Scusate il nuovo messaggio ma c'è un cambio di location per il seminario
che vi ho appena inoltrato.
-f
-------- Forwarded Message --------
Subject: [Dipartimento.di] Mauriana Pesaresi Seminar Update
Date: Wed, 11 May 2016 17:34:43 +0200
From: Marco Grandi <marco.grandi(a)di.unipi.it>
To: dipartimento(a)di.unipi.it
Dear all,
the location of tomorrow's Mauriana Pesaresi Seminar has been changed
from East Seminar Room to Open Lab.
Below updated information on the seminars.
Speaker: Giulio Masetti
Date: 12 May 2016, 13:00
Place: Open Lab (Room 306)
Marco Grandi
______________________________________________
Dipartimento.di mailing list
Dipartimento.di(a)listgateway.unipi.it
http://listgateway.unipi.it/mailman/listinfo/dipartimento.di
Inoltro questo avviso di seminario che sembra di argomento interessante
per gli iscritti alla lista.
-federico
-------- Forwarded Message --------
Subject: [Dipartimento.di] Mauriana Pesaresi Seminar
Date: Wed, 11 May 2016 10:53:01 +0200
From: Francesca Pratesi <pratesi(a)di.unipi.it>
Organization: University of Pisa
To: dottorandi(a)di.unipi.it, dipartimento(a)di.unipi.it
Dear all,
I would like to remind you that the next Mauriana Pesaresi Seminar will
be held tomorrow, 12 May.
Below further information on the seminars.
Title2: Impact of Equations Ordering on Inexact and Quasi-Inverse Newton
Methods.
Speaker2: Giulio Masetti
Date2: 12 May 2016, 13:00
Place2: East Seminar Room
Abstract2: The Newton-Raphson method has a prominent role in applied
science and engineering. Our research group at SEDC lab., ISTI/CNR, is
involved in dependability-related assessment of Smart Electrical Grids
and the Newton-Raphson method is used to solve numerically the system
of power-flow equations that characterize the electrical network.
In general, given a system of non-linear equations written in the form
F(u)=0, where F is a continuously differentiable function that maps a
n-dimensional vector u to a n-dimensional vector F(u), one of the
solutions can be found via the Newton-Raphson method. At each iteration
of this method, a linear system that involves the Jacobian matrix
J_{F}(u) of F has to be solved and the equation ordering does not
affect it. At increasing the size of the problem, solving with a direct
method the linear system is often impractical (w.r.t. time and space
complexity, and accuracy), even if the Jacobian is a sparse matrix.
Therefore, in these cases iterative methods have been studied, where,
the equation ordering becomes a critical aspect to analyse carefully.
Studies related to equations ordering are available on techniques
employed in medium-size linear systems, such as the Gauss-Seidel
method. In this method, at each iteration, permutations of Jacobian
rows and columns, that do not depend on the initial equation ordering,
are exploited to gain in CPU time.
Jacobian-free techniques, developed to solve very large linear
problems, offer interesting opportunities for investigations on the
impact of initial equations ordering over the number of iterations. One
of the most effective algorithms in this category is the
Inexact-Newton-Krylov: it gets rid of the Jacobian matrix and
approximates the matrix-vector product J_{F}(u)v with the finite
difference [F(u+sv)-F(u)]/s. Another variant of Newton- Raphson is the
Quasi-Inverse-Newton: it approximates the inverse of the Jacobian
J_{F}^{-1}(u) with a diagonal matrix and solves directly the linear
system. A seminal article, written by L. Dutto and published on the
International Journal for Numerical Methods in Engineering in 1993,
numerically presents the influence of initial ordering over the
preconditioner of Inexact- Newton-Krylov GMRES, and then on the number
of iterations. However, it does not address the impact of ordering on
the core of the method, that is the adopted Jacobian-free techniques.
To go further such existing results, our study focuses on Jacobian-
free methods and explores the influence of the initial ordering over
them.
In this talk, we discuss our approach to prove that the initial
equations ordering affects Inexact-Newton-Krylov and Quasi-
Inverse-Newton, also presenting a preliminary analysis to quantify the
resulting impact. A trivial bivariate function will be used as case
study and numerical experiments will be presented. Interestingly, the
equations ordering does not only affect the efficiency in reaching a
solution, but also the solution itself.
