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seminar by Puya Latafat on Tue 27
by Giancarlo Bigi 26 Feb '24

26 Feb '24

You are very welcome to attend the seminar below Best wishes Giancarlo ============ _/Time/_: Tuesday 27 February, 11:00 am _/Place/_: Sala Seminari Est, Dipartimento di Informatica /_Speaker_/: Puya Latafat, KU Leuven /_Title_: / Convergence of operator splitting methods for nonmonotone inclusions /_Abstract_/ Despite their popularity, convergence results of splitting methods have been largely limited to the convex/monotone setting. We present convergence results for several first-order methods, including the proximal point method, forward-backward-forward splitting, and Douglas-Rachford splitting, within a nonmonotone setting. To this end, we focus on a problem class characterized by an oblique weak Minty condition, which captures non-trivial structures as we demonstrate with examples. Moreover, we introduce the concept of semimonotonicity and provide sufficient conditions for the global convergence of splitting techniques for the sum of two semimonotone operators. Illustrative examples demonstrate the wide range of problems our theory is able to cover.

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26/02/2024 - Seminario CN1-SPOKE 10 (Quantum Computing)
by Paola Boito 23 Feb '24

23 Feb '24

Dear all, I am forwarding this seminar announcement on quantum computing, which may be of interest to some of you. Best regards, Paola Boito ============================================================================== Dear All, As part of the CN1-SPOKE 10 on Quantum Computing, we are organizing a* weekly* seminar series. This week’s seminar is: Title: *Quantum Software Engineering* Speakers: *Giuseppe Bisicchia and Antonio Brogi * Venue:* Sala Gerace, Dipartimento di Informatica* Time:* Monday, 26/02/2024, 17:00 * Everyone is welcome! ==============================================================================

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[Indico] Dr Stefano Pozza, How to express the solution of an ODE as a linear system (in a suitable algebra) and exploit it for fast computation., 13/02/2024, 15:00 Europe/Rome
by fabio.durastante＠unipi.it 12 Feb '24

12 Feb '24

Title: How to express the solution of an ODE as a linear system (in a suitable algebra) and exploit it for fast computation., Speaker(s): Dr Stefano Pozza, Charles University, Date and time: 13 Feb 2024, 15:00 (Europe/Rome), Lecture series: Seminar on Numerical Analysis, Venue: Scuola Normale Superiore (Aula Mancini). Address: P.za dei Cavalieri, 7, 56126 Pisa PI You can access the full event here: https://events.dm.unipi.it/e/254 -- Indico :: Email Notifier https://events.dm.unipi.it/e/254

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[Indico] Prof. Dario Fasino, Is there a Kemeny’s constant for second-order random walks?, 06/02/2024, 10:00 Europe/Rome
by fabio.durastante＠unipi.it 05 Feb '24

05 Feb '24

Title: Is there a Kemeny’s constant for second-order random walks?, Speaker(s): Prof. Dario Fasino, Università di Udine, Date and time: 6 Feb 2024, 10:00 (Europe/Rome), Lecture series: Seminar on Numerical Analysis, Venue: Dipartimento di Matematica (Aula Magna). Address: Largo Bruno Pontecorvo, 5 – 56127 Pisa You can access the full event here: https://events.dm.unipi.it/e/258 Abstract -------- Kemeny's constant is a measure of the navigability of a network by ordinary random walks, which appears in a famous result on Markov chains known as the Random Target Lemma. A second-order random walk is a random walk where the transition probabilities depend on two past states. It can be turned into a Markov chain by lifting the state space from the nodes to the directed edges of the graph. The corresponding Kemeny constant is well known but says very little about the second-order walk on the original network. We extend certain definitions and results on standard random walk's mean hitting and return times to the second-order case and provide simple formulas that allow us to compute these numbers by solving suitable systems of linear equations. New results show that there is an infinite family of graphs for which certain second-order random walks, including the best-known non-backtracking random walk, satisfy a precise second-order counterpart of the Random Target Lemma. So, in summary, the answer to the question in the title is: Yes, sometimes. -- Indico :: Email Notifier https://events.dm.unipi.it/e/258

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[Indico] Prof. Dario Fasino, Is there a Kemeny’s constant for second-order random walks?, 2/6/24, 10:00 AM Europe/Rome
by fabio.durastante＠unipi.it 02 Feb '24

