## Weekly Bulletin (it)

**Notiziario dei seminari di carattere matematico**

a cura del Dipartimento di Matematica

*G. Castelnuovo*, Sapienza Università di Roma

Settimana dal 18-02-2019 al 24-02-2019

**Lunedì 18 e martedì 19 febbraio 2019**

Aula V, Dipartimento di Matematica, Sapienza Università di Roma

Convegno *Due giorni di Algebra Lineare Numerica*

Pagina web del convegno: http://www.mat.uniroma1.it/rm2ggaln

- LUNEDI 18 FEBBRAIO mattina
- 9:10 Antonio Cicone,
*Nonstationary signals decomposition: an overview on the state of the art, current applications and possible future directions of research* - 9:35 Patricia Díaz de Alba,
*Linear and nonlinear models for EMI data inversion* - 10:00 Anna Concas,
*Photometric Stereo under unknown lights position* - 10:25 Domitilla Brandoni,
*Tensor techniques for image recognition* - 11:20 Federica Pes,
*Regularization methods for nonlinear ill-posed problems* - 11:45 Lothar Reichel,
*Arnoldi decomposition, GMRES, and preconditioning for linear discrete ill-posed problems* - 12:10 Ivan Gerace,
*An Edge-Preserving Regularization Model for the Demosaicing of Noisy Color Images* - 12:35 Valentina Giorgetti,
*A Blind Source Separation Technique for Document Restoration*

- 9:10 Antonio Cicone,
- LUNEDI 18 FEBBRAIO pomeriggio
- 14:15 Pietro Dell'Acqua,
*New boundary conditions for fast and accurate deblurring models* - 14:40 Noe Caruso,
*On Krylov solutions to infinite-dimensional inverse linear problems* - 15:05 Bruno Carpentieri,
*Spectrally preconditioned and initially deflated variants of the block GMRES method for the simultaneous solution of multiple right-hand sides linear systems* - 15:30 Mariarosa Mazza,
*Spectral properties of flipped Toeplitz matrices and related preconditioning* - 16:25 Mattia Tani,
*Space-time isogeometric preconditioners for parabolic problems* - 16:50 Fabio Durastante,
*Some fast algorithms for the large structured linear systems of FPDEs* - 17:15 Ken Trotti,
*Anisotropic multigrid preconditioners for space-fractional diffusion equations* - 17:40 Carlo Janna,
*Solving large size linear systems of equations on modern high-performance computers* - 18:05 Matteo Frigo,
*A Relaxed Physical Factorization Preconditioner for Mixed Finite Element Coupled Poromechanics*

- 14:15 Pietro Dell'Acqua,
- MARTEDI 19 FEBBRAIO mattina
- 9:10 Michela Redivo-Zaglia,
*Shanks' transformations, Anderson acceleration, and applications to systems of equations* - 9:35 Stefano Cipolla,
*Extrapolation Methods for Data Science* - 10:00 Dario Fasino,
*So, what is the Random Walk Centrality?* - 10:25 Pasqua D'Ambra,
*Bootstrap AMG in spectral clustering* - 11:20 Gian Maria Negri Porzio,
*A contour integral approach for the solution of nonlinear eigenvalue problems* - 11:45 Matteo Ronchetti,
*IKA: Independent Kernel Approximator* - 12:10 Paola Ferrari,
*The eigenvalue distribution of special 2-by-2 block matrix-sequences with applications to the case of symmetrized Toeplitz structures* - 12:35 Monica Dessole,
*Solving ABD systems on GPUs*

- 9:10 Michela Redivo-Zaglia,
- MARTEDI 19 FEBBRAIO pomeriggio
- 14:15 Lucia Romani,
*Even-symmetric interpolatory subdivision schemes: a constructive algebraic strategy* - 14:40 Rafael Díaz Fuentes,
*Interpolation of points and tangent directions by linear approximating subdivision schemes* - 15:05 Stefano Massei,
*Low-rank updates and divide-and-conquer methods for quadratic matrix equations* - 15:30 Alice Cortinovis,
*On maximum volume submatrices and cross approximation* - 16:25 Nicola Mastronardi,
*On computing the Jordan structure of Totally Nonnegative Matrices with high relative accuracy* - 16:50 Leonardo Robol,
*Distance from rank-structured matrices* - 17:15 Davide Palitta,
*The projected Newton-Kleinman method for the algebraic Riccati equation* - 17:40 Antonio Fazzi,
*Computing approximate common factors of matrix polynomials* - 18:05 Stefano Maset,
*Relative error analysis of matrix exponential approximations for numerical integration*

