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Pathwise Otto calculus

Walter Schachermayer, University of Vienna
Wednesday, May 29, 2019 - 3:30pm to 4:30pm
Communications 120, Walter Chapin Simpson Center Classroom

We revisit the Jordan, Kinderlehrer, and Otto variational characterization of diffusion as entropic gradient flux, and provide for it a probabilistic interpretation based on stochastic calculus. It was shown by Jordan, Kinderlehrer, and Otto in '98 that, for diffusions of Langevin-Smoluchowski type, the Fokker-Planck probability density flow minimizes the rate of relative entropy dissipation, as measured by the distance traveled in terms of the quadratic Wasserstein metric. We obtain novel, stochastic-process versions of these features, valid along almost every trajectory of the diffusive motion in both the forward and, most transparently, the backward, directions of time, using a very direct perturbation analysis; the original results follow then simply by taking expectations. As a bonus, we derive the Cordero-Erausquin version of the so-called HWI inequality relating relative entropy, Fisher information and Wasserstein distance. Joint work with Ioannis Karatzas and Bertram Tschiderer. 

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