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<< November 2017

Event Calendar December 2017

January 2018 >>

10 entries found

  • 01. December
    13:30 - 15:00
    Location: 48-210
    Graduate School

    Wlazlo, Jaroslaw: Elastic Image Registration with Strong Mass Preserving Constraints

  • 01. December
    13:45 - 15:15
    Location: Fraunhofer ITWM, Z03.07
    Graduate School

    Grün, Sarah: Discrete Dividends: Modeling, Estimation and Portfolio Optimization

  • 05. December
    15:30 - 17:00
    Location: 48-436
    AG Algebra, Geometrie und Computeralgebra

    Dan Roche/US Naval Academy Annapolis: nteger Polynomial Sparse Interpolation with Near-Optimal Complexity

    We investigate algorithms to discover the nonzero coefficients and exponents of an unknown sparse polynomial, provided a way to evaluate the polynomial over any modular ring. This problem has been of interest to the computer algebra community for decades, and its uses include multivariate      
    polynomial GCD computation, factoring, and sparse polynomial arithmetic. Starting with the early works of Zippel, Ben-Or and Tiwari, and Kaltofen, one line of investigation has a key advantage in achieving the minimal number of evaluations of the polynomial, and has received considerable  attention and improvements over the years. It is closely related to problems in coding theory and exponential analysis. The downside, however, is that these methods are not polynomial-time over arbitrary fields. A  separate line of work starting with Garg and Schost and continuing with a few papers by the speaker and coauthors, has developed a different approach that works over any finite field. After years of improvements, the             
    complexity of both approaches over ZZ[x] is currently the same. They scale well in most aspects except for the degree; the bit complexity in both cases is currently cubic in the bit-lengths of the exponents. By careful  combination of the techniques in both approaches and a few new tricks, we are now able to overcome this hurdle. We present an algorithm whose running time is softly-linear in the size of the output and performs nearly the minimal number of evaluations of the unknown polynomial. Preliminary           
    implementation results indicate good promise for practical use when the  unknown polynomial has a moderate number of variables and/or large  exponents.

  • 07. December
    15:30 - 17:00
    Location: 48-538
    AG Technomathematik

    Irina Kashuba/University of Sao Paulo: Indecomposable Modules over Jordan Superalgebras.

    In this talk we plan to give a survey of both classical and recent results obtained
    in the representation theory of Jordan algebras and superalgebras. Further we
    will construct indecomposable representations of both Kantor double superalgebra
    Kan(n), n  1 and the Jordan superalgebra of symmetric elements JP2. Our
    main tool is the famous Tits-Kantor-Koecher construction. The representations
    are given in terms of Ext quiver algebra of the category of representations with
    the short grading over certain Lie superalgebra. This is joint result with Vera

  • 07. December
    17:00 - 18:00
    Location: 48-436
    AG Algebra, Geometrie und Computeralgebra

    Emilio Rotilio, TU Kaiserslautern: Lie Superalgebras in Physics

    The current understanding of nature finds in the „Standard Model“ the most complete and verified theory (for now). The mathematics it involves heavily relies on Lie theory (Lie groups and Lie algebras). To better describe the universe, phisicists have come up with a „Supersymmetry“ theory (among others). This theory is described in terms of Lie superalgebras. The goal of this talk is to give an overview of which Lie algebras/superalgebras are used in Physics and why they help describing nature.

  • 12. December
    17:15 - 18:30
    Location: Raum 48-210

    Prof. Dr. Peter Benner, MPI -Magdeburg, "Feedback Stabilization of Unsteady Flow Problems"

    Optimizing a trajectory of any unsteady problem in practice requires a
    feedback strategy in order to attenuate disturbances, e.g., external
    influences or unmodeled dynamics, that would lead to a deviation from
    the desired, and possibly optimized, path. In this talk, we consider the
    unsteady incompressible 2D Navier-Stokes equations and discuss their
    feedback stabilization using Riccati-type controllers based on the
    Dirichlet boundary control problem for the flow field. Numerical
    methods to solve the resulting large-scale, descriptor-type algebraic
    Riccati equations will be discussed. Their performance will be
    illustrated by numerical experiments.

