******************************************************************* STATISTICS SEMINARS @ COLLEGIO CARLO ALBERTO *******************************************************************

Venerdi' 7 Novembre 2014 alle ore 12:00, presso la sala rossa del Collegio Carlo Alberto, Moncalieri (TO), si terra' il seguente seminario:

Alexandros BESKOS (University College London)

SMC SAMPLERS FOR APPLICATIONS IN HIGH DIMENSIONS

Abstract: Sequential Monte Carlo (SMC) methods are nowadays routinely applied in a variety of complex applications: hidden Markov models, dynamical systems, target tracking, control problems, just to name a few. Whereas SMC methods have been greatly refined in the last decades and are now much better understood, they are still known to suffer from the curse of dimensionality: algorithms can sometimes break down exponentially fast with the dimension of the state space. As a consequence, practitioners in high-dimensional Data Assimilation applications in atmospheric sciences, oceanography and elsewhere will typically use 3D-Var or Kalman-filter-type approximations that will provide biased estimates in the presence of non-linear model dynamics.

The talk will concentrate on a class of SMC algorithms and will look at ways to reduce the cost of the algorithms as a function of the dimension of the state space. Explicit asymptotic results will clarify the effect of the dimension at the properties of the algorithm and could provide a platform for algorithmic optimisation in high dimensions. Applications will be shown in the context of Data Assimilation, in a problem where the objective is to target the posterior distribution of the initial condition of the Navier-Stokes equation given a Gaussian prior and noisy observations at different instances and locations of the spatial field. The dimension of the signal is in theory infinite-dimensional - in practice 64x64 or more depending on the resolution – thus posing great challenges for the development and efficiency of SMC methods.

Tutti gli interessati sono invitati a partecipare.

Il seminario e' organizzato dalla "de Castro" Statistics Initiative (http://www.carloalberto.org/stats) in collaborazione con il Collegio Carlo Alberto.

Cordiali saluti, Matteo Ruggiero

--- Matteo Ruggiero University of Torino and Collegio Carlo Alberto http://sites.carloalberto.org/ruggiero