Events

More information: https://zucmap.ethz.ch/call_made

In this lecture, we will discuss recent results from our group that explore the relationship between control theory and machinevlearning, specifically supervised learning and universal approximation. We will take a novel approach by considering the simultaneous control of systems of Residual Neural Networks (ResNets). Each item to be classified corresponds to a different initial datum for the ResNet's Cauchy problem, resulting in an ensemble of solutions to be guided to their respective targets using the same control. We will introduce a nonlinear and constructive method that demonstrates the attainability of this ambitious goal, while also estimating the complexity of the control strategies. This achievement is uncommon in classical dynamical systems in mechanics, and it is largely due to the highly nonlinear nature of the activation function that governs the ResNet dynamics. This perspective opens up new possibilities for developing hybrid mechanics-data driven modeling methodologies. Throughout the lecture, we will also address some challenging open problems in this area, providing an overview of the exciting potential for further research and development.

In this talk, we will consider a stabilized version of the fundamental existence problem of symplectic structures (McDuff--Salamon, Problem 1). Given a formal symplectic manifold, i.e. a closed manifold M with a non-degenerate 2-form and a non-degenerate second cohomology class, we investigate when its natural stabilization to M x T^2 can be realized by a symplectic form. We show that this can be done whenever the formal symplectic manifold admits a symplectic divisor. It follows that the product with T^2 of an almost symplectic blow up admits a symplectic form. Another corollary is that if a formal symplectic 4-manifold M, which either satisfies that its positive/negative second betti numbers are both at least 2, or that is simply connected, then M x T^2 is symplectic. For instance (CP^2#CP^2#CP^2)xT^2 is symplectic, even though CP^2#CP^2#CP^2 is not, by work of Taubes. These results follow from a stabilized version of Eliashberg--Murphy's h-principle for symplectic cobordisms, which makes no assumptions on overtwistedness at the boundary. This is joint work with Fabio Gironella, Fran Presas, Lauran Toussaint.

Computer graphics has been developing since the advent of first displays in the 1950s. Nowadays we're enjoying the results of this research daily through medical imaging, computer-generated imagery in movies and computer games, through interacting with objects designed with computer-aided design, etc. The aim of this talk is to demonstrate applications of geometry in different areas of computer graphics: mesh acquisition, geometry processing, and rendering.

We consider one dimensional nonlinear Schrodinger equations around a traveling wave. We prove its asymptotic stability for general nonlinearities, under the hypotheses that the orbital stability condition of Grillakis-Shatah-Strauss is satisfied and that the linearized operator does not have a resonance and only has 0 as an eigenvalue. As a by-product of our approach, we show long-range scattering for the radiation remainder. Our proof combines for the first time modulation techniques and the study of space-time resonances. We rely on the use of the distorted Fourier transform, akin to the work of Buslaev and Perelman and, and of Krieger and Schlag, and on precise renormalizations, computations and estimates of space-time resonances to handle its interaction with the soliton. This is joint work with Pierre Germain.

We consider the Kyle model in continuous time, where the informed traders face additional frictions. These frictions may arise due to difficulties in executing large portfolio, or legal penalties in case the informed trader is trading illegally on inside information. The equilibrium is characterised via the solution of a backward stochastic differential equation (BSDE) whose terminal condition is determined as the fixed point of a non-linear operator in equilibrium. A curious connection between the terminal condition of this BSDE and an entropic optimal transport problem appears in equilibrium. We find that informed traders consistently trade a constant multiple of the difference between the fundamental value and their anticipated market price just before their private information is disclosed to the public, reminiscent of the behaviour of a large trader in an Almgren-Chris model. If time permits, as an application to insider trading regulation, we also consider a regulator’s challenge of balancing price informativeness with minimising losses for uninformed traders, given a budget constraint. High legal penalties deter illegal trading and protect uninformed traders but make prices less efficient. An optimal policy suggests that if the cost of investigation exceeds its benefits, it’s best not to investigate.

The quadratic Reciprocity Law for the Legendre or Jacobi-Symbol forms the starting point of all Reciprocity Laws as well as of class field theory. It is closely related to the product formula of the quadratic Hilbert-Symbol over local fields. Various mathematicians have established higher explicit formulae to compute higher Hilbert-Symbols. Analogs were found for formal (Lubin-Tate) groups. Eventually Perrin-Riou has formulated a Reciprocity Law, which allows the explicit computation of local cup product pairings by means of Iwasawa- and p-adic Hodge Theory. In this talk I shall try to give an overview of these topics, at the end I will explain recent developments in this regard.