Wednesday 16 November 2016 h. 14:30, Room 2BC30
Laura Cossu (Padova, Dip. Mat.)
“Products of elementary and idempotent matrices and noneuclidean pids”
Abstract
It is well known that Gauss Elimination produces a factorization into elementary matrices of any invertible matrix over a field. Is it possible to characterize integral domains different from fields that satisfy the same property? As a partial answer, in 1993, Ruitenburg proved that in the class of Bézout domains, any invertible matrix can be written as a product of elementary matrices if and only if any singular matrix can be written as a product of idempotents.
In this seminar we present some classical results on these factorization properties and we focus, in particular, on their connection with the notion of weakEuclidean algorithm. We then conclude with a conjecture on nonEuclidean principal ideal domains, rare and interesting objects in commutative algebra, and some related results.
In order to make the talk understandable to a general audience, we will recall basic definitions of Commutative Ring theory and provide easy examples of the objects involved.
The opening day of the Doctoral School in Mathematics will take place on October 5, 2016, at
15:30 in room 1BC45.
Schedule:
15:3016:15: presentation of the activities/courses of PhD Programme 2016/2017
16:1517:15: talk of Veronica Dal Sasso "Integer Linear Programming to solve LargeScale problems"
17:30: refreshments at the common room of 7th floor
For further information feel free to contact Pierpaolo Soravia.
Our first seminar of 2016/17 will be held as a special event
inside the Opening Day of the Doctoral School (15:30, 1BC45)
Wednesday 5 October 2016 h.16:15, Room 1BC45
Veronica Dal Sasso (Padova, Dip. Mat.)
“Integer Linear Programming to solve LargeScale problems"
Abstract
Integer linear programming is widely used to find optimal solutions to problems that arouse in the real world and are related to logistics, planning, management, biology and so on. However, if from a theoretical point of view it is easy to give a formulation for these problems, from a computational point of view their implementation can be impractical due to the high number of constraints and variables involved.
During this seminar I will present classical results for dealing with largescale integer linear programs and their application to a particular bioinformatic problem, related to the study of the human genome, that helps recovering information useful to study diseases and populations' behaviours.
Wednesday 15 June 2016 h. 15:00, Room 2BC30
Elena Morotti (Dip. Mat.)
"Computed Tomography: a real case example of inverse problem"
Abstract
Xray computed tomography (CT) is a well known medical imaging technique, that seeks to reveal internal structures hidden by the skin and bones. Mathematically, the CT process can be modelled as a linear system and the image reconstruction is a challenging inverse problem. In this talk I will show both phisical and mathematical basic concepts, to explain the CT process, and the two possible approaches to solve the problem (leading to analitical or iterative numerical methods). Finally, I will shortly introduce the Digital Breast Tomosynthesis (DBT) technology, that is a 3D emerging technique for the diagnosis of breast tumors, together with numerical results for a simulated problem.
Wednesday 1 June 2016 h. 14:30, Room 2BC30
Stefano Urbinati (Dip. Mat.)
"Polyhedral structures in algebraic geometry"
Abstract
Algebraic geometry studies the zero locus of polynomial equations connecting the related algebraic and geometrical structures. In several cases, nevertheless the theory is extremely precise and elegant, it is hard to read in a simple way the information behind such structures. A possible way of avoiding this problem is that of associating to polynomials some polyhedral structures that immediately give some of the information connected to the zero locus of the polynomial. In relation to this strategy I will introduce NewtonOkounkov bodies and Tropical Geometry.
Wednesday 25 May 2016 h. 14:30, Room 2BC30
Abdelsheed Ismail Gad Ameen (Dip. Mat.)
"Fractional Calculus: Numerical Methods and Models"
Abstract
In this talk, we first give a short introduction of fractional calculus (FC) and its geometrical, physical interpretation. Then, we discuss the differential equations of fractional order (Caputo type) which have recently proved to be valuable tools for modeling of many biological phenomena. Most of fractional ordinary differential equations (FODEs) do not have exact analytic solutions so that numerical techniques must be used. Hence, we present the fractional Euler method to solve systems of nonlinear FODEs and show how to use this method for solving the SusceptibleInfectedRecovered (SIR) model of fractional order.
