## 過去の記録

### 2011年11月21日(月)

#### 複素解析幾何セミナー

10:30-12:00   数理科学研究科棟(駒場) 128号室

Techniques of computations of Dolbeault cohomology of solvmanifolds (JAPANESE)

#### 諸分野のための数学研究会

13:30-14:30   数理科学研究科棟(駒場) 056号室

Ernie Esser 氏 (University of California, Irvine)
A convex model for non-negative matrix factorization and dimensionality reduction on physical space (ENGLISH)
[ 講演概要 ]
A collaborative convex framework for factoring a data matrix X into a non-negative product AS, with a sparse coefficient matrix S, is proposed. We restrict the columns of the dictionary matrix A to coincide with certain columns of the data matrix X, thereby guaranteeing a physically meaningful dictionary and dimensionality reduction. We focus on applications of the proposed framework to hyperspectral endmember and abundances identification and also show an application to blind source separation of NMR data.
This talk is based on joint work with Michael Moeller, Stanley Osher, Guillermo Sapiro and Jack Xin.

#### Kavli IPMU Komaba Seminar

16:30-18:00   数理科学研究科棟(駒場) 002号室
Siu-Cheong Lau 氏 (IPMU)
Enuemerative meaning of mirror maps for toric Calabi-Yau manifolds (ENGLISH)
[ 講演概要 ]
For a mirror pair of smooth manifolds X and Y, mirror symmetry associates a complex structure on Y to each Kaehler structure on X, and this association is called the mirror map. Traditionally mirror maps are defined by solving Picard-Fuchs equations and its geometric meaning was unclear. In this talk I explain a recent joint work with K.W. Chan, N.C. Leung and H.H. Tseng which proves that mirror maps can be obtained by taking torus duality (the SYZ approach) and disk-counting for a class of toric Calabi-Yau manifolds in any dimensions. As a consequence we can compute disk-counting invariants by solving Picard-Fuchs equations.

### 2011年11月19日(土)

#### 保型形式の整数論月例セミナー

10:15-12:30   数理科学研究科棟(駒場) 117号室

[ 講演概要 ]

この微分方程式の基本解が超楕円積分と超幾何関数を使って表示できることを示しさらに関連した話題を説明する。

[ 講演概要 ]