- 14:15 Lucia Romani,

**Lunedì 18 febbraio 2019**

Ore 11:00, Aula Dal Passo, Dipartimento di Matematica dell'Università di Roma "Tor Vergata"

Vincenzo Basco
*Infinite horizon control problems under state constraint and Hamilton-Jacobi-Bellman equations*

**Lunedì 18 febbraio 2019**

Ore 14:15, Aula Consiglio, Dipartimento di Matematica

Seminario di Analisi Matematica

Giovanni Bellettini (DIISM, Universita' di Siena)
*Contorni apparenti e ricostruzione di scene tridimensionali*

Verranno discussi alcuni aspetti di
un noto problema della teoria della visione:
come ricostruire una forma solida tridimensionale a partire
da un suo contorno apparente, cioe' da un grafo planare
con cuspidi e incroci trasversali.
Verrano in particolare descritti alcuni risultati di tipo topologico
e, se possibile, il ruolo del programma Appcontour.

**Lunedì 18 febbraio 2019**

Ore 14:30, Aula 116 (1 piano), IAC-CNR

Seminario di Fisica-Matematica

Prof. Luciano Rezzolla (Institut fur Theoretische Physik, Frankfurt, Germany)
*Relativistic hydrodynamics in strong gravitational fields*

Relativistic hydrodynamics is an incredibly successful approach to study a large variety of problems that range from relativistic collisions of heavy ions to the inspiral and merger of neutron stars. I will review the basic mathematical and numerical frameworks for the solution of the equations of relativistic hydrodynamics in arbitrary spacetimes and discuss how the corresponding solutions can be used to answer fundamental questions in physics and astrophysics.

**Martedì 19 febbraio 2019**

Ore 14:30, Aula D'Antoni, Dipartimento di Matematica, Università degli Studi di Roma "Tor Vergata"

Algebra and Representation Theory Seminar

Benoit Fresse (Università di Lille)
*Kontsevich's graph complexes, operadic mapping spaces, and the Grothendieck-Teichmüller group*

I will report on a joint work with Victor Turchin and Thomas Willwacher about the applications of graph complexes to the study of mapping spaces associated to \(E_n\)-operads. The class of \(E_n\)-operads consists of objects that are homotopy equivalent to a reference model, the operad of little \(n\)-disks, which was introduced by Boardman-Vogt in topology. I will briefly review the definition of these objects. The main goal of my talk is to explain that the rational homotopy of mapping spaces of \(E_n\)-operads has a combinatorial description in terms of the homology of Kontsevich's graph complexes. This approach can also be used for the study of homotopy automorphism spaces associated to \(E_n\)-operads. In the case \(n=2\), one can identify the result of this computation with the pro-unipotent Grothedieck-Teichmüller group. The proof of these statements relies on results on the rational homotopy of \(E_n\)-operads which I will also briefly explain in my talk.

**Martedì 19 febbraio 2019**

Ore 14:30, Aula Dal Passo, Dipartimento di Matematica, Università degli Studi di Roma "Tor Vergata"

Seminario di Equazioni Differenziali

Pietro Baldi (Università di Napoli Federico II)
*Control of water waves and quasilinear evolution PDEs*

The talk deals with recent results of exact controllability, with internal control, for dispersive quasilinear evolution PDEs in the space-periodic setting: the gravity-capillary water wave equations, and quasilinear perturbations of the Korteweg-de Vries (KdV) and nonlinear Schrodinger (NLS) equations. Two different approaches are considered: the work [1] is based on microlocal analysis with a quasilinear scheme, while [2,3,4] rely on a new Nash-Moser theorem, which is sharp regarding a certain regularity issue. [1] T. Alazard, P. Baldi and D. Han-Kwan, Control of water waves, J. Eur. Math. Soc. (JEMS) 20 (2018), 657-745. [2] P. Baldi, G. Floridia, E. Haus, Exact controllability for quasi-linear perturbations of KdV, Anal. PDE 10 (2017), 281-322. [3] P. Baldi, E. Haus, A Nash-Moser-Hormander implicit function theorem with applications to control and Cauchy problems for PDEs, J. Funct. Anal. 273 (2017), 3875-3900. [4] P. Baldi, E. Haus, R. Montalto, Controllability of quasi-linear Hamiltonian NLS equations, J. Differential Equations 264 (2018), 1786-1840.

