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Moved page from wikipedia:en:Feedback (history)
此词条暂由彩云小译翻译，未经人工整理和审校，带来阅读不便，请见谅。
此词条暂由彩云小译翻译，未经人工整理和审校，带来阅读不便，请见谅。
#REDIRECT [[Feedback]]
{{Other uses}}
{{short description|Process where information about current status is used to influence future status}}
{{Use dmy dates|date=September 2020}}
{{Complex systems}}[[File:General Feedback Loop.svg|thumb|A feedback loop where all outputs of a process are available as causal inputs to that process]]
A feedback loop where all outputs of a process are available as causal inputs to that process
一种反馈回路，其中一个过程的所有输出都可作为该过程的因果输入
'''Feedback''' occurs when outputs of a system are routed back as inputs as part of a [[Signal chain (signal processing chain)|chain]] of [[Causality|cause-and-effect]] that forms a circuit or loop.<ref name=Ford>{{cite book |title=Modeling the Environment |author=Andrew Ford |chapter=Chapter 9: Information feedback and causal loop diagrams |pages=99 ''ff'' |publisher=Island Press |year=2010 |isbn=9781610914253 |chapter-url=https://books.google.com/books?id=38PJahZTzC0C&pg=PA99lpg=PA99 |quote=This chapter describes [[causal loop diagram]]s to portray the information feedback at work in a system. The word ''causal'' refers to cause-and-effect relationships. The word''loop'' refers to a closed chain of cause and effect that creates the feedback.}}</ref> 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:
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.
当系统的输出作为输入路由回来，作为形成电路或回路的因果链的一部分时，反馈就发生了。
{{quote
Centrifugal governors were used to regulate the distance and pressure between millstones in windmills since the 17th century. In 1788, James Watt designed his first centrifugal governor following a suggestion from his business partner Matthew Boulton, for use in the steam engines of their production. Early steam engines employed a purely reciprocating motion, and were used for pumping water – an application that could tolerate variations in the working speed, but the use of steam engines for other applications called for more precise control of the speed.
自17世纪以来，离心调速器就被用来调节风车磨盘之间的距离和压力。1788年，James Watt 根据他的商业伙伴 Matthew Boulton 的建议设计了他的第一台离心式调速器，用于他们生产的蒸汽机。早期的蒸汽机采用纯往复运动，用于抽水——这种应用可以容忍工作速度的变化，但是蒸汽机用于其他应用需要更精确的速度控制。
|text=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.
|author=Karl Johan Åström and Richard M.Murray
In 1868, James Clerk Maxwell wrote a famous paper, "On governors", that is widely considered a classic in feedback control theory.
1868年，詹姆斯·克拉克·麦克斯韦写了一篇著名的论文，《论州长》 ，这被广泛认为是反馈控制理论的经典之作。
|title=''Feedback Systems: An Introduction for Scientists and Engineers''<ref>{{cite book |title=Feedback Systems: An Introduction for Scientists and Engineers |author1=Karl Johan Åström |author2=Richard M. Murray |chapter=§1.1: What is feedback? |chapter-url=https://books.google.com/books?id=cdG9fNqTDS8C&pg=PA1&dq=%22This+makes+reasoning+based+on+cause+and+effect+tricky%22 |isbn= 9781400828739 |year=2008 |page=1 |publisher=Princeton University Press}} Online version found [http://authors.library.caltech.edu/25062/1/Feedback08.pdf here].
</ref>}}
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.
多年来，关于反馈的最佳定义一直存在一些争议。按照阿什比(1956)的说法，对反馈机制原理感兴趣的数学家和理论家更喜欢“循环行动”的定义，这使得理论简单和一致。对于那些有更实际目标的人来说，反馈应该是通过一些更切实的联系而产生的有意的效果。
==History==
Self-regulating mechanisms have existed since antiquity, and the idea of feedback had started to enter [[Economics|economic theory]] in Britain by the 18th century, but it was not at that time recognized as a universal abstraction and so did not have a name.<ref name=mayr>
Even prior to the terms being applied, James Clerk Maxwell had described several kinds of "component motions" associated with the centrifugal governors used in steam engines, distinguishing between those that lead to a continual increase in a disturbance or the amplitude of an oscillation, and those that lead to a decrease of the same.