02 Feb '24

Title: Is there a Kemeny’s constant for second-order random walks?, Speaker(s): Prof. Dario Fasino, Università di Udine, Date and time: Feb 6, 2024, 10:00 AM (Europe/Rome), Lecture series: Seminar on Numerical Analysis, Venue: Dipartimento di Matematica (Aula Magna). Address: Largo Bruno Pontecorvo, 5 – 56127 Pisa You can access the full event here: https://events.dm.unipi.it/e/258 Abstract -------- Kemeny's constant is a measure of the navigability of a network by ordinary random walks, which appears in a famous result on Markov chains known as the Random Target Lemma. A second-order random walk is a random walk where the transition probabilities depend on two past states. It can be turned into a Markov chain by lifting the state space from the nodes to the directed edges of the graph. The corresponding Kemeny constant is well known but says very little about the second-order walk on the original network. We extend certain definitions and results on standard random walk's mean hitting and return times to the second-order case and provide simple formulas that allow us to compute these numbers by solving suitable systems of linear equations. New results show that there is an infinite family of graphs for which certain second-order random walks, including the best-known non-backtracking random walk, satisfy a precise second-order counterpart of the Random Target Lemma. So, in summary, the answer to the question in the title is: Yes, sometimes. -- Indico :: Email Notifier https://events.dm.unipi.it/e/258

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[Indico] Dr Stefano Pozza, How to express the solution of an ODE as a linear system (in a suitable algebra) and exploit it for fast computation., 2/13/24, 3:00 PM Europe/Rome
by fabio.durastante＠unipi.it 25 Jan '24

25 Jan '24

Title: How to express the solution of an ODE as a linear system (in a suitable algebra) and exploit it for fast computation., Speaker(s): Dr Stefano Pozza, Charles University, Date and time: Feb 13, 2024, 3:00 PM (Europe/Rome), Lecture series: Seminar on Numerical Analysis, Venue: Scuola Normale Superiore (Aula Mancini). Address: P.za dei Cavalieri, 7, 56126 Pisa PI You can access the full event here: https://events.dm.unipi.it/e/254 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. -- Indico :: Email Notifier https://events.dm.unipi.it/e/254

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Posizione tenure-track (RTT) al dipartimento di informatica
by Federico Poloni 24 Jan '24

24 Jan '24

Buongiorno, segnalo che è uscito il bando per una posizione RTT in analisi numerica (MAT/08) al dipartimento di informatica. Bando e istruzioni per fare domanda sono disponibili su https://bandi.unipi.it/public/Bandi/Detail/b34b7404-9d5a-4180-81e2-bd461bfe… . La scadenza per le domande è il 23 febbraio alle 13:00. La posizione è riservata a coloro che hanno trascorso un periodo di almeno 36 mesi in incarichi di ricerca o corsi di dottorato /al di fuori/ dell'università di Pisa. Tutti gli interessati sono invitati a partecipare! -- --Federico Poloni Dipartimento di Informatica, Università di Pisa https://www.di.unipi.it/~fpoloni/ tel:+39-050-2213143

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Fwd: I: 'TENORS' Marie Sklodowska Curie Network -- PhD positions available
by Paola Boito 27 Dec '23

27 Dec '23

Dear all, I would like to share this message from Iacopo Carusotto (iacopo.carusotto(a)unitn.it), in case someone you know is interested in the PhD positions advertised below. Best wishes, Paola Boito --------------------------------------------------- TENORS (*T*ensor mod*E*li*N*g, ge*O*met*R*y and optimi*S*ation) is a Marie Skłodowska-Curie Doctoral Network / Joint Doctorate (2024-2027), offering * * * 15 PhD positions.* The objective of TENORS is to conduct advanced research that addresses critical challenges in the fields of *tensor modeling and computation*, joining forces from *algebraic geometry, global optimisation, numerical computation, high performance computing, data science, quantum physics.* It aims to feed an innovative and ambitious *joint-PhD program* to train highly qualified young scientists in new scientific and technological knowledge. The PhD candidates will obtain joint/double PhD diplomas from reputed universities within TENORS project. For more information on TENORS see http://tenors-network.eu/ <http://tenors-network.eu/> Application deadline: March 31st, 2024. How to apply: https://project.inria.fr/tenors/phd-positions/ <https://project.inria.fr/tenors/phd-positions/> Where to submit your application: https://easychair.org/my/conference?conf=tenors2427 <https://easychair.org/my/conference?conf=tenors2427>

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Seminario PYSANUM Alessandro Filippo
by Nikita DENISKIN 11 Dec '23

