Thu, 20 Oct 2005

14:00 - 15:00
Comlab

From sparsity to block-sparsity: direct solution of linear systems of dimension 10^9

Prof Jacek Gondzio
(University of Edinburgh)
Abstract

We discuss a method for solving very large structured symmetric indefinite equation systems arising in optimization with interior point methods.

Many real-life economic models involve system dynamics, spatial distribution or uncertainty and lead to large-scale optimization problems. Such problems usually have a hidden structure: they are constructed by replication of some small generic block. The linear algebra subproblems which arise in optimization algorithms for such problems involve matrices which are not only sparse, but they additionally display a block-structure with many smaller blocks sparsely distributed in the large matrix.

We have developed a structure-exploiting parallel interior point solver for optimization problems. Its design uses object-orientated programming techniques. The progress OOPS (Object-Orientated Parallel Solver: http://www.maths.ed.ac.uk/~gondzio/parallel/solver.html) on a number of different computing platforms and achieves scalability on a number of different computing platforms. We illustrate its performance on a collection of problems with sizes reaching 109 variables arising from asset liability management and portfolio optimization.

This is a joint work with Andreas Grothey.

Mon, 17 Oct 2005
15:45
DH 3rd floor SR

Lattice gases and the Lov

Dr Alex Scott
(Mathematical Institute, Oxford)
Abstract

Given a family of independent events in a probability space, the probability

that none of the events occurs is of course the product of the probabilities

that the individual events do not occur. If there is some dependence between the

events, however, then bounding the probability that none occurs is a much less

trivial matter. The Lov

Fri, 14 Oct 2005
16:15

Frozen Light

Lene Hau
(Harvard)
Abstract

In Clarendon Lab

Mon, 10 Oct 2005
17:00
L1

Coupled Systems: Theory and Examples

Martin Golubitsky
(University of Houston)
Abstract
A coupled cell system is a collection of interacting dynamical systems.
Coupled cell models assume that the output from each cell is important and that signals from two or more cells can be compared so that patterns of synchrony can emerge. We ask: How much of the qualitative dynamics observed in coupled cells is the product of network architecture and how much depends on the specific equations?

The ideas will be illustrated through a series of examples and theorems. One theorem classifies spatio-temporal symmetries of periodic solutions and a second gives necessary and sufficient conditions for synchrony in terms of network architecture.