Upcoming Events

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Tuesday, 16.01.2018, 10:15 (WIAS-406)
Seminar Nichtlineare Optimierung und Inverse Probleme
Dr. I. Bremer, WIAS Berlin:
Introduction to a framework for nonlinear optimization with adaptation to probabilistic constraints
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Host
WIAS Berlin
Tuesday, 16.01.2018, 15:00 (WIAS-406)
Seminar Modern Methods in Applied Stochastics and Nonparametric Statistics
Prof. A. Gasnikov, Moscow Institute of Physics and Technology, Russia:
Recent developments of accelerated gradient descent, part I
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Host
WIAS Berlin
Tuesday, 16.01.2018, 15:15 (FU-140)
Oberseminar Nonlinear Dynamics
J.-Y. Dai, Freie Universität Berlin:
Existence of local solutions of Gowdy spacetimes
more ... Location
Freie Universität Berlin, Arnimallee 7, 14195 Berlin, Hinterhaus, Raum: 140

Abstract
We consider a class of Gowdy spacetimes that reduces the Einstein's field equation to a system of two semilinear wave equations, by assuming a universe without matter, in which the gravitational wave fronts repeat in space and are mutually parallel. To prove the existence of local solutions of the system, we add a linear perturbation and seek periodic-in-space solutions. The idea of the proof is to apply the Lyapunov-Schmidt reduction. We will solve a related small-divisor problem and discuss how to design the correct functional setting that fits to the nonlinearity. This ongoing research is a joint work with Dr. Hannes Stuke.

Host
Freie Universität Berlin
WIAS Berlin
Wednesday, 17.01.2018, 10:00 (WIAS-ESH)
Forschungsseminar Mathematische Statistik
Prof. A. Nouy, École Centrale de Nantes, Frankreich:
Learning high-dimensional functions with tree tensor networks
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
Tensor methods are among the most prominent tools for the approximation of high- dimensional functions. Such approximation problems naturally arise in statistical learning, stochastic analysis and uncertainty quanti cation. In many practical situations, the approximation of high- dimensional functions is made computationally tractable by using rank-structured approximations. In this talk, we give an introduction to tree-based (hierarchical) tensor formats, which can be interpreted as deep neural networks with particular architectures. Then we present adaptive algorithms for the approximation in these formats using statistical methods.

Host
Humboldt-Universität zu Berlin
Universität Potsdam
WIAS Berlin
Wednesday, 17.01.2018, 15:15 (WIAS-ESH)
Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Prof. Dr. J. Sprekels, WIAS Berlin:
Cahn--Hilliard systems with general fractional-order operators
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Further Informations
Berliner Oberseminar “Nichtlineare Partielle Differentialgleichungen” (Langenbach Seminar)

Host
WIAS Berlin
Humboldt-Universität zu Berlin
Thursday, 18.01.2018, 14:00 (WIAS-ESH)
Seminar Numerische Mathematik
Prof. W. Dreyer, WIAS Berlin:
Modeling of non-Newtonian fluids without material frame indifference
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
In the fifties the modeling of non-Newtonian fluids initiated the search for invariant time derivatives with respect to certain space time transformations. Then Euclidean Transformations were selected to establish the Principle of Material Frame Indifference and moreover, the introduction of Nth grade fluids. However, the two concepts lead to serious inconsistencies in both thermodynamic modeling and experimental observations. In 1986 the subject has been resolved in a remarkable paper by I. Müller and K. Wilmanski. In this lecture we show how an appropriate model of non-Newtonian fluids may be incorporated in Continuum Thermodynamics as it was laid down by D. Bothe and W. Dreyer.

Host
WIAS Berlin
Friday, 19.01.2018, 14:00 (WIAS-ESH)
Joint Research Seminar on Nonsmooth Variational Problems and Operator Equations / Mathematical Optimization
Prof. Dr. S. Bartels, Albert-Ludwigs-Universität Freiburg:
Finite element methods for nonsmooth problems and application to a problem in optimal insulation
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
Nonsmooth problems arise in the mathematical modeling of contact and obstacle problems, the description of plastic material behavior, and mathematical image processing. The unknown functions are typically characterized as minimizers of nondifferentiable functionals. Numerical schemes approximately solve these problems either via duality methods or classically by making use of appropriate regularizations. In the talk we discuss the discretization and iterative solution of a model problem defined on functions of bounded variation. The numerical analysis of finite element discretizations leads to reduced convergence rates which can be improved using adaptive mesh refinement. Suitable iterative solution procedures are ADMM schemes, for which we propose an automatic step size adjustment strategy, and gradient flows, for which we demonstrate the unconditional stability of a semi-implicit time discretization. The methods are applicable in the numerical determination of optimal insulating films for heat conducting bodies. Below a critical value of available insulation mass an unexpected break of symmetry occurs.

Further Informations
Joint Research Seminar on Mathematical Optimization / Non-smooth Variational Problems and Operator Equations

Host
WIAS Berlin
Humboldt-Universität zu Berlin