Editing Observability (section)

{{Short description|In control theory, visible state of a system}}
{{for-multi|the concept in quantum mechanics|Observable|the concept in software|Observability (software)}}
'''Observability''' is a measure of how well internal states of a [[system]] can be inferred from knowledge of its external outputs.
In [[control theory]], the observability and [[controllability]] of a linear system are mathematical [[duality (mathematics)|duals]].

The concept of observability was introduced by the Hungarian-American engineer [[Rudolf E. Kálmán]] for linear dynamic systems.<ref>{{cite journal|doi=10.1016/S1474-6670(17)70094-8|title=On the general theory of control systems |year=1960 |last1=Kalman |first1=R.E. |journal=IFAC Proceedings Volumes |volume=1 |pages=491–502 |doi-access= }}</ref><ref>{{cite journal|doi=10.1137/0301010|title=Mathematical Description of Linear Dynamical Systems |year=1963 |last1=Kalman |first1=R. E. |journal=Journal of the Society for Industrial and Applied Mathematics, Series A: Control |volume=1 |issue=2 |pages=152–192 }}</ref> A dynamical system designed to estimate the state of a system from measurements of the outputs is called a ''[[state observer]]'' for that system, such as [[Kalman filter]]s.