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Introduction to Local Level Model and Kalman Filter

Introduction to Local Level Model and Kalman Filter

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<strong>Kalman</strong> <strong>Filter</strong><br />

The unobserved variable µt can be estimated from the<br />

observations with the <strong>Kalman</strong> filter:<br />

vt = yt − at,<br />

Ft = Pt + σ 2 ε,<br />

Kt = PtF −1<br />

t ,<br />

at+1 = at + Ktvt,<br />

Pt+1 = Pt + σ 2 η − K 2 t Ft,<br />

for t = 1, . . . , n <strong>and</strong> starting with given values for a1 <strong>and</strong> P1.<br />

◮ Writing Yt = {y1, . . . , yt}, define<br />

at+1 = E(µt+1|Yt), Pt+1 = var(µt+1|Yt).

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