11 Dec '23

Carǝ tuttǝ, Vi segnalo che domani *12 dicembre* alle ore *16:00* ci sarà un seminario tenuto da Alessandro Filippo (Roma Tor Vergata) in *Aula Seminari*. I seminari PYSANUM sono dei seminari informali di analisi numerica e matematica applicata rivolti a studenti, organizzati da alcuni dottorandi Unipi e SNS, con l'obiettivo di presentare in maniera accessibile argomenti di ricerca di analisi numerica ad un pubblico studentesco. Si possono trovare ulteriori informazioni sul nostro sito <https://pysanum.dm.unipi.it/>. A presto, Nikita ----- Titolo: *"Reti complesse: Robustezza, indici di centralità e nuove strategie per il ranking dei nodi"* Abstract: Determinare quali siano i nodi più importanti in una rete complessa è uno dei problemi principali dell’analisi delle reti. Tale problema, anche noto come il problema del ranking, viene tipicamente risolto attraverso il calcolo delle misure di centralità. Tuttavia, cambiamenti strutturali improvvisi, quali la rimozione di alcuni nodi o archi, possono invalidare la nostra conoscenza dei nodi più critici. Per esempio, nodi dapprima cruciali potrebbero perdere tutta la loro importanza qualora rimanessero isolati. Quindi, per studiare l’impatto della rimozione dei nodi più influenti da una rete, sarebbe necessario ricalcolare costantemente le misure di centralità, un’operazione spesso impraticabile per reti di grandi dimensioni. Al contrario, evitare del tutto il ricalcolo potrebbe fornire una rappresentazione della realtà poco accurata. In questo talk illustrerò due nuove strategie per ridurre il costo computazionale del calcolo sequenziale delle centralità, fornendo giustificazioni teoriche a supporto. Infine, mostrerò come sia possibile impiegare queste strategie per valutare la robustezza di una rete ad attacchi mirati. Tratto da un lavoro in collaborazione con Daniele Bertaccini. D. Bertaccini, A. Filippo. *A proposal for ranking through selective computation of centrality measures*. PLOS ONE, 18, 2023.

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Seminario PYSANUM Martina Iannacito
by Igor SIMUNEC 24 Nov '23

24 Nov '23

Carǝ tuttǝ, Vi scrivo per segnalare che lunedì 27 novembre Martina Iannacito (KU Leuven) terrà un seminario in Aula Riunioni alle 16.00, nell'ambito del ciclo di seminari PYSANUM. Di seguito titolo e abstract della presentazione. I seminari PYSANUM sono dei seminari informali di analisi numerica e matematica applicata rivolti a studenti, organizzati da alcuni dottorandi Unipi e SNS, con l'obiettivo di presentare in maniera accessibile argomenti di ricerca di analisi numerica ad un pubblico studentesco. Si possono trovare ulteriori informazioni sul nostro sito <https://pysanum.dm.unipi.it/>. A presto, Igor ----- Titolo: Introduzione ai tensori: dalle applicazioni alle sfide contemporanee Abstract: Per oltre un secolo, i matematici sono stati affascinati dallo studio delle proprietà di famiglie di matrici. Gli oggetti con cui allora iniziarono a confrontarsi sono oggi noti come tensori o array multidirezionali. Lo studio dei tensori ha acquisito particolare rilevanza grazie alle molteplici applicazioni in cui forniscono importanti benefici. Queste strutture matematiche multidimensionali garantiscono l’unicità della fattorizzazione (sotto ipotesi non eccessivamente complesse), consentono rappresentazioni più adatte di fenomeni complessi e delle loro intricate interazioni. Infine, se rappresentati in modo ottimale, i tensori offrono vantaggi computazionali. Tutte queste loro proprietà hanno aperto diverse nuove direzioni di ricerca in campo matematico, numerico e computazionale. Nella prima metà di questa presentazione, esamineremo problemi provenienti da applicazioni concrete in cui i tensori sono stati di innovazione. Contemporaneamente, verrà fornita una panoramica di alcune tecniche di decomposizione tensoriale che meglio si adattano al problema considerato di volta in volta. Il focus della seconda parte si sposterà sulle sfide contemporanee incontrate nello sviluppo di tecniche basate su array multidimensionali, e nell’implementazione di nuovi algoritmi per la fattorizzazione tensoriale. Questa discussione offrirà spunti di riflessione sul panorama in evoluzione della ricerca sui tensori, evidenziandone la rilevanza e il potenziale.

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Nuova edizione del reading course: Riemannian Optimization (17/11, 16:00, Aula Riunioni)
by Fabio Durastante 25 Oct '23

25 Oct '23

Buonasera, A seguito del voto, l'argomento scelto per questa nuova edizione del Reading Course sarà /Riemannian Optimization/; abbiamo impostato una bozza di programma e contattato alcuni di voi per iniziare (in modo da concedere il tempo per preparare il materiale): il primo incontro sarà il 17/11 alle 16:00, in Aula Riunioni. Trovate tutti i dettagli qui: https://numpi.dm.unipi.it/reading-course-in-numerical-analysis/ C'è ancora spazio per candidarsi a tenere gli altri incontri. A presto! Fabio, Leonardo e Stefano.

