Talk:Negative feedback/Archive 2

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Reprise

It is hard to say whether there is continued opposition to the simple definition:

Negative feedback is the type of feedback that operates to oppose changes. Negative feedback can produce equilibrium and can reduce the influence of perturbations. Negative feedback loops in which just the right amount of correction is applied in the most timely manner can be very stable, accurate, and responsive.

Sources

It appears that Dicklyon and Trevithj accept this version, although perhaps only because alternatives are worse. Trevithj and GliderMaven appeared initially not to understand that this definition fits the negative feedback amplifier, but I hope the explanation that the feedback in this amplifier opposes both increases and decreases in output, with no aim to eliminate variation in output (it's an amplifier), and without the use of error measurement relative to a set-point, now is understood.

I don't think there is any doubt that this definition fits error-controlled regulation, where change is identified using an error measurement (departure from a set-point), and the system feedback opposes any error. Trevithj would prefer to say the feedback is negative if it reduces error, which is accurate in this case, but is less applicable to a more general context, and is less often used in sources.

Dicklyon dislikes the vagueness of 'change', preferring an 'input/output' description (like Morton's in the references above). However, the designation of 'departure from a set-point' as an 'output' is not an obvious use of 'output' and entails extending the intro into a discussion of the monitoring of system behavior, not to mention the explanation that some negative feedback usages do not employ such monitoring at all.

Unless there is more to be said, let's implement the 'opposition-to-change' formulation. Brews ohare (talk) 16:06, 12 August 2014 (UTC)

Reversion to unacceptable version by GliderMaven

In a series of edits 1, 2, 3, 4, 5 GliderMaven has reverted changes accepted by Trevithj and by Dicklyon following a protracted Talk page back-and-forth. GliderMaven's Talk page discussion of his motivations do not document any errors in the presentation of sources, but rest entirely upon GliderMaven's personal views. His views are inconsistent with the sources used in the removed material and with those discussed (by other editors) on this Talk page.

In short, GliderMaven's changes are not based upon reference to specific text in sources, and conflict with other editors, as stated and documented on this Talk page. GliderMaven's changes should be replaced with this well-sourced version. Brews ohare (talk) 20:33, 9 August 2014 (UTC)

No it shouldn't, and thank you GliderMaven. Johnuniq (talk) 01:28, 10 August 2014 (UTC)

While I agree with several here that the lead image was not a great one, and had that ambiguity about the different things that could be called input, I thought we did have some progress on a lead definition and a few things like that. GliverMaven's revert referred to a consensus, but I don't see what talk he was referring to. The lead definition that he reverted to, "Negative feedback occurs when a result of a process influences the operation of the process itself in such a way as to reduce changes", is way too mushy to be useful, in my opinion. Dicklyon (talk) 01:44, 10 August 2014 (UTC)

"Negative feedback is feedback that opposes change."???

I remind you in this context, a change is a temporal variation in input of some kind. If that's not what it is, then I have no idea what 'change' means.

Really? So what if a negative feedback system is being pushed/held by an external perturbation away from its natural equilibrium and a subsequent change actively pushes it back towards the equilibrium- does negative feedback oppose that subsequent change?

Nope. In that case the negative feedback and the change are in the same direction and add.

Indeed, I read it, and immediately knew it was wrong. The reason it's wrong is that isn't negative feedback; it's damping. Damping is feedback that opposes change!!! I mean, sure damping is A form of negative feedback on a velocity vector or state velocity change vector, but it's not a general form of negative feedback.

Think about it.

For the record, I'm very, very tired of Brews Ohares non consensus edits.GliderMaven (talk) 02:36, 10 August 2014 (UTC)

It is possible to progress if we stick to the objective of reporting a balanced view of sourced material. There is no point in claiming a 'consensus' among editors that do not share this goal, and assert 'consensus' over their personal views, however strongly held. Arguing over hypothetical examples goes nowhere, especially when the aim is to show published sources are wrong, not by citing other sources, but by personal assertions. Get back to reporting sourced material. Brews ohare (talk) 02:55, 10 August 2014 (UTC)

Yes. However, the point where we have to use our consensus understanding as editors is knowing what to put in, and leave out of the article. At this point, there is I believe, really strong evidence that 'management' use of the term 'negative feedback' is not congruent with the central meaning that the article is covering. This article is not primarily about damping, and the lead cannot state that it is.GliderMaven (talk) 04:00, 10 August 2014 (UTC)

Okay, Glidermaven has offered a counter-example to the proposed definition - namely that not all changes are opposed by negative feedback, but only changes with respect to some sort of reference point. While he hasn't provided sources, I can recall the point being made in the literature.

... any system, if it is to achieve a predetermined goal, must have available to it at all times an indication of its degree of attainment.

I must point out that his criticism towards the new definition is equally true of the old definition, so don't believe that is sufficient motivation for the reversion. Especially since that reversion involved removal of cited sources. The criticism however is worth considering, IMO. Trevithj (talk) 04:44, 10 August 2014 (UTC)

While I'm not totally happy with it currently on clarity grounds, the criticisms are not equally true. The original/current definition talks about reducing change, not opposing change. If you break any strongly active negative feedback loop, you will very often get huge changes to the output; it really has been actively reducing changes, and that does seem to be characteristic. But most loops are incapable of stopping change, and they don't characteristically oppose change, although some do i.e. damping is a form of negative feedback on a state rate change, but not all negative feedback is damping.

But that's a fine point, and that you as someone who understands negative feedback brings it up shows that it's not a clear and accessible enough definition. And I think Brews also understands negative feedback, and if he slows down and stops randomly copying incomplete references into the article we may get somewhere.GliderMaven (talk) 09:53, 10 August 2014 (UTC)

Source

Trevithj: There is no doubt at all that there are a variety of applications of feedback, including in particular various forms of regulation, a correction toward a desired goal. But the point is not that some forms of negative feedback involve regulation. The larger point is that not every application of negative feedback involves regulation. In particular, op-amp circuits like the op-amp voltage amplifier, and also the negative feedback amplifier, have nothing to do with regulation. So there are two points to be made - one is the poor framing and lack of sourcing by GliderMaven, and the second is that even if all this is cleaned up a general definition of negative feedback will not have been achieved. The general and sourced definition is that negative feedback is feedback that opposes change. That definition applies to a wide variety of forms for negative feedback, even to some of its uses in management and psychology, as indicated by the sources selected from those fields. Brews ohare (talk) 05:38, 10 August 2014 (UTC)

Trevithj: To quote your source further, "Every goal-seeking system involves feedback", which by no means suggests that "Every feedback system is goal-seeking", which is a point I'm sure you recognize. Brews ohare (talk) 12:31, 10 August 2014 (UTC)

Here is one possible discussion of exceptions. Brews ohare (talk) 12:57, 10 August 2014 (UTC)

Damping is, indeed an example of negative feedback (on the state rate change vector, towards zero), but feedback of any state vector so as to tend to push the system towards any equilibrium point is negative feedback.

For example, in the inverting negative feedback amplifier the equilibrium point is the input/signal, and the output value will approach stable point that is a negative multiple of that. An ideal inverting negative feedback amplifier does not necessarily have any damping at all, but a practical system will typically have damping as well as the negative feedback.GliderMaven (talk) 09:53, 10 August 2014 (UTC)

This conception of the operation of the negative feedback amplifier is unsourced nonsense unrelated to the common analysis found in innumerable EE texts, representative examples of which are already cited . Brews ohare (talk) 11:31, 10 August 2014 (UTC)

Unlike systems like thermostatic control, the negative feedback amplifier does not attempt to achieve some 'stable point' by countering deviancy using feedback and bringing the system back to some set-point. What it does is render system operation insensitive to disturbances introduced by the open-loop amplifier, not by regulation, but by arranging the system gain to be controlled by the feedback loop itself, independent of the open-loop gain, and therefore of any disturbances it might intrude. As an amplifier, the input signal is amplified (by 1/β) and, as the analysis used in customary EE texts shows, this operation has nothing to do with 'equilibrium' or homeostasis in any form, and the standard analysis never introduces such mechanisms. Brews ohare (talk) 13:37, 10 August 2014 (UTC)

We seem to be leaning towards a definition based on the effects of negative feedback, rather than on the purpose/mechanism. The idea is that if the feedback isn't reducing changes, then (by definition) it isn't negative. This approach may avoid lots of awkward and sometimes conflicting terminology. To that end, I suggest that we can still further simplify the existing/original definition:

Negative feedback occurs when the feedback reduces changes.

Are there cases of negative feedback that the above does not cover? Bearing in mind that the valence sense of negative is out of scope. Trevithj (talk) 19:46, 10 August 2014 (UTC)

I would resist any definition that starts with "negative feedback occurs when". It's not an event. As for whether it reduces changes or not, hard to say. In the real world, negative feedback systems have a tendency to move toward positive feedback at high enough frequencies. Whether there's a net reduction in "change" depends on various things, like the spectrum of the source of change. Or maybe there are no changes or fluctuations to be reduced; the lack of such fluctuations wouldn't make negative feedback cease to exist. Nevertheless, it's probably OK to say that negative feedback is feedback that tends to counteract or reduce change, or something to that effect; I think we showed that many sources do something like that. As for damping, that's a sort of 90-degree phased feedback, which pushes back in proportion to a velocity, so it tends to reduce a rate of change, without affecting the net extent of change at low frequencies. It's neither positive nor negative, in that sense. It's not usually implemented as feedback per se, but can be. Dicklyon (talk) 22:12, 10 August 2014 (UTC)

I'd take Dicklyon's remarks as supporting the restoration of:

Negative feedback is feedback that opposes change.

