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'''Positive feedback''' ('''exacerbating feedback''', '''self-reinforcing feedback''') is a process that occurs in a [[feedback loop]] which exacerbates the effects of a small disturbance. That is, the effects of a perturbation on a system include an increase in the magnitude of the perturbation.

'''Positive feedback''' ('''exacerbating feedback''', '''self-reinforcing feedback''') is a process that occurs in a [[feedback loop]] which exacerbates the effects of a small disturbance. That is, the effects of a perturbation on a system include an increase in the magnitude of the perturbation.Positive feedback (exacerbating feedback, self-reinforcing feedback) is a process that occurs in a feedback loop which exacerbates the effects of a small disturbance. That is, the effects of a perturbation on a system include an increase in the magnitude of the perturbation. That is, A produces more of B which in turn produces more of A. In contrast, a system in which the results of a change act to reduce or counteract it has negative feedback.<ref name="theorymodelling" /> Both concepts play an important role in science and engineering, including biology, chemistry, and [[cybernetics]] .

Positive feedback (exacerbating feedback, self-reinforcing feedback) is a process that occurs in a feedback loop which exacerbates the effects of a small disturbance. That is, the effects of a perturbation on a system include an increase in the magnitude of the perturbation. That is, A produces more of B which in turn produces more of A. In contrast, a system in which the results of a change act to reduce or counteract it has negative feedback.<ref name="theorymodelling" /> Both concepts play an important role in science and engineering, including biology, chemistry, and [[cybernetics]] .

正反馈(加剧反馈，自我强化反馈) 是一种在反馈循环中加剧微小扰动影响的过程。也就是说，一个扰动对系统的影响包括它自身扰动幅度的增大。或者说，A会产生更多的B，而B又会产生更多的A，与之相反的是，[[负反馈]]指的是一个系统中，变化的结果会减少或抵消它自己的影响。<ref name="theorymodelling" />这两个概念在科学和工程等领域中发挥着重要作用，包括生物学、化学和控制论。

正反馈(加剧反馈，自我强化反馈) 是一种在反馈循环中加剧微小扰动影响的过程。也就是说，一个扰动对系统的影响包括它自身扰动幅度的增大。或者说，A会产生更多的B，而B又会产生更多的A，与之相反的是，[[负反馈]]指的是一个系统中，变化的结果会减少或抵消它自己的影响。<ref name="theorymodelling" />这两个概念在科学和工程等领域中发挥着重要作用，包括生物学、化学和控制论。

<nowiki></ref></nowiki> <ref name="theorymodelling" /> Positive feedback reinforces and negative feedback moderates the original process. ''Positive'' and ''negative'' in this sense refer to loop gains greater than or less than zero, and do not imply any [[value judgement]]s as to the desirability of the outcomes or effects.<ref name=":0">{{cite web|title=Feedback|url=http://metadesigners.org/Feedback-Glossary|work=Glossary|publisher=Metadesigners Network|accessdate=15 April 2014|url-status=live|archiveurl=https://web.archive.org/web/20140416183720/http://metadesigners.org/Feedback-Glossary|archivedate=16 April 2014}}</ref>  A key feature of positive feedback is thus that small disturbances get bigger. When a change occurs in a system, positive feedback causes further change, in the same direction.

<nowiki></ref></nowiki> <ref name="theorymodelling" /> Positive feedback reinforces and negative feedback moderates the original process. ''Positive'' and ''negative'' in this sense refer to loop gains greater than or less than zero, and do not imply any [[value judgement]]s as to the desirability of the outcomes or effects.<ref name=":0">{{cite web|title=Feedback|url=http://metadesigners.org/Feedback-Glossary|work=Glossary|publisher=Metadesigners Network|accessdate=15 April 2014|url-status=live|archiveurl=https://web.archive.org/web/20140416183720/http://metadesigners.org/Feedback-Glossary|archivedate=16 April 2014}}</ref>  A key feature of positive feedback is thus that small disturbances get bigger. When a change occurs in a system, positive feedback causes further change, in the same direction.

在数学上，正反馈被定义为一个环绕在闭合因果循环下的正循环增益。从结果到始发过程的反馈可以是直接的，或者它可以通过其他状态变量。<ref name="theorymodelling" /> 这样的系统可以给出丰富的定性行为，但反馈的瞬时信号是正向还是负向，对结果有极其重要的影响。<ref name="theorymodelling" /> 正反馈强化原过程，而负反馈调节原过程。在这个含义下，''正''和''负''指的是大于或小于零的循环收益，并不代表着最终结果或效果的正负性。<ref name=":0" />因此，正反馈的一个重要特点是小扰动变大。当系统发生变化时，正反馈会引起进一步的同方向变化。

在数学上，正反馈被定义为一个环绕在闭合因果循环下的正循环增益。<ref name="zuckerman" /><ref>Bernard P. Zeigler; Herbert Praehofer; Tag Gon Kim Section (2000). "3.3.2 Feedback in continuous systems". ''Theory of Modeling and Simulation: Integrating Discrete Event and Continuous Complex Dynamic Systems''. Academic Press. p. 55. ISBN <bdi>9780127784557</bdi>. Archived from the original on 2017-01-03. <q>A positive feedback loop is one with an even number of negative influences [around the loop].</q></ref><ref name="theorymodelling" /><ref name="zuckerman" /> 从结果到始发过程的反馈可以是直接的，也可以通过其他状态变量。这样的系统可以给出丰富的定性行为，但反馈的瞬时信号是正向还是负向，对结果有极其重要的影响。<ref name="theorymodelling" /> 正反馈强化原过程，而负反馈调节原过程。在这个含义下，''正''和''负''指的是大于或小于零的循环收益，并不代表着最终结果或效果的正负性。<ref name=":0" />因此，正反馈的一个重要特点是小扰动变大。当系统发生变化时，正反馈会引起进一步的同方向变化。

