# Talk:State observer

WikiProject Systems (Rated Start-class, Mid-importance)
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## Context

"The usual state space model for a (plant) system can be written as..." — What on earth is a "(plant) system"? This article needs either context (to explain its arcane terminology) or cleanup (to replace the arcana with clearer language). --Quuxplusone 21:36, 28 October 2006 (UTC)

'plant' is a term used in control theory to denote the system!!! Anyone searching for state observers is likely to know this

Wikipedia is not only for people who already know bout these things. I followed a link from another page and was rather confused by this. Somebody should at least explecitly state in the main article what "plant" means in this context but I think that somebody who actually knows more about this could say it better than me.109.148.236.26 (talk) 21:19, 15 June 2012 (UTC)

"The observer is called asymptotically stable if the observer error ${\displaystyle \mathbf {e} (k)=\mathbf {\hat {x}} (k)-\mathbf {x} (k)}$ converges to zero when ${\displaystyle k\rightarrow \infty }$ . For a Luenberger observer, the observer error satisfies ${\displaystyle \mathbf {e} (k+1)=(A-LC)\mathbf {e} (k)}$. The Luenberger observer is therefore asymptotically stable when the matrix A − LC has all the eigenvalues with strictly negative real part (is Hurwitz in the continuous case)." ---The eigenvalues of a discrete system have to lie in the unit circle of the complex plane to be asymptotically stable and only for continuous system the real parts have to be strictly negative. In my opinion, this section is therefore misleading/wrong. Xlr8t (talk) 00:11, 6 March 2009 (UTC)

I agree with Xlr88, in fact, it's called Schur Stable for a discrete case. Wangyan Li 03:48, 20 June 2015 (UTC) — Preceding unsigned comment added by Liwangyan (talkcontribs)

## Nonlinear case is duplicated content

The recently added section (by an anonymous IP) on the "nonlinear case" seems superfluous. Already there is a sentence discussing that a sliding mode observer can be used, and on the sliding mode control page, the design of a sliding mode observer is already included, and that design is nearly identical to the added mess. Does all of that need to be included here? (without any reference to its sliding mode roots?) —TedPavlic (talk/contrib/@) 13:09, 6 July 2009 (UTC)

I've gone through and cleaned up the new section a bit. I'm not familiar with the references given, but it appears like there were some mistakes in the content given in the new section. I've done my best to correct them, but I have to imagine the primary sources present the material in a more elegant way. Someone should feel free to clean up the content a bit more. —TedPavlic (talk/contrib/@) 15:22, 6 July 2009 (UTC)

## Assessment comment

The comment(s) below were originally left at Talk:State observer/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

 "The observer is called asymptotically stable if the observer error ${\displaystyle \mathbf {e} (k)=\mathbf {\hat {x}} (k)-\mathbf {x} (k)}$ converges to zero when ${\displaystyle k\rightarrow \infty }$ . For a Luenberger observer, the observer error satisfies ${\displaystyle \mathbf {e} (k+1)=(A-LC)\mathbf {e} (k)}$. The Luenberger observer is therefore asymptotically stable when the matrix A − LC has all the eigenvalues with strictly negative real part (is Hurwitz in the continuous case)." The eigenvalues of a discrete system have to lie in the unit circle of the complex plane to be asymptotically stable and only for continuous system the real parts have to be strictly negative. In my opinion, this section is therefore misleading.

Last edited at 21:53, 17 February 2009 (UTC). Substituted at 06:57, 30 April 2016 (UTC)