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Reading Course Analisi Numerica 2024
by Fabio Durastante 11 Oct '23

11 Oct '23

Carə tuttə, Vi scriviamo perché abbiamo l'intenzione di ripartire con una nuova edizione del Reading Course Analisi Numerica. Si tratta di una serie di incontri dove verranno presentati alcuni risultati recenti vicini ad argomenti di ricerca di interesse, solitamente da studentə e/o dottorandə. Ogni iterazione del corso è dedicata ad un argomento specifico, e può essere seguito in modo indipendente dagli altri. Le proposta per questo semestre è una tra: - Ottimizzazione Riemanniana, - Operatori di Koopman. Aiutateci a decidere tra le due compilando il seguente form (su cui trovate anche alcune informazioni bibliografiche e contenutistiche sulle due proposte): - https://forms.gle/QfHpfE1WdjJH9Z6Q8 Se avete idee riguardo altri possibili argomenti che volete suggerire potete inserirle all'interno del modulo, insieme a delle preferenze orientative per il giorno di svolgimento. Trovate ulteriori informazioni sulle passate edizioni sul sito: - https://numpi.dm.unipi.it/reading-course-in-numerical-analysis/ E potete restare aggiornati sugli sviluppi iscrivendovi alla mailing list: - https://lists.dm.unipi.it/postorius/lists/reading-num.lists.dm.unipi.it/ A parte queste mail di annuncio, le informazioni riguardanti l'organizzazione circoleranno /unicamente/ sulla mailing list dedicata, per cui se siete interessati a seguire il corso iscrivetevi lì. Avete tempo per esprime le vostre preferenze fino a *Mercoledì 18 Ottobre* (incluso). Cordiali saluti, Fabio Durastante, Stefano Massei & Leonardo Robol

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[Indico] Mrs Lu Xia, On the influence of stochastic rounding bias in implementing gradient descent with applications in low-precision training, 18/07/2023, 14:00 Europe/Rome
by stefano.massei＠unipi.it 17 Jul '23

17 Jul '23

Title: On the influence of stochastic rounding bias in implementing gradient descent with applications in low-precision training, Speaker(s): Mrs Lu Xia, Eindhoven University of Technology, Date and time: 18 Jul 2023, 14:00 (Europe/Rome), Lecture series: Seminar on Numerical Analysis, Venue: Dipartimento di Matematica (Aula Magna). You can access the full event here: https://events.dm.unipi.it/e/201 Abstract -------- In the context of low-precision computation for the training of neural networks with thegradient descent method (GD), the occurrence of deterministic rounding errors often leadsto stagnation or adversely affects the convergence of the optimizers. The employ-ment of unbiased stochastic rounding (SR) may partially capture gradient updates thatare lower than the minimum rounding precision, with a certain probability. Weprovide a theoretical elucidation for the stagnation observed in GD when training neuralnetworks with low-precision computation. We analyze the impact of floating-point round-off errors on the convergence behavior of GD with a particular focus on convex problems.Two biased stochastic rounding methods, signed-SR$_\varepsilon$ and SR$_\varepsilon$, are proposed, which havebeen demonstrated to eliminate the stagnation of GD and to result in significantly fasterconvergence than SR in low-precision floating-point computation.We validate our theoretical analysis by training a binary logistic regression model onthe Cifar10 database and a 4-layer fully-connected neural network model on the MNISTdatabase, utilizing a 16-bit floating-point representation and various rounding techniques.The experiments demonstrate that signed-SR$_\varepsilon$ and SR$_\varepsilon$ may achieve higher classificationaccuracy than rounding to the nearest (RN) and SR, with the same number of trainingepochs. It is shown that a faster convergence may be obtained by the new roundingmethods with 16-bit floating-point representation than by RN with 32-bit floating-pointrepresentation. -- Indico :: Email Notifier https://events.dm.unipi.it/e/201

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[Indico] Mrs Lu Xia, On the influence of stochastic rounding bias in implementing gradient descent with applications in low-precision training, 18/07/2023, 14:00 Europe/Rome
by stefano.massei＠unipi.it 10 Jul '23

