Past Seminars

Tue, 05/03
15:45 		Frances Brown (visiting Newton Institute) Algebraic and Symplectic Geometry Seminar Add to calendar L3
Modular forms and multiple zeta values
Tue, 05/03
14:30 		Dan Hefetz (Birmingham) Combinatorial Theory Seminar Add to calendar L3
Optimal covers of random graphs with Hamilton cycles
We prove that if $ \frac{\log^{117} n}{n} \leq p \leq 1 - n^{-1/8} $, then asymptotically almost surely the edges of $ G(n,p) $ can be covered by $ \lceil \Delta(G(n,p))/2 \rceil $ Hamilton cycles. This is clearly best possible and improves an approximate result of Glebov, Krivelevich and Szabó, which holds for $ p \geq n^{-1 + \varepsilon} $. Based on joint work with Daniela Kuhn, John Lapinskas and Deryk Osthus.
Tue, 05/03
12:00 		Francis Brown (Paris, visiting Newton Institute) Quantum Field Theory Seminar Add to calendar L3
Modular forms in quantum field theory
Tue, 05/03
10:15 		Dr Wolfgang Erb (Universität zu Lübeck) OCCAM Wednesday Morning Event Add to calendar OCCAM Common Room (RI2.28)
Accelerated Landweber methods based on co-dilated orthogonal polynomials

******************** PLEASE NOTE THIS SEMINAR WILL TAKE PLACE ON TUESDAY ********************

Well-known iterative schemes for the solution of ill-posed linear equations are the Landweber iteration, the cg-iteration and semi-iterative algorithms like the $\nu$-methods. After introducing these methods, we show that for ill-posed problems a slight modification of the underlying three-term recurrence relation of the $\nu$-methods provides accelerated Landweber algorithms with better performance properties than the $\nu$-methods. The new semi-iterative methods are based on the family of co-dilated ultraspherical polynomials. Compared to the standard $\nu$-methods, the residual polynomials of the modified methods have a faster decay at the origin. This results in an earlier termination of the iteration if the spectrum of the involved operator is clustered around the origin. The convergence order of the modified methods turns out to be the same as for the original $\nu$-methods. The new algorithms are tested numerically and a simple adaptive scheme is developed in which an optimal dilation parameter is determined. At the end, the new semi-iterative methods are used to solve a parameter identification problem obtained from a model in elastography.
Mon, 04/03
16:00 		Lillian Pierce (Oxford) Junior Number Theory Seminar Add to calendar SR1
A primer on Burgess bounds

We'll present a proof of the basic Burgess bound for short character sums, following the simplified presentation of Gallagher and Montgomery.
Mon, 04/03
15:45 		SAMUEL COHEN (University of Oxford) Stochastic Analysis Seminar Add to calendar Oxford-Man Institute
Uniformly Uniformly-Ergodic Markov Chains and applications
If one starts with a uniformly ergodic Markov chain on countable states, what sort of perturbation can one make to the transition rates and still retain uniform ergodicity? In this talk, we will consider a class of perturbations, that can be simply described, where a uniform estimate on convergence to an ergodic distribution can be obtained. We shall see how this is related to Ergodic BSDEs in this setting and outline some novel applications of this approach.
Mon, 04/03
15:45 		David Barnes (Belfast) Topology Seminar Add to calendar
Orthogonal Calculus and Model Categories.

Orthogonal calculus is a calculus of functors, inspired by Goodwillie calculus. It takes as input a functor from finite dimensional inner product  spaces to topological spaces and as output gives a tower of  approximations by well-behaved functors.  The output captures a lot of important homotopical information and is an important tool for calculations.

