Thu, 15 Mar 2007

14:00 - 15:00
Rutherford Appleton Laboratory, nr Didcot

New developments in LAPACKJ and ScaLAPACK

Sven Hammarling
(Numerical Algorithms Group & University of Manchester)
Abstract

In this talk we shall be looking at recent and forthcoming developments in the widely used LAPACK and ScaLAPACK numerical linear algebra libraries.

Improvements include the following: Faster algorithms, better numerical methods, memory hierarchy optimizations, parallelism, and automatic performance tuning to accommodate new architectures; more accurate algorithms, and the use of extra precision; expanded functionality, including updating and downdating and new eigenproblems; putting more of LAPACK into ScaLAPACK; and improved ease of use with friendlier interfaces in multiple languages. To accomplish these goals we are also relying on better software engineering techniques and contributions from collaborators at many institutions.

After an overview, this talk will highlight new more accurate algorithms; faster algorithms, including those for pivoted Cholesky and updating of factorizations; and hybrid data formats.

This is joint work with Jim Demmel, Jack Dongarra and the LAPACK/ScaLAPACK team.

Fri, 09 Mar 2007
14:15
Dennis Sciama LT

TBA

Beatriz de Carlos
(Southampton)
Thu, 08 Mar 2007
16:30
DH Common Room

Analysis for the Nonlinear Electrolyte Wedge Problem

Joseph Fehribach
(Worcester Polytechnic Institute, USA)
Abstract

This talk will discuss recent work on 3-phase junctions (electrolyte wedges)

in porous electrodes, including nonlinear reaction kinetics. Recent work on

reaction route representations (Kirchoff graphs) will also be discussed.

Thu, 08 Mar 2007
16:15
Fisher Room of NAPL

TBA

John March-Russell
(Oxford)
Wed, 07 Mar 2007
12:00
Comlab

Team Meeting

Guest speaker Antonio Orlando
(Swansea)
Abstract

The modelling of the elastoplastic behaviour of single

crystals with infinite latent hardening leads to a nonconvex energy

density, whose minimization produces fine structures. The computation

of the quasiconvex envelope of the energy density involves the solution

of a global nonconvex optimization problem. Previous work based on a

brute-force global optimization algorithm faced huge numerical

difficulties due to the presence of clusters of local minima around the

global one. We present a different approach which exploits the structure

of the problem both to achieve a fundamental understanding on the

optimal microstructure and, in parallel, to design an efficient

numerical relaxation scheme.

This work has been carried out jointly with Carsten Carstensen

(Humboldt-Universitaet zu Berlin) and Sergio Conti (Universitaet

Duisburg-Essen)

Mon, 05 Mar 2007
14:15
DH 3rd floor SR

Pinning of a polymer in a random medium and interacting particle system.

Dr Vincent Beffara
(ENS Lyon)
Abstract
  We present a link between polymer pinning by a columnar defect in a random medium and a particular model of interacting particles on the line, related to polynuclear growth. While the question of whether an arbitrarily small intensity for the defect always results in pinning is still open, in a 'randomized' version of the model, which is closely related to the zero-temperature Glauber dynamics of the Ising model, we are able to obtain explicit results and a complete understanding of the process. This is joint work with Vladas Sidoravicius and Maria Eulalia Vares.  
Fri, 02 Mar 2007
16:30
L2

How model theory looks at Lie groups and Lie Algebra

Prof. Angus MacIntyre
(Queen Mary University, London)
Abstract
  Model theory typically looks at classical mathematical structures in novel ways. The guiding principle is to understand what relations are definable, and there are usually related questions of effectivity. In the case of Lie theory, there are two current lines of research, both of which I will describe, but with more emphasis on the first. The most advanced work concerns exponentials and logarithms, in both real and complex situations. To understand the definable relations, and to show various natural problems are decidable, one uses a mixture of analytic geometry with number-theoretic conjectures related to Schanuel's Conjecture. More recent work, not yet closely connected to the preceding, concerns the limit behaviour (model-theoretically), of finite -dimensional modules over semisimple Lie algebras, and here again, for decidability, one seems obliged to consider number-theoretic decision problems, around Siegel's Theorem.
Thu, 01 Mar 2007

14:00 - 15:00
Comlab

Linear and nonlinear semidefinite programs in structural optimization

Prof Michal Kocvara
(University of Birmingham)
Abstract

Several formulations of structural optimization problems based on linear and nonlinear semidefinite programming will be presented. SDP allows us to formulate and solve problems with difficult constraints that could hardly be solved before. We will show that sometimes it is advantageous to prefer a nonlinear formulation to a linear one. All the presented formulations result in large-scale sparse (nonlinear) SDPs. In the second part of the talk we will show how these problems can be solved by our augmented Lagrangian code PENNON. Numerical examples will illustrate the talk.

Joint work with Michael Stingl.

Wed, 28 Feb 2007
16:00
L3

On possible non-homeomorphic substructures of the real line.

Philip Welch
(Bristol)
Abstract

 

We consider as a starting point a problem raised by Kunen and Tall as to whether

the real continuum can have non-homeomorphic versions in different submodels of

the universe of all sets. Its resolution depends on modest large cardinals.

In general Junqueira and Tall have made a study of such "substructure spaces"

where the topology of a subspace can be different from the usual relative

topology.

Tue, 27 Feb 2007
17:00
L1

Spectra of Groups

Professor Andrzej Zuk
(Paris & Newton Inst.)
Tue, 27 Feb 2007
12:00
L3

J vs m

Piotr Chrusciel
(Oxford)
Abstract
  We will shortly review the known bounds on the angular momentum J in terms of mass m assuming a negative cosmological constant, and describe in more detail Brill's proof of the axisymmetric positive energy theorem, and Dain's upper bound on angular momentum J for vacuum initial data sets with an axial Killing vector and with two asymptotically flat regions.
Mon, 26 Feb 2007
15:45
DH 3rd floor SR

On linear and nonlinear interacting particle systems

Mr Lihu Xu
(Imperial College, London)
Abstract
  We start from the stochastic Ising model(or Glauber Dynamics) and have a short review of some important topics in Particle Systems such as ergodicity, convergence rates and so on. Then an abstract nonlinear model will be introduced by an evolution differential equation. We will build the existence and uniqueness theorem, and give some nice properties such as convergence exponentially and monotonicity for the abstract systems. To apply our abstract theory, we will study a family of nonlinear interacting particle systems generalized from Glauber Type Dynamics(we call them nonlinear Glauber Type Dynamics) and prove that such generalization can be done in infinitely many ways. For nonlinear Glauber Type Dynamics, we have two interesting inequalities related to Gibbs measures. Finally, we will concentrate on one specific nonlinear dynamics, and provide the relation between nonlinear system and the linear one, and that between Gibbs measures and tangent functionals to a nonlinear transfer operator.
Mon, 26 Feb 2007
14:15
DH 3rd floor SR

Markov loops, determinants and Gaussian fields

Prof Yves Le Jan
(University of Paris XI)
Abstract

 

We will see how Dynkin's isomorphism emerges from the "loop soup" introduced by

Lawler and Werner.