甚至在这些术语被使用之前，詹姆斯·克拉克·麦克斯韦就已经描述了几种与蒸汽发动机中使用的离心调速器相关的“组件运动” ，区分那些导致扰动持续增加或振幅振荡的组件运动，以及那些导致扰动减少的组件运动。
{{Cite book |author= Otto Mayr|title=Authority, liberty, & automatic machinery in early modern Europe |year=1989 |isbn=978-0-8018-3939-9 | publisher=Johns Hopkins University Press |author-link=Otto Mayr }}</ref>
the valence of the action or effect that alters the gap, based on whether it has a happy (positive) or unhappy (negative) emotional connotation to the recipient or observer.}}
改变差距的行为或效果的效价，基于它是否对接受者或观察者有快乐(积极)或不快乐(消极)的情感内涵。}
The first ever known artificial feedback device was a [[Ballcock|float valve]], for maintaining water at a constant level, invented in 270 BC in [[Alexandria]], [[Ancient Egypt|Egypt]].<ref name=":0">{{Cite book|title=Designing Kinetics for Architectural Facades|last=Moloney|first=Jules|publisher=Routledge|year=2011|isbn=978-0415610346}}</ref> This device illustrated the principle of feedback: a low water level opens the valve, the rising water then provides feedback into the system, closing the valve when the required level is reached. This then reoccurs in a circular fashion as the water level fluctuates.<ref name=":0" />
In general, feedback systems can have many signals fed back and the feedback loop frequently contain mixtures of positive and negative feedback where positive and negative feedback can dominate at different frequencies or different points in the state space of a system.
一般来说，反馈系统可以有多个信号反馈，反馈回路常常包含正反馈和负反馈的混合，其中正反馈和负反馈可以在系统的不同频率或状态空间的不同点占主导地位。
[[Centrifugal governor]]s were used to regulate the distance and pressure between [[millstone]]s in [[windmill]]s since the 17th century. In 1788, [[James Watt]] designed his first centrifugal governor following a suggestion from his business partner [[Matthew Boulton]], for use in the [[steam engine]]s of their production. Early steam engines employed a purely [[reciprocating motion]], and were used for pumping water – an application that could tolerate variations in the working speed, but the use of steam engines for other applications called for more precise control of the speed.
The term bipolar feedback has been coined to refer to biological systems where positive and negative feedback systems can interact, the output of one affecting the input of another, and vice versa.
双极反馈一词被创造出来，指的是生物系统中正反馈系统可以相互作用，一个系统的输出影响另一个系统的输入，反之亦然。
In [[1868]], [[James Clerk Maxwell]] wrote a famous paper, "On governors", that is widely considered a classic in feedback control theory.<ref>{{cite journal|last=Maxwell|first=James Clerk|title=On Governors|journal=Proceedings of the Royal Society of London|volume= 16|year= 1868 |pages= 270–283 | doi = 10.1098/rspl.1867.0055 | jstor=112510|doi-access=free}}</ref> This was a landmark paper on [[control theory]] and the mathematics of feedback.
The Great Eastern was one of the largest steamships of its time and employed a steam powered rudder with feedback mechanism designed in 1866 by John McFarlane Gray. Joseph Farcot coined the word servo in 1873 to describe steam-powered steering systems. Hydraulic servos were later used to position guns. Elmer Ambrose Sperry of the Sperry Corporation designed the first autopilot in 1912. Nicolas Minorsky published a theoretical analysis of automatic ship steering in 1922 and described the PID controller.
大东方号是当时最大的轮船之一，它使用了一个带有反馈机制的蒸汽动力舵，由约翰 · 麦克法兰 · 格雷在1866年设计。约瑟夫 · 法科特在1873年创造了“伺服”这个词来描述蒸汽动力转向系统。液压伺服系统后来被用来定位枪支。史派里公司的 Elmer Ambrose Sperry 在1912年设计了第一个自动驾驶仪。尼古拉斯·米诺尔斯基在1922年发表了一篇关于船舶自动操舵的理论分析，并描述了 PID 控制器。
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,<ref>
''"Heretofore ... it has been necessary to reverse the motion of the rollers, thus causing the material to travel or feed back, ..."''
