NumPI September 2022

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Reading course (Randomized linear algebra -- starting October 2022)
by Leonardo Robol 28 Sep '22

28 Sep '22

Cari tutti, insieme a Fabio e Stefano abbiamo pensato di organizzare per questo semestre un "Reading course", dove i partecipanti potranno alternarsi a presentare risultati significativi di analisi numerica presi da articoli e/o capitoli di libri. L'idea è di avere degli incontri informali di durata maggiore rispetto ai seminari (2h), in cui chi presenta abbia il tempo di spiegare le cose con calma (magari approfondendo anche alla lavagna, o mostrando degli esperimenti numerici). Gli incontri sono aperti a tutti, e speriamo che possano essere di particolare utilità per dottorandi / studenti magistrali. L'argomento con cui vorremmo iniziare è "Randomized Linear Algebra", per poi continuare successivamente (ammesso che l'iniziativa abbia successo) con un tema scelto in base ai desideri di chi partecipa. Anche per questo semestre abbiamo selezionato gli articoli introduttivi da cui partire, ma poi potremo scegliere cosa approfondire in base alle preferenze dell'audience. Trovate maggiori informazioni sulla pagina web: https://numpi.dm.unipi.it/reading-course Invitiamo chi volesse partecipare a segnarsi sul Doodle per la prima sessione, programmata agli inizi di Ottobre: https://doodle.com/meeting/participate/id/eXoknmgd Segnatevi entro venerdì 09/09, in modo che poi possiamo scegliere la prima data, e pubblicizzare ulteriormente l'iniziativa. A presto, -- Leonardo.

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Annuncio Seminario di Matematica, Dr. Anna Weller (26.09.2022)
by Fabio Durastante 21 Sep '22

21 Sep '22

*Avviso Seminario di Matematica* Data: Monday, September 26, 2022 Ora: 16:15 - 17:15 Luogo: Aula Volterra, Normale Speaker: Anna Weller University of Cologne Titolo: *A spectral Galerkin method for the solution of reaction-diffusion equations on metric graphs* Abstract: Weinvestigateaspectralsolutionapproachforreaction-diffusionequationsongraphs interpretedastopologicalspace(metricgraphs).Ofspecialinterestisthenumerical computationofeigenfunctionsofthenegativesecondorderderivativeactingoneach edge.Remarkably,itispossibletogiveanexplicitcharacterizationoftheseeigenfunctions andcorrespondingeigenvalues.Moreover,forequilateralgraphs,wewillshow howtoefficientlycomputeanarbitrarylowerpartofthespectrumusingaveryuseful relationshiptothegraphLaplacianmatrixoftheunderlyingcombinatorialgraph. Finally,wecanusethebasisofeigenfunctionsinaGalerkinapproachtosolvevarious PDEsonmetricgraphs,wereweherefocusonreaction-diffusionequations.This problemismotivatedbyarecentcollaborationwiththeInstituteofGeophysicsand MeteorologyoftheUniversityofCologneonthemodelingofproteindistributionin Alzheimer’sdiseasetogetherwiththeUniversityHospitalCologne1.Partofmynumerical resultsarejointworkwithProf.Dr.MarkAinsworth(BrownUniversity)and withChong-SonDroege(UniversityofCologne). References [1]M.Ainsworth,A.Weller,AspectralGalerkinmethodforthesolutionofpartialdifferential equationsonmetricgraphs,inpreparation. [2]M.Ainsworth,A.Weller,AspectralGalerkinmethodforthesolutionofreaction-diffusion equationsonmetricgraphs,OberwolfachReports,WorkshopReport36,2021. [3]A.Kunoth,A.Weller,T.Yilmaz,Acomputationalbrainspheremodelforthesimulationof Alzheimer’sDisease.SnapshotsofmodernmathematicsfromOberwolfach,inpreparation. [4]A.Weller,G.N.Bischof,P.Schl̈uter,N.Richter,J.Dronse,̈O.Onur,J.Kukolja,B.Neu- maier,A.Kunoth,Y.Shao,T.vanEimeren,A.Drzezga,Findingnewcommunities:A principleofneuronalnetworkreorganizationinAlzheimersdisease.BrainConnectivity, 11(3):225-238,2021.DOI:10.1089/brain.2020.0889 ThisworkwassupportedbytheExcellenceInitiativeoftheUniversityofCologne

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[NOMADS] Seminar today by Emre Mengi
by Francesco Tudisco 19 Sep '22

