# CAM Colloquium: Nick Trefethen (Oxford University) - Random Functions, Random Odes, and Chebfun

Friday, September 1, 2017 at 3:30pm

What is a random function?  What is noise?  The standard answers are nonsmooth, defined pointwise via the Wiener process and Brownian motion.  In the Chebfun project, we have found it more natural to work with smooth random functions defined by finite Fourier series with random coefficients.  The length of the series is determined by a wavelength parameter $\lambda$. Integrals give smooth random walks, which approach Brownian paths as $\lambda\to 0$, and smooth random ODEs, which approach stochastic DEs of the Stratonovich variety.  Numerical explorations become very easy in this framework.  There are plenty of conceptual challenges in this subject, starting with the fact that white noise has infinite amplitude and infinite energy, a paradox that goes back two different ways to Einstein in 1905.

Bio:
Nick Trefethen is Professor of Numerical Analysis and head of the Numerical Analysis Group at Oxford University.  He was educated at Harvard and Stanford and held positions at NYU, MIT, and Cornell before moving to Oxford in 1997.  He is a Fellow of the Royal Society and a member of the US National Academy of Engineering, and served during 2011-2012 as President of SIAM. As an author Trefethen is known for his books including Numerical Linear Algebra (1997), Spectral Methods in MATLAB (2000), Spectra and Pseudospectra (2005), Approximation Theory and Approximation Practice (2013), and Exploring ODEs (to appear in 2018).  He organized the SIAM 100-Dollar, 100-Digit Challenge in 2002 and is the inventor of Chebfun.

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Nick Trefethen

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Numerical Analysis Group, Oxford University

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