Positive feedback does not necessarily imply instability of an equilibrium, for example stable ''on'' and ''off'' states may exist in positive-feedback architectures.<ref name="ReferenceA">{{cite journal|last1=Lopez-Caamal|first1=Fernando|last2=Middleton|first2=Richard H.|last3=Huber|first3=Heinrich|title=Equilibria and stability of a class of positive feedback loops|journal=Journal of Mathematical Biology|date=February 2014|pages=609–645|doi = 10.1007/s00285-013-0644-z|pmid=23358701|volume=68|issue=3}}</ref>

Positive feedback does not necessarily imply instability of an equilibrium, for example stable ''on'' and ''off'' states may exist in positive-feedback architectures.<ref name="ReferenceA">{{cite journal|last1=Lopez-Caamal|first1=Fernando|last2=Middleton|first2=Richard H.|last3=Huber|first3=Heinrich|title=Equilibria and stability of a class of positive feedback loops|journal=Journal of Mathematical Biology|date=February 2014|pages=609–645|doi = 10.1007/s00285-013-0644-z|pmid=23358701|volume=68|issue=3}}</ref>

正反馈并不一定意味着平衡的不稳定性，例如，在正反馈结构中可能存在稳定的开关状态。.<ref name="ReferenceA">{{cite journal|last1=Lopez-Caamal|first1=Fernando|last2=Middleton|first2=Richard H.|last3=Huber|first3=Heinrich|title=Equilibria and stability of a class of positive feedback loops|journal=Journal of Mathematical Biology|date=February 2014|pages=609–645|doi = 10.1007/s00285-013-0644-z|pmid=23358701|volume=68|issue=3}}</ref>

正反馈并不一定意味着平衡的不稳定性，例如，在正反馈结构中可能存在稳定的开关状态。<ref name="ReferenceA" />

 

在现实世界中，正反馈循环通常不会引起不断增长，而是通过某种限制效应来改变。根据Donella Meadows的说法：

在现实世界中，正反馈循环通常不会引起不断增长，而是通过某种限制效应来改变。根据Donella Meadows的说法：

"Positive feedback loops are sources of growth, explosion, erosion, and collapse in systems. A system with an unchecked positive loop ultimately will destroy itself. That’s why there are so few of them. Usually a negative loop will kick in sooner or later."<ref name="meadows">

"Positive feedback loops are sources of growth, explosion, erosion, and collapse in systems. A system with an unchecked positive loop ultimately will destroy itself. That’s why there are so few of them. Usually a negative loop will kick in sooner or later."

 

正反馈回路是系统增长、爆炸、腐蚀和崩溃的根源。一个系统如果有一个不受控制的正反馈，最终将会自我毁灭。这就是为什么正反馈如此稀少的原因。通常情况下，负反馈迟早会发生。

正反馈回路是系统增长、爆炸、腐蚀和崩溃的根源。一个系统如果有一个不受控制的正反馈，最终将会自我毁灭。这就是为什么正反馈如此稀少的原因。通常情况下，负反馈迟早会发生。<ref>Donella Meadows, ''[http://www.sustainabilityinstitute.org/pubs/Leverage_Points.pdf Leverage Points: Places to Intervene in a System]''2013-10-08 at the Wayback Machine, 1999</ref>

Hysteresis, in which the starting point affects where the system ends up, can be generated by positive feedback. When the gain of the feedback loop is above 1, then the output moves away from the input: if it is above the input, then it moves towards the nearest positive limit, while if it is below the input then it moves towards the nearest negative limit.

Hysteresis, in which the starting point affects where the system ends up, can be generated by positive feedback. When the gain of the feedback loop is above 1, then the output moves away from the input: if it is above the input, then it moves towards the nearest positive limit, while if it is below the input then it moves towards the nearest negative limit.

[[迟滞]]，即起点影响系统的终点的现象，正是通过正反馈产生的。当反馈循环的增益高于1时，那么输出就会远离输入：如果大于输入，则向最近的正极限移动，而如果小于输入，则向最近的负极限移动。

[[迟滞]]，即起点影响系统的终点的现象，可以通过正反馈产生。当反馈循环的增益高于1时，那么输出就会远离输入：如果大于输入，则向最近的正极限移动，而如果小于输入，则向最近的负极限移动。

Once it reaches the limit, it will be stable. However, if the input goes past the limit,{{clarify|date=June 2012}} then the feedback will change sign{{dubious|date=June 2012}} and the output will move in the opposite direction until it hits the opposite limit. The system therefore shows [[bistability|bistable]] behaviour.

Once it reaches the limit, it will be stable. However, if the input goes past the limit,{{clarify|date=June 2012}} then the feedback will change sign{{dubious|date=June 2012}} and the output will move in the opposite direction until it hits the opposite limit. The system therefore shows [[bistability|bistable]] behaviour.

== Terminology ==

== Terminology ==