10 Jul '23

Title: On the influence of stochastic rounding bias in implementing gradient descent with applications in low-precision training, Speaker(s): Mrs Lu Xia, Eindhoven University of Technology, Date and time: 18 Jul 2023, 14:00 (Europe/Rome), Lecture series: Seminar on Numerical Analysis, Venue: Dipartimento di Matematica (Aula Magna). You can access the full event here: https://events.dm.unipi.it/e/201 Abstract -------- In the context of low-precision computation for the training of neural networks with thegradient descent method (GD), the occurrence of deterministic rounding errors often leadsto stagnation or adversely affects the convergence of the optimizers. The employ-ment of unbiased stochastic rounding (SR) may partially capture gradient updates thatare lower than the minimum rounding precision, with a certain probability. Weprovide a theoretical elucidation for the stagnation observed in GD when training neuralnetworks with low-precision computation. We analyze the impact of floating-point round-off errors on the convergence behavior of GD with a particular focus on convex problems.Two biased stochastic rounding methods, signed-SR$_\varepsilon$ and SR$_\varepsilon$, are proposed, which havebeen demonstrated to eliminate the stagnation of GD and to result in significantly fasterconvergence than SR in low-precision floating-point computation.We validate our theoretical analysis by training a binary logistic regression model onthe Cifar10 database and a 4-layer fully-connected neural network model on the MNISTdatabase, utilizing a 16-bit floating-point representation and various rounding techniques.The experiments demonstrate that signed-SR$_\varepsilon$ and SR$_\varepsilon$ may achieve higher classificationaccuracy than rounding to the nearest (RN) and SR, with the same number of trainingepochs. It is shown that a faster convergence may be obtained by the new roundingmethods with 16-bit floating-point representation than by RN with 32-bit floating-pointrepresentation. -- Indico :: Email Notifier https://events.dm.unipi.it/e/201

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Fwd: [Random] (PMS)^2 talk - Cazzaniga - July 3 at 17.00
by Federico Poloni 27 Jun '23

27 Jun '23

Inoltro anche su questa lista, visto che l'argomento può essere interessante. Un saluto a tutti! Federico -------- Forwarded Message -------- Subject: [Random] (PMS)^2 talk - Cazzaniga - July 3 at 17.00 Date: Tue, 27 Jun 2023 15:48:24 +0200 From: Carlo Orrieri <carlo.orrieri(a)unipv.it> To: random(a)fields.dm.unipi.it Dear colleagues, We are happy to announce the following *hybrid - that is, in person with online streaming -* talk: Speaker: *Alberto Cazzaniga*** (Area Science Park) Title: What is the probability that a random symmetric tensor is close to rank-one? *Abstract*: We address the problem of estimating the probability that a real symmetric tensor is close to rank-one tensors, motivated by the many applications of low-rank approximation. We discuss how the question can be addressed by studying metric invariants of the real Veronese variety thanks to the Weyl's tube formula. We describe the role of the reach and the curvature coefficients with respect to the Bombieri-Weyl metric in obtaining an explicit estimate, and outline the main ideas employed to tackle their calculation. We conclude by discussing some asymptotic results for the case of rational normal curves. Based on joint work with A. Lerario and A. Rosana. Date and time: *Monday July 3, 17:00-18:00 (Rome time zone)* Place: Laboratorio didattico*, dipartimento di matematica dell’università di Pavia, via Ferrata 5, Pavia.* Entra nella riunione in Zoom https://us02web.zoom.us/j/81154155086?pwd=Rit2Ymd3eE1lUWIrc0ErQlRMcGNVdz09 <https://us02web.zoom.us/j/81154155086?pwd=Rit2Ymd3eE1lUWIrc0ErQlRMcGNVdz09> ID riunione: 811 5415 5086 Passcode: 317594 This talk is part of the *(PMS)^2: Pavia-Milano Seminar series on Probability and Mathematical Statistics* organized jointly by the universities Milano-Bicocca, Pavia, Milano-Politecnico. Participation is free and welcome! Best regards The organizers (Carlo Orrieri, Maurizia Rossi, Margherita Zanella)

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[Indico] Luca Saluzzi, A Tensor Gradient Cross for Hamilton-Jacobi-Bellman equations, 05/06/2023, 16:00 Europe/Rome
by leonardo.robol＠unipi.it 05 Jun '23

05 Jun '23

Title: A Tensor Gradient Cross for Hamilton-Jacobi-Bellman equations, Speaker(s): Luca Saluzzi, Scuola Normale Superiore, Pisa, Date and time: 5 Jun 2023, 16:00 (Europe/Rome), Lecture series: Seminar on Numerical Analysis, Venue: Dipartimento di Matematica (Aula Seminari). You can access the full event here: https://events.dm.unipi.it/e/199 Abstract -------- Hamilton-Jacobi-Bellman (HJB) equation plays a central role in optimal control and differential games, enabling the computation of robust controls in feedback form. The main disadvantage for this approach depends on the so-called curse of dimensionality, since the HJB equation and the dynamical system live in the same, possibly high dimensional, space. In this talk, I will present a data-driven method for approximating high-dimensional HJB equations based on tensor decompositions. The approach presented in this talk is based on the knowledge of the value function and its gradient on sample points and on a tensor train decomposition of the value function. The collection of the data will be derived by two possible techniques: Pontryagin Maximum Principle and State-Dependent Riccati Equations. The numerical experiments will demonstrate an at most linear complexity in the dimension and a better stability in presence of noise. Moreover, I will present an application to an agent-based model and a comparison with Deep Learning techniques. Finally, time permitting, I will consider the coupling of the proposed method with Model Order Reduction techniques and their application to boundary feedback control for the Navier-Stokes equations. -- Indico :: Email Notifier https://events.dm.unipi.it/e/199

