tilstandsfrie

Tilstandsfrie is a Norwegian term used to describe modeling or analysis that does not rely on the internal state variables of a system. The compound word derives from tilstand meaning "state" and fri meaning "free." In English-language texts the closest equivalents are "state-free" or "without internal states."

In engineering and systems theory, tilstandsfrie approaches emphasize input-output behavior rather than the detailed evolution of internal states. A common tilstandsfrie representation is the transfer function of a linear time-invariant system, which relates input signals to output signals without referencing state variables. Such representations can simplify analysis and controller design when the internal state structure is uncertain or when a fast, approximate description of input-output behavior is sufficient. However, not all systems admit a purely tilstandsfrie description; nonlinear dynamics or time-varying properties often necessitate state-space models or other state-based formulations.

Applications include initial system identification, signal processing, and certain control design methods where a high-level input-output model is adequate. Advantages include reduced modeling complexity and easier data-driven identification; drawbacks include potential loss of insight into internal dynamics, controllability, observability concerns, and limitations in scenarios requiring state information or state feedback.

The term is used primarily in Norwegian technical literature and translations; in English sources the concept is usually described with terms like "state-free modeling," "input-output modeling," or "transfer-function representation." As with any modeling choice, suitability depends on the problem context and the availability of data.