## Seminar information archive

### 2010/03/29

#### Seminar on Probability and Statistics

13:00-14:10   Room #002 (Graduate School of Math. Sci. Bldg.)
Catherine Laredo (MIA, INRA)
Inference for partially observed Markov processes and applications
[ Abstract ]
We present some statistical methods for estimating the param- eters of a population dynamics model of annual plants. It is modelled using multitype branching processes with immigration. The data consist of counts in each type that are measured in several populations for a few consecu- tive years. Parametric inference is first carried out when count data of all types are observed. We prove statistical identifiability for all the parameters ruling the population dynamics model and derive consistent and asymptot- ically Gaussian estimators. However, it often occurs that, in practice, one or more types cannot be observed, leading to partially observed processes. Parametric inference is first studied in the case of Poisson distributions. We characterize the parameter subset where identifiability holds and de- rive consistent and asymptotically normal estimators for this parameter subset. Theses results are then extended to other distributions.

We apply these results to feral oilseed data. The model takes account of reproduction, immigration, and seed survival in a seed bank. The data consist of the number of plants in several developmental stages that were measured in a number of populations for few consecutive years. They are incomplete since seeds could not be counted.
[ Reference URL ]
http://www.ms.u-tokyo.ac.jp/~kengok/statseminar/2009/17.html

### 2010/03/25

#### Lectures

17:00-18:00   Room #370 (Graduate School of Math. Sci. Bldg.)
Dr Bangti Jin (Center for Industrial Mathematics University of Bremen, Germany)
Heuristic Choice Rules for Convex Variational Regularization
[ Abstract ]
In this talk we shall consider heuristic rules for choosing regularization parameters for general convex variational regularization of linear inverse problems. Several rules of recent origin are described, and some theoretical issues, e.g. existence, convergence, and a posteriori error estimates, are discussed. Numerical examples will be presented to demonstrate their accuracy and practical utility.

#### Lectures

16:00-17:00   Room #370 (Graduate School of Math. Sci. Bldg.)
M.M. Lavrentiev, Jr. (Sobolev Institute of Mathematics, Novosibirsk, Russia)
Modern computer architectures for tsunami simulation
[ Abstract ]
Simulation of tsunami wave propagation over the deep water is one of the most time consuming tasks of the tsunami warning system. The authors utilize Method of Splitting Tsunami (MOST) package, accepted by the National Ocean & Atmospheric Administration (NOAA), USA. The software generates calculation of wave propagation at deep water by splitting along coordinate axis. Nonlinear shallow water system is used as the governing equations. Some tasks of the algorithm could be executed in parallel mode, however, direct application of multi processor systems results only in two times performance gain. After a number of optimizations, the authors achieved 16 times performance gain. OpenMP technology was applied. When utilizing Sony PlayStation3 platform (IBM CELL BE architecture) 60 times code acceleration was accomplished. The best result was achieved with modern GPU (GForce 8800 and TESLA), 100 times performance gain.

### 2010/03/23

#### GCOE Seminars

15:00-17:15   Room #370 (Graduate School of Math. Sci. Bldg.)
Mourad Bellassoued (Univ. of Bizerte) 15:00-16:00
Stability estimates for the anisotropic wave and Schrodinger equations from
the Dirichlet to Neumann map
[ Abstract ]
In this talk we want to obtain stability estimates for the inverse problem of determining the electric potential or the conformal factor in a wave or Schrodinger equations in an anisotropic media with Dirichlet data from measured Neumann boundary observations. This information is enclosed in the dynamical Dirichlet-to-Neumann map associated to the wave equation. We prove in dimension $n\\geq 2$ that the knowledge of the Dirichlet to Neumann map for the wave equation measured on the boundary uniquely determines the electric potential and we prove H\\"older-type stability in determining the potential. We prove similar results for the determination of a conformal factor close to 1.
Johannes Elschner (Weierstrass Institute Berlin, Germany) 16:15-17:15
On uniqueness in inverse elastic obstacle scattering
[ Abstract ]
The talk is on joint work with M. Yamamoto on the third and fourth exterior boundary value problems of linear isotropic elasticity. We present uniqueness results for the corresponding inverse scattering problems with polyhedral-type obstacles and a finite number of incident plane elastic waves.
Our approach is essentially based on a reflection principle for the Navier equation.

