Observability

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 duals.

The concept of observability was introduced by the Hungarian-American engineer Rudolf E. Kálmán for linear dynamic systems.^[1]^[2] 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 filters.

^ Kalman, R.E. (1960). "On the general theory of control systems". IFAC Proceedings Volumes. 1: 491–502. doi:10.1016/S1474-6670(17)70094-8.
^ Kalman, R. E. (1963). "Mathematical Description of Linear Dynamical Systems". Journal of the Society for Industrial and Applied Mathematics, Series A: Control. 1 (2): 152–192. doi:10.1137/0301010.

[1] Kalman, R.E. (1960). "On the general theory of control systems". IFAC Proceedings Volumes. 1: 491–502. doi:10.1016/S1474-6670(17)70094-8.

[2] Kalman, R. E. (1963). "Mathematical Description of Linear Dynamical Systems". Journal of the Society for Industrial and Applied Mathematics, Series A: Control. 1 (2): 152–192. doi:10.1137/0301010.

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