Sources

It would appear that Trevithj is not really opposed to this idea either, leaving only GliderMaven opposed without any supporting source, and Johnuniq and Blackburne opposed only as me too’s supporting GliderMaven's personal opinions. Brews ohare (talk) 22:37, 10 August 2014 (UTC)

And half of your sources for the "oppose change" definition actually do it the way I prefer, which is to talk about output being fed back to input. Traditionally, that's what feedback means: "back" from output to input. It covers both the control case and the amplifier case. Trying to generalize it much beyond that gets into all sorts of difficulties, as you point out here. Dicklyon (talk) 23:06, 10 August 2014 (UTC)

So what is your stance? Pro, con, or undecided? You might notice that in the case of error-controlled regulation, for example, controlling the speed if a car, the output is the speed of the car, the input is the gas to the carburetor, and the feedback is decided by how far the speedometer needle suggests the car is from the targeted speed. Saying the 'output' (speed) is fed back to the 'input' (gas to the carburetor) doesn't quite work. Aside from relating 'speed' to 'gas', the trigger for action (speedometer reading) plays a crucial role. In some systems, the connection between the triggering phenomenon and the ultimate controlled output may be rather convoluted. It may be easiest to say the 'feedback' opposes a change. Depending upon the regulated process, a number of things may have to occur, requiring some abstraction from the details to fit an 'input/output' description . Brews ohare (talk) 23:55, 10 August 2014 (UTC)

So? Nobody would argue that the connections have to be trivial for the definition to apply. Dicklyon (talk) 00:43, 11 August 2014 (UTC)

Au contraire, mon ami. The proposed definition that ' negative feedback is feedback that opposes change' works fine even in complicated cases, because it requires no specific details. They are all subsumed in the term 'feedback' that is examined in the article feedback, and need not be examined here (other than in subsections devoted to a few examples). In contrast, if 'input' and 'output' are invoked, we need a recipe for their identification, which is non-obvious. How is the 'output' identified? Is it the 'product' of a process, or a monitored indicator of process operation, or something else? What identifies a 'trigger'? Some examples of negative feedback employ a trigger (for example, error-controlled regulation), while others do not (for example, the negative feedback amplifier). What modifies the 'input', which may be different in form and nature from the 'output'? Is it a management directive, heat from a furnace, or some other kind of 'thing'? Every case is different and to understand the connection to the input-output model, the specifics must be related by case-by-case identification or some abstract prescription connecting them to the 'input/output' formulation. Brews ohare (talk) 13:41, 11 August 2014 (UTC)

In any event, we digress - the definition that 'negative' feedback is feedback that opposes change' is uncomplicated, sourced, and universally applicable, so let's use it. Brews ohare (talk) 03:13, 11 August 2014 (UTC)

More from GliderMaven

But as I have already pointed out, it is actually wrong, since if the output is already held away from the equilibrium, a change back towards the equilibrium is not opposed. Negative feedback does not characteristically oppose changes.

If you have a pendulum and the wind is holding it away from the vertical, the feedback is pushing it back to the vertical. If the wind changes- specifically has a negative change in strength; the feedback is still in the same direction, back towards the vertical, and is in the same direction as the change, and both will pull the pendulum back towards the vertical.

I have no problem with your quoting that definition within the article as something that is claimed, but I hold no truck with putting definitions that are known not to be correct in the lead. The implications of doing that is that anything that doesn't meet the definition would theoretically have to be moved out of the article, and since it's wrong, that would be spectacularly awful.GliderMaven (talk) 14:06, 11 August 2014 (UTC)

Fundamentally, it's our job as editors to sift through the big pile of potential references and use the best possible ones we can. These are clearly not good references for the definition of negative feedback; just because you like them, doesn't mean we can or should use them.GliderMaven (talk) 14:11, 11 August 2014 (UTC)

GliderMaven: Your approach to discussion is based upon your personally contrived examples, and doesn't use sources. In fact, your claims contradict numerous published sources. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. Here is a Google search with 37 sources.

The way WP works is that regardless of your logic (supposing there is such) and eloquence (again supposing there is such) if published sources are all wrong, it doesn't matter. WP's purpose is to report what published sources say, not WP editors. In cases where published sources disagree, WP's purpose is to provide a balanced reporting of the various sources.

So, the bottom line here is: use sources to frame your position. If you can't find any, then your thoughts are not pertinent. Brews ohare (talk) 14:42, 11 August 2014 (UTC)

As for your initial point, "if the output is already held away from the equilibrium, a change back towards the equilibrium is not opposed", it is incomplete. If the system departs from its set-point, the error signal triggers the feedback that reduces this error. So the pendulum on its way back to center is moving because of the feedback, which is indeed opposing the triggering displacement from the rest position of the bob. Rather than argue the point, find a source that suggests that negative feedback does not oppose change, rather than coming up with examples of your own devising that can be interpreted ad nauseam on this talk page. Brews ohare (talk) 15:20, 11 August 2014 (UTC)

There are three points of view here that need closer examining, it seems to me.

1. feedback is only negative if it is actually reducing change.
2. feedback is negative if it is opposing change that would otherwise get larger, even if it isn't reducing that change.
3. we can't use a reference point when discussing change because that isn't generic.

The first two seem to arise indirectly from the third. That is, if we talk about change from an agreed reference, the two views can be brought into alignment.

The third POV seems odd - how can we define change without at least an implied reference?

Trevithj (talk) 20:53, 11 August 2014 (UTC)

Hi Trevithj: Well according to Beerel, if the amount in nicotine in cigarettes is changed, that is the change and the response tending to maintain the status quo is to smoke more cigarettes. So there is a reference point here, the amount of nicotine intake, and the smoker acts to oppose a reduction in intake. However, according to Yadav, in the negative feedback amplifier the feedback is 180° out of phase with the input signal, so when the output increases, the input after the summer is reduced by the feedback, making it negative feedback. In this case, there is no set-point, the sole criterion is that an increase in the output is reduced by the feedback. Of course, if the signal input drops, lowering the output, the feedback, being out of phase with the input, will increase the input after the summer. So a general statement about the negative feedback amplifier is that all changes in the output are opposed by the feedback, although of course they are not nullified. There are two cases here - one is error-controlled regulation using a set-point and aiming at equilibrium (nicotine example), and the other is not error controlled, uses no set-point, and is not aimed toward preserving some status of the system (amplifier example). Brews ohare (talk) 22:29, 11 August 2014 (UTC)

Thanks Brews for the clarity. I pondered this, and came up with the following analogy that helped to clarify my thinking.

1. If I drive a car down a straight road, I need only occasional corrections to the steering to stay in the lane. Most of the time, I don't need to touch the steering at all. I can "reduce the change" to near-zero.
2. If I drive a car around a circular track, I need constant corrections to the steering in order to stay in the lane. If I released the steering, the car would drift to the outside of the curve. I need to "oppose the change" in order to maintain position.
3. In the first case, I reduce change between desired and actual path. In the second, I'm doing the same thing but with the added complication that something in the system is constantly pulling me off path even without perturbations.

I get that there is difficulty talking about "desired" states in natural systems. And so the idea of an "error" is somewhat anthropomorphic. It still seems to me that there is a case for introducing something of the sort as a reference point in either case when describing change. By definition, change is always with respect to something. The negative feedback amplifier is a confusing case, because the summer component is doing elegant double-duty as comparator/regulator combined. I don't think the case is sufficiently different to warrant a separate treatment though. At least, not here.

Trevithj (talk) 19:44, 12 August 2014 (UTC)

Trevorj: In the negative feedback amplifier, the 'change' is the time variation of the output that must happen because the amplifier is amplifying a time varying input signal. The summer has only one purpose, namely, to subtract a fraction β of the output from the input signal. What that does is fix the closed loop gain at 1/β, and that 'fix' is not an adjustment of some measured value toward a set-point. The value of β is set by, for instance, a resistor ratio. That ratio is fixed by the resistor values, and is not a fluctuating quantity that has to be kept constant by the feedback. The feedback fraction β has nothing to do with an 'aim' or 'goal' of the circuit, although, of course, it reflects the aim of the designer who chose the resistors. The summer is not a comparator finding an 'error', and there is no set-point toward which the summer pushes the operation.

The negative feedback amplifier is a completely different use of feedback than the error-controlled regulator, so naturally it is confusing if one insists upon seeing it as an error-controlled regulator. In fact, it has no analogy to it whatsoever. You don't have to take it that this is my personal viewpoint - just look at the many EE textbook analyses of the amplifier which never talk about an error or a set-point or a comparator. Brews ohare (talk) 22:09, 12 August 2014 (UTC)

Grounds

Well, it is difficult to cite analyses on the grounds of what they don't mention. In point of fact, I think treating the negative feedback amplifier as separate from error-controlled regulation is actually more confusing. I have pondering this, and it still seems like a terminology issue, rather than any fundamental change in process or concept. The only tangible distinction I could find was the idea of "constant correction" vs "occasional correction" that I described above.

Consider this quote from Black's original patent:[1]

"One improvement [of negative feedback] is in lowered distortion arising in the amplifier. Another improvement is greater constancy of operation, in particular a more nearly constant gain despite variable factors such as ordinarily would influence the gain."