### 2010/03/19

#### Lectures

11:00-12:00   Room #366 (Graduate School of Math. Sci. Bldg.)

A Regularization Parameter for Nonsmooth Tikhonov Regularization
[ Abstract ]
We develop a novel criterion for choosing regularization parameters for nonsmooth Tikhonov functionals. The proposed criterion is solely based on the value function, and thus applicable to a broad range of functionals. It is analytically compared with the local minimum criterion, and a posteriori error estimates are derived. An efficient numerical algorithm for computing the minimizer is developed, and its convergence properties are also studied. Numerical results for several common nonsmooth functionals are presented.

### 2010/03/17

#### Lectures

16:30-17:30   Room #128 (Graduate School of Math. Sci. Bldg.)

### 2010/03/15

#### Seminar on Probability and Statistics

15:00-16:00   Room #002 (Graduate School of Math. Sci. Bldg.)
Cecilia Mancini (University of Florence)
BROWNIAN COVARIATION AND CO-JUMPS, GIVEN DISCRETE OBSERVATION
[ Abstract ]
We consider two processes driven by Brownian motions plus drift and possibly infinite activity jumps.

Given discrete observations we separately estimate the covariation between the two Brownian parts and the sum of the co-jumps. This allows to gain insight into the dependence structure of the processes and has important applications in finance.

Our estimator is based on a threshold principle allowing to isolate the jumps over a threshold.

The estimator of the continuous covariation is asymptotically Gaussian and converges at speed square root of n when the jump components have finite variation. In presence infinite variation jumps the speed is heavily influenced both by the small jumps dependence structure and by their jump activity indexes.

This talk is based on Mancini and Gobbi (2009), and Mancini (2010).
[ Reference URL ]
http://www.ms.u-tokyo.ac.jp/~kengok/statseminar/2009/16.html

#### Seminar on Probability and Statistics

14:00-15:00   Room #002 (Graduate School of Math. Sci. Bldg.)
Alexandre Brouste (Université du Maine)
Statistical inference in the partial observation setting, in continuous time
[ Abstract ]
In various fields, the {\\it signal} process, whose law depends on an unknown parameter $artheta \\in \\Theta \\subset \\R^p$, can not be observed directly but only through an {\\it observation} process. We will talk about the so called fractional partial observation setting, where the observation process $Y=\\left( Y_t, t \\geq 0 ight)$ is given by a stochastic differential equation: egin{equation} \\label{mod:modelgeneral} Y_t = Y_0 + \\int_0^t h(X_s, artheta) ds + \\sigma W^H_t\\,, \\quad t > 0 \ where the function $h: \\, \\R imes \\Theta \\longrightarrow \\R$ and the constant $\\sigma>0$ are known and the noise $\\left( W^H_t\\,, t\\geq 0 ight)$ is a fractional Brownian motion valued in $\\R$ independent of the signal process $X$ and the initial condition $Y_0$. In this setting, the estimation of the unknown parameter $artheta \\in \\Theta$ given the observation of the continuous sample path $Y^T=\\left( Y_t , 0 \\leq t \\leq T ight)$, $T>0$, naturally arises.
[ Reference URL ]
http://www.ms.u-tokyo.ac.jp/~kengok/statseminar/2009/15.html

### 2010/03/12

#### Colloquium

15:00-17:30   Room #050 (Graduate School of Math. Sci. Bldg.)

ガルニエ系の数理
[ Abstract ]
ガルニエ系は,パンルヴェ方程式の拡張であり,完全積分可能な多時間ハミルトン系として与えられる。これは2階線型常微分方程式のホロノミック変形を与える非線型完全積分可能な偏微分方程式系であり,講演の対象である2次元系では,8つのタイプの基本形がある。ガルニエ系の研究は,初期値空間やソリトン方程式系の相似簡約などの立場から行われているが,材料が揃ってくれば,一般リーマン・ヒルベルト対応を経由して考察することが自然であるし,数学的であるだろう。パンルヴェ方程式の場合もそのような方向に進んでいる。一方,パンルヴェ方程式については,そのハミルトニアンの満足する非線型常微分方程式が,アフィンワイル群の対称性など数学的な材料を与える上で一定の役割を果たした。ガルニエ系についても,そのハミルトニアンについての非線型偏微分方程式系を具体的に書き下すことは,意味のあることと信じているが,未完である。この話題について,部分的な結果を紹介する。

[ Abstract ]
40年近くの間,さまざまな幾何構造に関する特性類と不変量の研究を続けてきた.葉層構造やリーマン面のモジュライ空間の特性類,そして3次元多様体の位相不変量等である.これらについて振り返りつつ,これからの目標をいくつかの予想を交えてお話ししたい.