### 2011年11月18日(金)

#### 講演会

15:00-16:00   数理科学研究科棟(駒場) 052号室

Inverse problems for heat equations with discontinuous conductivities
(JAPANESE)
[ 講演概要 ]
In a bounded domain $\\Omega \\subset {\\bf R}^n$, consider the heat
equation $\\partial_tu = \\nabla(\\gamma(t,x)\\nabla u)$. The heat
conductivity is assumed to be piecewise constant : $\\gamma = k^2$ on
$\\Omaga_1(t) \\subset\\subset \\Omega$, $\\gamma(t,x) = 1$ on
$\\Omega\\setminus\\Omega_1(t)$. In this talk, we present recent results
for the inverse problems of reconstructing $\\gamma(t,x)$ from the
Dirichlet-to-Neumann map :
$u(t)|_{\\partial\\Omega} \\to$\\partial_{\\nu}u|_{\\partial\\Omega}$for a time interval$(0,T)$. These are the joint works with P.Gaitan, O.Poisson, S.Siltanen, J.Tamminen. ### 2011年11月17日(木) #### GCOEレクチャーズ 17:00-18:00 数理科学研究科棟(駒場) 370号室 Oleg Emanouilov 氏 (Colorado State University) Recovery of weakly coupled system from partial Cauchy data (ENGLISH) [ 講演概要 ] We consider the inverse problem for recovery of coefficients of weakly coupled system of elliptic equations in a bounded 2D domain. #### 作用素環セミナー 16:30-18:00 数理科学研究科棟(駒場) 117号室 山ノ内毅彦 氏 (東京学芸大学) エルゴード的測度付き同値関係におけるヘッケペアーについて (JAPANESE) ### 2011年11月16日(水) #### 複素解析幾何セミナー 16:30-18:00 数理科学研究科棟(駒場) 128号室 Franc Forstneric 氏 (University of Ljubljana) Disc functionals and Siciak-Zaharyuta extremal functions on singular varieties (ENGLISH) [ 講演概要 ] A disc functional on a complex space,$X$, is a function P that assign a real number$P(f)$(possibly minus infinity) to every analytic disc$f$in$X$. An examples is the Poisson functional$P_u$of an upper semicontinuous function$u$on$X$: in that case$P_u(f)$is the average of u over the boundary curve of the disc$f$. Other natural examples include the Lelong and the Riesz functionals. The envelope of a disc functional$P$is a function on$X$associating to every point$x$of$X$the infimum of the values$P(f)$over all analytic discs$f$in$X$satisfying$f(0)=x$. The main point of interest is that the envelopes of many natural disc functionals are plurisubharmonic functions solving certain extremal problems. In the classical case when$X=\mathbf{C}^n$this was first discovered by E. Poletsky in the early 1990's. In this talk I will discuss recent results on plurisubharmonicity of envelopes of all the classical disc functional mentioned above on locally irreducible complex spaces. In the second part of the talk I will give formulas expressing the classical Siciak-Zaharyuta maximal function of an open set in an affine algebraic variety as the envelope of certain disc functionals. We establish plurisubharmonicity of envelopes of certain classical disc functionals on locally irreducible complex spaces, thereby generalizing the corresponding results for complex manifolds. We also find new formulae expressing the Siciak-Zaharyuta extremal function of an open set in a locally irreducible affine algebraic variety as the envelope of certain disc functionals, similarly to what has been done for open sets in$\mathbf{C}^n$by Lempert and by Larusson and Sigurdsson. #### GCOEセミナー 10:00-11:00 数理科学研究科棟(駒場) 270号室 Alfred Ramani 氏 (Ecole Polytechnique) All you never really wanted to know about QRT, but were foolhardy enough to ask (ENGLISH) [ 講演概要 ] We discuss various extensions of the famous QRT second order, first degree, integrable mapping. We show how these extensions can be combined. A discussion of integrable correspondences related to these extended QRT mappings is also presented. ### 2011年11月15日(火) #### トポロジー火曜セミナー 16:30-18:00 数理科学研究科棟(駒場) 056号室 Tea: 16:00 - 16:30 コモンルーム Francois Laudenbach 氏 (Univ. de Nantes) Singular codimension-one foliations and twisted open books in dimension 3. (joint work with G. Meigniez) (ENGLISH) [ 講演概要 ] The allowed singularities are those of functions. According to A. Haefliger (1958), such structures on manifolds, called$\\Gamma_1$-structures, are objects of a cohomological theory with a classifying space$B\\Gamma_1$. The problem of cancelling the singularities (or regularization problem) arise naturally. For a closed manifold, it was solved by W.Thurston in a famous paper (1976), with a proof relying on Mather's isomorphism (1971): Diff$^\\infty(\\mathbb R)$as a discrete group has the same homology as the based loop space$\\Omega B\\Gamma_1^+$. For further extension to contact geometry, it is necessary to solve the regularization problem without using Mather's isomorphism. That is what we have done in dimension 3. Our result is the following. {\\it Every$\\Gamma_1$-structure$\\xi$on a 3-manifold$M$whose normal bundle embeds into the tangent bundle to$M$is$\\Gamma_1$-homotopic to a regular foliation carried by a (possibily twisted) open book.} The proof is elementary and relies on the dynamics of a (twisted) pseudo-gradient of$\\xi\$.

All the objects will be defined in the talk, in particular the notion
of twisted open book which is a central object in the reported paper.

#### Lie群論・表現論セミナー

16:30-18:00   数理科学研究科棟(駒場) 126号室
Laurant Demonet 氏 (Nagoya University)
Categorification of cluster algebras arising from unipotent subgroups of non-simply laced Lie groups (ENGLISH)
[ 講演概要 ]
We introduce an abstract framework to categorify some antisymetrizable cluster algebras by using actions of finite groups on stably 2-Calabi-Yau exact categories. We introduce the notion of the equivariant category and, with similar technics as in [K], [CK], [GLS1], [GLS2], [DK], [FK], [P], we construct some examples of such categorifications. For example, if we let Z/2Z act on the category of representations of the preprojective algebra of type A2n-1 via the only non trivial action on the diagram, we obtain the cluster structure on the coordinate ring of the maximal unipotent subgroup of the semi-simple Lie group of type Bn [D]. Hence, we can get relations between the cluster algebras categorified by some exact subcategories of these two categories. We also prove by the same methods as in [FK] a conjecture of Fomin and Zelevinsky stating that the cluster monomials are linearly independent.

