### Seminari

### Prossimi Seminari

**Laser "su misura" per il trattamento di tumori**

Paola Saccomandi, Politecnico di Milano

mercoledì 27 marzo 2019 alle ore 12:15, Politecnico di Milano Campus Bonardi Edificio14 aula B21**Some remarks on the forces exerted by a viscous fluid on a bluff body**

Gianmarco Sperone, Politecnico di Milano

giovedì 28 marzo 2019 alle ore 15:15, Aula seminari 3° piano**Simplicial splines for representation of density functions**

Karel Hron e Jitka Machalova, Palacky University di Olomouc

martedì 2 aprile 2019 alle ore 15:00 precise, Aula Seminari 'Saleri' VI Piano MOX-Dipartimento di Matematica, Politecnico di Milano - Edificio 14**Stima del valore aggiunto di scuola: stato dell'arte del modello INVALSI e prospettive. Quali implicazioni di policy?**

Tommaso Agasisti, Politecnico di Milano

mercoledì 3 aprile 2019 alle ore 12:15, Politecnico di Milano Campus Bonardi Edificio14 aula B21**On the modelling of particle and pedestrian motion with Fokker-Planck equations**

Alfio Borzì, University of Wuerzburg -Germania-

giovedì 4 aprile 2019 alle ore 14:00, Aula Consiglio VII Piano - Edificio 14, Dipartimento di Matematica POLITECNICO DI MILANO**Problemi di frontiera libera nelle scienze applicate**

Sandro Salsa, Politecnico di Milano

mercoledì 10 aprile 2019 alle ore 12:15, Politecnico di Milano Campus Bonardi Edificio14 aula B21**Errori sistematici e confondimento degli studi osservazionali basati sui dati dal mondo reale**

Giovanni Corrao, Università degli Studi di Milano-Bicocca

mercoledì 8 maggio 2019 alle ore 12:15, Politecnico di Milano Campus Bonardi Edificio14 aula B21**Inverse Problems in Adaptive Optics**

Ronny Ramlau, RICAM, Austrian Academy of Sciences, Linz, Austria

mercoledì 8 maggio 2019 alle ore 14:00, Aula Consiglio VII Piano - Edificio 14, Dipartimento di Matematica POLITECNICO DI MILANO**Forma e complessità in Natura: perché il mondo è matematico?**

Pasquale Ciarletta, Politecnico di Milano

mercoledì 15 maggio 2019 alle ore 12:15, Politecnico di Milano Campus Bonardi Edificio14 aula B21**Matematica, società, economia e sviluppo**

Giulia di Nunno, University di Oslo

mercoledì 22 maggio 2019 alle ore 12:15, Politecnico di Milano Campus Bonardi Edificio14 aula B21**Comunicare il progetto. Storytelling e tecniche di rappresentazione**

Francesca Piredda, Politecnico di Milano

mercoledì 29 maggio 2019 alle ore 12:15, Politecnico di Milano Campus Bonardi Edificio14 aula B21**Semi-implicit finite-volume integrators for all-scale atmospheric dynamics**

Piotr Smolarkiewicz, European Centre for Medium-Range Weather Forecasts, Reading, Berkshire, United Kingdom

giovedì 30 maggio 2019 alle ore 14:00, Aula Consiglio VII Piano - Edificio 14, Dipartimento di Matematica POLITECNICO DI MILANO

### Seminari Passati

**L’avventura dell'infinitamente piccolo oltre il bosone di Higgs: LHC e i futuri super-acceleratori del CERN**

Lucio Rossi, CERN

mercoledì 20 marzo 2019 alle ore 12:15, Politecnico di Milano Campus Bonardi Edificio14 aula B21**Il futuro dell'uomo nello Spazio: Marte prossima frontiera**

Luigi Bignami, Giornalista scientifico

mercoledì 13 marzo 2019 alle ore 12:15, Politecnico di Milano Campus Bonardi Edificio14 aula B21**The SQRA Operator: Convergence Behaviour and Applications**

Martin Heida, Weierstrass Institute Berlin

mercoledì 13 marzo 2019 alle ore 15:15 precise, Aula Seminari III pianoABSTRACTThe Squareroot Approximation Operator (SQRA) is a numerical FV-operator that has recently been derived by M. Weber and coworkers and has the form of a discrete spatial chemical master equation. We use methods from stochastic homogenization to prove convergence in the context of high dimensional numerical implementation. We furthermore show that the SQRA is equivalent with the Scharfetter-Gummel scheme and use this insight to prove convergence of order 1 of both schemes in low dimensional settings. This is particularly possible due to a deep connection between the SQRA and the gradient structure of the Fokker-Planck equation discussed by Jordan, Kinderlehrer and Otto. We finally discuss physical implications of our insights and possible future applications to hydrodynamic limits arising in the modelling of organic semiconductors.**Lanford’s Theorem and the Emergence of Irreversibility**

