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Kalman Filtering Tutorial

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The covariance update<br />

Numerical Rounding Problems<br />

P( k + 1| k + 1) = P( k + 1| k ) − W( k + 1) S( k + 1) W(<br />

k + 1)'<br />

involves subtraction and can results in loss of symmetry and positive<br />

definiteness due to rounding errors.<br />

Joseph’s form covariance update avoids this at expense of computation<br />

burden:<br />

[ ] [ ]<br />

P( k + 1| k + 1) = I − W( k + 1) H( k + 1) P( k + 1| k) I − W( k + 1) H(<br />

k + 1)<br />

'<br />

+ W( k + 1) R( k + 1) W(<br />

k + 1)'<br />

Only subtraction is “squared” and preserves symmetry.<br />

28

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