Wednesday 4 May 2016 h. 14:30, Room 2BC30
Valentina Franceschi (Dip. Mat.)
"Isoperimetric inequalities in CarnotCaratheodory spaces"
Abstract
One of the most ancient mathematical problems is Dido's problem, appearing in Virgil's Aeneid: what is the shape to give to a rope in order to enclose a maximal region of land? The expected solution is of course the circle. Despite the ancient origins, a rigorous mathematical formulation and solution is quite recent, dating back to the 1950s when Caccioppoli and De Giorgi introduced the notion of perimeter in the ndimensional Euclidean space. The latter notion led to the study of isoperimetric inequalities and to the solution of Dido's problem generalized to n dimensions. Mathematicians then generalized isoperimetric inequalities to different frameworks, such as riemannian manifolds and metric spaces. After an overview of the classical definitions, in this talk, we present isoperimetric inequalities in a class of metric spaces arising from the study of hypoelliptic differential operators, called CarnotCaratheodory spaces. We conclude presenting the main conjecture in this framework (Pansu's conjecture) ad some related results.
Wednesday 13 April 2016 h. 14:30, Room 2BC30
Michele Barbato (LIPN, Univ. Paris 13, France)
"Cheapest Routes with Integer Linear Programming"
Abstract
Combinatorial Optimization deals with the optimization of a function over a finite, but huge, set of elements.
It has a great impact on real life, as several problems arising in logistics, scheduling, facility location, to cite a few, can be stated as Combinatorial Optimization problems. Often problems of this kind can be expressed as Integer Linear Programs (ILP), i.e., problems in which the function to be optimized is linear and so are the constraints that define the feasibility set. In the first part of the talk, we provide an introductory presentation of some wellestablished methods in Integer Linear Programming. These methods are presented through examples that, in several cases, also motivate theoretical questions (e.g., the polyhedral study). We will consider as initial case of study the Traveling Salesman Problem (TSP). The TSP consists in finding the cheapest route that visits a prescribed set of cities exactly once, before returning to the starting point. As such, the TSP is a prototype of several other problems arising in logistics. In the second part of the presentation we will talk about the Double Traveling Salesman Problem with Multiple Stacks, that combines the construction of a cheapest route with loading constraints. We will reveal links between this problem and the TSP, as well as the limitations that a purely routingbased approach has for this problem.
Summer Research Graduate Programme 2016
con scadenza 13/04/2016 e rivolto a iscritti al terzo anno dei corsi di dottorato negli ambiti di Economia, Finanza, Statistica e Matematica.
Informazioni sul bando
Wednesday 16 March 2016 h. 14:30, Room 2BC30
Pietro Polesello (Dip. Mat.)
"Cosheaves, an introduction"
Abstract
It is well known that locally defined distributions glue together, that is, they define a sheaf. In fact, this follows immediately from the fact that test functions (i.e. smooth functions with compact support) form a cosheaf, which is the dual notion of a sheaf. By definition, cosheaves on a space X and with values in category C are dual to sheaves on X with values in the opposite category C'. For this reason, cosheaves did not attract much attention, being considered as part of sheaf theory. However, passing from C to C', may cause difficulties, as in general C and C' do not share the same good properties needed for sheaf theory. Moreover, dealing with cosheaves may be more convenient, as they appear naturally in analysis (as the compactly supported sections of csoft sheaves, such as smooth functions or distributions), in algebraic analysis (e.g. as the subanalytic cosheaf of Schwartz functions), in topology (in relation with Fox's theory of topological branched coverings), and in tops theory. Moreover, as sheaves are the natural coefficient spaces for cohomology theories, cosheaves play the same role for homology theories, such as Cech homology, and they are (hidden) ingredients of Poincare' duality (recently, cosheaves infiltrated Poincare'Verdier duality in the context of Lurie's "higher topos theory"). In this seminar, I will give a brief introduction to cosheaves, giving examples and explaining the relation with sheaves and with Fox's theory.