### 2010/03/09

#### PDE Real Analysis Seminar

10:30-11:30   Room #123 (Graduate School of Math. Sci. Bldg.)
Joachim Escher (Leibniz University of Hanover)
Shallow water waves with singularities
[ Abstract ]
The Degasperis-Procesi equation is a recently derived shallow water wave equation, which is - similar as the Camassa-Holm equation - embedded in a family of spatially periodic third order dispersive conservation laws.
The coexistence of globally in time defined classical solutions, wave breaking solutions, and spatially periodic peakons and shock waves is evidenced in the talk, and the precise blow-up scenario, including blow-up rates and blow-up sets, is discussed in detail. Finally several conditions on the initial profile are presented, which ensure the occurence of a breaking wave.

### 2010/02/24

#### Lectures

15:00-16:30   Room #370 (Graduate School of Math. Sci. Bldg.)
Robert Penner (Aarhus University / University of Southern California)
Protein Moduli Space
[ Abstract ]
Recent joint works with J. E. Andersen and others
provide explicit discrete and continuous models
of protein geometry. These models are inspired
by corresponding constructions in the study of moduli
spaces of flat G-connections on surfaces, in particular,
for G=PSL(2,R) and G=SO(3). These models can be used
for protein classification as well as for folding prediction,
and computer experiments towards these ends will
be discussed.

### 2010/02/23

#### Lectures

14:00-15:00   Room #122 (Graduate School of Math. Sci. Bldg.)
Bendong LOU (同済大学)
Homogenization Limit and Singular Limit of the Allen-Cahn equation
[ Abstract ]
We consider the Allen-Cahn equation in a cylinder with periodic undulating boundaries in the plane. Our problem involves two small parameters $\\delta$ and $\\epsilon$, where $\\delta$ appears in the equation to denote the scale of the singular limit and $\\epsilon$ appears in the boundary conditions to denote the scale of the homogenization limit. We consider the following two limiting processes:
(I): taking homogenization limit first and then taking singular limit;
(II) taking singular limit first and then taking homogenization limit.

We formally show that they both result in the same mean curvature flow equation, but with different boundary conditions.

### 2010/02/19

#### Lie Groups and Representation Theory

16:30-18:00   Room #126 (Graduate School of Math. Sci. Bldg.)
Yves Benoist (Orsay)
Discrete groups acting on homogeneous spaces V
[ Abstract ]
I will focus on recent advances on our understanding of discrete subgroups of Lie groups.
I will first survey how ideas from semisimple algebraic groups, ergodic theory and representation theory help us to understand properties of these discrete subgroups.

I will then focus on a joint work with Jean-Francois Quint studying the dynamics of these discrete subgroups on finite volume homogeneous spaces and proving the following result:

We fix two integral matrices A and B of size d, of determinant 1, and such that no finite union of vector subspaces is invariant by A and B. We fix also an irrational point on the d-dimensional torus. We will then prove that for n large the set of images of this point by the words in A and B of length at most n becomes equidistributed in the torus.

### 2010/02/18

#### GCOE lecture series

10:30-17:00   Room #126 (Graduate School of Math. Sci. Bldg.)
Yves Benoist (Pars Sud) 10:30-11:30
Discrete groups acting on homogeneous spaces III
[ Abstract ]
In this course I will focus on recent advances
on our understanding of discrete subgroups of Lie groups.

I will first survey how ideas from semisimple algebraic groups,
ergodic theory and representation theory help us to understand properties of these discrete subgroups.

