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282 discussions

Next NUMPI seminar: set the date
by Fabio Durastante 15 Apr '25

15 Apr '25

Good morning, We would like to fix the date for the next NUMPI seminar in May. It will be a seminar held by Federica Mugnaioni (Ph.D. Scuola Normale Superiore) on the topic of preconditioners for discretization of fictitious domain problems. Please reply with your availability for the days of May 12/13 and we will try to organize it at a time convenient for most of us: https://date.dm.unipi.it/Vh6AwjL3MKGWBESp Best, Fabio

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[Indico] Raf Vandebril, On inverse eigenvalue problems for multiple orthogonal polynomials, 14/04/2025, 11:30 Europe/Rome
by leonardo.robol＠unipi.it 14 Apr '25

14 Apr '25

Title: On inverse eigenvalue problems for multiple orthogonal polynomials, Speaker(s): Raf Vandebril, KU Leuven, Date and time: 14 Apr 2025, 11:30 (Europe/Rome), Lecture series: Seminar on Numerical Analysis, Venue: Dipartimento di Matematica (Saletta Riunioni). You can access the full event here: https://events.dm.unipi.it/e/318 Abstract -------- Multiple orthogonal polynomials (MOP's) arise in various applications, including approximation theory, random matrix theory, and numerical integration. To define MOP's, one needs multiple inner products, leading to two types of MOP’s, which are mutually biorthogonal. These MOP's satisfy recurrence relations, which can be linked to linear algebra, via discretization. As a result we get an inverse eigenvalue problem to retrieve the matrix of recurrences directly. We provide two algorithms for solving the inverse eigenvalue problem, one based on classical equivalence transformations and one linked to (block) Krylov methods. Numerical illustrations are provided to demonstrate correctness of the approach and also reveal the strong sensitivity of the problem. -- Indico :: Email Notifier https://events.dm.unipi.it/e/318

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[Indico] Raf Vandebril, On inverse eigenvalue problems for multiple orthogonal polynomials, 14/04/2025, 11:30 Europe/Rome
by leonardo.robol＠unipi.it 08 Apr '25

08 Apr '25

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[Indico] Prof. Michiel Hochstenbach, Recent Progress in Steplengths in Gradient Methods for Unconstrained Optimization, 3/27/25, 2:00 PM Europe/Rome
by stefano.massei＠unipi.it 26 Mar '25

26 Mar '25

Title: Recent Progress in Steplengths in Gradient Methods for Unconstrained Optimization, Speaker(s): Prof. Michiel Hochstenbach, Eindhoven University of Technology, Date and time: Mar 27, 2025, 2:00 PM (Europe/Rome), Lecture series: Seminar on Numerical Analysis, Venue: Dipartimento di matematica (Aula riunioni). You can access the full event here: https://events.dm.unipi.it/e/314 Abstract -------- We review recent progress in stepsizes in gradient methods for unconstrained numerical optimization, for both quadratic and general nonlinear problems, including several very valuable contributions from Italian experts such as Prof. Zanni and colleagues. We will review Barzilai-Borwein steps and secant equations, and show developments in harmonic stepsizes and homogeneous secant equations. The key idea is that the steplength is selected as the inverse Ritz value of an average Hessian. For limited memory methods, we will address several challenges, including how to avoid negative or non-real stepsize candidates. We will also present some open problems. This talk reflects joint work with Giulia Ferrandi. -- Indico :: Email Notifier https://events.dm.unipi.it/e/314

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Discussione tesi di dottorato di Alberto Bucci
by Leonardo Robol 21 Feb '25

21 Feb '25

Cari tutti e tutte, lunedì 24/02, alle 10.00, Alberto Bucci discuterà la sua tesi di dottorato in Aula Magna del Dipartimento di Matematica. Il titolo della tesi è "Randomized techniques for low-rank approximation of matrices and tensors with applications". Chiunque volesse partecipare è benvenuto/a! A presto, -- Leonardo.

