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Título: Stochastic algorithms for trace estimation and inverse problems involving many PDE inversions

Palestrante: Prof. Uri Ascher, University of British Columbia, Canada.

Data: 07/05/2014

Horário: 13h

Local: CT, SALA G-205

Contato: Prof. Hélcio R. B. Orlande - Este endereço de email está sendo protegido de spambots. Você precisa do JavaScript ativado para vê-lo.



Inverse problems involving systems of partial differential equations (PDEs) can be very expensive to solve numerically. This is so especially when many experiments, involving different combinations of sources and receivers, are employed in order to obtain reconstructions of acceptable quality.
The mere evaluation of a mis t function (the distance between predicted and observed data) often requires thousands of PDE solves. We develop and assess randomized algorithms for dimensionality reduction, to make the corresponding computational burden tolerable.
The essence of such algorithms boils down to estimating the least squares mis t function, which in turns leads to Monte-Carlo methods for trace estimation for implicit matrices. We state and prove theoretical probabilistic bounds regarding the efficiency of such methods, depending on the probability distribution and the matrix properties.
We demonstrate our approach and algorithms on the DC resistivity and EIT problems with rough solutions. Highly efficient variants of the resulting algorithms are identifi ed.


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