References
[CK] P. Caldero, B. Keller, From triangulated categories to cluster algebras, Invent. Math. 172 (2008), no. 1, 169--211.
[DK] R. Dehy, B. Keller, On the combinatorics of rigid objects in 2-Calabi-Yau categories, arXiv: 0709.0882.
[D] L. Demonet, Cluster algebras and preprojective algebras: the non simply-laced case, C. R. Acad. Sci. Paris, Ser. I 346 (2008), 379--384.
[FK] C. Fu, B. Keller, On cluster algebras with coefficients and 2-Calabi-Yau categories, arXiv: 0710.3152.
[GLS1] C. Geiss, B. Leclerc, J. Schröer, Rigid modules over preprojective algebras, Invent. Math. 165 (2006), no. 3, 589--632.
[GLS2] C. Geiss, B. Leclerc, J. Schröer, Cluster algebra structures and semicanoncial bases for unipotent groups, arXiv: math/0703039.
[K] B. Keller, Categorification of acyclic cluster algebras: an introduction, arXiv: 0801.3103.
[P] Y. Palu, Cluster characters for triangulated 2-Calabi--Yau categories, arXiv: math/0703540.

### 2011年11月14日(月)

#### GCOEレクチャーズ

17:00-18:00   数理科学研究科棟(駒場) 470号室
Oleg Emanouilov 氏 (Colorado State University)
Recovery of weakly coupled system from partial Cauchy data (ENGLISH)
[ 講演概要 ]
We consider the inverse problem for recovery of coefficients of weakly coupled system of elliptic equations in a bounded 2D domain.

#### 代数幾何学セミナー

15:30-17:00   数理科学研究科棟(駒場) 122号室

On projective manifolds swept out by cubic varieties (JAPANESE)
[ 講演概要 ]
The structures of embedded complex projective manifolds swept out by varieties with preassigned properties have been studied by several authors. In this talk, we study structures of embedded projective manifolds swept out by cubic varieties.

### 2011年11月10日(木)

#### GCOEレクチャーズ

17:00-18:00   数理科学研究科棟(駒場) 370号室
Oleg Emanouilov 氏 (Colorado State University)
Inverse boundary value problem for Schroedinger equation in two dimensions (ENGLISH)
[ 講演概要 ]
We relax the regularity condition on potentials of Schroedinger equations in uniqueness results on the inverse boundary value problem recently proved in A.Bukhgeim (2008) and O. Imanuvilov, G.Uhlmann and M. Yamamoto (2010).

#### 応用解析セミナー

15:00-16:00   数理科学研究科棟(駒場) 128号室

[ 講演概要 ]

において中心的な課題である。細胞体積調節を記述する標準的な数理
モデルはpump-leak model と呼ばれ、数学的には常微分方程式に

#### 応用解析セミナー

16:30-17:30   数理科学研究科棟(駒場) 128号室
この日はダブルヘッダーです。
Bernold Fiedler 氏 (Free University of Berlin)
Schoenflies spheres in Sturm attractors (ENGLISH)
[ 講演概要 ]
In gradient systems on compact manifolds the boundary of the unstable manifold of an equilibrium need not be homeomorphic to a sphere, or to any compact manifold.
For scalar parabolic equations in one space dimension, however, we can exlude complications like Reidemeister torsion and the Alexander horned sphere. Instead the boundary is a Schoenflies embedded sphere. This is due to Sturm nodal properties related to the Matano lap number.

### 2011年11月09日(水)

#### 代数学コロキウム

18:00-19:00   数理科学研究科棟(駒場) 056号室
いつもと時間が異なりますのでご注意下さい.

On extension and restriction of overconvergent isocrystals (ENGLISH)
[ 講演概要 ]
First we explain two theorems concerning (log) extension of overconvergent isocrystals. One is a p-adic analogue of the theorem of logarithmic extension of regular integrable connections, and the other is a p-adic analogue of Zariski-Nagata purity. Next we explain a theorem which says that we can check certain property of overconvergent isocrystals by restricting them to curves.

(本講演は「東京パリ数論幾何セミナー」として、インターネットによる東大数理とIHESとの双方向同時中継で行います。)

### 2011年11月08日(火)

#### トポロジー火曜セミナー

16:30-18:00   数理科学研究科棟(駒場) 056号室
Tea: 16:00 - 16:30 コモンルーム

Fiberwise bordism groups and related topics (JAPANESE)
[ 講演概要 ]
We have recently introduced the notion of fiberwise bordism. In this talk, after a quick review of some of the classical (co)bordism theories, we will explain motivations of considering fiberwise bordism and some results and connections with other known works, such as M. Kreck's bordism groups of orientation preserving diffeomorphisms and Emerson-Meyer's bivariant K-theory etc. An essential motivation is our recent work towards constructing a bivariant-theoretic analogue (in the sense of Fulton-MacPherson) of Levine-Morel's or Levine-Pandharipande's algebraic cobordism.