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[Indico] Michele Rinelli, Stochastic probing methods for estimating the trace of functions of sparse symmetric matrices, 30/05/2023, 16:00 Europe/Rome
by fabio.durastante＠unipi.it 29 May '23

29 May '23

Title: Stochastic probing methods for estimating the trace of functions of sparse symmetric matrices, Speaker(s): Michele Rinelli, Scuola Normale Superiore, Date and time: 30 May 2023, 16:00 (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/198 Abstract -------- We consider the combination of two approaches for the trace estimation of a symmetric matrix function f(A) when the only feasible operations are matrix-vector products and quadratic forms with f(A): stochastic estimators, such as the Hutchinson estimator and its refined variants Hutch++ and the recent XTrace, and probing methods based on graph colorings. Particularly effective is the case where we replace the indicator vectors for the coloring used in probing by random vectors whose non-zero entries have Rademacher distribution. A theoretical analysis exposes conditions under which using just one Rademacher probing vector per color is provably better than the classical probing approach. Numerical experiments show that existing methods are also outperformed under suitable conditions on the sparsity pattern of A and on the spectrum of f(A). This talk is based on a joint work with Andreas Frommer and Marcel Schweitzer. -- Indico :: Email Notifier https://events.dm.unipi.it/e/198

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[Indico] Michele Rinelli, Stochastic probing methods for estimating the trace of functions of sparse symmetric matrices, 30/05/2023, 16:00 Europe/Rome
by fabio.durastante＠unipi.it 23 May '23

23 May '23

Title: Stochastic probing methods for estimating the trace of functions of sparse symmetric matrices, Speaker(s): Michele Rinelli, Scuola Normale Superiore, Date and time: 30 May 2023, 16:00 (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/198 Abstract -------- We consider the combination of two approaches for the trace estimation of a symmetric matrix function f(A) when the only feasible operations are matrix-vector products and quadratic forms with f(A): stochastic estimators, such as the Hutchinson estimator and its refined variants Hutch++ and the recent XTrace, and probing methods based on graph colorings. Particularly effective is the case where we replace the indicator vectors for the coloring used in probing by random vectors whose non-zero entries have Rademacher distribution. A theoretical analysis exposes conditions under which using just one Rademacher probing vector per color is provably better than the classical probing approach. Numerical experiments show that existing methods are also outperformed under suitable conditions on the sparsity pattern of A and on the spectrum of f(A). This talk is based on a joint work with Andreas Frommer and Marcel Schweitzer. -- Indico :: Email Notifier https://events.dm.unipi.it/e/198

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Fwd: POSTDOC at AROMATH, Inria of Université Côte d'Azur.
by Paola Boito 23 May '23

23 May '23

Dear all, I am forwarding this announcement in case anyone is interested. All the best, Paola -------- Forwarded Message -------- Subject: [DKIM Failed - Firma mittente non verificata][gdrmoa] POSTDOC at AROMATH, Inria of Université Côte d'Azur. Date: Tue, 23 May 2023 10:16:57 +0200 From: Bernard Mourrain <Bernard.Mourrain(a)inria.fr> Reply-To: Bernard Mourrain <Bernard.Mourrain(a)inria.fr> To: gdrmoa(a)listes.math.cnrs.fr Dear Colleagues, A POSTDOC position is available in Aromath <https://es.sonicurlprotection-fra.com/click?PV=2&MSGID=20230523083043027614…> team at Inria of Université Côte d'Azur <https://es.sonicurlprotection-fra.com/click?PV=2&MSGID=20230523083043027614…>. The duration of the contract is _1+1 years (one year renewable one additional year)_. The starting date is flexible, ideally in fall 2023. Here is the link to the official announcement and to apply <https://es.sonicurlprotection-fra.com/click?PV=2&MSGID=20230523083043027614…> to the position. Please feel free to contact me for any questions you may have. Please also forward this message to any potential interested candidates you may know. Best regards, Bernard Mourrain

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Seminario Luca Heltai 26/5
by Beatrice Meini 22 May '23

