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Convergence of Sequential Monte Carlo Methods

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## Convergence of Sequential Monte Carlo Methods

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**Convergence of Sequential Monte Carlo Methods**Dan Crisan, Arnaud Doucet**Problem Statement**• X: signal, Y: observation process • X satisfies and evolves according to the following equation, • Y satisfies**Bayes’ recursion**• Prediction • Updating**A Sequential Monte Carlo Methods**• Empirical measure • Transition kernel • Importance distribution • : abs. continuous with respect to • : strictly positive Radon Nykodym derivative • Then is also continuous w.r.t. and**Algorithm**• Step 1:Sequential importance sampling • sample: • evaluate normalized importance weights and let**Step 2: Selection step**• multiply/discard particles with high/low importance weights to obtain N particles let assoc.empirical measure • Step 3: MCMC step • sample ,where K is a Markov kernel of invariant distribution and let**Convergence Study**• denote • convergence to 0 of average mean square error under quite general conditions • Then prove (almost sure) convergence of toward under more restrictive conditions**Bounds for mean square errors**• Assumptions • 1.-A Importance distribution and weights • is assumed abs.continuous with respect to for all is a bounded function in argument define**There exists a constant s. t. for all**there exists with s.t. • There exists s. t. and a constant s.t.**First Assumption ensures that**• Importance function is chosen so that the corresponding importance weights are bounded above. • Sampling kernel and importance weights depend “ continuously” on the measure variable. • Second assumption ensures that • Selection scheme does not introduce too strong a “discrepancy”.**Lemma 1**• Let us assume that for any then after step 1, for any • Lemma 2 • Let us assume that for any then for any**Lemma 3**• Let us assume that for any then after step 2, for any • Lemma 4 • Let us assume that for any then for any**Theorem 1**• For all , there exists independent of s.t. for any