月)

#### 複素解析幾何セミナー

10:30-12:00   オンライン開催

On Levi flat hypersurfaces with transversely affine foliation
[ 講演概要 ]
In this talk, we discuss the classification problem of Levi flat hypersurfaces in complex surfaces by restricting ourselves to the case that the Levi foliation is transversely affine. After presenting known examples, we give a proof for the non-existence of real analytic Levi flat hypersurface whose complement is 1-convex and Levi foliation is transversely affine in a compact Kähler surface. This is a joint work with Severine Biard (arXiv:2011.06379).
[ 参考URL ]
https://zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

### 2020年12月10日(木)

#### 作用素環セミナー

16:45-18:15   オンライン開催
Gabor Szabo 氏 (KU Leuven)
Towards an equivariant Kirchberg-Phillips theorem (English)
[ 参考URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

#### 東京名古屋代数セミナー

16:30-18:00   オンライン開催
オンライン開催の詳細は下記URLをご覧ください。

Subcategories of module/derived categories and subsets of Zariski spectra (Japanese)
[ 講演概要 ]
The classification problem of subcategories has been well considered in many areas. This problem is initiated by Gabriel in 1962 by giving a classification of localizing subcategories of the module category Mod R via specialization-closed subsets of the Zariski spectrum Spec R for a commutative noetherian ring. After that several authors tried to generalize this result in many ways. For example, four decades later, Krause introduced the notion of coherent subsets of Spec R and used it to classify wide subcategories of Mod R. In this talk, I will introduce the notions of n-wide subcategories of Mod R and n-coherent subsets of Spec R for a (possibly infinite) non-negative integer n. I will also introduce the notion of n-uniform subcategories of the derived category D(Mod R) and prove the correspondences among these classes. This result unifies/generalizes many known results such as the classification given by Gabriel, Krause, Neeman, Takahashi, Angeleri Hugel-Marks-Stovicek-Takahashi-Vitoria. This talk is based on joint work with Ryo Takahashi.
[ 参考URL ]
http://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html

#### 情報数学セミナー

16:50-18:35   オンライン開催

[ 講演概要 ]

世界的ネットワーク機器企業とサイバーセキュリティの最もホットな話題であるスタートアップ企業が、「誰も信用しないゼロトラストネットワーク」に注力している。
そこで、本講では、自動車会社サプライチェーンへのサイバー攻撃の本質と、シスコシステムズとサイバーセキュリティベンチャー企業（ SentinelOne社 とStackPath社）の動向とその技術について概観する。
[ 参考URL ]
https://forms.gle/Uhy8uBujZatjNMsGA

### 2020年12月09日(水)

#### 離散数理モデリングセミナー

17:00-18:30   オンライン開催
Zoomを用いてオンラインで行います．参加希望の方はウィロックスまでZoomのリンクをお尋ねください．
Anton DZHAMAY 氏 (University of Northern Colorado)
Gap probabilities in the Laguerre unitary ensemble and discrete Painlevé equations (English)
[ 講演概要 ]
We use Sakai’s geometric theory of discrete Painlevé equations to study a recurrence relation that can be used to generate ladder operators for the Laguerre unitary ensemble. Using a recently proposed identification procedure for discrete Painlevé equations we show how this recurrence can be transformed into one of the standard equations on the affine D5-algebraic surface. This is a joint work with Yang Chen and Jie Hu.

### 2020年12月08日(火)

#### トポロジー火曜セミナー

17:30-18:30   オンライン開催

The intersection polynomials of a virtual knot (JAPANESE)
[ 講演概要 ]
We define two kinds of invariants of a virtual knot called the first and second intersection polynomials. The definition is based on the intersection number of a pair of curves on a closed surface. We study several properties of the polynomials. By introducing invariants of long virtual knots, we give connected sum formulae of the intersection polynomials, and prove that there are infinitely many connected sums of any two virtual knots as an application. Furthermore, by studying the behavior under a crossing change, we show that the intersection polynomials are finite type invariants of order two, and find an invariant of a flat virtual knot derived from the the intersection polynomials. This is a joint work with R. Higa, T. Nakamura, and Y. Nakanishi.
[ 参考URL ]
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html

### 2020年12月03日(木)

#### 東京名古屋代数セミナー

16:00-17:30   オンライン開催
オンライン開催の詳細は下記URLをご覧ください。

Full strong exceptional collections for invertible polynomials of chain type
[ 講演概要 ]
Constructing a tilting object in the stable category of graded maximal Cohen-Macaulay modules over a given graded Gorenstein ring is an important problem in the representation theory of graded Gorenstein rings. For a hypersurface S/f in a graded regular ring S, this problem is equivalent to constructing a tilting object in the homotopy category of graded matrix factorizations of f. In this talk, we discuss this problem in the case when S is a polynomial ring, f is an invertible polynomial of chain type and S has a rank one abelian group grading (called the maximal grading of f), and in this case we show the existence of a tilting object arising from a full strong exceptional collection. This is a joint work with Genki Ouchi.
[ 参考URL ]
http://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html

#### 情報数学セミナー

16:50-18:35   オンライン開催

PC-LAN攻防史・フリンの分類・量子ゲートの実際 (Japanese)
[ 講演概要 ]
コンピュータ間を高速で構内接続するLAN技術の進化は、激しい競争と共に起こったことが歴史に残っている。また、コンピュータ高速化は、コンピュータアーキテクチャの研究によって、大きく前進した。さらに、古典コンピュータを超える可能性が示されている量子ゲート式の量子コンピュータが、実際に試作され始めている。
そこで、本講では、 PC-LAN攻防史、古典コンピューティングにおけるアーキテクチャ分類と量子コンピューティングを実現するための量子ゲートの実際について数理科学的視点から概観する。
[ 参考URL ]
https://forms.gle/Uhy8uBujZatjNMsGA

