Cybernetics Forrester at MIT in the 1950s, is a related field. Cybernetics has been defined in a variety of ways, by a variety of people, from a variety of disciplines. Cybernetician Stuart Umpleby reports some notable definitions: Other notable definitions include: The term "cybernetics" stems from κυβερνήτης ("cybernḗtēs") "steersman, governor, pilot, or rudder". As with the ancient Greek pilot, independence of thought is important in cybernetics. French physicist and mathematician André-Marie Ampère first coined the word "cybernetique" in his 1834 essay "Essai sur la philosophie des sciences" to describe the science of civil government. The term was borrowed by Norbert Wiener,
Wiener–Lévy theorem Wiener–Lévy theorem Wiener–Lévy theorem is a theorem in Fourier analysis, which states that a function of an absolutely convergent Fourier series has an absolutely convergent Fourier series under some conditions. The theorem was named after Norbert Wiener and Paul Lévy. Norbert Wiener first proved Wiener's 1/"f" theorem, see Wiener's theorem. It states that if has absolutely convergent Fourier series and is never zero, then its inverse also has an absolutely convergent Fourier series. Paul Levy generalized Wiener's result, showing that Let formula_1 be a absolutely convergent Fourier series with The values of formula_3 lie on a curve formula_4, and formula_5