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Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause-and-effect that forms a circuit or loop. The system can then be said to ''feed back'' into itself. The notion of cause-and-effect has to be handled carefully when applied to feedback systems: :"Simple causal reasoning about a feedback system is difficult because the first system influences the second and second system influences the first, leading to a circular argument. This makes reasoning based upon cause and effect tricky, and it is necessary to analyze the system as a whole." 〔 Online version (found here ). 〕 == History == Self-regulating mechanisms have existed since antiquity, and the idea of feedback had started to enter economic theory in Britain by the eighteenth century, but it wasn't at that time recognized as a universal abstraction and so didn't have a name.〔 〕 The verb phrase "to feed back", in the sense of ''returning to an earlier position'' in a mechanical process, was in use in the US by the 1860s,〔 ''"Heretofore ... it has been necessary to reverse the motion of the rollers, thus causing the material to travel or feed back, ..."'' HH Cole, "Improvement in Fluting-Machines", (US Patent 55,469 (1866) ) accessed 23 Mar 2012. 〕〔 ''"When the journal or spindle is cut ... and the carriage is about to feed back by a change of the sectional nut or burr upon the screw-shafts, the operator seizes the handle..."'' JM Jay, "Improvement in Machines for Making the Spindles of Wagon-Axles", (US Patent 47,769 (1865) ) accessed 23 Mar 2012. 〕 and in 1909, Nobel laureate Karl Ferdinand Braun used the term "feed-back" as a noun to refer to (undesired) ''coupling'' between components of an electronic circuit.〔 ''"...as far as possible the circuit has no feed-back into the system being investigated."'' () Karl Ferdinand Braun, ("Electrical oscillations and wireless telegraphy" ), Nobel Lecture, 11 December 1909. Retrieved 19 Mar 2012.〕 By the end of 1912, researchers using early electronic amplifiers (audions) had discovered that deliberately coupling part of the output signal back to the input circuit would boost the amplification (through regeneration), but would also cause the audion to howl or sing.〔 () 〕 This action of feeding back of the signal from output to input gave rise to the use of the term "feedback" as a distinct word by 1920.〔 Over the years there has been some dispute as to the best definition of feedback. According to Ashby (1956), mathematicians and theorists interested in the ''principles'' of feedback mechanisms prefer the definition of ''circularity of action'', which keeps the theory simple and consistent. For those with more ''practical'' aims, feedback should be a deliberate effect via some more tangible connection. ::"(experimenters ) object to the mathematician's definition, pointing out that this would force them to say that feedback was present in the ordinary pendulum ... between its position and its momentum—a 'feedback' that, from the practical point of view, is somewhat mystical. To this the mathematician retorts that if feedback is to be considered present only when there is an actual wire or nerve to represent it, then the theory becomes chaotic and riddled with irrelevancies."〔 Focusing on uses in management theory, Ramaprasad (1983) defines feedback generally as "...information about the gap between the actual level and the reference level of a system parameter" that is used to "alter the gap in some way." He emphasizes that the information by itself is not feedback unless translated into action.〔Arkalgud Ramaprasad, "On The Definition of Feedback", Behavioral Science, Volume 28, Issue 1. 1983. (Online PDF ) last accessed 16 March 2012.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「feedback」の詳細全文を読む スポンサード リンク
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