In this talk I will report on joint work with Peter Oman in which we use model categories to improve the foundations of orthogonal calculus. This provides a cleaner set of results and makes the role of O(n)-equivariance clearer.  The classification of n-homogeneous functors in terms of spectra with O(n)-action can then be phrased as a zig-zag of Quillen equivalences.
Mon, 04/03
14:15 		IOAN MANOLESCU (University of Cambridge) Stochastic Analysis Seminar Add to calendar Oxford-Man Institute
Bond Percolation on Isoradial Graphs
The star-triangle transformation is used to obtain an equivalence extending over a set bond percolation models on isoradial graphs. Amongst the consequences are box-crossing (RSW) inequalities and the universality of alternating arms exponents (assuming they exist) for such models, under some conditions. In particular this implies criticality for these models. (joint with Geoffrey Grimmett)
Fri, 01/03
16:00 		John Crosby (visiting Professor of Finance at Glasgow University Adam Smith Business School and a Managing Director at Grizzly Bear Capital) Nomura Seminar Add to calendar DH 1st floor SR
No good deals - no bad models
The banking industry lost a trillion dollars during the global financial crisis. Some of these losses, if not most of them, were attributable to complex derivatives or securities being incorrectly priced and hedged. We introduce a new methodology which provides a better way of trying to hedge and mark-to-market complex derivatives and other illiquid securities which recognise the fundamental incompleteness of markets and the presence of model uncertainty. Our methodology combines elements of the No Good Deals methodology of Cochrane and Saa-Requejo with the Robustness methodology of Hansen and Sargent. We give some numerical examples for a range of both simple and complex problems encompassing not only financial derivatives but also “real options”occurring in commodity-related businesses.
Fri, 01/03
10:00 		Paul Duinveld (Philips) Industrial and Interdisciplinary Workshops Add to calendar DH 1st floor SR
The fluid mechanics of household appliances; a fascinating world!
An overview will be given for several examples of fluid mechanical problems in developing household appliances, we discuss some examples of e.g. baby bottles, water treatment, irons, fruit juicers and focus on oral health care where a new air floss product will be discussed.
Thu, 28/02
17:00 		Gareth Jones (Manchester) Logic Seminar Add to calendar L3
Rational values of certain analytic functions
Masser recently proved a bound on the number of rational points of bounded height on the graph of the zeta function restricted to the interval [2,3]. Masser's bound substantially improves on bounds obtained by Bombieri-Pila-Wilkie. I'll discuss some results obtained in joint work with Gareth Boxall in which we prove bounds only slightly weaker than Masser's for several more natural analytic functions.
Thu, 28/02
16:00 		Emmanuel Villermaux (IRPHE France) Industrial and Applied Mathematics Seminar Add to calendar DH 1st floor SR
Breaking Threads and Fragmenting Necklaces
Abstract available upon request - Ruth Preston preston@maths.ox.ac.uk
Thu, 28/02
16:00 		Rainer Dietmann (Royal Holloway University of London) Number Theory Seminar Add to calendar L3
Probabilistic Galois Theory
Van der Waerden has shown that `almost' all monic integer polynomials of degree n have the full symmetric group S_n as Galois group. The strongest quantitative form of this statement known so far is due to Gallagher, who made use of the Large Sieve. In this talk we want to explain how one can use recent advances on bounding the number of integral points on curves and surfaces instead of the Large Sieve to go beyond Gallagher's result.
Thu, 28/02
15:00 		Henry Bradford Junior Geometry and Topology Seminar Add to calendar SR1
From Riches to RAAGs: Special Cube Complexes and the Virtual Haken Theorem (Part 1)
In this first of two talks, I shall introduce the Virtual Haken Conjecture and the major players involved in the proof announced by Ian Agol last year. These are the special cube complexes studied by Dani Wise and his collaborators, with a large supporting cast including the not-inconsiderable presence of Perelman’s Geometrization Theorem and the Surface Subgroup Theorem of Kahn and Markovic. I shall sketch how the VHC follows from Agol’s result that, in spite of the name, specialness is entirely generic among non-positively curved cube complexes.
Thu, 28/02
14:00 		Dr Boris Khoromskij (MPI Leipzig) Computational Mathematics and Applications Add to calendar Gibson Grd floor SR
Introduction to tensor numerical methods in higher dimensions
Tensor numerical methods provide the efficient separable representation of multivariate functions and operators discretized on large $ n^{\otimes d} $-grids, providing a base for the solution of $ d $-dimensional PDEs with linear complexity scaling in the dimension, $ O(d n) $. Modern methods of separable approximation combine the canonical, Tucker, matrix product states (MPS) and tensor train (TT) low-parametric data formats.

The recent quantized-TT (QTT) approximation method is proven to provide the logarithmic data-compression on a wide class of functions and operators. Furthermore, QTT-approximation makes it possible to represent multi-dimensional steady-state and dynamical equations in quantized tensor spaces with the log-volume complexity scaling in the full-grid size, $ O(d \log n) $, instead of $ O(n^d) $.

We show how the grid-based tensor approximation in quantized tensor spaces applies to super-compressed representation of functions and operators (super-fast convolution and FFT, spectrally close preconditioners) as well to hard problems arising in electronic structure calculations, such as multi-dimensional convolution, and two-electron integrals factorization in the framework of Hartree-Fock calculations. The QTT method also applies to the time-dependent molecular Schr{ö}dinger, Fokker-Planck and chemical master equations.

Numerical tests are presented indicating the efficiency of tensor methods in approximation of functions, operators and PDEs in many dimensions.

http://personal-homepages.mis.mpg.de/bokh
Thu, 28/02
13:00 		Gechun Liang (Mathematics (Oxford)) Mathematical Finance Internal Seminar Add to calendar DH 1st floor SR
Stochastic Control Representations for Penalized Backward Stochastic Differential Equations
In this talk, We show that both reflected BSDE and its associated penalized BSDE admit both optimal stopping representation and optimal control representation. We also show that both multidimensional reflected BSDE and its associated multidimensional penalized BSDE admit optimal switching representation. The corresponding optimal stopping problems for penalized BSDE have the feature that one is only allowed to stop at Poisson arrival times.

For any corrections/updates to these listings, please contact seminars [-at-] maths [dot] ox [dot] ac [dot] uk.

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