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Online seminar at University of Rome "Tor Vergata": Stefano Pozza: 6 febbraio alle 12:30
by Fabio Durastante 29 Jan '25

29 Jan '25

Dear everybody, Forwarding of a NA seminar announcement that can also be followed online at the University of Rome "Tor Vergata". Best, Fabio ________________________________ Da: Mariarosa Mazza <mariarosa.mazza(a)uniroma2.it> Inviato: mercoledì 29 gennaio 2025 18:49 A: mariarosa.mazza(a)uniroma2.it Oggetto: seminario Pozza: 6 febbraio alle 12:30 Car* tutt*, giovedi 6 febbraio alle 12.30 in aula Dal Passo, Dipartimento di Matematica, Roma Tor Vergata, il Dott. Stefano Pozza (Charles University) terrà un seminario dal titolo (abstract in calce): "How to express the solution of an ODE as a linear system (in a suitable algebra) and exploit it for fast computation and network analysis". Il seminario può essere seguito online usando il link: https://teams.microsoft.com/l/meetup-join/19%3ad48916dee7364e0bbb08216ea621… Vi prego di diffondere l'annuncio fra i possibili interessati. Un caro saluto e grazie, Mariarosa --------------------------------------- Abstract: The solution of systems of non-autonomous linear ordinary differential equations is crucial in various applications, such as nuclear magnetic resonance spectroscopy. We introduced a new solution expression in terms of a generalization of the Volterra composition. Such an expression is linear in a particular algebraic structure of distributions, which can be mapped onto a subalgebra of infinite matrices. It is possible to exploit the new expression to devise fast numerical methods for linear non-autonomous ODEs. As a first example, we present a new method for the operator solution of the generalized Rosen-Zener model, a system of linear non-autonomous ODEs from quantum mechanics. The new method’s computing time scales linearly with the model’s size in the numerical experiments. A second example is the analysis of temporal network, where the new expression might lead to novel extension of subgraph centrality indexes. -- ------------------------------------- Dr. Mariarosa Mazza University of Rome Tor Vergata Via della Ricerca Scientifica, 1 00133, Rome, Italy Email: mariarosa.mazza(a)uniroma2.it<mailto:mariarosa.mazza@uniroma2.it> Tel: 0039 06-7259-4636 Url: https://sites.google.com/site/mariarosamazza1/ ---------------------------------

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Online Seminar: Peter Taylor, "The Role of Physical Understanding in Matrix-Analytic Methods"
by Federico Poloni 14 Jan '25

14 Jan '25

In case someone is interested, let me share this online event. A flyer is attached. Speaker: Professor Peter Taylor, The University of Melbourne Date: Thursday, February 6 2025 Time: 22:00 Italian time (!!) Title: The Role of Physical Understanding in Matrix-Analytic Methods Abstract: Since Marcel Neuts first showed that Markov chains of GI/M/1 type have a matrix-geometric stationary distribution in the 1970s and 1980s, the interplay between analytic properties and physical interpretation has played a major part in the development of matrix-analytic methods for stochastic models. Most performance measures of interest in such models can be expressed in terms of the solutions of equations involving matrix power series, which have to be solved numerically. Over the years, various iterative algorithms have been proposed for doing this. In order to establish convergence, and gain information about the speed of convergence, it is often helpful to think about the physical interpretation of the iterates. I shall discuss the physical interpretation of matrix-analytic algorithms that have been proposed for analysing block-structured Markov additive models. -- --Federico Poloni Dipartimento di Informatica, Università di Pisa https://www.di.unipi.it/~fpoloni/ tel:+39-050-2213143

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Lauri Nyman, "Riemann-Oracle: A framework for matrix nearness problems" 10/12/2024, 16:00
by Federico Poloni 10 Dec '24

10 Dec '24

The following seminar will take place next week; Lauri Nyman and Vanni Noferini from Aalto University are visiting the department of computer science in that week. Title: Riemann-Oracle: A framework for matrix nearness problems Speaker: Lauri Nyman, Aalto University, Espoo, Finland Where: Sala Seminari Est, Dipartimento di Informatica When: Tuesday December 10, 2024; 16:00 Abstract: In this talk, we propose a versatile approach for addressing a large family of matrix nearness problems. In these problems, the task is to find a matrix nearest to a given one that satisfies a desired constraint. The method is based on splitting a matrix nearness problem into two nested optimization problems, of which the inner one can be solved cheaply and exactly, while the outer one can be recast as an unconstrained optimization task over a smooth real Riemannian manifold. We also show that the objective function to be minimized on the Riemannian manifold can be discontinuous, thus requiring regularization techniques, and we give conditions for this to happen. Finally, we demonstrate the practical applicability of our method by implementing it for a number of matrix nearness problems that are relevant for applications, including nearest singular matrix with a given sparsity structure, nearest singular matrix polynomial, approximate GCD and nearest unstable matrix. -- --Federico Poloni Dipartimento di Informatica, Università di Pisa https://www.di.unipi.it/~fpoloni/ tel:+39-050-2213143