Granted his description is convoluted, probably due to the terminology still being very new then. Even so, he is clear on what change is being opposed/reduced. And as far as analogy goes, isn't "improvement" analogous to "error-correction"? Trevithj (talk) 08:14, 13 August 2014 (UTC)

Trevithj: The reason sources discussing the negative feedback amplifier do not mention set-points, errors, and comparators is that they have no more relevance than the stock market. The remarks of Black are perfectly clear and also make no mention of these factors, nor do his patents. They are understandable as he intended them- the use of feedback bypasses the inadequacies of the nonlinear, variable, and uncontrollable properties of the large-gain open loop amplifier, as very easily seen in the gain analysis that shows the closed-loop gain to be set at 1/β, as fixed by a resistor divider, for example, by making the closed-loop gain independent entirely of the open-loop gain. I don't think you fully appreciate the simple algebra that governs this circuit. Brews ohare (talk) 12:33, 13 August 2014 (UTC)

Trevithj: Your request for a citation that sources don't invoke irrelevant matters because they are irrelevant seems unnecessary, eh? It suffices to look at the sources dealing with the negative feedback ampifier and notice that indeed they do not invoke set-points, errors, and comparators. Brews ohare (talk) 21:01, 13 August 2014 (UTC)

That would be acceptable if we could really look at all the literature and say that no-one invokes set-points, errors and comparators. Or if we could be sure of the motives of those writers who do not mention these things. Further to our separate discussion: [2][3][4]

I was hoping you could provide a source that explicitly rejected the negative feedback amplifier as being related to error-regulation. I had a look myself. David Mindell had this entry, related to the work of Hazen.[5] There is also discussion on the historical sources and nature of confusion around this area related to Black's work. It still appears to come down to a difference in notation/terminology.

Trevithj (talk) 08:56, 15 August 2014 (UTC)

Your source Mindell comes close to explicit rejection. On p. 124 he says Black's patent suggests the negative feedback principle applies widely, but a "steam engine governor, an automatic pilot, or a servomechanism hardly fit into the category...Neither the patent, not any of Black's early writings, nor any Bell Labs feedback theory for at least ten years mentions regulators, governors, automatic pilots, or any of the myriad devices we now understand as employing negative feedback."

Of course, the reason is simple - these examples that Bell fails to mention all are error-controlled regulators that use measured deviations from set-points, while the negative feedback amplifier does not.

This separation of servomechanisms is consistent with Mindell's discussion of Hazen on p. 165, where he points out Hazen's view of feedback was applied to control systems that are based upon a setpoint, such as the servomechanism, "in which the restoring force,..., is approximately proportional to the deviation of the output." Brews ohare (talk) 18:58, 15 August 2014 (UTC)

Regarding your reference Mauro, he defines "error signal" as synonymous with the difference between the input signal and the feedback signal, which definition is used even though this difference does not involve a set-point and the circuit operation makes no attempt to set the so-called "error signal" to zero. The same applies to your reference Cordell. On the other hand your reference to Maclean appears to apply to the unity gain buffer, where the aim is to replicate the input signal and β≡1. In this case, because the aim is to replicate the input, the departure of the output from the input is indeed an error signal. However this example has nothing to do with setting or enforcing the value of β, which is beyond reach of any regulation. Brews ohare (talk) 19:08, 15 August 2014 (UTC)

So, indeed, there is some confusion over the meaning of "error signal". However, we can be quite clear that in error-controlled regulation the "error" is to be minimized, and the "error signal" is the deviation of the measurement of a essential variable from its set-point. This definition of "error" is completely contrary in behavior to the "error" conceived of as the 'difference between the input signal and the feedback signal', which is the "error" described by some for the negative feedback amplifier. This 'difference error' is understood always to be non-zero and there is no attempt to make it zero or even to minimize it. Brews ohare (talk) 19:13, 15 August 2014 (UTC)

Algebraically, the input-feedback difference called the 'error' by some is I−βO= I/(1+βA) ≠ 0; of course, that means the output is A(I−βO) ≃ (1/β)I, a linear and fluctuation-free amplification of I. If I−βO actually were zero, there would be no signal to amplify and the amplifier would have zero output. Brews ohare (talk) 03:07, 16 August 2014 (UTC)

Operation of the negative feedback amplifier

Perhaps it would be helpful for us to discuss the subsection on the negative feedback amplifier at this point inasmuch as it's operation appears to be an issue here. Most probably you do not agree with that subsection. Or do not see the connection to negative feedback as opposition to change. What do you think? Brews ohare (talk) 13:22, 13 August 2014 (UTC)

For example, the statement

"The negative feedback amplifier does not attempt to correct variations in the open-loop gain by opposing such changes, but simply reduces their impact on the overall system behavior."

is correct but is confusing when juxtaposed with the definition of negative feedback as opposition to change. The change opposed by the feedback is indeed not 'variations in the open-loop gain', but is the variation in amplifier output as a result of its operation in amplifying a time-varying input signal. This opposition reduces the variation in the output, and lowers the gain from the large open-loop gain to 1/β, regardless of the value of the open loop gain, which can vary from (say) 10⁶ to 10¹⁰V/V with zero impact. Brews ohare (talk) 13:51, 13 August 2014 (UTC)

This opposition that results in a gain of 1/β is not in response to nor is it tailored by the particular, immediate value of the open-loop gain. This value of 1/β is fixed once and for all by some resistor network, and you can physically replace the open-loop amplifier with a very different one and the closed- loop amplifier continues to operate the same way. Brews ohare (talk) 14:04, 13 August 2014 (UTC)

The opposition by feedback is to the output signal itself, not to the vagaries leading to that signal, such as the peculiarities of the internal state of the open-loop amplifier. That situation is different from error-controlled regulation, which constantly monitors the internal state of some system, and responds by keeping that state in place by adjusting its essential parameters to their set-points. Brews ohare (talk) 11:53, 14 August 2014 (UTC)

Proposed change to lede

A simple negative feedback system, and many electronic amplifiers, can be represented by this diagram. The feedback is negative if the loop gain AB is negative.

Negative feedback is feedback that opposes change. Opposition can take the form of error correction, for example, reducing the departure of an essential system variable from its set point. It also can take the form simply of reducing sensitivity to change, which need not involve error-correction, as is accomplished by the simple negative feedback system pictured at the right. There are other possibilities discussed below.

Sources

---

The above is proposed to replace the present lead paragraph. It serves these purposes not presently satisfied:

1. It is sourced.

2. It uses a general definition of negative feedback that applies to a wide variety of applications. The existing lede refers to a "process", not a system, a restricted view. It also uses an input/output formulation that is inapplicable to homeostasis, for example, where there is no output beyond a reaction of the system to correct departures from its normal configuration.

3. It points out, using two sources to a detailed algebraic analysis, that the system in the attached figure "reduces sensitivity" without employing error correction, which does not occur in this system.

Brews ohare (talk) 16:49, 26 August 2014 (UTC)

An extended comparison of examples of error control versus the operation of the pictured negative feedback system can be found here that does not involve the more definitive algebraic analysis used by (for example) Bhattacharya. Brews ohare (talk) 17:04, 26 August 2014 (UTC)

Commentary

If there are no objections to this change, I propose its implementation in the main text. Brews ohare (talk) 12:56, 27 August 2014 (UTC)

• Doesn't work for me: it's far too narrow. Negative feedback doesn't just consist of error correction and reducing sensitivity to change. And I don't think it makes sense to enumerate examples so early. Best just start with a general definition, as now. Then mention examples and applications in the second paragraph, as is done already. I.e. the current lead is fine, certainly much clearer than the proposed change.--JohnBlackburne^words_deeds 13:21, 27 August 2014 (UTC)

Blackburne: There is no restriction to these cases that are mentioned merely as examples, as you have noticed yourself. The broader definition is the first sentence, which encompasses every possibility that I can find. If you have more, let's hear about it. Brews ohare (talk) 15:01, 27 August 2014 (UTC)

For reasons enumerated above that you continue to ignore, your comment "Best just start with a general definition, as now" is incorrect. The present definition is faulty as pointed out in item #2 immediately above: it is not at all 'general'. In particular, it is inapplicable to the figure in the lede. Brews ohare (talk) 15:31, 27 August 2014 (UTC)

Because you do not understand this point, I will elaborate. If we interpret the amplification of the input signal as an example of the 'process' referred to in the first sentence of the present lede, then the output O, contrary to the lede, does not "influence the operation of the process". Instead, the process is governed by the feedback ratio B and the amplification A, neither of which has anything to do with the output. Moreover, the input to the amplifier A is I/(1+BA), which is determined by the input signal I and the aforementioned B and A, and none of these involve the output at all. The system operation is fixed by the circuit topology and parameters independent of O. O is a dependent variable given in the usual case of large gain by O = AI/(1+BA) ≈ I/B and it controls or influences nothing. Brews ohare (talk) 15:47, 27 August 2014 (UTC)

To underline the point: the definition of negative feedback used in the present lede does not apply to the system in the accompanying figure, which constitutes perhaps the best known example of negative feedback, the negative feedback amplifier. Brews ohare (talk) 20:09, 27 August 2014 (UTC)

