NumPI December 2020

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4 discussions

[NOMADS] Seminar - Alexander Viguerie - Dec 16 at 17:00
by Francesco Tudisco 16 Dec '20

16 Dec '20

Dear all, You are all invited to this week's NOMADS seminar at GSSI. The seminar will be given on *Wednesday December 16 at 17:00* (CET) by *Alexander Viguerie* from GSSI. Title, abstract and zoom link are below. This is the last seminar of 2020 and we will then be back on Jan 13, 2021. Further info about past and future meetings are available at the webpage: https://num-gssi.github.io/seminar/ Please feel free to distribute this announcement as you see fit. Hope to see you all on Wednesday! Francesco and Nicola ================================================== Zoom link: https://us02web.zoom.us/j/89492628943 Speaker: Alexander Viguerie <https://www.gssi.it/people/post-doc/post-doc-maths/item/11289-viguerie-alex> Title: Efficient, stable, and reliable solvers for the Steady Incompressible Navier-Stokes equations: application to Computational Hemodynamics. Abstract: Over the past several years, computational fluid dynamics (CFD) simulations have become increasingly popular as a clinical tool for cardiologists at the patient-specific level. The use of CFD in this area poses several challenges. The clinical setting places heavy restrictions on both computational time and power. Simulation results are usually desired within minutes and are usually run on standard computers. For these reasons, steady-state Navier-Stokes simulations are usually preferred, as they can be completed in a fraction of the time required to run an unsteady computation. However, in many respects the steady problem is more difficult than the unsteady one, particularly in regards to solving the associated linear and nonlinear systems. Additionally, boundary data for patient-specific problems is often missing, incomplete, or unreliable. This makes the determination of a useful model challenging, as it requires the generation of reliable boundary data without introducing heavy computational costs. This seminar will address these challenges, as well as some others, and introduce new techniques for workarounds. Results from patient-specific cases will be presented and discussed. — Francesco Tudisco Assistant Professor School of Mathematics GSSI Gran Sasso Science Institute Web: https://ftudisco.gitlab.io -- You received this message because you are subscribed to the Google Groups "nomads-list" group. To unsubscribe from this group and stop receiving emails from it, send an email to nomads-list+unsubscribe(a)gssi.it. To view this discussion on the web visit https://groups.google.com/a/gssi.it/d/msgid/nomads-list/54b94f9a-5840-e31c-…. For more options, visit https://groups.google.com/a/gssi.it/d/optout.

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Seminario di Des Higham
by Dario A. Bini 04 Dec '20

04 Dec '20

Buongiorno, vi informo che oggi alle 15:00 Desmond Higham (University of Edinburgh), presenterà un seminario dal titolo "/A Hierarchy of //Network Models Giving Bistability Under Triadic Closure/". L'abstract e' allegato. Per registrarsi e ricevere il link per partecipare via Zoom cliccare su https://sites.google.com/unisa.it/nepaseminars A presto, Dario --- Abstract: Triadic closure describes the tendency for new friendships to form between individuals who already have friends in common. It has been argued heuristically that the triadic closure effect can lead to bistability in the formation of large-scale social interaction networks. Here, depending on the initial state and the transient dynamics, the system may evolve towards either of two long-time states. In this work, we study a hierarchy of network evolution models that incorporate triadic closure, building on the work of Grindrod, Higham and Parsons [Internet Mathematics, 8, 2012, 402--423]. In a macroscale regime, we show rigorously that a bimodal steady state distribution is admitted. Computational simulations will be used to support the analysis. This is joint work work with Stefano Di Giovacchino (L'Aquila) and Kostas Zygalakis (Edinburgh).

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[NOMADS] Seminar - Martin Stoll - Today at 17:00
by Francesco Tudisco 02 Dec '20

02 Dec '20

Good morning everyone, This is just a gentle reminder about today's seminar "From PDEs to data science: an adventure with the graph Laplacian" by Martin Stoll (TU-Chemnitz). Abstract below. The seminar is at 17:00 (CET). To attend, please use the zoom link: https://us02web.zoom.us/j/81317396646 Hope to see you there! Francesco and Nicola ------ Martin Stoll <https://www.tu-chemnitz.de/mathematik/wire/prof.php>, TU-Chemnitz From PDEs to data science: an adventure with the graph Laplacian In this talk we briefly review some basic PDE models that are used to model phase separation in materials science. They have since become important tools in image processing and over the last years semi-supervised learning strategies could be implemented with these PDEs at the core. The main ingredient is the graph Laplacian that stems from a graph representation of the data. This matrix is large and typically dense. We illustrate some of its crucial features and show how to efficiently work with the graph Laplacian. In particular, we need some of its eigenvectors and for this the Lanczos process needs to be implemented efficiently. Here, we suggest the use of the NFFT method for evaluating the matrix vector products without even fully constructing the matrix. We illustrate the performance on several examples. — Francesco Tudisco Assistant Professor School of Mathematics GSSI Gran Sasso Science Institute Web: https://ftudisco.gitlab.io -- You received this message because you are subscribed to the Google Groups "nomads-list" group. To unsubscribe from this group and stop receiving emails from it, send an email to nomads-list+unsubscribe(a)gssi.it. To view this discussion on the web visit https://groups.google.com/a/gssi.it/d/msgid/nomads-list/002e39cd-038e-e9cc-…. For more options, visit https://groups.google.com/a/gssi.it/d/optout.

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Seminar on 01/12 (Fabio Durastante)
by Leonardo Robol 01 Dec '20

01 Dec '20

Speaker: Fabio Durastante Affiliation: IAC-CNR (...that will soon become University of Pisa) Time: Tuesday, 01/12/2020, 16:00 Title: (Sparse) Linear Algebra at the Extreme Scales Sparse linear algebra is essential for a wide variety of scientific applications. The availability of highly parallel sparse solvers and preconditioners lies at the core of pretty much all multi-physics and multi-scale simulations. Technology is nowadays expanding to target exascale platforms. I am going to present some work on Algebraic Multigrid Preconditioners in which we try to face these challenges to make Exascale Computing possible. The talk will focus on one side on the theoretical aspects pertaining to the construction of the multigrid hierarchy for which the main novelty is the design and implementation of new parallel smoothers and a coarsening algorithm based on aggregation of unknowns employing weighted graph matching techniques. On the other, the talk also focuses on the libraries developed to cover the needs of having parallel BLAS feature for sparse matrices that are capable of running on machines with thousands of high-performance cores; and to discuss the advancements made by the new smoothers and coarsening algorithm as an improvement in terms of numerical scalability at low operator complexity over the algorithms available in previous releases of the package. I will present weak scalability results on two of the most powerful supercomputers in Europe, for linear systems with sizes up to O(10^10) unknowns for a benchmark Poisson problem, and strong scaling result for a wind-simulation benchmark problem. This is a joint work with P. D’Ambra, and S. Filippone. This work is supported by the EU under the Horizon 2020 Project Energy oriented Centre of Excellence: toward exascale for energy (EoCoE-II), Project ID: 824158 Meeting link: <https://hausdorff.dm.unipi.it/b/leo-xik-xu4>

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NumPI December 2020