Oscillators are often characterized by the frequency of their output signal:
振荡器的频率通常与其输出信号的频率成拥有属性:
HH Cole, "Improvement in Fluting-Machines", [http://www.google.co.nz/patents/US55469 US Patent 55,469 (1866)] accessed 23 March 2012.
</ref><ref>
''"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", [http://www.google.co.nz/patents/US47769 US Patent 47,769 (1865)] accessed 23 March 2012.
</ref> and in 1909, Nobel laureate [[Karl Ferdinand Braun]] used the term "feed-back" as a noun to refer to (undesired) [[Coupling (electronics)|coupling]] between components of an [[electronic circuit]].<ref>''"...as far as possible the circuit has no feed-back into the system being investigated."''
[http://www.cdvandtext2.org/Braun-Nobel-lecture%201909.pdf]
Karl Ferdinand Braun, [https://www.nobelprize.org/nobel_prizes/physics/laureates/1909/braun-lecture.html "Electrical oscillations and wireless telegraphy"], Nobel Lecture, 11 December 1909. Retrieved 19 March 2012.</ref>
Oscillators designed to produce a high-power AC output from a DC supply are usually called inverters.
为从直流电源产生大功率交流输出而设计的振荡器通常称为逆变器。
By the end of 1912, researchers using early electronic amplifiers ([[audion tube|audions]]) had discovered that deliberately coupling part of the output signal back to the input circuit would boost the amplification (through [[Regenerative circuit|regeneration]]), but would also cause the audion to howl or sing.<ref name="bennett">{{Cite book|url=http://worldcat.org/isbn/0-906-04807-9|title=A history of control engineering, 1800–1930|author=Stuart Bennett|publisher=Peregrinus for the Institution of Electrical Engineers|year=1979|isbn=978-0-906048-07-8|location=Stevenage; New York}}
There are two main types of electronic oscillator: the linear or harmonic oscillator and the nonlinear or relaxation oscillator.
振盪器有两种主要类型: 线性的或谐振子的和非线性的或张弛振荡器的。
[https://books.google.com/books?id=1gfKkqB_fTcC]
</ref> 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.<ref name=bennett/>
A 4-bit [[ring counter using D-type flip flops]]
4位[使用 d 型触发器的环形计数器]
Over the years there has been some dispute as to the best definition of feedback. According to [[William Ross Ashby|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.
{{Quote|[Practical 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.<ref name=Ashby>
A latch or a flip-flop is a circuit that has two stable states and can be used to store state information. They typically constructed using feedback that crosses over between two arms of the circuit, to provide the circuit with a state. The circuit can be made to change state by signals applied to one or more control inputs and will have one or two outputs. It is the basic storage element in sequential logic. Latches and flip-flops are fundamental building blocks of digital electronics systems used in computers, communications, and many other types of systems.
锁存器或触发器是具有两个稳定状态的电路，可用于存储状态信息。它们通常利用电路的两个臂之间交叉的反馈来构造，以便为电路提供一个状态。该电路可以通过施加到一个或多个控制输入的信号来改变状态，并且具有一个或两个输出。它是时序逻辑电路的基本存储元素。锁存器和触发器是用于计算机、通信和许多其他类型系统的数字电子系统的基本构件。
{{cite book |author=W. Ross Ashby |title=An introduction to cybernetics |publisher=Chapman & Hall |year=1957 |url=http://pcp.vub.ac.be/books/IntroCyb.pdf}}</ref>{{rp|page=54}}}}
Latches and flip-flops are used as data storage elements. Such data storage can be used for storage of state, and such a circuit is described as sequential logic. When used in a finite-state machine, the output and next state depend not only on its current input, but also on its current state (and hence, previous inputs). It can also be used for counting of pulses, and for synchronizing variably-timed input signals to some reference timing signal.
