Editing State observer (section)

{{Short description|System in control theory}}
{{Use dmy dates|date=August 2023}}

In [[control theory]], a '''state observer''', '''state estimator''', or '''Luenberger observer''' is a system that provides an [[estimate]] of the [[state space (controls)|internal state]] of a given real system, from measurements of the [[Input/output|input]] and output of the real system.  It is typically computer-implemented, and provides the basis of many practical applications.

Knowing the system state is necessary to solve many [[control theory]] problems; for example, stabilizing a system using [[Full state feedback|state feedback]]. In most practical cases, the physical state of the system cannot be determined by direct observation. Instead, indirect effects of the internal state are observed by way of the system outputs.  A simple example is that of vehicles in a tunnel: the rates and velocities at which vehicles enter and leave the tunnel can be observed directly, but the exact state inside the tunnel can only be estimated.  If a system is [[Observability|observable]], it is possible to fully reconstruct the system state from its output measurements using the state observer.