  • 14. December
    11:30 - 12:15
    Location: 32-349

    Prof. C. Schillings, Univ. Mannheim, Uncertainty Quantification for Inverse Problems

    Uncertainty Quantification (UQ) is an interesting, fast growing research area aimed at developing methods to address the impact of parameter, data and model uncertainty in complex systems. In this talk we will focus on the identification of parameters through observations of the response of the system – the inverse problem. The uncertainty in the solution of the inverse problem will be described via the Bayesian approach. In cases, where the model evaluations are prohibitively expensive, ad hoc methods such as the Ensemble Kalman Filter (EnKF) for inverse problems are widely and successfully used by practitioners in order to approximate the solution of the Bayesian problem.
    The low computational costs, the straightforward implementation and their non-intrusive nature make them appealing in various areas of application, but, on the downside, they are underpinned by very limited theoretical understanding. In this talk, we will discuss an analysis of the EnKF based on the continuous time scaling limits, whichallows to derive estimates on the long-time behaviour of the EnKF and, hence, provides insights into the convergence properties of the algorithm. In particular, we are interested in the properties of the EnKF for a fixed ensemble size. Results from various numerical experiments supporting the theoretical findings will be presented.

  • 14. December
    12:15 - 13:00
    Location: 32-349

    J. Kusch, KIT, An approximate Newton Smoothing Method for Shape Optimization

    In this talk, we derive a smoothing method for shape optimization in Stokes and Navier-Stokes flows. The smoothing routine automatically picks a spatially dependent smoothing parameter in such a way that the optimization process is accelerated, turning the smoothing routine into an approximate Newton method.
    This task is achieved by analytically deriving the symbol of the Hessian for the Stokes equations. We numerically investigate the Hessian symbol for convective flows and demonstrate the applicability of the symbol for the Navier-Stokes equations.
    The constructed preconditioner approximates the derived symbol using windowed Fourier transform and thereby accelerates the optimization process while yielding a smooth search direction. Due to the fact that the smoothing is performed locally, the method will identify areas in which a non-smooth design is physically meaningful and will automatically turn off smoothing in these regions.

  • 14. December
    17:00 - 18:00
    Location: 48-436
    AG Algebra, Geometrie und Computer Algebra

    Stefano Sannella/University of Birmingham: Broué's conjecture and perverse equivalences

    The representation theory of a finite group G over a field F of positive characteristic carries many questions that have not been answered yet. Most of them can be stated as global/local conjectures: in various forms, they state that the representation theory of G is somehow controlled by its p-local subgroups. Here we will mostly focus on one of these conjectures, Broué's Abelian Defect Group Conjecture, which might be considered as an attempt to give a structural explanation of what is actually connecting G and its local p-subgroups in the abelian defect case. In particular, we explain how the strategy of looking for a perverse equivalence (a specific type of derived equivalence) works successfully in some cases and how this procedure is related to some Deligne-Lusztig varieties.

  • 21. December
    17:00 - 18:00
    Location: 48-436
    AG Algebra, Geometrie und Computer Algebra

    Patrick Wegener/TU Kaiserslautern: Hurwitz action in elliptic Weyl groups and coherent sheaves on a weighted projective line

    Since 2000 the poset of noncrossing partitions attached to a Coxeter group (independently introduced by Bessis and Brady-Watt) has gained a lot of attention from different areas of mathematics. In 2010 Igusa, Schiffler and Thomas showed that there exists an order preserving bijection between this poset and the set of thick subcategories in the derived category of mod(A) generated by an exceptional sequence, where A is a hereditary Artin algebra. Following Happel's classification of hereditary categories, it seems natural to ask if there is an analogous statement when replacing mod(A) by the category of coherent sheaves on a weighted projective line. I will give a short summary on hereditary categories, explain how elliptic Weyl groups show up in this context and then generalize the result of Igusa-Schiffler-Thomas to tubular weighted projective lines. (This is joint work with B. Baumeister and S. Yahiatene.)