22 May '23

Carissimi, vi inoltro il seguente annuncio di seminario, nell'ambito delle manifestazioni d'interesse del Progetto di Eccellenza. Saluti, Beatrice -------- Forwarded Message -------- Subject: [Personale.docente.dm] Prossimi seminari Dipartimento di Eccellenza Date: Mon, 22 May 2023 07:54:42 +0000 From: Maria Stella Gelli <maria.stella.gelli(a)unipi.it> To: personale.docente(a)dm.unipi.it <personale.docente(a)dm.unipi.it> Cari tutti, vi segnalo che venerdì alle ore 11.00 in Aula Magna si terrà il quarto dei seminari collegati alla manifestazione di interesse del Progetto di Eccellenza. Lo speaker è Luca Heltai (Sissa) https://www.dm.unipi.it/eventi/an-overview-on-non-matching-approximation-me… <https://www.dm.unipi.it/eventi/an-overview-on-non-matching-approximation-me…> I seminari proseguiranno nelle prossime settimane, potete seguire il calendario (in continua evoluzione) al seguente link https://www.dm.unipi.it/seminari-di-dipartimento/ <https://www.dm.unipi.it/seminari-di-dipartimento/> Vi segnaliamo sul canale Colloquia del Team Dipartimento di Matematica trovate la registrazione dei seminari passati, inoltre, a meno di problematiche dell'ultimo minuto, i seminari sono trasmessi in streaming sullo stesso canale. Cari saluti Maria Stella Gelli & Francesco Sala per il Direttore

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[Indico] Federica Pes, Grassmann extrapolation of density matrices as a tool to accelerate Born-Oppenheimer molecular dynamics, 19/05/2023, 15:00 Europe/Rome
by leonardo.robol＠unipi.it 16 May '23

16 May '23

Title: Grassmann extrapolation of density matrices as a tool to accelerate Born-Oppenheimer molecular dynamics, Speaker(s): Federica Pes, Università di Pisa, Date and time: 19 May 2023, 15:00 (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/192 Abstract -------- Born-Oppenheimer molecular dynamics (BOMD) is a powerful but expensive technique. The main bottleneck in a density functional theory (DFT) BOMD calculation is the solution to the DFT nonlinear equations that requires an iterative procedure that starts from a guess for the density matrix. To speed up such calculations, various extrapolation strategies have been developed to use densities available at previous simulation steps as a guess for the iterative procedure. However, density matrices belong in a Grassmann manifold, which is not a vector space. Therefore the linear extrapolation is performed in a tangent space of the manifold, thanks to a locally bijective map between the manifold and its tangent space.In this contribution, we introduce an approximately time reversible approach to extrapolate density matrices. Some numerical experiments show optimal performance, compared to the state of the art. -- Indico :: Email Notifier https://events.dm.unipi.it/e/192

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Fwd: Faculty position Numerical Methods for Quantum Computing at KU Leuven
by Paola Boito 11 May '23

11 May '23

Buongiorno, inoltro questo annuncio per una posizione a KU Leuven. La posizione è nel gruppo di analisi numerica ed è orientata al quantum computing. A presto, Paola -------- Forwarded Message -------- Subject: Faculty position Numerical Methods for Quantum Computing at KU Leuven Date: Tue, 9 May 2023 13:15:26 +0200 From: Nick Vannieuwenhoven <nick.vannieuwenhoven(a)kuleuven.be> To: paola.boito(a)unipi.it Dear Prof. Paola Boito, We would like to draw your attention to the job offer for the full-time faculty position in /Numerical Methods for Quantum Computing/ at KU Leuven, with application deadline September 14, 2023. A short description is included below. A detailed description is available at https://www.kuleuven.be/personeel/jobsite/jobs/60205789 Since we believe that the position could be of interest to some of your group members, colleagues or collaborators, we would kindly ask you to forward the message, in particular to excellent post-docs and junior group leaders. Best regards, Nick Vannieuwenhoven ---- Prof. dr. Nick Vannieuwenhoven, Member of the search committee. KU Leuven, Department of Computer Science, Celestijnenlaan 200A, bus 2402, 3001 Heverlee, Belgium. *Faculty Position, Numerical Methods for Quantum Computing, KU Leuven * The Science, Engineering, and Technology Group of KU Leuven invites applications for a full time research professorship in the research unit Numerical Analysis and Applied Mathematics (NUMA). The research in NUMA covers many aspects of computational mathematics, including approximation theory, numerical integration, numerical (multi-) linear algebra, numerical partial differential equations, uncertainty quantification, optimization and control, discrete optimization and scheduling, and high-performance computing. The research unit also performs research in collaboration with industry. The new position aims to strengthen the experience in the domain of quantum computing. Quantum computing is a novel computing paradigm relying on fundamental properties of quantum physics. It features new core building blocks that can lead to exponential speedups relative to traditional computing. This requires a fundamental shift in the design of numerical algorithms and their optimized mapping to available quantum circuits. Candidates are expected to have already obtained excellent research results within the research field of design, analysis, development, and implementation of new quantum algorithms for numerical computing. The successful candidate is expected to develop a research program on quantum computing, ensure high-quality education within the area of mathematical engineering, and be prepared to provide scientific and administrative services. For further details, contact information and the application procedure (deadline September 14, 2023), follow the link: https://www.kuleuven.be/personeel/jobsite/jobs/60205789 The vacancy fits within the KU Leuven Quantum initiative: https://set.kuleuven.be/en/about-us/vacancies/quantum

