# Difference between state and parameters of a system

1. In my previous question, based on the information I have so far, my understanding about a system is that a system transforms an input function to an output function.

So I think all the things involved in the transformation, except input and output, are the parameters of the system. Am I right?

2. But there is another concept, the state of the system, which is neither input nor output. So I wonder if the state of the system is also part of the parameters of the system?

If yes, what distinguishes state parameters and non-state parameters of the system?

Thanks and regards!

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The term parameter is used loosely. The state typically encapsulates all past history. In my experience, the term parameter is typically used to describe something like a design or environmental parameter which remains fixed, or is 'slowly varying'. But there is no law dictating what is or is not called a parameter. – copper.hat May 9 '12 at 2:51

+1 Thanks! But I think the non-state parameters can also change over time, see the state space model for Kalman filter $\textbf{x}_{k} = \textbf{F}_{k} \textbf{x}_{k-1} + \textbf{B}_{k} \textbf{u}_{k} + \textbf{w}_{k}$, where $x_k$ is state at time k, and $F_k, B_k$ are all non-state parameters and also change over time k. – Tim May 9 '12 at 14:53