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I wish to know if there is a known relationship between the infinity norm (or any other norms) of a vector and the trace of its covariance matrix?

I have found a paper that used the following inequality for the estimation error covariance matrix in Kalman filter. This relationship can be found on Page 4 below Equation 14. The relationship is:

$$E(\|\mathbf{\hat{s}}(k)-\mathbf{s}(k)\|_\infty)\leq\sqrt{\operatorname{tr}(\Sigma(k))},$$

where $\mathbf{\hat{s}}(k)$ is the estimated state vector at time step $k$, $\mathbf{s}(k)$ is the actual state vector, and $\Sigma(k)$ is the estimation error covariance matrix. The Kalman filter equations are taken from the original paper by Kalman.

I could not find any reference for this inequality.

Is this inequality a general relationship between a vector and its covariance matrix?

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    $\begingroup$ you should take the expectation value on the left-hand-side of your inequality; isn't this then just the statement that $\|x\|_\infty\leq \|x\|_2$ ? $\endgroup$ Commented Jan 7, 2022 at 21:27
  • $\begingroup$ @CarloBeenakker 1- Are you saying that the trace of square root of the covariance matrix is the same as the 2-norm? 2- What does expected value has to due with the inequality? $\endgroup$ Commented Jan 7, 2022 at 22:06
  • $\begingroup$ 1) yes; 2) just look directly below the equation 14 you are citing; the expectation value is there. $\endgroup$ Commented Jan 7, 2022 at 22:14
  • $\begingroup$ @CarloBeenakker 1) Thanks 2) yes, I missed the expectation operator. $\endgroup$ Commented Jan 7, 2022 at 22:20

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