Jos Uffink, University of Minnesota

martedì 12 marzo 2019 alle ore 16:30 precise, Sala Consiglio, 7 piano, Ed. La NaveABSTRACTIt is a longstanding problem to show how the irreversible behaviour of macroscopic systems can be reconciled with the time-reversal invariance of these same systems when considered from a microscopic point of view. A theorem by Lanford shows that, under certain conditions, the famous Boltzmann equation, describing the irreversible behaviour of a dilute gas, can be obtained from the time-reversal invariant Hamiltonian equations of motion for the hard spheres model. This raises the question whether and how Lanford’s theorem succeeds in deriving this remarkable emergence of irreversibility. Many authors (Cercignani, Illner & Pulvirenti, 1994; Lebowitz 1983, Spohn 1991) have expressed very different views on this question. In this talk, I will argue that the theorem actually does not imply irreversibility at all.**Tame topology and algebraic geometry**

Bruno Klingler, Humboldt Universitaet Berlino

lunedì 11 marzo 2019 alle ore 16:30 precise, Aula Seminari 6 piano, Ed. La NaveABSTRACTIn "Esquisse d'un programme" Grothendieck argues that general topology, which was developed for the needs of analysis, should be replaced by a "tame topology" if one wants to study the topological properties of natural geometric forms.

Such a tame topology has been developed by model theorists under the name "o-minimal structures". The goal of this lecture will be to explain in simple topological terms the notion of o-minimal structure and its applications in algebraic geometry, in particular for studying periods of algebraic varieties.**Stochastic atomic congestion games: Price-of-Anarchy and convergence for large games**

Roberto Cominetti, Universidad Adolfo Ibáñez

venerdì 8 marzo 2019 alle ore 11:00, Sala del Consiglio 7° pianoABSTRACTWe consider atomic congestion games with stochastic demand in which each player participates in the game with probability p, and incurs no cost with probability 1-p. For congestion games with affine costs, we provide a tight upper bound for the Price-of-Anarchy as a function of p, which is monotonically increasing and converges to the well-known bound of 5/2 when p converges 1. On the other extreme, for p? 1/4 the bound is constant and equal to 4/3 independently of the game structure and the number of players. For general costs we also analyze the asymptotic convergence of such games when the number of players n grows to infinity but the probability tends to zero as $p_n=\lambda/n$, in which case we establish the convergence towards a Poisson limit game. In a different approach where the weight of the players tend to zero, we find that the limit yields a Wardrop equilibrium for a corresponding nonatomic game.**Optimization with expensive and uncertain data - challenges and improvements**

Coralia Cartis, Mathematical Institute, University of Oxford, UK

giovedì 7 marzo 2019 alle ore 15:30, Aula Consiglio VII Piano - Edificio 14, Dipartimento di Matematica POLITECNICO DI MILANOABSTRACT: Real-life applications often require the optimization of nonlinear functions with several unknowns or parameters - where the function is the result of highly expensive and complex model simulations involving noisy data (such as climate or financial models, chemical experiments), or the output of a black-box or legacy code, that prevent the numerical analyst from looking inside to find out or calculate problem information such as derivatives. Thus classical optimization algorithms, that use derivatives (steepest descent, Newton's methods) often fail or are entirely inapplicable in this context. Efficient derivative-free optimization algorithms have been developed in the last 15 years in response to these imperative practical requirements. As even approximate derivatives may be unavailable, these methods must explore the landscape differently and more creatively. In state of the art techniques, clouds of points are generated judiciously and sporadically updated to capture local geometries as inexpensively as possible; local function models around these points are built using techniques from approximation theory and carefully optimised over a local neighbourhood (a trust region) to give a better solution estimate.

In this talk, I will describe our implementations and improvements to state-of-the-art methods. In the context of the ubiquitous data fitting/least-squares applications, we have developed a simplified approach that is as efficient as state of the art in terms of budget use, while achieving better scalability. Furthermore, we substantially improved the robustness of derivative-free methods in the presence of noisy evaluations. Theoretical guarantees of these methods will also be provided. Finally, despite derivative-free optimisation methods being able to only provably find local optima, we illustrate that, due to their construction and applicability, these methods can offer a practical alternative to global optimisation solvers, with improved scalability. This work is joint with Lindon Roberts (Oxford), Katya Scheinberg (Lehigh), Jan Fiala (NAG Ltd) and Benjamin Marteau (NAG Ltd).

Contact: alfio.quarteroni@polimi.it

**Testing families of analytic discs**

Luca Baracco, Università di Padova

giovedì 7 marzo 2019 alle ore 14:30 precise, Aula seminari del 3 pianoABSTRACT

It is a well-known fact in the theory of several complex variables that a function

is holomorphic if and only if it is holomorphic in each variable separately. This

result goes back to Hartogs. It is natural to consider a boundary version of Hartogs’ theorem. The general problem is to take a boundary function and ask if holomorphic extensions on some families of complex curves are enough to guarantee an extension which is holomorphic in all variables simultaneously.

We will talk about the known results on the subject and show some new results obtained in collaboration with M. Fassina and S. Pinton for the spiecial case of the unit ball in C^n.