Summary
Let x(t) be a diffusion process satisfying a stochastic differential equation and let the observed process y(t) be related to x(t) by dy(t) = g(x(t)) + dw(t) where w(t) is a Brownian motion. The problem considered is that of finding the conditional probability of x(t) conditioned on the observed path y(s), 0≦s≦t. Results on the Radon-Nikodym derivative of measures induced by diffusions processes are applied to derive equations which determine the required conditional probabilities.
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Zakai, M. On the optimal filtering of diffusion processes. Z. Wahrscheinlichkeitstheorie verw Gebiete 11, 230–243 (1969). https://doi.org/10.1007/BF00536382
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DOI: https://doi.org/10.1007/BF00536382