• This would not be an improvement. To take the three numbered points above:
  1. Statements in the WP:LEDE do not have to be sourced as they should be a summary of the main points made in the article. In this case, every example, described and referenced in sections 3.1 to 3.7 of the article, are systems in which negative feedback operates as described in the existing opening sentences.
  2. Per the LEDE guideline, "The first sentence should tell the nonspecialist reader what (or who) the subject is." The proposed opening sentence is so short as to be virtually meaningless to the nonspecialist or casual reader. It is immediately followed by specific examples that are not generally applicable. I do not know in what sense you find 'process' more restricted than 'system': In fact the opposite is true - there are many processes in nature for which it is hard, or remains to be done, to isolate the 'system' that is entirely responsible. The existing first para does not mention input or output. It mentions a result, and in the case of homeostasis there is always a clearly defined result: perhaps it is body temperature, pH, or a concentration.
  3. At the level of the opening paragraph, we are describing a real process or configuration, and the effects of that process or configuration; we are not describing a mathematical model of such a process. It is misleading and inappropriate to base a description of a real thing on a description of one of its mathematical models: all such models are approximate and provisional, whereas the real thing actually exists and can be (and has been) observed. Later in the article, currently useful mathematical models can be introduced but they should be distinguished from the reality to which they approximate. Regarding 'reducing sensitivity', as I described to you at 14:31, 24 June 2014 (UTC) above, (omitting parentheses this time) "In the case of the op-amp, disturbances can come in the form of an increase in load current, a change in supply voltage, a change in the open-loop gain due to temperature change, and other factors." Because the negative feedback amplifier employs 'error correction' it also automatically exhibits reduced sensitivity to such changes. The error correction derives from the fact that a proportion of the output signal is fed back, inverted, to the input circuitry. This means that if the external input signal is constant (just like a constant setpoint), and if the output signal were to change for whatever reason, then the effect of the negative feedback would be to "influence the operation of the process itself in such a way as to reduce changes" - just like the existing opening sentence says. The 'process' in this sense refers to the whole amplifier: differencer, op-amp, feedback circuit, power supplies, ambient environment, external load etc. Equally, if the external input were to change, then the output would also change, but by less than it would if the negative feedback were not present. --Nigelj (talk) 21:59, 27 August 2014 (UTC)

Your explanations are simply your own opinions and are not supported by sources. Your explanations of insensitivity contradict the sources I have cited. Your notion that the supplied figure in the lede cannot be tied to the math provided also contradicts all sources and trying to avoid that fact is hopeless. Brews ohare (talk) 23:03, 27 August 2014 (UTC)

Your sentence "Because the negative feedback amplifier employs 'error correction' it also automatically exhibits reduced sensitivity to such changes." is simply nonsense according to the analysis of Kal and of Bhattacharya which demonstrate insensitivity using arguments unrelated to error-correction. Brews ohare (talk) 23:17, 27 August 2014 (UTC)

A lot of wheel-spinning could be avoided if you discussed what sources say, instead of your own opinions. It then could be decided whether your reading of these sources is accurate. Brews ohare ([c[User talk:Brews ohare|talk]]) 23:35, 27 August 2014 (UTC)

You might start by discussing the views of Kal and of Bhattacharya mentioned above and its lack of connection to error-controlled regulation. Brews ohare (talk) 00:51, 28 August 2014 (UTC)

This is the lead paragraph, it's meant to summarise the whole article, not be based on particular source or sources. The relevant policy is WP:LEDE. As for 'opinions' that's how WP works, by editors discussing their opinions of content, giving sometimes policy based reasons for their views, sometimes judging the content on other grounds such as clarity, appropriateness. The process is called consensus and is fundamental to how WP works. Other editors views are not "hokum" just because you disagree with them. Stick to discussing the content, not disparaging other editors or their contributions.--JohnBlackburne^words_deeds 01:41, 28 August 2014 (UTC)

Blackburne: Having several sources that support the definition provided does not constitute being based upon particular sources. It is being based upon some sources, as contrasted with the present imaginings of some WP editors. As for opinions, opinions that are not based upon sources indeed are worthless here, being no more than the imaginings of WP editors. Likewise, consensus is not important if that agreement is about editors' opinions that differ with sources, but it is important if it is informed agreement upon what sources say. You say: "Stick to content" - what a laugh! There is no source cited here except those I have cited, and their explanations have been ignored entirely. Instead we have WP editors' opinions repeated ad nausea. Editors views are indeed hokum unless they reflect sourced opinion.

It is unfortunate that neither you nor Nigel, nor from earlier, GliderMaven, have any interest in the literature cited and simply repeat your prejudices about error-controlled regulation. Well, so be it. Obdurate avoidance of sources, extending even to the point where it is claimed that sources are neither necessary nor need be discussed in preparing the lede, will not lead to an accurate framing of the subject. Brews ohare (talk) 05:38, 28 August 2014 (UTC).

Brews ohare (talk · contribs), WP:TPG is very clear when it says, "Never edit or move someone's comment to change its meaning". You have filled my lengthy and detailed comment above with your own interjections and entirely wrecked the numbered-list formatting that I used. This discussion is now over as no one can read what I wrote. You have been arguing a range of self-contradictory positions on this talk page since you arrived here on the 6 June. You have not received consensus for the changes you have tried to make, and most of your edits to the article have been reverted. I think it is time to start asking if these contributions are a net benefit to improving the article, or if they are actually disruptive. --Nigelj (talk) 09:36, 28 August 2014 (UTC)

Nigel: My apologies - I have restored your remarks in their original form without interspersed replies. Brews ohare (talk) 14:26, 28 August 2014 (UTC)

This Commentary remains an all-time low in my experience on WP in terms of its disdain for published sources and refusal to discuss published analyses. It is the most extreme (and obvious) insistence upon editors' personal and unsupported opinions, over WP's mission to provide reliable summary of relevant published literature on each of its topics, that I have encountered. Brews ohare (talk) 14:32, 28 August 2014 (UTC)

None of these sources has been mentioned and the very clear analyses of insensitivity by Kal and by Bhattacharya are apparently beyond these editors' interest (or ken). Brews ohare (talk) 14:44, 28 August 2014 (UTC)

Brews you need to lay off the personal attacks. You asked for feedback you got it. Please read and understand the comments, which address precisely your points about sources. It's not 'hokum', 'nonsense', 'disdain', 'refusal', certainly not "insistence upon editors' personal and unsupported opinions". It is you who is making disparaging assertions about other editors that are unsupported by their contributions. If you are unable to work constructively and civilly to improve the article you really should take a break and find something else to do. --JohnBlackburne^words_deeds 15:44, 28 August 2014 (UTC)

Blackburne: I wish your comment had substance. Please point out where these sources have been reviewed and where the very clear analyses of insensitivity by Kal and by Bhattacharya are addressed. Brews ohare (talk) 16:30, 28 August 2014 (UTC)

Analyses of insensitivity by Kal and by Bhattacharya

A simple negative feedback system, and many electronic amplifiers, can be represented by this diagram. The feedback is negative if the loop gain AB is negative.

Kal and Bhattacharya have analyzed feedback systems with the block diagram shown in the figure at right from the present lede. Their discussions are typical of virtually all electronics textbooks. To summarize their discussion, Bhattacharya begins with the comment:

"The primary advantage of using feedback in control systems is to reduce the system's sensitivity to parameter variations."

Both he and Kal proceed to show that this circuit leads to a reduction in variations by a factor of 1/(1+BA) [see Kal, Eq. 6.11, p. 194] where, because of the large size of the gain A, this is a very small fraction. This reduction is simply an algebraic consequence of the circuit arrangement, and does not involve the measuring of a system parameter (such as internal parameters governing B or A) nor a comparison with a setpoint value for any such parameters, nor does the feedback undertake to reduce any such (unavailable and unknown) error.

A confusion in terminology can arise in this connection because some sources refer to the input I–BO to the block A as an 'error'. However, no source claims that (I - BO) involves an "error" serving the same function as the error in error-correcting regulation. The 'error' given by the difference I–BO is provided by:

$I-BO=I\left(1-\beta {\frac {O}{I}}\right)={\frac {I}{1+BA}}$

and is therefore fixed by the (arbitrary) input I and the invariant values of B and A, and is not 'adjusted' or 'reduced' as a matter of circuit operation and is not a parallel with error-controlled regulation involving a measured departure from a setpoint. In particular, (I - BO) is not corrected or minimized by the feedback.

In sum, the desensitization of variations calculated to be a factor of 1/(1+BA) is unrelated to the idea of error-controlled regulation, while the present lede incorrectly suggests this possibility when it proposes:

"Negative feedback occurs when a result of a process influences the operation of the process itself in such a way as to reduce changes"

as applicable to the provided pictured system. The result (output O) does not influence the "operation of the process itself" (amplification of the input I) and no attempt in this circuit is made to "reduce changes" if such changes are taken to indicate variation in I–BO or either of A or B. Brews ohare (talk) 17:21, 28 August 2014 (UTC)

Simply doing maths on a stability condition actually says very little about feedback. Realistically, feedback loops spend no time at the stability point. Fundamentally, it's not an exaggeration to say that if you don't acknowledge how and why this equation isn't in general true for that feedback amplifier:

$I-BO=I\left(1-\beta {\frac {O}{I}}\right)={\frac {I}{1+BA}}$

Then you shouldn't be editing the article at all.

