
Filtering Equations, Density Methods, and Particle Approximations
What does an observation allow us to conclude about a hidden diffusion?
The answer is a conditional distribution. This book follows that distribution from conditional expectation and Bayesian updating to the equations of nonlinear filtering, then to the approximations needed when exact closure fails.
Kalman–Bucy filtering provides an exact Gaussian benchmark. Reference measures, the Zakai equation and innovations lead to the general filtering equations. Later chapters develop stability, conditional densities, projection methods and particle approximations, keeping the target law and the assumptions of each construction explicit.
Analytic contours, worked examples, proofs and full algorithm descriptions connect the theory to concrete calculations. The final chapter separates approximation errors and examines how errors in a posterior affect a decision.
For graduate students, researchers and mathematically trained practitioners with a background in probability, Itô calculus, linear algebra and elementary differential equations.