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[Indico] Federica Pes, Grassmann extrapolation of density matrices as a tool to accelerate Born-Oppenheimer molecular dynamics, 19/05/2023, 15:00 Europe/Rome
by leonardo.robol＠unipi.it 06 May '23

06 May '23

Title: Grassmann extrapolation of density matrices as a tool to accelerate Born-Oppenheimer molecular dynamics, Speaker(s): Federica Pes, Università di Pisa, Date and time: 19 May 2023, 15:00 (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/192 Abstract -------- Born-Oppenheimer molecular dynamics (BOMD) is a powerful but expensive technique. The main bottleneck in a density functional theory (DFT) BOMD calculation is the solution to the DFT nonlinear equations that requires an iterative procedure that starts from a guess for the density matrix. To speed up such calculations, various extrapolation strategies have been developed to use densities available at previous simulation steps as a guess for the iterative procedure. However, density matrices belong in a Grassmann manifold, which is not a vector space. Therefore the linear extrapolation is performed in a tangent space of the manifold, thanks to a locally bijective map between the manifold and its tangent space.In this contribution, we introduce an approximately time reversible approach to extrapolate density matrices. Some numerical experiments show optimal performance, compared to the state of the art. -- Indico :: Email Notifier https://events.dm.unipi.it/e/192

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[Indico] Prof. Vandebril Raf, Perfect Shifted QR for Rank Structured Pencils, 13/04/2023, 11:00 Europe/Rome
by leonardo.robol＠unipi.it 11 Apr '23

11 Apr '23

Title: Perfect Shifted QR for Rank Structured Pencils, Speaker(s): Prof. Vandebril Raf, KU Leuven, Date and time: 13 Apr 2023, 11:00 (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/182 Abstract -------- It is known that executing a perfect shifted QR step via the implicit QR algorithm performs poor in terms of stability, and accuracy. Typically several steps are required before deflation actually takes place. This behavior can be remedied by determining the similarity transformation via the associated eigenvector. Similar techniques can be deduced for the QZ algorithm and the rational QZ algorithm. In this talk we generalize this even further and present an approach for executing a perfect shifted QR step for general rank structured pencils. We prove that the rank structures of the matrices involved in the pencil are preserved, and moreover we examine the preservation of spectral properties of subblocks in the pencil.Authors: Nicola Mastronardi, Marc Van Barel, Raf Vandebril, and Paul Van Dooren -- Indico :: Email Notifier https://events.dm.unipi.it/e/182

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[Indico] Cecilia Pagliantini, Model order reduction of parametric Hamiltonian systems on matrix manifolds, 28/03/2023, 16:00 Europe/Rome
by leonardo.robol＠unipi.it 27 Mar '23

27 Mar '23

Title: Model order reduction of parametric Hamiltonian systems on matrix manifolds, Speaker(s): Cecilia Pagliantini, University of Pisa, Date and time: 28 Mar 2023, 16:00 (Europe/Rome), Lecture series: Seminar on Numerical Analysis, Venue: Dipartimento di Matematica (Aula Seminari). You can access the full event here: https://events.dm.unipi.it/e/176 Abstract -------- Model order reduction of parametric differential equations aims at constructing low-complexity high-fidelity surrogate models that allow rapid and accurate solutions under parameter variation. The development of reduced order models for Hamiltonian systems is challenged by several factors: (i) failing to preserve the geometric structure encoding the physical properties of the dynamics, such as invariants of motion or symmetries, might lead to instabilities and unphysical behaviors of the resulting approximate solutions; (ii) the slowly decaying Kolmogorov n-width of transport-dominated and non-dissipative phenomena demands large reduced spaces to achieve sufficiently accurate approximations; and (iii) nonlinear operators require hyper-reduction techniques that preserve the gradient structure of the flow velocity.We will discuss how to address these aspects via a structure-preserving nonlinear reduced basis approach based on dynamical low-rank approximation. The gist of the proposed method is to adapt in time an approximate low-dimensional phase space endowed with the geometric structure of the full model and to ensure that the reduced flow is still Hamiltonian. -- Indico :: Email Notifier https://events.dm.unipi.it/e/176

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