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Short-term Research Associate position @ University of Pisa -- dealii-X project
by Luca Heltai 09 Dec '24

09 Dec '24

Dear all, please share the following information with possible candidates, and to colleagues that may know of possible candidates. Thanks! Luca. Numerical Analysis Group @ University of Pisa Start Date: March 1st Application Deadline: January 24th Application Portal: <https://bandi.unipi.it/public/Bandi/Detail/150eaadb-8fec-4fc5-acb6-593dc7a2…> The University of Pisa invites applications for a short-term Research Associate position within the dealii-X project. This role, based in the Department of Mathematics, will concentrate on Numerical Analysis and the creation of advanced numerical tools for high-performance simulations using the deal.II library. The dealii-X project aims to create an Exascale Framework for Digital Twins of the Human Body. This initiative seeks to enhance personalized medicine through sophisticated computational models, enabling scalable and detailed simulations of human organs. We are looking for dynamic individuals with a strong scientific CV relevant to numerical analysis and simulations (a Master degree in a scientific subject is mandatory, a PhD is a plus). The successful candidate will work on the development and optimization of numerical tools for high-performance simulations in the deal.II library, focusing on meshing techniques, advanced coupling methods, non-matching techniques, reduced order methods, and large scale preconditioning techniques. The role will involve a tight collaboration with other international teams and team members, contributing to the development of the deal.II library. Key information: - Research Focus: Development and optimization of numerical tools for high-performance simulations in the deal.II library - Department of Mathematics, University of Pisa - Numerical Analysis and High Performance Scientific Computing - Contract Duration: 24 months - Gross Annual Salary: €32,427.96 - Application Deadline: 24th January 2025 - Starting Date: 1st March 2025 or as soon as possible thereafter

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Due Giorni di Algebra Lineare Numerica e Applicazioni @ UNIPI 20/21 January 2025 (Reminder)
by Fabio Durastante 25 Nov '24

25 Nov '24

A friendly reminder that registration for the /20th Due Giorni di Algebra Lineare Numerica e Applicazioni/ (January 20-21, 2025, at the University of Pisa) will close on *November 30, 2024*. This is the 20th workshop in a series dedicated to Numerical Linear Algebra and Applications. It aims at gathering the Italian Numerical Linear Algebra scientific community to discuss recent advances in this area and to promote the exchange of novel ideas and collaboration among researchers. We strongly encourage contributions by junior scholars on theoretical and computational topics, as well as on applications. Contributions covering other areas requiring tools from Numerical Linear Algebra are very welcome. Topics of interest include (but are not limited to): iterative methods for large-scale linear systems, preconditioning, eigen and singular values, numerical optimization, numerical dynamical systems, mathematics of machine learning, structured matrices, tensors, matrix functions, Krylov methods, randomized linear algebra algorithms, and high-performance computing for matrix computations. Applications include optimization and control, image processing and inverse problems, networks and graphs, machine learning and artificial neural networks, uncertainty quantification, finance, material sciences, life sciences, and industrial processes. Steering committee: M. Benzi, M. Donatelli, N. Guglielmi, B. Meini, V. Simoncini Important dates: - Registration is open with Deadline 30 Nov 2024 - Call for Abstracts is open with Deadline 30 Nov 2024 Location: - Area Bruno Pontecorvo of the University of Pisa The conference is without registration fee, but registration is mandatory. There is a limited amount of support for PhD students who want to attend the event, application can be done through the registration form. Full information are available at the web-page: https://events.dm.unipi.it/event/280/ The organizing committee, P. Boito, G.M. Del Corso, F. Durastante, S. Gazzola, L. Heltai, S. Massei, C. Pagliantini, F. Poloni, L. Robol.

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