锁存器和触发器用作数据存储元件。这样的数据存储可以用来存储状态，这样的电路被描述为时序逻辑电路。当用于有限状态机时，输出和下一状态不仅取决于其当前输入，还取决于其当前状态(因此，以前的输入)。它也可以用于计数脉冲，并用于同步一些参考定时信号的变时输入信号。
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.<ref name="Ramaprasad">{{Cite journal | doi=10.1002/bs.3830280103|title = On the definition of feedback| journal=Behavioral Science| volume=28| pages=4–13|year = 1983|last1 = Ramaprasad|first1 = Arkalgud}}</ref>
Flip-flops can be either simple (transparent or opaque) or clocked (synchronous or edge-triggered). Although the term flip-flop has historically referred generically to both simple and clocked circuits, in modern usage it is common to reserve the term flip-flop exclusively for discussing clocked circuits; the simple ones are commonly called latches.
触发器可以是简单的(透明的或者不透明的)或者是计时的(同步的或者边缘触发的)。虽然触发器这个术语在历史上一直泛指简单电路和时钟电路，但在现代用法中，通常将触发器这个术语专门用于讨论时钟电路，简单的电路通常称为锁存电路。
==Types==
Using this terminology, a latch is level-sensitive, whereas a flip-flop is edge-sensitive. That is, when a latch is enabled it becomes transparent, while a flip flop's output only changes on a single type (positive going or negative going) of clock edge.
使用这个术语，锁存器是电平敏感的，而触发器是边缘敏感的。也就是说，当锁存器启用时，它变得透明，而触发器的输出只在时钟边缘的单一类型(正向或负向)上发生变化。
===Positive and negative feedback===
{{Main|Negative feedback|Positive feedback}}
[[File:Set-point control.png|thumb|350px|Maintaining a desired system performance despite disturbance using negative feedback to reduce system error]]
Feedback loops provide generic mechanisms for controlling the running, maintenance, and evolution of software and computing systems. Feedback-loops are important models in the engineering of adaptive software, as they define the behaviour of the interactions among the control elements over the adaptation process, to guarantee system properties at run-time. Feedback loops and foundations of control theory have been successfully applied to computing systems. In particular, they have been applied to the development of products such as IBM's Universal Database server and IBM Tivoli. From a software perspective, the autonomic (MAPE, monitor analyze plan execute) loop proposed by researchers of IBM is another valuable contribution to the application of feedback loops to the control of dynamic properties and the design and evolution of autonomic software systems.
反馈回路为控制软件和计算系统的运行、维护和进化提供了通用机制。反馈回路是自适应软件工程中的重要模型，它定义了自适应过程中控制元件之间相互作用的行为，以保证系统在运行时的性能。反馈环路和控制理论的基础已成功地应用于计算系统。特别是，它们已经应用于产品的开发，如 IBM 的 Universal Database server 和 IBM Tivoli。从软件的角度来看，IBM 研究人员提出的自主(MAPE，monitor analyze plan execute)回路是对反馈回路应用于动态特性控制和自主软件系统设计与演化的另一个有价值的贡献。
[[File:Outcome Feedback Negative Feedback Loop.png|thumb|An example of a negative feedback loop with goals]]
[[File:Process Feedback Loop.png|thumb|A positive feedback loop example]]
Positive feedback: If the signal fed back from output is in phase with the input signal, the feedback is called positive feedback.
Negative feedback: If the signal fed back is of opposite polarity or out of phase by 180° with respect to input signal, the feedback is called as negative feedback.
As an example of negative feedback, the diagram might represent a [[cruise control]] system in a car, for example, that matches a target speed such as the speed limit. The controlled system is the car; its input includes the combined torque from the engine and from the changing slope of the road (the disturbance). The car's speed (status) is measured by a [[speedometer]]. The error signal is the departure of the speed as measured by the speedometer from the target speed (set point). This measured error is interpreted by the controller to adjust the accelerator, commanding the fuel flow to the engine (the effector). The resulting change in engine torque, the feedback, combines with the torque exerted by the changing road grade to reduce the error in speed, minimizing the road disturbance.
