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A normal EWMA filter is a special case of a Kalman filter and I bet this could be re-cast as one too. Might need an extra state or adaptive process noise though.

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How is EWMA a special case of Kalman? I typically frame it in terms of laplace/Z transform, in which case it's just a 1-pole LPF

It’s actually shown in the Wikipedia article: https://en.wikipedia.org/wiki/Kalman_filter#Details

I don't see the EWMA mentioned anywhere there?

"A more intuitive way to express the updated state estimate..."

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