v 19-20, 2007

Matematiska kollokviet

Wednesday 9 May 2007, Gavril Farkas, University of Texas at Austin speaks.

Title: The global geometry of the moduli space of curves.

Abstract: The moduli space of curves $M_g$ is the universal parameter space for Riemann surfaces of given genus. Its study has been initiated by Riemann in 1857 and it has been a long-standing problem to describe the nature of the moduli space as an algebraic variety. I will survey the history of the problem starting with Severi's conjecture from 1915 predicting that $M_g$ is always unirational (that is close to a projective space and admitting an explicit parametrization) and continuing with the work of Harris and Mumford from 1982, spectacularly disproving Severi's conjecture. I will finish by discussing a very recent result which settles this problem in one of the most interesting remaining cases, that of genus 22.

Wednesday 16 May 2007, Veronica Crispin, KTH speaks.

Wednesday 23 May 2007, Elena Kreines, Mittag-leffler Institute speaks.

Wednesday 30 May 2007, talar Anna Torstensson, KTH.

Place: Glashuset.

Välkomna!

Armen Asratian, Milagros Izquierdo, Vladimir Kozlov, Stefan Rauch-Wojchiechowski.

Seminarium i beräkningsvetenskap

Måndagen den 14 maj kl 13.15 talar professor Michael Thuné över

Title: Abstraction and modularization in software for scientific computing.

Summary: Is it possible to combine high run-time efficiency with high implementation-time efficiency in software for scientific computing? My presentation will address that question for the case of software for solving partial differential equations (PDE) numerically. Implementation-time efficiency---i.e, that the software can be implemented in relatively short time---can be achieved via abstraction and modularization. The challenge is to do this in a way that does not lead to a significant reduction in execution speed.

In the seminar, I will discuss various object-oriented software frameworks for construction of numerical PDE solvers. I will give examples of frameworks that raise the level of abstraction without sacrificing execution time. The focus will be on research issues that were addressed in the development of these frameworks.

Lokal: Glashuset

Välkomna!

Lars Eldén

Licentiatseminarium i beräkningsvetenskap

Ingegerd Skoglund presenterar sin licentiatavhandling i beräkningsvetenskap tisdagen den 29 maj kl 10.15.

Title: Algorithms for a partially regularized least squares problem.

Opponent: Docent Inge Söderkvist, Luleå Tekniska Universitet.

Abstract: Se http://www.mai.liu.se/~insko/abstract.pdf

Lokal: Glashuset, hus B.

Välkomna!

Lars Eldén, Tommy Elfving

Disputationer i optimeringslära

Maria Mitradjieva-Daneva defends her PhD thesis Friday 25 May 2007 at 10.15.

Title: Feasible Direction Methods for Constrained Nonlinear Optimization - Suggestions for Improvements

Opponent: Professor Anders Forsgren, KTH.

Abstract:This thesis concerns the development of novel feasible direction type algorithms for constrained nonlinear optimization. The new algorithms are based upon enhancements of the search direction determination and the line search steps.

The Frank--Wolfe method is popular for solving certain structured linearly constrained nonlinear problems, although its rate of convergence is often poor. We develop improved Frank--Wolfe type algorithms based on conjugate directions. In the conjugate direction Frank--Wolfe method a line search is performed along a direction which is conjugate to the previous one with respect to the Hessian matrix of the objective. A further refinement of this method is derived by applying conjugation with respect to the last two directions, instead of only the last one.

The new methods are applied to the single-class user traffic equilibrium problem, the multi-class user traffic equilibrium problem under social marginal cost pricing, and the stochastic transportation problem. In a limited set of computational tests the algorithms turn out to be quite efficient. Additionally, a feasible direction method with multi-dimensional search for the stochastic transportation problem is developed.

We also derive a novel sequential linear programming algorithm for general constrained nonlinear optimization problems, with the intention of being able to attack problems with large numbers of variables and constraints. The algorithm is based on inner approximations of both the primal and the dual spaces, which yields a method combining column and constraint generation in the primal space.

Place: Alan Turing (House E).

Välkomna!

Maud Göthe-Lundgren

Patrik Flisberg defends his PhD thesis Wednesday 30 May 2007 at 10.15.

Title: Application of Operations Research in operative planning in the forest industry

Opponent: Professor Jens Clausen, IMM, Technical University of Denmark, Lyngby, Denmark.

Abstract: The focus of this thesis is the use of Operations Research for applications in the forest industry. Optimization models and methods have been developed for problems in the forest supply chain and they have been integrated in decision support systems.

The problems considered in this thesis are operative with a planning horizon of less than a month.

Short solution times for the methods and the feasibility of the models used are important aspects.

The body of this thesis consists of eight research papers where six of them consider operative problems and follows the forest supply chain. The industrial applications include routing of forwarders, routing of logging trucks, a process control problem, and roll cutting problems. The other two papers consider an operative planning problem in the home care sector. They are spin offs from one of the other projects in this thesis.

In these applications both linear and nonlinear problems occur.

The forwarding problem is to decide routes for forwarders to pick up the small piles of logs the harvesters have left in the harvest areas. The forwarders then put the logs adjacent to forest roads.

The logging truck problem is to decide routes for logging trucks to pick up the piles created by the forwarders and transport them to demand points, for example pulp or paper mills.

The process control problem appear in the bleaching stage of a pulp mill where the control variables are the bleaching chemical charges. The cost of bleaching chemicals is minimized while a finishing brightness within target values is ensured.

Mainly two roll cutting problems are studied.

One is to minimize the number of cutting patterns and one is to minimize the number of reels when defects in the papper reels are considered. The solution methods developed for the forwarding problem have also been applied to a routing problem which appears in staff planning for home care operations.

The different DSS developed and implemented have been tested and several are in daily industrial use. In each of the papers, we have developed robust OR models and quick and effective OR methods. The savings from using the systems vary, typically in the range 5-20\%.

Place: C3 (C-huset).

Välkomna!

Mikael Rönnqvist

För avläggande av filosofie doktorsexamen i optimeringslära försvarar Helene Gunnarsson sin avhandling fredagen den 1 juni 2007 kl 10.15.

Title: Supply chain optimization in the forest industry.

Fakultetsopponent är professor Eldon Gunn, Department of Industrial Engineering, Dalhousie University, Nova Scotia, Kanada.

Abstract: The scope of this thesis is modelling and solving large-scale planning problems in the supply chain within the forest industry. Five research papers are included, the first three of which focus on the modelling, and the last two on the solution methods. All problems included are tactical multi-commodity problems expressed as mixed integer programming (MIP) models. The work has been done in collaboration with two Swedish companies within the forest industry.

Personalnytt

Christer Bergsten har den 20 april av tekniska fakulteten antagits som docent i matematik med ämnesdidaktisk inriktning.

Lars-Erik Andersson

Nästa nummer av Lite Mat

Då det är Kristi Himmelfärdsdag torsdagen den 17 maj utges Lite Mat dagen innan.

Bodil Stavklint

Material till Lite Mat lämnas till Bodil Stavklint senast torsdagar kl 08.00.
Linköpings universitet, 581 83 Linköping
Tel 013-281000, Fax 013-100746
E-mail: litemat@mai.liu.se