Feedback is also a useful design principle for designing user interfaces.
反馈也是设计用户界面的一个有用的设计原则。
The terms "positive" and "negative" were first applied to feedback prior to WWII. The idea of positive feedback was already current in the 1920s with the introduction of the [[regenerative circuit]].<ref name=mindell>
{{Cite book
|author=David A. Mindell
Video feedback is the video equivalent of acoustic feedback. It involves a loop between a video camera input and a video output, e.g., a television screen or monitor. Aiming the camera at the display produces a complex video image based on the feedback.
视频反馈是视频等效的声学反馈。它涉及一个循环之间的视频摄像机输入和视频输出，例如，一个电视屏幕或显示器。将摄像机对准显示器，根据反馈信息生成复杂的视频图像。
|title=Between Human and Machine : Feedback, Control, and Computing before Cybernetics.
|year= 2002
|publisher=Johns Hopkins University Press
|location=Baltimore, MD, US
|url=https://books.google.com/books?id=sExvSbe9MSsC|isbn=9780801868955
}}
</ref> Friis and Jensen (1924) described regeneration in a set of electronic amplifiers as a case where ''the "feed-back" action is positive'' in contrast to negative feed-back action, which they mention only in passing.<ref name=friis>
The stock market is an example of a system prone to oscillatory "hunting", governed by positive and negative feedback resulting from cognitive and emotional factors among market participants. For example:
股票市场就是这样一个系统的例子，它倾向于振荡性的”捕猎” ，由市场参与者的认知和情感因素所产生的正反馈和负反馈来控制。例如:
Friis, H.T., and A.G.Jensen. "High Frequency Amplifiers" Bell System Technical Journal 3 (April 1924):181–205.</ref> [[Harold Stephen Black]]'s classic 1934 paper first details the use of negative feedback in electronic amplifiers. According to Black:
{{Quote|Positive feed-back increases the gain of the amplifier, negative feed-back reduces it.<ref name=black>
H.S. Black, "Stabilized feed-back amplifiers", ''Electrical Engineering'', vol. 53, pp. 114–120, January 1934.</ref>}}
According to Mindell (2002) confusion in the terms arose shortly after this:
George Soros used the word reflexivity, to describe feedback in the financial markets and developed an investment theory based on this principle.
乔治•索罗斯(George Soros)用“反身性”(reflexivity)一词来描述金融市场的反馈，并根据这一原则发展了一套投资理论。
{{Quote|...Friis and Jensen had made the same distinction Black used between "positive feed-back" and "negative feed-back", based not on the sign of the feedback itself but rather on its effect on the amplifier's gain. In contrast, Nyquist and Bode, when they built on Black's work, referred to negative feedback as that with the sign reversed. Black had trouble convincing others of the utility of his invention in part because confusion existed over basic matters of definition.<ref name=mindell/>{{rp|page=121}}}}
The conventional economic equilibrium model of supply and demand supports only ideal linear negative feedback and was heavily criticized by Paul Ormerod in his book The Death of Economics, which, in turn, was criticized by traditional economists. This book was part of a change of perspective as economists started to recognise that chaos theory applied to nonlinear feedback systems including financial markets.
传统的经济均衡/需求模型只支持理想的线性负反馈，Paul Ormerod 在他的《经济学之死》一书中对此进行了严厉的批评，而这本书反过来又遭到了传统经济学家的批评。随着经济学家开始认识到混沌理论适用于包括金融市场在内的非线性反馈系统，这本书是观点转变的一部分。
Even prior to the terms being applied, [[James Clerk Maxwell]] had described several kinds of "component motions" associated with the [[centrifugal governor]]s used in steam engines, distinguishing between those that lead to a continual ''increase'' in a disturbance or the amplitude of an oscillation, and those that lead to a ''decrease'' of the same.<ref name=maxwell>{{cite journal|last=Maxwell|first=James Clerk|title=On Governors|url=http://en.wikipedia.org/wiki/File:On_Governors.pdf|journal=Proceedings of the Royal Society of London|volume= 16|year= 1868 |pages= 270–283|doi=10.1098/rspl.1867.0055}}</ref>
====Terminology====
{{cmn|
{{ cmn |
The terms positive and negative feedback are defined in different ways within different disciplines.