**Martedì 19 febbraio 2019**

Ore 14:30, stanza 311, Dipartimento di Matematica e Fisica, Universita' degli Studi Roma Tre, Largo San Leonardo Murialdo 1

Seminario di Fisica Matematica

Prof. G. Gallavotti (Univ. Roma Sapienza)
*Navier-Stokes equation: irreversibility, turbulence and ensembles equivalence*

The NS equation is considered (in 2 & 3 dimensions) with a fixed forcing on large scale; the stationary states form a family of probability distributions on the fluid velocity fields depending on a parameter R (Reynolds number). It is proposed that other equations could lead to -exactly- the same distributions and that the mechanism is closelyanalogous to the coincidence of the canonical and microcanonical averages of local observables in statistical mechanics in the thermodynamic limit (which in NS is proposed to correspond to the limit in which the UV cut-off N is removed to infinity).

**Martedì 19 febbraio 2019**

Ore 15:30, Dal Passo (1201), Dipartimento di Matematica, Università di Roma Tor Vergata

Seminario Dipartimentale

Gilberto Bini (Università di Milano Statale)
*Invariants and Classification*

Classification is extremely important in various scientific disciplines, such as Chemistry and Biology, as well as Mathematics. In this talk, we will recall some examples and give some more, specially in relation with projective geometry and birational geometry, in order to give a classification of low dimensional complex projective varieties with respect to suitable invariants. [Department Seminar (general audience talk) - in the framework of the Research Project "Families of curves: their moduli and their related varieties" - Mission Sustainability Tor Vergata, CUP: E81|18000100005, Principal Investigator: F. Flamini]

**Martedì 19 febbraio 2019**

Ore 16:30, Aula di Consiglio, Dipartimento di Matematica, Sapienza Università di Roma

Esame finale di Dottorato

Federico Luigi Dipasquale (Dipartimento di Matematica, Sapienza Università di Roma)
*Variational methods in the Landau-de Gennes theory of nematic liquid crystals*

In this talk, I will present the main results of my Ph.D. thesis, focused on biaxial torus solutions in the Landau-de Gennes (LdG) model for nematic liquid crystals. These are smooth minimizers, so far only known through numerical experiments, of a widely-studied LdG energy functional w.r.t. a radial Dirichlet boundary datum, in conditions of "low temperature", with a very rich structure and a peculiar S^1-equivariant profile. We analytically prove that minimizing the energy in the class of S^1-equivariant Q-tensors of constant pointwise norm (which is, surprisingly, physically reasonable) agreeing the assigned boundary condition on the boundary gives back either biaxial torus solutions or the analogue of a special kind of singular solution, also expected from simulations. We then investigate the behavior of minimizers w.r.t. deformations of the boundary datum and, exploiting the very precise classification we got of the possible singularities, we also establish counterparts of some well-known theorems in harmonic maps. Joint work with Vincent Millot (Paris Diderot) and Adriano Pisante (Sapienza).

**Mercoledì 20 febbraio 2019**

Ore 14:00, Consiglio, Dipartimento di Matematica, Sapienza Università di Roma

Seminario di algebra e geometria

Tamas Hausel (Vienna)
*Intersection of mirror branes on Higgs moduli spaces*

I will discuss a computational approach for the semiclassical limit of mirror symmetry for Higgs moduli spaces for Langlands dual groups, by comparing the equivariant indices of intersections of mirror branes.