#### 解析学火曜セミナー

16:30-18:00   数理科学研究科棟(駒場) 128号室

[ 講演概要 ]

の存在と一意性について考察する。 非ニュートン流体としては、粘性
が変形速度テンソルの大きさの冪乗 の形で依存する冪乗法則流体を考

Ruzicka('93)において、確率的外力項を伴わない、 決定方程式に関し
て示された弱解の存在と一意性の主張を、 確率的摂動項を持つ方程式
に対して示す。 解の存在の証明は、ガレルキン近似によって得られた

により、 解の列のコンパクト性を示すこと及び、解の部分列が収束し
、 その収束先が方程式を弱い意味で満たすことを示すことでなされる。
なお、本講演は、吉田伸生氏(京都大学)との共同研究に基づく。

#### 諸分野のための数学研究会

16:30-17:30   数理科学研究科棟(駒場) 052号室

Ralph Bruckschen 氏 (ベルリン工科大学、MATHEON)
Interactive Data Visualization challenges, approaches and examples (ENGLISH)
[ 講演概要 ]
Data visualization is probably the most important method to analyze scientific datasets. In the time of petaflop supercomputers and high resolution sensors, the visualization of such datasets became a challenge because of the sheer magnitude. Using the latest technology I will describe some of the challenges and approaches to visualize large and massive datasets. The main bottle necks will be explained, as some algorithms and data structures to widen them. Finally I will show some examples of data visualization using a CAVE environment and virtual prototyping from the 3D Labor at the Technical University of Berlin.

### 2011年11月07日(月)

#### GCOEレクチャーズ

17:00-18:00   数理科学研究科棟(駒場) 470号室
Oleg Emanouilov 氏 (Colorado State University)
Inverse boundary value problem for Schroedinger equation in two dimensions (ENGLISH)
[ 講演概要 ]
We relax the regularity condition on potentials of Schroedinger equations in uniqueness results on the inverse boundary value problem recently proved in A.Bukhgeim (2008) and O. Imanuvilov, G.Uhlmann and M. Yamamoto (2010).

#### 代数幾何学セミナー

15:30-17:00   数理科学研究科棟(駒場) 122号室

Okounkov bodies and Seshadri constants (JAPANESE)
[ 講演概要 ]
Okounkov bodies, which are convex bodies associated to big line bundles, have rich information of the line bundles. On the other hand, Seshadri constants are invariants which measure the positivities of line bundles. In this talk, I will explain a relation between Okounkov bodies and Seshadri constants.

#### 複素解析幾何セミナー

10:30-12:00   数理科学研究科棟(駒場) 128号室

[ 講演概要 ]
The main part of this talk is a joint work with my colleagues, M. Abe and S. Hamano. After the solution of Cousin II problem by K. Oka III in 1939, he thought an extra-zero problem in 1945 (his posthumous paper) asking if it is possible to solve an arbitrarily given Cousin II problem adding some extra-zeros whose support is disjoint from the given one. Some special case was affirmatively confirmed in dimension two and a counter-example in dimension three or more was obtained. We will give a complete solution of this problem with examples and to discuss some new questions. An example on a toric variety of which idea is based on K. Stein's paper in 1941 has some special interest and will be discussed. I would like also to discuss some analytic intersections form the viewpoint of Nevanlinna theory.

### 2011年11月04日(金)

#### 談話会・数理科学講演会

16:30-17:30   数理科学研究科棟(駒場) 123号室

お茶&Coffee&お菓子: 16:00～16:30 (コモンルーム)。

[ 講演概要 ]

このわずか二十年少々の間にも複比に関する新たなそして重要な発見が

いまだに限られているようである.そのような現状について,個人的な

### 2011年11月02日(水)

#### 代数学コロキウム

16:30-17:30   数理科学研究科棟(駒場) 056号室

Hypergeometric series and arithmetic-geometric mean over 2-adic fields (JAPANESE)
[ 講演概要 ]
Dwork proved that the Gaussian hypergeometric function on p-adic numbers
can be extended to a function which takes values of the unit roots of
ordinary elliptic curves over a finite field of characteristic p>2.
We present an analogous theory in the case p=2.
As an application, we give a relation between the canonical lift
and the unit root of an elliptic curve over a finite field of
characteristic 2
by using the 2-adic arithmetic-geometric mean.