#### 作用素環セミナー

16:45-18:15   オンライン開催
Benoit Collins 氏 (京大理)
Generalized strong asymptotic freeness (English)
[ 参考URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

### 2020年12月01日(火)

#### トポロジー火曜セミナー

17:00-18:00   オンライン開催

Goeritz groups of bridge decompositions (JAPANESE)
[ 講演概要 ]
For a bridge decomposition of a link in the 3-sphere, we define the Goeritz group to be the group of isotopy classes of orientation-preserving homeomorphisms of the 3-sphere that preserve each of the bridge sphere and link setwise. The Birman-Hilden theory tells us that this is a $\mathbb{Z} / 2 \mathbb{Z}$-quotient of a "hyperelliptic Goeritz group". In this talk, we discuss properties, mainly of dynamical nature, of this group using a measure of complexity called the distance of the decomposition. We then give an application to the asymptotic behavior of the minimal entropies for the original Goeritz groups of Heegaard splittings. This talk is based on a joint work with Susumu Hirose, Daiki Iguchi and Eiko Kin.
[ 参考URL ]
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html

#### 数値解析セミナー

16:30-18:00   オンライン開催

[ 講演概要 ]

[ 参考URL ]
https://forms.gle/Ubeccm8neLkacjbk8

#### PDE実解析研究会

10:30-11:30   数理科学研究科棟(駒場) 　Zoomによるオンライン開催　号室
Michał Łasica 氏 (Institute of Mathematics of the Polish Academy of Sciences / University of Tokyo)
Existence of the $1$-harmonic map flow (English)
[ 講演概要 ]
Similarly as in the real-valued case, the total variation of maps taking values in a Riemannian manifold extends to a lower semicontinuous functional on $L^2$. However, in general this functional is not geodesically semiconvex, so the existence of its gradient flow is not provided by general variational theory. Alternatively, one can try to apply the theory of parabolic PDE systems, mimicking the approach used for $p$-harmonic map flows, $p>1$. This poses some difficulties, because the PDE system corresponding to the flow is strongly nonlinear, singular and degenerate. However, in some cases, this approach was successful. In this talk, I will describe known results on the existence of the flow, focusing on my work with Lorenzo Giacomelli and Salvador Moll.

### 2020年11月30日(月)

#### 複素解析幾何セミナー

10:30-12:00   オンライン開催

On asymptotic base loci of relative anti-canonical divisors
[ 講演概要 ]

この講演では, $-K_{X/Y}$から定まる"asymptotic base loci"という集合を用い て, 上記の結果が巨大や擬有効へ拡張できることを紹介する. また 「$-K_{X/Y}$から定まる"asymptotic base loci"が, 空集合か水平方向に存在す るかのどちらかである」ことも紹介する. この研究は大阪大学の江尻祥氏と東北 大学の松村慎一氏との共同研究である.
[ 参考URL ]
https://zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

### 2020年11月27日(金)

#### 統計数学セミナー

17:00-18:10   数理科学研究科棟(駒場) on-line号室

Yuliya Mishura 氏 (Taras Shevchenko National University of Kyiv)
Processes with small ball estimate: properties, examples, statistical inference (ENGLISH)
[ 講演概要 ]
The notion of a process with small ball estimate is introduced and studied. In particular, divergence of integral functional of such process is established and applied to statistical estimation. Several interesting examples are provided, and various modifications of the main group of properties are considered. The talk is based on the common research with Prof. Nakahiro Yoshida.
[ 参考URL ]

### 2020年11月26日(木)

#### 情報数学セミナー

16:50-18:35   オンライン開催

AIを支える強化学習と回帰アルゴリズム (Japanese)
[ 講演概要 ]
現代AIの基本は、ディープラーニングであるが、ディープラーニングと融合してAIの性能を上げる手法として、強化学習と回帰アルゴリズムがある。そこで、今回は、強化学習のための統計学の基本としてのP値とQ値、Q-Learning、および回帰アルゴリズムの基本と応用について述べる。さらにAIの実用例として、サービス業におけるテクニカル・サポート業務の自動化について紹介する。
[ 参考URL ]
https://forms.gle/Uhy8uBujZatjNMsGA

#### 数理人口学・数理生物学セミナー

15:00-16:00   数理科学研究科棟(駒場) 号室
zoomによる遠隔セミナーです。視聴希望者は稲葉までご連絡ください。

いくつかの再感染数理モデルについて (Japanese)
[ 講演概要 ]

### 2020年11月24日(火)

#### トポロジー火曜セミナー

17:30-18:30   オンライン開催

Intersection of Poincare holonomy varieties and Bers' simultaneous uniformization theorem (JAPANESE)
[ 講演概要 ]
Given a marked compact Riemann surface X, the vector space of holomorphic quadratic differentials on X is identified with the space of CP1-structures on X. Then, by the holonomy representations of CP1-structures, this vector space properly embeds into the PSL(2, C)-character variety, the space of representations of the fundamental group of X into PSL(2,C).

In this manner, different Riemann surfaces structures yield different half-dimensional smooth analytic subvarieties in the character variety. In this talk, we discuss some properties of their intersection. To do so, we utilize a cut-and-paste operation, called grafting, of CP1-structures.
[ 参考URL ]
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html