I will then focus on a joint work with Jean-Francois Quint
studying the dynamics of these discrete subgroups on finite volume homogeneous spaces and proving the following result:

We fix two integral matrices A and B of size d, of determinant 1,
and such that no finite union of vector subspaces is invariant by A and B.
We fix also an irrational point on the d-dimensional torus. We will then prove that for n large the set of images of this point by the words in A and B of length at most n becomes equidistributed in the torus.
Yves Benoist (Paris Sud) 15:00-16:00
Discrete groups acting on homogeneous spaces IV

#### Operator Algebra Seminars

16:30-18:00   Room #128 (Graduate School of Math. Sci. Bldg.)
Roberto Longo (University of Rome, Tor Vergata)
Von Neumann Algebras and Boundary Quantum Field Theory

#### Applied Analysis

16:00-17:30   Room #002 (Graduate School of Math. Sci. Bldg.)
Bendong LOU (同済大学)
Homogenization limit of a parabolic equation with nonlinear boundary conditions
[ Abstract ]
We consider a quasilinear parabolic equation with the following nonlinear Neumann boundary condition:
"the slope of the solution on the boundary is a function $g$ of the value of the solution". Here $g$ takes values near its supremum with the frequency of $\\epsilon$. We show that the homogenization limit of the solution, as $\\epsilon$ tends to 0, is the solution satisfying the linear Neumann boundary condition: "the slope of the solution on the boundary is the supremum of $g$".

#### GCOE Seminars

10:10-11:00   Room #122 (Graduate School of Math. Sci. Bldg.)

#### GCOE Seminars

11:00-11:50   Room #122 (Graduate School of Math. Sci. Bldg.)

#### GCOE Seminars

13:20-14:10   Room #122 (Graduate School of Math. Sci. Bldg.)

#### GCOE Seminars

14:10-14:40   Room #122 (Graduate School of Math. Sci. Bldg.)

#### GCOE Seminars

14:50-15:40   Room #122 (Graduate School of Math. Sci. Bldg.)
O. Iliev (フラウンホーファー産業数学研究所、ドイツ)
Flow and material simulation for industrial purposes

### 2010/02/17

#### GCOE lecture series

10:30-16:00   Room #126 (Graduate School of Math. Sci. Bldg.)
Yves Benoist (Paris Sud) 10:30-11:30
Discrete groups acting on homogeneous spaces I
[ Abstract ]
In this course I will focus on recent advances
on our understanding of discrete subgroups of Lie groups.

I will first survey how ideas from semisimple algebraic groups,
ergodic theory and representation theory help us to understand properties of these discrete subgroups.

I will then focus on a joint work with Jean-Francois Quint
studying the dynamics of these discrete subgroups on finite volume homogeneous spaces and proving the following result:

We fix two integral matrices A and B of size d, of determinant 1,
and such that no finite union of vector subspaces is invariant by A and B.
We fix also an irrational point on the d-dimensional torus. We will then prove that for n large the set of images of this point by the words in A and B of length at most n becomes equidistributed in the torus.
Yves Benoist (Paris Sud) 15:00-16:00
Discrete groups acting on homogeneous spaces II

#### Seminar on Probability and Statistics

15:00-16:10   Room #128 (Graduate School of Math. Sci. Bldg.)

[ Abstract ]

[ Reference URL ]
http://www.ms.u-tokyo.ac.jp/~kengok/statseminar/2009/14.html

### 2010/02/16

#### Tuesday Seminar on Topology

17:30-18:30   Room #056 (Graduate School of Math. Sci. Bldg.)
Dieter Kotschick (Univ. M\"unchen)
Characteristic numbers of algebraic varieties
[ Abstract ]
The Chern numbers of n-dimensional smooth projective varieties span a vector space whose dimension is the number of partitions of n. This vector space has many natural subspaces, some of which are quite small, for example the subspace spanned by Hirzebruch--Todd numbers, the subspace of topologically invariant combinations of Chern numbers, the subspace determined by the Hodge numbers, and the subspace of Chern numbers that can be bounded in terms of Betti numbers. I shall explain the relation between these subspaces, and characterize them in several ways. This leads in particular to the solution of a long-standing open problem originally formulated by Hirzebruch in the 1950s.

### 2010/02/05

#### thesis presentations

09:45-11:00   Room #118 (Graduate School of Math. Sci. Bldg.)
Takahiro Tsushima (University of Tokyo)
Elementary computation of ramified components of Jacobi sum Hecke characters (JAPANESE)