In the context of this article, that equation is essentially never true. That's only the stability condition, feedback loops are never at stability, they're always wandering around, up, down.

If you assume, as you have implicitly done, that a feedback loop is only operating AT stability, then yes, the feedback loop isn't doing anything. But you cannot then correctly draw the conclusions you have done from that. That's known as 'begging the question'. Feedback is what happens when something is not in equilibrium, not when it is.

The people that wrote that textbook knew that perfectly well, they were simply deriving the gain, and the output of the circuit will be close to that point nearly all the time. But this isn't an article on amplifier gain, it's an article on feedback.

I shouldn't have to explain this.GliderMaven (talk) 18:33, 28 August 2014 (UTC)

No, it isn't you who should explain. You should supply a published source that reflects your ideas (supposing that is possible).

This discussion of yours of "operating at stability", of "doing maths on a stability condition", is a misconception of this analysis. The statement that the expression for I-BO is "essentially never true" is astounding given that it is unsourced opinion contradicting sourced material that treats fluctuations using these expressions for I and O. You might notice that Bhattacharya treats fluctuations in the gain, his ΔG, and Kal discusses "a change in the gain of the base amplifier due to some reason" dA. Brews ohare (talk) 19:23, 28 August 2014 (UTC)

And it is another misconception to think these authors are not discussing feedback. "One important property of negative feedback...is the reduction of sensitivity to changes in parameters" (Bhattacharya, p. 135) "Negative feedback makes the amplifier less sensitive to these parameters...We consider a situation in which there is a change in the gain of the basic amplifier due to some reason." (Kal. §6.3.1 Gain Stability, p. 193) Brews ohare (talk) 19:31, 28 August 2014 (UTC)

To attempt to get to the bottom of this disconnect, your view that "feedback loops are never at stability, they're always wandering around, up, down" is a carryover from something like a thermostatic control of temperature, where the temperature departs from set point, the departure is registered by the thermostat, and the furnace is adjusted to restore the set point. That is all fine for error-controlled regulation. But the entire point here is that this is not what is going on in the negative feedback amplifier, as the analysis of these two sources show. You will be unable to find any source that suggests error-controlled regulation, setpoints, and measurement of errors and their reduction is at work in this situation. Brews ohare (talk) 19:47, 28 August 2014 (UTC)

Whatever the origins of GliderMaven's unsourced views, it remains the case that this summary accurately reflects the analysis published by Kal and by Bhattacharya, and that these authors describe the insensitivity introduced by feedback without any mention of the various components of error-controlled regulation, attributing it entirely to an attenuation of variations by the factor 1/(1+BA). See Kal, Eq. 6.11, p. 194 Brews ohare (talk) 14:44, 29 August 2014 (UTC)

GliderMaven, have you accepted that your description of feedback is based upon the model of error-controlled regulation? And have you accepted the fact that Kal and Bhattacharya do not do this? And finally, have you accepted the fact that the analysis of gain stability against variations in gain used by Kal and by Bhattacharya is accepted in every textbook (so far as I know) on the subject of negative feedback for systems using the block diagram of the lede? Brews ohare (talk) 00:18, 30 August 2014 (UTC)

So let me get this straight, you are claiming that a negative feedback amplifier is not an example of an error-controlled regulator, and you are basing this on something that a textbook did not say, and then writing it into Wikipedia as true?.GliderMaven (talk) 17:33, 30 August 2014 (UTC)

There's room for convergence here. The negative feedback amplifier can be cast as an example of error-controlled regulation if you like, but its inventor didn't mentioned that concept, and this paper about its invention specifically contrasts what Black came up with with that concept. Dicklyon (talk) 18:22, 30 August 2014 (UTC)

Convergence is always desirable, but to paraphrase Einstein , only enough, and not over-convergence. Dick, for this to work we need more detail from you. As far as I can see, GliderMaven thinks the standard analysis of Kal is incorrect, but has no source to back him up. Of courser, if he is right, 3 decades of university texts would hit the trash. Brews ohare (talk) 19:38, 30 August 2014 (UTC)

I do not disagree with any standard texts, and no standard text states your position as fact, because it is not true. You clearly misunderstand how a negative feedback amplifier operates, as I pointed out above, the output of the summer is not in general in agreement with that equation you quote; that is only the equilibrium state with a DC input. In general there are propagation delays through all of the elements. Indeed, that is specifically why Black had so much trouble with real world implementation of his initial idea; all his initial attempts oscillated wildly.GliderMaven (talk) 21:44, 30 August 2014 (UTC)

It only notes that error controlled regulators existed before Black extended negative feedback to linearise high-gain amplifiers, it does not state that there is any specific difference.GliderMaven (talk) 21:44, 30 August 2014 (UTC)

Analyses of insensitivity by Kal and by Bhattacharya (cont'd)

GliderMaven: We have to take this one step at a time.

• Step 1:

Can we agree that Kal discusses gain stability in his section §6.3.1 he titles: gain stability? He says: "We consider a situation in which there is a change in the gain of basic amplifier due to some reason." He denotes the change by dA. He shows that the change dA_f in the closed loop gain A_f is then:

${\frac {dA_{f}}{A_{f}}}={\frac {1}{1+BA}}{\frac {dA}{A}}\$

and concludes:

"[This equation] indicates that the percentage change in A_f is smaller than the percentage change in A by an amount of feedback factor (1+BA)."

This is his conclusion supporting his beginning thesis that:

"Negative feedback in amplifiers makes them less sensitive to parameter variations of the active devices, reduces non-linear distortion..."

Now, in my opinion he has shown that the gain A_f is less sensitive to variations than is A and that is due to the feedback factor 1+AB and this factor shows up using the block diagram of the feedback system of the lede. Can you take the time to say where you disagree with any of this? I take your claim to be that you do not disagree with any of this standard treatment of textbooks. Is that the case, please? Brews ohare (talk) 22:17, 30 August 2014 (UTC)

• Step 2:

Now you think this analysis is based upon "only the equilibrium state with a DC input. In general there are propagation delays through all of the elements." In other words, you feel that this circuit is limited to a DC analysis. I suggest you revisit that assumption. First, let's look at Bhattacharya who uses the same diagram and reaches the same conclusions but with Laplace transforms of all transfer functions and signals. That is, time dependence can be recovered by inverse transforms. Then look at Step response where the time dependent behavior of this circuit is examined in great detail for step-function inputs, about as far from a DC excitation as one can imagine.

There is no implied restriction to any particular time dependence of the variations dA in A, or Bhattacharya's ΔG(s) in G(s) (p.135). I think the idea of such limitations is a misconception. Perhaps you would like to comment further? Brews ohare (talk) 22:17, 30 August 2014 (UTC)

• Step 3:

You say: " the output of the summer is not in general in agreement with that equation you quote", that is, you claim the output of the summer is not I–BO. Now, according to the diagram in the lede, it must be I-BO. Inasmuch as

$I-BO=I\left(1-B{\frac {O}{I}}\right)\ ,$

and

${\frac {O}{I}}={\frac {A}{1+BA}}\ ,$

it is impossible to avoid the formula;

$I-BO={\frac {I}{1+BA}}\ ,$

unless you dispute the gain formula, the second equation. As I understand you, that is exactly what you do - dispute this formula on the basis that it cannot apply except at DC or 'equilibrium' situations, by which you mean cases where the system is at its setpoint already so no feedback restoration of setpoint is needed. In other words, Kal and Bhattacharya are discussing gain stability under circumstances where the system is always kept at its setpoint, and there are no disturbances present; in short, the changes they discuss, their dA and ΔG(s) never upset the system to cause departure from setpoint, so no feedback comes into play. Their concept of feedback is limited to feedback only when no feedback is necessary. Is that your position? Can you source it? (Of course, I'd say the concept of setpoint has no place here at all, and these authors never consider dA and ΔG(s) as introducing upset of system balance, because such considerations are irrelevant.)

How would you modify the circuit to include the issues you feel it leaves out? Brews ohare (talk) 23:35, 30 August 2014 (UTC)

No that is not my position, and under the circumstances I'm not even going to answer that. I find your repeated and completely excessive spamming of the talk page like this incredibly offensive. Do you think that you own this talk page? How many topic titles do you think you deserve? Because trust me, you're not that important. Nobody is. How many times do you think you can or need to cut and paste here to somehow make an untrue point true??? How many times can you refuse to directly reply to a question that debunks your points before we completely ignore you? The answer is you are already well past that point on all fronts.GliderMaven (talk) 23:55, 30 August 2014 (UTC)

I have to agree with GliderMaven that the paragraph he removed here was completely inappropriate to the article. And I agree that it will be unlikely that this article can be converged as long as Brews completely dominates the talk page. That's why I have said I will not participate in editing this article. I might come back and try to help some day, when Brews is not part of the process. Dicklyon (talk) 00:23, 31 August 2014 (UTC)

OK folks. I'll leave it to you. Notice that none of you has addressed the substantive issues or discussed sources. You have no idea what Kal and Bhattacharya are talking about, and can see negative feedback only as some version of homeostasis, entirely myopic and contrary to sources.