**Giovedì 21 febbraio 2019**

Ore 14:15, Aula B, Dipartimento di Matematica, Sapienza Università di Roma

Esame finale di Dottorato

Davide Palmigiani (Dipartimento di Matematica, Sapienza Università di Roma)
*Stochastic Models of Biological Evolution*

We deal with the problem of creating a model that describes a population of agents undergoing Darwinian Evolution, which takes into account the basic phenomena of this process. According to the principles of evolutionary biology, Evolution occurs if there is selection and adaptation of phenotypes, mutation of genotypes, presence of physical space. The evolution of a biological population is then described by a system of ordinary stochastic differential equations; the basic model of dynamics represents the trend of a population divided into different types, with relative frequency in a simplex. The law governing this dynamics is called Replicator Dynamics: the growth rate of type k is measured in terms of evolutionary advantage, with its own fitness compared to the average in the population. The replicator dynamics model turns into a stochastic process when we consider random mutations that can transform fractions of individuals into others. The two main forces of Evolution, selection and mutation, act on different layers: the environment acts on the phenotype, selecting the fittest, while the randomness of the mutations affects the genotype. This difference is underlined in the model, where each genotype express a phenotype, and fitness influences emerging traits, not explicitly encoded in genotypes. The presence of a potentially infinite space of available genomes makes sure that variants of individuals with characteristics never seen before can be generated. In conclusion, numerical simulations are provided for some applications of the model, such as a variation of Conway's Game of Life.

**Giovedì 21 febbraio 2019**

Ore 14:30, Aula di Consiglio, Dipartimento di Matematica, Sapienza Università di Roma

Aula di Consiglio

Eugenio Vecchi (Università degli Studi di Trento)
*Symmetry and rigidity for composite membranes and plates*

The composite membrane problem is an eigenvalue optimization problem that can be formulated as follows: Build a body of prescribed shape out of given materials (of varying densities) in such a way that the body has a prescribed mass and so that the basic frequency of the resulting membrane (with fixed boundary) is as small as possible. In the first part of the talk we will review the known results and present a Faber-Krahn-type result obtained in collaboration with G. Cupini (Università di Bologna). A natural extension of the above problem to plates is the composite plate problem, which is an eigenvalue optimization problem involving the bilaplacian operator. The Euler-Lagrange equation associated to it is a fourth-order PDE that is coupled with Navier boundary conditions (for the hinged plate), or with Dirichlet boundary conditions (for the clamped plate). In the second part of the talk we will focus on symmetry properties of optimal pairs highlighting the differences between the hinged and the clamped case. These results have been obtained in collaboration with F. Colasuonno (Università di Torino).

**Giovedì 21 febbraio 2019**

Ore 15:00, Dal Passo (1201), Dipartimento di Matematica, Università di Roma Tor Vergata

Seminario di Geometria Algebrica

Gilberto Bini (Università Milano Statale)
*A meaningful invariant in birational geometry*

In this talk we will survey on the state of the art of some relevant conjectures for the birational classification of complex projective varieties with respect to an invariant that has not been completely utilised but seems to be potentially meaningful: the pseudo-effective dimension. [Algebraic Geometry Seminar - in the framework of the Research Project "Families of curves: their moduli and their related varieties" - Mission Sustainability Tor Vergata, CUP: E81|18000100005]

**Venerdì 22 febbraio 2019**

Ore 12:00, Aula di Consiglio, Dipartimento di Matematica

seminario MoMA

Karl Sigmund
*Social learning leads to the recurrence of corruption*

Cooperation can be sustained by institutions that punish free-riders. Such institutions, however, tend to be subverted by corruption if they are not closely watched. Monitoring can uphold a regime of honesty and cooperation, but usually comes at a price. The temptation to skip monitoring regularly leads to outbreaks of corruption and the breakdown of cooperation. We model the corresponding cycle by means of evolutionary game theory, using analytical methods and numerical simulations. The results confirm the view that transparency is a major factor in fighting corruption.

**Venerdì 22 febbraio 2019**

Ore 16:00, Aula Picone, Dipartimento di Matematica, Sapienza Università di Roma

Seminario per insegnanti (Piano Lauree Scientifiche)

Giuseppe Accascina*, Patrizia Berneschi**, Elena Possamai** (*Sapienza Università di Roma, **Liceo Nomentano)
*Dalle immagini ai modelli*

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