# the altering of the ''gap'' between reference and actual values of a parameter, based on whether the gap is ''widening'' (positive) or ''narrowing'' (negative).<ref name="Ramaprasad" />
# the [[Valence (psychology)|valence]] of the ''action'' or ''effect'' that alters the gap, based on whether it has a ''happy'' (positive) or ''unhappy'' (negative) emotional connotation to the recipient or observer.<ref name=herold1977>Herold, David M., and Martin M. Greller. "Research Notes. FEEDBACK THE DEFINITION OF A CONSTRUCT." Academy of management Journal 20.1 (1977): 142-147.</ref>
The two definitions may cause confusion, such as when an incentive (reward) is used to boost poor performance (narrow a gap). Referring to definition 1, some authors use alternative terms, replacing ''positive/negative'' with ''self-reinforcing/self-correcting'',<ref name="senge">
{{Cite book
|author=Peter M. Senge
|title=The Fifth Discipline: The Art and Practice of the Learning Organization
|year=1990
|publisher=Doubleday
|location=New York
|isbn=978-0-385-26094-7
|page=424
|url=https://archive.org/details/fifthdisciplineasen00seng
}}
}}
}}
</ref> ''reinforcing/balancing'',<ref name="sterman">
John D. Sterman, ''Business Dynamics: Systems Thinking and Modeling for a Complex World'', McGraw Hill/Irwin, 2000. {{ISBN|978-0-07-238915-9}}
</ref> ''discrepancy-enhancing/discrepancy-reducing''<ref name="carver">
Charles S. Carver, Michael F. Scheier: ''On the Self-Regulation of Behavior'' Cambridge University Press, 2001
</ref> or ''regenerative/degenerative''<ref>
Hermann A Haus and Richard B. Adler, ''Circuit Theory of Linear Noisy Networks'', MIT Press, 1959
</ref> respectively. And for definition 2, some authors advocate describing the action or effect as positive/negative ''[[Reinforcement#Reinforcement|reinforcement]]'' or ''[[Reinforcement#Punishment|punishment]]'' rather than feedback.<ref name="Ramaprasad" /><ref name="skinner">
BF Skinner, ''The Experimental Analysis of Behavior'', American Scientist, Vol. 45, No. 4 (SEPTEMBER 1957), pp. 343-371</ref>
Yet even within a single discipline an example of feedback can be called either positive or negative, depending on how values are measured or referenced.<ref>
"However, after scrutinizing the statistical properties of the structural equations, the members of the committee assured themselves that it is possible to have a significant positive feedback loop when using standardized scores, and a negative loop when using real scores."
Ralph L. Levine, Hiram E. Fitzgerald. ''Analysis of the dynamic psychological systems: methods and applications'', {{ISBN|978-0306437465}} (1992) page 123</ref>
This confusion may arise because feedback can be used for either ''informational'' or ''motivational'' purposes, and often has both a ''[[Qualitative property|qualitative]]'' and a ''[[Quantitative property|quantitative]]'' component. As Connellan and Zemke (1993) put it:
{{Quote|''Quantitative'' feedback tells us how much and how many. ''Qualitative'' feedback tells us how good, bad or indifferent.<ref name=Connellan>Thomas K. Connellan and Ron Zemke, "Sustaining Knock Your Socks Off Service" AMACOM, 1 July 1993. {{ISBN|0-8144-7824-7}}</ref>{{rp|page=102}}}}
====Limitations of negative and positive feedback====
While simple systems can sometimes be described as one or the other type, many systems with feedback loops cannot be so easily designated as simply positive or negative, and this is especially true when multiple loops are present.
Category:Control theory
范畴: 控制理论
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<small>This page was moved from [[wikipedia:en:Feedback loops]]. Its edit history can be viewed at [[反馈环/edithistory]]</small></noinclude>
<small>This page was moved from [[wikipedia:en:Feedback]]. Its edit history can be viewed at [[反馈环/edithistory]]</small></noinclude>
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