Goodbye, and good luck. Brews ohare (talk) 00:29, 31 August 2014 (UTC)

Note that the article has been bloated up by about 20% in the last few weeks; this due only to the exhaustion of those who would hold Brews back. Yes, there's work to do. Dicklyon (talk) 00:31, 31 August 2014 (UTC)

It's impossible to see how we can take someone who writes this on the talk page seriously:

Operational amplifier circuits: In thinking over the various Op amp amplifier circuits, I now doubt that these are feedback circuits at all. First, they do not feedback anything - they set the input independent of any output and are feedforward circuits in this sense. Moreover, they are not designed to minimize 'disturbance' of the system in any way. So they do not satisfy the definition of the intro as an example of the "monitoring of a process used to influence the operation of the process itself, minimizing undesirable variations in its operation". The subsection on op amp applications should be deleted... I have modified the discussion of the op-amp section to reflect these remarks. Brews ohare (talk) 15:53, 26 June 2014 (UTC)

This betrays such incredible lack of knowledge of the subject matter that it really isn't remotely funny. The last sentence chills me to the bone; I now have to go check what he did.

You probably can't easily find this written explicitly but I'm pretty damn sure operational amplifiers were specifically invented as electronic building blocks to create feedback loops with.GliderMaven (talk) 02:59, 31 August 2014 (UTC)

Be careful of your interpretation. It's not a lack of knowledge that is causing these problems. Dicklyon (talk) 03:12, 31 August 2014 (UTC)

Actually that seems to be precisely the problem here. There's a useful distinction to be made between facts and knowledge. Any good article is not a collection of facts, it's a collection of knowledge.GliderMaven (talk) 04:04, 31 August 2014 (UTC)

The first source cited at Operational_amplifier#Historical_timeline confirms your interpretation of the original intent of opamps, even before they were called that. Dicklyon (talk) 03:31, 31 August 2014 (UTC)

Yeah. He may well be top-notch at some other parts of electronics, semiconductor physics or whatever, but somebody who doesn't know what an opamp is for has absolutely no right to be editing the electronics sections in an article on feedback.

Actually, this article should probably say that. Also, the rolloff that is present in many opamps should be at least mentioned; in fact stability is a general problem in all negative feedback loops, and this article needs to cover it.GliderMaven (talk) 04:04, 31 August 2014 (UTC)

He knows what it's for; he just has odd ways of looking at things, and is overly insistent about inflicting his idiosyncratic views on wikipedia. Dicklyon (talk) 05:11, 31 August 2014 (UTC)

Hey, Dick, more compliments like that and I might join others here in thinking WP is about me, not about sources, eh? Brews ohare (talk) 05:49, 31 August 2014 (UTC)

Idiosyncratic views are WP:OR and are not at all welcome in Wikipedia.GliderMaven (talk) 10:42, 31 August 2014 (UTC)

I was trying to suggest a return to examination of sources, instead of me, for example, #Analyses of insensitivity by Kal and by Bhattacharya . My idea of 'idiosyncrasy' is the assertion of unsourced personal opinion, and discussing how to present these authors' work doesn't fit that category. Brews ohare (talk) 17:08, 31 August 2014 (UTC)

So far, your comments regarding this work, that it is only for DC, doesn't apply to situations involving your concept of feedback, and so forth, appear to be mistaken or at least incoherent. (You say: "Simply doing maths on a stability condition actually says very little about feedback. Realistically, feedback loops spend no time at the stability point." The concept of 'stability point' doesn't arise in these authors' presentation, and introducing it requires connection.) You have yet to suggest a cogent alternative presentation stripped of unsourced, personal opinion that might (yes) be idiosyncratic. Brews ohare (talk) 17:20, 31 August 2014 (UTC)

These feedback circuits are always non linear; the particular analysis you keep cut and pasting onto the talk page is a DC analysis. The AC, linear analysis is a trivial extension of that, A and B become frequency dependent complex variables. But the real A transfer functions are usually completely non linear, and that mathematical approach fails except as an approximation.

So how can we be sure, how could Black be sure, that the overall effect is highly linear? Well, one thing you still might want to derive before we give up on the linear analysis is the sensitivity of the loop to variations in B. You'll find that it doesn't stabilise the loop to changes in B at all! Thus, linearity of this type of feedback loop will normally only happen iff B is linear.

And that's what's really happening; the error controlled feedback loop matches the rest of the response through A to B. It's not some magical effect of negative feedback linearising it; it's that the negative feedback permits the system to track a linear transfer function (built using passive components) using an error controlled feedback loop. The error controlled feedback makes the non linearities in A virtually irrelevant. A still needs to be monotonic, and to have as high a gain as possible, but that's about it. A can even be a bang-bang function, provided you capacitively smooth the output; and that fact is used all over the place.GliderMaven (talk) 18:42, 2 September 2014 (UTC)

So the linear analysis is really only a shadow of what's really going on here; B is the real heart of the circuit, and the fact that this is an error controlled feedback loop is completely the whole point. And you can easily make non linear amplifiers simply by changing B; put a diode in there and it suddenly isn't, irrespective of the gain of A. Negative feedback circuits are not inherently linear, they're mostly just tracking B.GliderMaven (talk) 18:42, 2 September 2014 (UTC)

GliderMaven: Your understanding of these matters expressed above is completely unsourced. It is an amalgam of your own conceptions. And it is overstated if not largely wrong. There is no mystery as why the negative feedback amplifier is linear - its operation is almost entirely independent of the behavior of the nonlinear gain A so long as this gain is large. For large A the closed loop gain is 1/B, and because B is a constant deciding the fraction of the output returned to the input, the gain 1/B is linear. That is what Kal and Bhattacharya have to say, and to say their work is only a 'shadow of what is really going on' is an assertion of yours without a source to back it up. Likewise, the claim that we have here an 'error controlled' feedback loop is also an unsupported and unsupportable assertion - there is no assessment of error in this circuit, and there is no error control of the feedback. Please supply links to statements in published sources rather than making wild assertions. Brews ohare (talk) 01:14, 3 September 2014 (UTC)

GliderMaven has given an extremely good and accurate account of negative feedback. Previous cases such as WP:Arbitration/Requests/Case/Speed of light show that it is possible to talk forever about what sources say, and to draw idiosyncratic interpretations from those sources. There is no logic that can limit the discussion because it is always possible to make a counter argument, even if it is only repeating an earlier point. The only defense available is WP:SHUN. Johnuniq (talk) 02:14, 3 September 2014 (UTC)

Johnuniq: I'm unsure your me too bereft of substance and based on no source is a major forward step here. It surely would be more useful and more credible if it went beyond me too. Brews ohare (talk) 03:12, 3 September 2014 (UTC)

The basis behind editor conflict

I believe the differences between editors exhibited on this talk page are consequences of supporting one of two different ways to use negative feedback to the exclusion of the other.

One use is error-controlled regulation, as discussed by (for example) Ashby, The error-controlled regulator pp. 219–243. This approach has much in common with homeostasis and deals with a system driven by disturbances away from its normal state. Feedback is used to reduce a measured departure of an 'essential' variable defining the system state from its setpoint value. If this departure is driven to zero by the feedback (an idealistic goal) the system is brought back to its normal state.

A second approach is that of Kal and Bhattacharya, who are not concerned with a system pushed by disturbances away from its standard state. Instead, they focus upon designing the system from the outset so that even when such fluctuations occur, they have little effect upon the system because its normal state is left basically undisturbed. The system is so-designed that it is inherently insensitive to these fluctuations: disturbances cannot drive the system significantly away from its normal state. The basic result of their design is that a variation in the open-loop amplifier gain ΔG(s) results only in a much reduced variation in the closed-system gain, a reduction by the feedback factor 1+BA to only ΔG(s)/(1+BA).

In the first case, the system is rendered stable by counteracting individual disturbances as they occur, and in the second by rendering the system generally immune to disturbances. Feedback is used in both approaches, but in different ways.

The question to resolve on this talk page is whether this distinction of approach is recognized by WP editors, and if not, how do they interpret the work of Kal and Bhattacharya? Brews ohare (talk) 03:56, 2 September 2014 (UTC)

While I agree that negative feedback is important both in systems with identifiable setpoints and errors and in systems without, I do not agree that the kind of parameter insensitivity that those guys talk about is the first-order way to look at negative feedback; it's a secondary effect, and applies to both types system with and without setpoints and errors. You have jumped to an odd interpretation of those sources that makes it impossible for you to converge with others. And I though you said you were going to go away and let it get worked out... Dicklyon (talk) 05:25, 2 September 2014 (UTC)

Well, I hoped that my departure would lead to discussion beyond complaints about me. I think perhaps we could come to some agreement if I understood your comments. You speak of two types of system: (i) those with setpoints and (ii) those without. I'd guess that the thermostatic control of house temperature is a case with setpoints, and you probably would agree with the discussion of error-controlled regulation. If I am mistaken, please tell me what an example of a system (i) is. As for systems of type (ii), I suppose the negative feedback amplifier is an example. Again, if I am wrong let me know what you do consider to be an example.

It could be argued that the feedback loop in the negative feedback amplifier does set the feedback factor B, and constitutes a setpoint. Maybe a clearer separation of types (i) and (ii) than use of a setpoint is the way a setpoint is used: in type (i) to compare with a measured parameter and quantify a departure from targeted operation, and in type (ii) not used to monitor departures but as unmonitored instruction (e.g., "transfer a fraction B of the output"). Just a thought.

