State estimation

In control theory, a state observer or state estimator is a system that provides an estimate of the internal state of a given real system , from measurements of the input and output of the real system. It is typically computer-implemented, and provides the basis of many practical applications.

An observer is one who engages in observation or in watching an experiment .

The observer effect is the fact that observing a situation or phenomenon necessarily changes it . Observer effects are especially prominent in physics where observation and uncertainty are fundamental aspects of modern quantum mechanics.