As next step, we are working on exploring more realistic scenarios in
the power grid domain. Traditionally, the characteristics of the domain
at hand has influenced the application of mathematical structures. For
example, when using Gauss-Seidel in the power-flow context, there
exists a particular initial ordering such that the Jacobian is a
four-block matrix and each block corresponds to well defined electrical
quantities. Using Jacobian-free methods the application-oriented
initial equations ordering could not be the best choice with respect to
iterations number and reachable solutions. We believe this is an
important feature, that the user of these methods need to be aware of.
--
Francesca Pratesi
Ph.D. Student - University of Pisa
Room 296a - Phone 050 2212731
Department of Computer Science, Largo B. Pontecorvo 3, 56127 Pisa
______________________________________________
Dipartimento.di mailing list
Dipartimento.di(a)listgateway.unipi.it
http://listgateway.unipi.it/mailman/listinfo/dipartimento.di
Il funerali della madre di Grazia Lotti sono domani alle 11 alla cappella del cimitero della Misericordia.
Francesco.
____________________________
Prof. Francesco Romani
Dipartimento di Informatica
Via Buonarroti 2, 56127 PISA, ITALY
Tel +39-050-2212734
FAX +39-050-2212726
http://www.di.unipi.it/~romani
(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
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
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
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…
Speaker: Raf Vandebril
Affiliation: KU Leuven
Time: Thursday, April 7, h. 10:00
Place: Sala Seminari Ovest, Dipartimento di Informatica, Università di Pisa
Title: A framework for structured linearizations of matrix polynomials
in various bases
Abstract: We present a framework for the construction of linearizations
for scalar and matrix polynomials based on dual bases which, in the case
of orthogonal polynomials, can be described by the associated recurrence
relations. The framework provides an extension of the classical
linearization theory for polynomials expressed in non-monomial bases and
allows to represent polynomials expressed in product families, that is,
as a linear combination of elements of the form $\phi_i(x) \psi_j(x)$,
where $\{ \phi_i(x) \}$ and $\{ \psi_j(x) \}$ can either be polynomial
bases or polynomial families which satisfy some mild assumptions.
We show that this general construction can be used for many different
purposes. Among them, we show how to linearize sums of polynomials and
rational functions expressed in different bases. As an example, this
allows to look for intersections of functions interpolated on different
nodes without converting them to the same basis.
===
Everyone is welcome!
--
--federico poloni
Dipartimento di Informatica, Università di Pisa
http://www.di.unipi.it/~fpoloni/ tel:+39-050-2213143
Speaker: Yaroslav D. Sergeyev
Affiliation: Università della Calabria and N.I. Lobachevsky University
of Nizhni Novgorod, Russia.
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:
The lecture presents a recent methodology allowing one to execute
numerical computations with finite, infinite, and infinitesimal numbers
on a new type of a computer – the Infinity Computer – patented in EU,
USA, and Russia (see [23]). The new approach is based on the principle
‘The whole is greater than the part’ (Euclid’s Common Notion 5) that is
applied to all numbers (finite, infinite, and infinitesimal) and to all
sets and processes (finite and infinite). It is shown that it becomes
possible to write down finite, infinite, and infinitesimal numbers by a
finite number of symbols as particular cases of a unique framework
different from that of the non-standard analysis [...]
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
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: Global optimization is a thriving branch of applied
mathematics and an extensive literature is dedicated to it (see e.g.,
[1–24]). In this lecture, the global optimization problem of a
multidimensional function satisfying the Lipschitz condition over a
hyperinterval with an unknown Lipschitz constant is considered. It is
supposed that the objective function can be “black box”, multiextremal,
and non-differentiable. It is also assumed that evaluation of the
objective function at a point is a time-consuming operation. Many
algorithms for solving this problem have been discussed in literature.
They can be distinguished, for example, by the way of obtaining
information about the Lipschitz constant and by the strategy of
exploration of the search domain. Different exploration techniques based
on various adaptive partition strategies are analyzed. [...]
http://pages.di.unipi.it/fpoloni/files/seminari/Sergeyev.pdf
===
Everyone is welcome!
--
--federico poloni
Dipartimento di Informatica, Università di Pisa
http://www.di.unipi.it/~fpoloni/ tel:+39-050-2213143