NumPI April 2016

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3 participants
5 discussions

Reminder: Optimization & Numerical Analysis seminars: Brugiapaglia
by Federico Poloni 20 Jun '16

20 Jun '16

Speaker: Simone Brugiapaglia Affiliation: Politecnico di Milano --- Laboratory for Modeling and Scientific Computing MOX Time: Tuesday, December 15, 11 am Place: Sala Seminari Est, Dipartimento di Informatica, Università di Pisa Title: CORSING: Sparse approximation of PDEs based on Compressed Sensing Abstract: We present a novel method for the numerical approximation of PDEs, motivated by recent developments in sparse representation, and particularly by compressed sensing. We named this approach CORSING (COmpRessed SolvING). Establishing an analogy between the sampling of a signal and the Petrov-Galerkin discretization of a PDE, the CORSING method can recover the best s-term approximation to the solution with respect to N suitable trial functions, with s<<N, by evaluating the bilinear form associated with the PDE against a randomized choice of m<<N test functions. This yields an underdetermined m x N linear system, that is solved by means of sparse optimization techniques. A theoretical analysis of the CORSING procedure is presented, based on the concepts of local a-coherence and restricted inf-sup property, along with numerical experiments that confirm the robustness and reliability of the proposed strategy. === Everyone is welcome! -- --federico poloni

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Optimization & Numerical Analysis seminars: Massei
by Federico Poloni 27 Apr '16

27 Apr '16

(This message also serves as a reminder that Claudio Sterle's seminar on "Flow intercepting facility location routing problem: formulation and branch-and-cut solving approach" is scheduled in two days: Friday, 29 April 2016, h. 14:30. ) Speaker: Stefano Massei Affiliation: Scuola Normale Superiore, Pisa Time: Thursday, 5 May 2016, h. 10:00 Place: Sala Seminari Est, Dipartimento di Informatica, Università di Pisa Title: Numerical quasiseparable preservation in matrix functions and in the cyclic reduction Abstract: The quasiseparable structure can be efficiently exploited - in order to speed up computations and storage - by using hierachical representations. This theme has raised much interest in the last two decades, in particular in the context of elliptic partial differential equations, matrix functions and Sylvester equations. Our aim is to provide a framework for the analysis of the off-diagonal singular values, focusing on the structures that can ensure an exponential decay of them. We see how this structures appears in the computation of matrix functions and in the execution of the cyclic reduction paving the way for a theoretical understanding of the preservation of the quasiseparable rank. We provide family of bounds that highlight which parameters of the model can affect the rate of decay. Finally, we show how to practically exploit the low quasiseparable rank using hierarchical matrices. === Everyone is welcome! -- --federico poloni Dipartimento di Informatica, Università di Pisa http://www.di.unipi.it/~fpoloni/ tel:+39-050-2213143

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Optimization & Numerical Analysis seminars: Sterle
by Federico Poloni 14 Apr '16

14 Apr '16

Speaker: Claudio Sterle Affiliation: University “Federico II” of Naples Time: Friday, 29 April 2016, h. 14:30 Place: Sala Seminari Ovest, Dipartimento di Informatica, Università di Pisa Title: Flow intercepting facility location routing problem: formulation and branch-and-cut solving approach Abstract: In the last ten years the research activity on location-routing problem (LRP) has significantly increased and many effective exact and approximated approaches have been presented for its solution. Following from this, great attention has been also devoted to several variants of the LRP, most of them coming from real applications. In particular, with reference to the city logistic (CL) context, several variants of the LRP have been proposed to design single-tier and two-tier freight distribution systems. In this case, LRP location decisions concern the number and position of one or more types of logistic facilities, whereas, routing decisions, concern the definition of dedicated or multi-stop routes of homogeneous or heterogeneous vehicle fleets. However most of the present literature deals with single-commodity LRP, whereas the multi-commodity case is still scarcely investigated. This issue can assume an important role in LRP real applications and in particular in the CL context. Indeed the freight to be distributed in an urban area are highly heterogeneous and consequently the problem is inherently multi-commodity. In order to contribute to fill this gap, an original formulation for the multi-commodity LRP is presented. The problem is referred to as the flow intercepting facility location-routing problem (FIFLOR), since its formulation is obtained merging the flow intercepting facility location and the vehicle routing models. A branch-and-cut algorithm for its solution is described and results obtained on test instances reproducing different urban network topologies are discussed. === Everyone is welcome! -- --federico poloni Dipartimento di Informatica, Università di Pisa http://www.di.unipi.it/~fpoloni/ tel:+39-050-2213143

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Reminder: Optimization and numerical analysis seminars
by Federico Poloni 08 Apr '16

08 Apr '16

Speaker: Yaroslav D. Sergeyev Affiliation: Università della Calabria and N.I. Lobachevsky University of Nizhni Novgorod, Russia. Time: Monday, 11 April 2016, 15:00 Place: Sala Seminari Ovest, Dipartimento di Informatica, Università di Pisa Title: Lipschitz global optimization Abstract: http://pages.di.unipi.it/fpoloni/files/seminari/Sergeyev.pdf and Time: Tuesday, 12 April 2016, 12:00 Place: Sala Seminari Ovest, Dipartimento di Informatica, Università di Pisa Title: The Infinity Computer and numerical computations with infinities and in infinitesimals Abstract: http://pages.di.unipi.it/fpoloni/files/seminari/Sergeyev_Infinity.pdf === Everyone is welcome! -- --federico poloni Dipartimento di Informatica, Università di Pisa http://www.di.unipi.it/~fpoloni/ tel:+39-050-2213143

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Cena di giovedì 7 Aprile
by massei＠student.dm.unipi.it 05 Apr '16

05 Apr '16

Cari tutti, in occasione della partenza di Raf Vandebril e come scusa per stare un po' insieme, si pensava di fare una cena giovedì sera alla trattoria di Montemagno [1]. Chi ha piacere di partecipare è ben accetto. Dovreste però comunicarmi chi viene e se ha un mezzo a disposizione, così prenoto e ci organizziamo per raggiungere il posto. A presto e buona giornata, Stefano [1] https://www.tripadvisor.it/Restaurant_Review-g580236-d1867657-Reviews-Tratt…

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NumPI April 2016