Assuming I'm on track so far, I now get confused. Do you say that Kal and Bhattacharya are discussing secondary effects (what I've called designing for 'generalized immunity' to fluctuations in gain), and so their work on this amplifier is of secondary importance here? That seems to me to be your view. You add that there is a more important first-order effect, not addressed by these authors, and operative in the negative feedback amplifier. What effect is that? Does this first- order effect show up anywhere in electronics textbook discussions of this amplifier? Can you help me out here? Brews ohare (talk) 13:32, 2 September 2014 (UTC)

In both of those sources, if you back up a few pages and look at what feedback is, rather than stick to their later interpretation of its advantages, you'll be in a better place. In the case of negative feedback around an amplifier, the primary effect is to reduce the gain; that is, to reduce the output fluctuations caused by input fluctuations. Better gain stability and reduced distortion are important, but secondary. Teh fluctuation reduction that some define negative feedback in terms of is not about gain fluctuations and distortion fluctuatoins, but about gain reduction, in amplifier terms. Not about parameters, but about signals, primarily; effect on parametric sensitivity is secondary to that, and can as well be said to be due to the high forward gain as to the feedback. Dicklyon (talk) 14:34, 2 September 2014 (UTC)

This, a hundred times this. Negative feedback exists for an input signal when the feedback opposes that signal.GliderMaven (talk) 15:05, 2 September 2014 (UTC)

Dick: Going back to the beginning of Kal's chapter 6 as you suggest, I don't find the identification of the primary effect of feedback as "to reduce the output fluctuations caused by input fluctuations". Looking at the circuit diagram, the only input is the signal to be amplified, and according to the diagram, the amplifier cannot separate spurious signal variations from meaningful ones. Both will be amplified the same way. Of course, a reduced gain will reduce both components equally, so no improvement in signal-to-noise results from gain reduction. See this. Can you point out the relevant text that would convey a different view? Brews ohare (talk) 15:17, 2 September 2014 (UTC)

Kal's subsection on noise reduction using feedback is confined to internally generated noise, and doesn't claim filtering of noise from the applied signal takes place. Brews ohare (talk) 15:23, 2 September 2014 (UTC)

A perhaps more explicit treatment is given by Bhattacharya, who treats disturbances arising within the system loop and not originating in the input signal itself. Changes in open-loop gain due to temperature or component variations are of this type, so the sensitivity analysis of these authors is a special case of their noise analysis. Brews ohare (talk) 15:51, 2 September 2014 (UTC)

If you can link excerpts from these authors that casts a different light on feedback, please do so. Brews ohare (talk) 16:11, 2 September 2014 (UTC)

I think you know that I am not interested in having this discussion. Dicklyon (talk) 03:29, 3 September 2014 (UTC)

I'm sorry to hear that. I believe a closer look at these two sources by the two of us could straighten things out. I have provided quotes and links to these works that support my understanding of their views. It would seem that if you did the same, matters would clarify, to the benefit of WP. Perhaps one of us is off the beam a bit, or maybe it's just a case of blind men and an elephant. However it might work out, a resolution would be helpful. Brews ohare (talk) 04:10, 3 September 2014 (UTC)

My experience leads me to believe it would be pointless to try, since you never let go of your unique interpretations of sources. Dicklyon (talk) 04:45, 3 September 2014 (UTC)

Dick: You have presented absolutely no interpretation by any published source. Only statements of your own beliefs. In contrast, I have simply parroted what sources say. So it is not the pointlessness of dealing with me that is the problem here. Try presenting what sources say. Brews ohare (talk) 05:16, 3 September 2014 (UTC)

Brews, Dicklyon is being polite with the phrase 'idiosyncratic views'. First, it's clear to me you've never actually had any significant amount of formal training in feedback systems. I realise this is the case because I have at least been formally trained in both analogue filtering and digital signal processing theory, both are areas where feedback is extensively used. Because you've had no formal training in that area, there's simply things you've never been taught, lacuna. Because you've never been taught, you don't know what you don't know.

So unfortunately, overall, your behavior on this talk page is largely indistinguishable from that of a crank (person).

From that article:

"According to these authors, virtually universal characteristics of cranks include:

• Cranks overestimate their own knowledge and ability, and underestimate that of acknowledged experts.
• Cranks insist that their alleged discoveries are urgently important.
• Cranks rarely, if ever, acknowledge any error, no matter how trivial.
• Cranks love to talk about their own beliefs, often in inappropriate social situations, but they tend to be bad listeners, being uninterested in anyone else's experience or opinions."

You're hitting most of them in spades, and even the urgency one is supportable, because of the rate you're posting to the talk page, to the point of effectively spamming it and driving away other editors.GliderMaven (talk) 11:09, 3 September 2014 (UTC)

GliderMaven: It is a symptom of having a weak position to try to divert attention. Your remarks again avoid any discussion of negative feedback, and provide no attempt to come to grips with Kal and Bhattacharya. To claim I exhibit idiosyncrasy and am a crank, when I have simply quoted the sources to summarize their views, and when you yourself have yet to identify a single source supporting your own opinions, is just belligerence. Why is it that your only discussion of these published sources, which simply reiterate the presentation of every electronics textbook of the last 4 decades, is to say (i) you agree with them completely and (ii) their work represents "a mere shadow" of what (in your unsupported opinion) is 'really' going on? So far your attempts to flesh out this 'reality' of your creation is unsourced, and makes one wonder why these published authors have failed to see the light. Dicklyon is following in your footsteps with similar assertions about this amplifier's use of feedback to clean up spurious content in input signals, a claim you support emphatically with the comment "a hundred times this". When confronted with a specific contrary statement by Kal, that the amplifier cannot do this, Dick retreats by saying it is pointless to address this extremely unequivocal statement found in every electronics textbook. And you simply repeat and cheer for these same contradictions.

Tut tut. Brews ohare (talk) 13:26, 3 September 2014 (UTC)

Rather than engage in verbal ping pong, it seems to me that one thing you might have in mind is that the feedback network can be much more complex than simply returning a fraction B of the output. That certainly can be done, and would broaden the discussion beyond the traditional design of the negative feedback amplifier. However, to introduce this additional complexity it is not necessary to discredit the traditional approach, nor to spread calumny. Most probably, such extensions also can be sourced. Brews ohare (talk) 13:45, 3 September 2014 (UTC)

Another possible cause of difficulty here is a tendency I've noticed with you and Dick to unconsciously switch discussion from the negative feedback amplifier, a rather limited circuit, to the more diverse family of op-amp circuits, which use negative feedback in a much wider variety of ways. Brews ohare (talk) 14:23, 3 September 2014 (UTC)

Brews, it is not possible to address your continued cycle of intransigence by playing your game. We tried that for a few years; you got banned, more than once, for disruption. The root problem is that you are unable to work with others, to take input, to compromise, etc., not that all other editors ignore sources. Dicklyon (talk) 14:47, 3 September 2014 (UTC)

Oh, baloney. I know you are a whiz at Googling up sources when you are inclined, so your failure to do that here is just a reflection of awareness that you have wandered out into the wilderness. Your intuitions are not necessarily wrong; they just have to be put in the right context (maybe op-amp circuits?), and when you directly contradict Kal the thing to do is discover what it is that you actually want to say that agrees with sources. Making proposed content into a personality issue is a cop out, Dick. We are capable of conversation. Brews ohare (talk) 14:57, 3 September 2014 (UTC)

On the contrary, you're not. The basis of the editor conflict is your not listening and engaging with other's points of view. Repeatedly quoting the same sources over and over again and stating your opinion as to what they say is not engaging with others.

As I have noted, your behavior is entirely consistent with you being a crank. Whether you are right or not at the very least you are behaving like a crank. Perhaps only you know the truth/correct way to interpret the sources, but a crank would think that, and since you don't actually meaningfully engage with anyone else, we'll never know for sure. This talk page is too full of your stuff, and in the history list in the article- your changes are having to be reverted way too often.GliderMaven (talk) 15:51, 3 September 2014 (UTC)

GliderMaven: So now your objective is to prove I satisfy the WP definition of a 'crank'? Fun! maybe! but... Brews ohare (talk) 18:29, 3 September 2014 (UTC)

No, dealing with other editors bad behavior is really not fun.GliderMaven (talk) 21:21, 3 September 2014 (UTC)

GliderMaven: You made some sensible edits on Feedback back in mid-August, so that is within the possible. However, your intemperate screaming at me here is unwarranted. I have no idea why you think my summaries of Kal and Bhattacharya are crank contributions, nor why my replies to yourself based upon links to text from these authors doesn't deserve a considered reply. Your ideas about these authors describing only a pale "shadow" of reality, being restricted to DC, or being disqualified because their analyses are linear, or that the time dependent step response of this circuit is a trivial extension of DC, or your enthusiastic support for Dicklyon's absurd claims of filtering out input signal noise as an accomplishment of this circuit - all this stuff is simple assertion on your part, and contradicts the existing sources. You just don't want to address the sources, but wish to rule them out as minor, trivial, and not getting the crux of the matter. But you have not made any reference to sources to support this attack, and yet want to say my efforts, entirely based upon sources, is 'idiosyncrasy'. Can't we just calm down and try to provide a sourced presentation stripped of personal preconceptions? Perhaps Kal and Bhattacharya's approach is limited in scope, but it isn't wrong. More general treatments can be made, but they need to be sourced. Brews ohare (talk) 22:04, 3 September 2014 (UTC)

The lead definition is the one part of the article that can't necessarily be sourced, it has to say what we the editors consider as negative feedback for the purposes of constructing the article. Other people who are writing a book will be defining it for their book or paper, which are usually a much, much more narrow purpose.

