Backward Nonlinear Smoothing Diffusions
- Publisher:
- Society for Industrial and Applied Mathematics
- Publication Type:
- Journal Article
- Citation:
- Theory of Probability and Its Applications, 2019, 66, (2), pp. 235-262
- Issue Date:
- 2019-11-01
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We present a backward diffusion flow (i.e., a backward-in-time stochastic differential equation) whose marginal distribution at any (earlier) time is equal to the smoothing distribution when the terminal state (at a later time) is distributed according to the filtering distribution. This is a novel interpretation of the smoothing solution in terms of a nonlinear diffusion (stochastic) flow. This solution contrasts with, and complements, the (backward) deterministic flow of probability distributions (viz. a type of Kushner smoothing equation) studied in a number of prior works. A number of corollaries of our main result are given, including a derivation of the time-reversal of a stochastic differential equation, and an immediate derivation of the classical Rauch--Tung--Striebel smoothing equations in the linear setting.
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