Veranstaltungen
- Dienstag, 27.05.2025, 15:00 Uhr (WIAS-ESH)
- Forschungsseminar Mathematische Modelle der Photonik
Prof. Dmitry Turaev, Imperial College London, GB:
Universality conjecture for Hamiltonians that split a homoclinic tangency
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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal
Abstrakt
We discuss the following conjecture: every Hamiltonian systems with 2 degrees of freedom is universal (i.e., approximates all symplectic dynamics possible in a 2-dimensional disc with arbitrarily good precision) if the change of energy unfolds a homoclinic tangency at some energy level.
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Forschungsseminar Mathematische Modelle der Photonik
Veranstalter
WIAS Berlin
- Mittwoch, 28.05.2025, 10:00 Uhr (WIAS-HVP-3.13)
- Forschungsseminar Mathematische Statistik
Professor Jason Klusowski, Princeton University, USA:
Statistical-computational trade-offs for recursive adaptive partitioning estimators
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Weierstraß-Institut, Hausvogteiplatz 11A, 10117 Berlin, 3. Etage, Raum: 3.13
Abstrakt
Recursive adaptive partitioning estimators, like decision trees and their ensembles, are effective for high-dimensional regression but usually rely on greedy training, which can become stuck at suboptimal solutions. We study this phenomenon in estimating sparse regression functions over binary features, showing that when the true function satisfies a certain structural property, greedy training achieves low estimation error with only a logarithmic number of samples in the feature count. However, when this property is absent, estimation becomes exponentially more difficult. Interestingly, this dichotomy between efficient and inefficient estimation resembles the behavior of two-layer neural networks trained with SGD in the mean-field regime. Meanwhile, ERM-trained recursive adaptive partitioning estimators always achieve low estimation error with logarithmically many samples, revealing a fundamental statistical-computational trade-off for greedy training.
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Dieser Vortrag findet hybrid statt. Die Teilnahme per Zoom ist über den (neuen!) Link: https://hu-berlin.zoom-x.de/j/64809417303?pwd=iLT5xbdDZspAcUCuLrwNnaN90ZQBpj.1
Veranstalter
Humboldt-Universität zu Berlin
Universität Potsdam
WIAS Berlin
- Mittwoch, 28.05.2025, 14:15 Uhr (WIAS-405-406)
- Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Moritz Immanuel Gau:
A variational approach to well-posedness and relaxation in viscoelastic phase separation
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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406
Veranstalter
Humboldt-Universität zu Berlin
WIAS Berlin
- Dienstag, 03.06.2025, 15:00 Uhr (WIAS-405-406)
- Seminar Modern Methods in Applied Stochastics and Nonparametric Statistics
Josha Dekker, University of Amsterdam, Niederlande:
Optimal decision-making with randomly arriving decision moments
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406
Abstrakt
Control problems with randomly arriving control moments occur naturally. Financial situations in which control moments may arrive randomly are e.g., asset-liquidity spirals or optimal hedging in illiquid markets. We develop methods and algorithms to analyze such problems in a continuous time finite horizon setting, under mild conditions on the arrival process of control moments. Operating on the random timescale implied by the control moments, we obtain a discrete time, infinite-horizon problem. This problem may be solved accordingly or suitably truncated to a finite-horizon problem. We develop a stochastic primal-dual simulation-and-regression algorithm that does not require knowledge of the transition probabilities, as these may not be readily available for such problems. To this end, we present a corresponding dual representation result. We then apply our methods to several examples, where we explore in particular the effect of randomly arriving rebalancing moments on the optimal control. Joint work with Roger J.A. Laeven, John G.M. Schoenmakers and Michel H. Vellekoop.
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Dieser Vortrag findet auch via Zoom statt: https://zoom.us/j/492088715
Veranstalter
WIAS Berlin
- Mittwoch, 04.06.2025, 11:30 Uhr (WIAS-405-406)
- Seminar Interacting Random Systems
Elena Pulvirenti, Delft University of Technology:
tba
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406
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Seminar Interacting Random Systems
Veranstalter
WIAS Berlin
- Donnerstag, 05.06.2025, 14:00 Uhr (WIAS-405-406)
- Seminar Numerische Mathematik
Adrian Hill, TU Berlin:
SparseConnectivityTracer.jl
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406
Veranstalter
WIAS Berlin
- Mittwoch, 11.06.2025, 11:30 Uhr (WIAS-405-406)
- Seminar Interacting Random Systems
Michiel Renger, Technische Universität München:
tba
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406
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Seminar Interacting Random Systems
Veranstalter
WIAS Berlin
- 16. – 18. Juni 2025 (WIAS-ESH)
- Workshop/Konferenz: Nonlinear Dynamics in Semiconductor Lasers 2025
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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal
Veranstalter
WIAS Berlin
- 23. – 26. Juni 2025 (Harnack-Haus)
- Workshop/Konferenz: 4th Annual Conference of SPP 2265 Random Geometric Systems 2025
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Harnack-Haus -- Tagungsstätte der Max-Planck-Gesellschaft
Veranstalter
WIAS Berlin
- Mittwoch, 09.07.2025, 14:15 Uhr (WIAS-ESH)
- Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Prof. Dr. Amru Hussein, Universität Kassel:
The three limits of the hydrostatic approximation
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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal
Abstrakt
The primitive equations are a large scale model for ocean and atmosphere. Formally, they are derived from the 3D-Navier--Stokes equations by the assumption of a hydrostatic balance. This can be formalized by a rescaling procedure on an $varepsilon$-thin domain where one considers anisotropic viscosities with vertical viscosity $varepsilon^gamma$ and $varepsilon$-independent horizontal viscosity. Now, the choice of the order $gamma$ leads to different limit equations:
For $gamma=2$, one obtains the primitive equations with full viscosity term $-Delta$;
For $gamma>2$, one obtains the primitive equations with only horizontal viscosity term $- Delta_H$;
For $gamma <2$, one obtains the 2D Navier-Stokes equations.
Thus, there are three possible limits of the hydrostatic approximation depending on the assumption on the vertical viscosity. Here, we show how maximal regularity methods and quadratic inequalities - reminiscent of the Fujita-Kato methods - can be an efficient approach to prove norm-convergences in all three cases. This is a joint work with Ken Furukawa, Yoshikazu Giga, Matthias Hieber, Takahito Kashiwabara, and Marc Wrona, see https://arxiv.org/abs/2312.03418 for a preprint.
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Oberseminar “Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Veranstalter
Humboldt-Universität zu Berlin
WIAS Berlin
- 29. September – 1. Oktober 2025 (WIAS-ESH)
- Workshop/Konferenz: Mathematical Analysis of Fluid Flows by Variational Methods
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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal
Veranstalter
Freie Universität Berlin
Universität Leipzig
WIAS Berlin
- 15. – 17. Oktober 2025 (WIAS-ESH)
- Workshop/Konferenz: Recent Developments in Spatial Interacting Random Systems
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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal
Veranstalter
WIAS Berlin
- 3. – 7. November 2025 (WIAS-Library)
- Workshop/Konferenz:
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Weierstraß-Institut, Hausvogteiplatz 5-7, 10117 Berlin, R411
Abstrakt
The ARISE project (Analysis of Robust Numerical Solvers for Innovative Semiconductors in View of Energy Transition) brings together the RAPSODI team at Inria Lille and the NUMSEMIC team at WIAS Berlin. It focuses on developing advanced mathematical and numerical models for drift-diffusion models for charge transport with mobile ions, with applications for novel semiconductor devices such as perovskite solar cells and memristors, as well as ionic solutions or corrosion phenomena.
Veranstalter
WIAS Berlin