19 Sep '22

Dear all, It is my great pleasure to invite you all to today’s NOMADS seminar by Emre Mengi<http://home.ku.edu.tr/~emengi/> from Koc University (Turkey), who will present recent work on the computation of the dominant poles of a transfer function of a descriptor system. The seminar will take place **today Sept 19 at 14:30 (CET) in GSSI’s Library (NOT the main lecture hall as previously announced). Remote participation will also be possible via the zoom link: https://us02web.zoom.us/j/89668910844?pwd=TmVwQUFoNklUajAzMlEyMzB6ZVZzUT09 Below you can find title and abstract. Hope to see you all later today! All the best, —Francesco Tudisco ====== Emre Mengi, Koc University, Istanbul, Turkey http://home.ku.edu.tr/~emengi/<https://www.google.com/url?q=http://home.ku.edu.tr/~emengi/&sa=D&source=cal…> Title: Large-Scale Estimation of the Dominant Poles of a Transfer Function Abstract: The dominant poles of the transfer function of a descriptor system provide important insight into the behavior of the system. They indicate the parts of the imaginary axis where the transfer function exhibits large norm. Moreover, the dominant poles and corresponding eigenvectors can be put in use to form a reduced-order approximation to the system. In the talk, I will describe a subspace framework to compute a prescribed number of dominant poles of a large-scale descriptor system. The framework applies Petrov-Galerkin projections to the original system, then computes the dominant poles of the projected small-scale system, for instance by the QZ algorithm, and expands the subspaces so that the projected system after the subspace expansion interpolates the original system at these dominant poles. I will explain why the subspace framework converges at a quadratic rate, and report numerical results illustrating the rapid convergence, and accuracy of the approach. For more information, please see: https://num-gssi.github.io/seminar/<https://www.google.com/url?q=https://num-gssi.github.io/seminar/&sa=D&sourc…> The seminar will take place in the Library, but remote participation will also be possible via the zoom link: https://us02web.zoom.us/j/89668910844?pwd=TmVwQUFoNklUajAzMlEyMzB6ZVZzUT09<https://www.google.com/url?q=https://us02web.zoom.us/j/89668910844?pwd%3DTm…> -- 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/DB6PR05MB32237075AF…. For more options, visit https://groups.google.com/a/gssi.it/d/optout.

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[NOMADS] Seminar today by Stefano Massei
by Francesco Tudisco 14 Sep '22

14 Sep '22

Dear all, It is my great pleasure to invite you all to today’s NOMADS seminar by Stefano Massei<https://sites.google.com/view/stefanomassei/home>, University of Pisa, who will present his recent work on fast parallel-in-time numerical integration of differential equations. The seminar will take place today, Sept 14, at 15:00 (CET) in GSSI’s Main Lecture Hall (the “red room”). Remote participation will also be possible via the zoom link: https://us02web.zoom.us/j/89668910844?pwd=TmVwQUFoNklUajAzMlEyMzB6ZVZzUT09 Below you can find title and abstract. Hope to see you all later today! All the best, –– Francesco Tudisco Associate Professor School of Mathematics GSSI Gran Sasso Science Institute Web: https://ftudisco.gitlab.io<https://ftudisco.gitlab.io/> Stefano Massei University of Pisa, Italy https://sites.google.com/view/stefanomassei/home<https://www.google.com/url?q=https://sites.google.com/view/stefanomassei/ho…> Title of the talk: Improved parallel-in-time integration via low-rank updates and interpolation Abstract: This work is concerned with linear matrix equations that arise from the space-time discretization of time-dependent linear partial differential equations (PDEs). Such matrix equations have been considered, for example, in the context of parallel-in-time integration leading to a class of algorithms called ParaDiag. We develop and analyze two novel approaches for the numerical solution of such equations. Our first approach is based on the observation that the modification of these equations performed by ParaDiag in order to solve them in parallel has low rank. Building upon previous work on low-rank updates of matrix equations, this allows us to make use of tensorized Krylov subspace methods to account for the modification. Our second approach is based on interpolating the solution of the matrix equation from the solutions of several modifications. Both approaches avoid the use of iterative refinement needed by ParaDiag and related space-time approaches in order to attain good accuracy. In turn, our new approaches have the potential to outperform, sometimes significantly, existing approaches. This potential is demonstrated for several different types of PDEs. For more information, please see: https://num-gssi.github.io/seminar/<https://www.google.com/url?q=https://num-gssi.github.io/seminar/&sa=D&sourc…> The seminar will take place in the Main Lecture Hall, but remote participation will also be possible via the zoom link: https://us02web.zoom.us/j/89668910844?pwd=TmVwQUFoNklUajAzMlEyMzB6ZVZzUT09<https://www.google.com/url?q=https://us02web.zoom.us/j/89668910844?pwd%3DTm…> -- 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/DB6PR05MB32231F13C7…. For more options, visit https://groups.google.com/a/gssi.it/d/optout.

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NumPI September 2022