We need a property that is undeniably true of negative feedback, that is not present when negative feedback is not present. It should apply to economics as well as it applies to spacecraft as it applies to negative feedback amplifiers as it applies to geophysics.

In short, if you can find a source that truly blows everyone's socks off and does that, great we'll use it. But I don't think you will. I'm certainly not saying Kal & co are wrong only that they're too narrow.GliderMaven (talk) 02:09, 4 September 2014 (UTC)

Kal says "On the other hand if the feedback signal reduces the input signal, i.e. it is out of phase with the input, it is called negative feedback." Many others say similarly. Bhattacharya uses the control definition, where the result of the subtraction is an error signal. Both are a bit narrow, but the union of them covers a lot of ground. Dicklyon (talk) 02:18, 4 September 2014 (UTC)

Several definitions of error are used in feedback theory.

The 'error' in the Figure 3.1: Error detector of Bhattacharya is the difference between a 'reference signal' R(s) and the feedback B(s) in a feedback control system, and is said by him to be the "deviation of the output from the desired output". That error is a definition of the error used in error-controlled regulation and in homeostasis.

However, in Figure 3.3: Canonical form of block diagram for a negative feedback system Bhattacharya modifies this departure definition to say instead "Here a fraction of output B(s)=C(s)H(s) is brought to the summing point for producing an error." [Emphasis added] Obviously, this version of 'error' is not the difference between a reference signal representing the desired output and the realized output. Instead it is the error defined by Rashid, namely, "The difference between the input and the feedback signals, called the error signal."

Obviously the difference between the input and the actual output, the first type of error I–O, is not the same as the second type of error I–BO, unless B ≡ 1. As already indicated in earlier threads, for the negative feedback amplifier this second type of error is I–BO=I/(1+BA), while the desired output is O=AI/(1+BA).

The point is that the term error refers to a departure from the desired mode of operation in the first case, but not in the second. The 'error' of the first case is used in error-controlled regulation and is minimized using feedback to restore normal operation as described by Ashby, Chapter 12: The error-controlled regulator pp. 219 ff. The 'error' of the second case is not a departure from the desired state, and is not minimized by the feedback. The two types of error and their uses are different. Brews ohare (talk) 03:29, 4 September 2014 (UTC)

How's this?

Negative feedback is an opposing response of a system or entity that is triggered by a perturbation or disturbance of that system or entity.¹

¹Camazine, p. 16

It is sourced. Brews ohare (talk) 19:27, 16 September 2014 (UTC)

The dilemma seems to be getting clearer. We want to describe negative feedback in an intuitive and tangible way, one in common use - which means the output-to-input view. We also want to cover as many examples as possible - which means the circular-causality view. Attempts to reach a compromise between the views seem mutually unsatisfying.

Maybe a historical approach would work. That is hopefully less controversial.

Negative feedback originally described the practice of using the output signal of an amplifier to partially cancel (or negate) the input signal. In general, negative feedback loops are any balancing or self-correcting circle of cause-and-effect.

Trevithj (talk) 06:00, 17 September 2014 (UTC)

Trevithj: The history of negative feedback is not as described. The use of negative feedback in steering of ships (the PID controller), an example of error-controlled regulation, predates the negative feedback amplifier, as you well know. As a reminder, see Sperry's (1911) ship-steering mechanism "that incorporated PID control and automatic gain adjustment to compensate for the disturbances when the sea conditions changed" and the 1922 presentation by Minorsky of a "clear analysis of the control involved in position control and formulation [of] a control law that we now refer to as three-term or PID control." (from Stuart Bennett)

The 'dilemma' is not resolved by an historical approach, which involves the same issues of separation between error-control and other forms of negative feedback found on this Talk page. The failure is rather the failure to use sourced discussion, and also one of generality of definition. On one hand, the definition of Camazine, p. 16 views negative feedback as a form of response by an entity. That also is the view of the those sources that use the 'opposition to change' formulation. This general approach based upon an opposing response does not go into specifics about the implementation of the response, nor the triggering of the response, nor even the objective of the response, which detail enjoyed by those engaged here automatically leads to controversy because such details tend to overly restrict the concept and rule out some examples in favor of other examples of negative feedback. Brews ohare (talk) 14:37, 17 September 2014 (UTC)

In this regard, as you well know, your first definition of negative feedback above is too restrictive, limiting itself to amplifiers. The second form is far too loose, as the mechanism described includes many forms of response, even feed forward, that have nothing to do with negative feedback. Brews ohare (talk) 14:49, 17 September 2014 (UTC)

And, again, reliance upon sources about negative feedback would help focus discussion upon what sources say. Discussion about what published sources say is likely to be less controversial than discussion of what WP editors think. Brews ohare (talk) 15:13, 17 September 2014 (UTC)

Lead sentence/definition (only) thread

Definition of negative feedback

The following thread is intended for use only for discussion of the lead sentence (any off-topic discussion will be moved somewhere else on this page without mercy or warning.)

I note that Encyclopedia Britannica defines negative feedback in 'coupling amplifiers' to be:

"In negative feedback, the feedback signal is of a sense opposite to the signal present at the point in the circuit where the feedback signal is applied."

It's clumsy, but so far as I can tell that's nearly a general definition that applies to DC behavior, as well as AC behavior, although it's restricted by the language to circuits.

There's a somewhat similar definition used at hyperphysics:

"...part of the output signal is taken back to the input with a negative sign."

I think the concept of a 'signal' is very general, and could be applied to other systems than circuits, but the 'taken back' bit is too vague.

For example, something like this seems to get the gist of it:

"In negative feedback, an output signal from a system feeds back so as to reduce an input signal of that system."

(I noticed that sometimes negative feedback involves subtraction, but other times it's attenuation; but in both cases the term 'reduce' covers it and it solves the 'taken back' vagueness.)

It 'feels' right, and it would also appear to cover geophysical things like cloud formation, where the cloud forms due to heat of the sun, rises up and condenses and blocks out the sun.

Is that considered better than what we have at the moment? Can anyone improve it or have a clearly better definition?GliderMaven (talk) 01:51, 4 September 2014 (UTC)

It's never attenuation; always subtraction (unless the signals are levels, as in an automatic gain control, but that's best recast in terms of subtraction of levels, I think). I got a lot of pushback when proposing a definition based on input and output. It's one common type of definition, when talking about amplifiers, but is not quite general enough as a complete definition. Dicklyon (talk) 02:08, 4 September 2014 (UTC)

I think attenuation does count, but either way AGC doesn't seem to be a counterexample. If there's a counterexample, then we need it, so we can try to generalise to cover it.GliderMaven (talk) 02:19, 4 September 2014 (UTC)

Earlier proposal

An earlier proposal, well sourced:

Negative feedback is feedback that opposes change.

Sources

Brews ohare (talk) 02:30, 4 September 2014 (UTC)

I was OK with that one proposed by Trevithj. Unfortunately it seems to have been put in with kilobytes of extra baggage, so it got caught up in a big revert. Dicklyon (talk) 02:39, 4 September 2014 (UTC)

I quite liked that one too. :) Glidermaven's suggestion of a 'signal' seems similar to the idea of "information about the gap" from Ramaprasad.¹ Frustrating that there doesn't seem to be a free online source for his paper - it is very good. [

¹ Arkalgud Ramaprasad, On The Definition of Feedback, Behavioral Science, Volume 28, Issue 1. 1983. Accessed on 16-03-2012.

[User:Trevithj|Trevithj]] (talk) 02:58, 4 September 2014 (UTC)

Anyway, a refinement of Glidermaven's proposition based on Ramaprasad's definition could be:

In negative feedback, information about a gap (between a system parameter and a reference value) is used to reduce the gap.

Is that broadly applicable? To touch on Dicklyon's point, I feel we should get away from control-of-output-by-adjusting-input cases. There are alternatives, especially in non-electronic systems. The control of water level in a hydroelectric plant's reservoir is a possible example: an internal state is being regulated by altering one of the outputs. Trevithj (talk) 20:57, 4 September 2014 (UTC)

Negative feedback is a form of feedback, so the primary purpose of the definition is to demarcate negative feedback from feedback in general. Feedback does not necessarily take the form of a signal, unless that term is broadly understood to include such things as a glance, a warning beep, or even a detailed recommendation. Also, negative feedback is not always of a form that can be 'subtracted' from something else in a quantitative fashion. The link to feedback and the notion of 'opposition to change' avoids the need to go into such details. Brews ohare (talk) 13:00, 4 September 2014 (UTC)

That 'definition' "Negative feedback is feedback that opposes change" is both awful and wrong. It's awful because 'change' is ridiculously vague, and it's wrong because negative feedback doesn't characteristically oppose change. On the contrary, it actively creates change to try to bring things back to an equilibrium state.

For example, if the room temperature is 10C and the thermostat is set at 20C, negative feedback DOES NOT keep the room at 10C- it warms it up to 20C. In what sense is negative feedback opposing change there??? The answer is, it isn't.

Either a thermostat is not using negative feedback or that definition is deeply, deeply flawed. If you try to claim that thermostats don't use negative feedback in that situation, I will laugh at you.

Nobody who has understood that 'definition' and really understands negative feedback can think that that is correct or any good. It's worse than simply being wrong, because it's super vague as well as wrong. Let us never mention it again.GliderMaven (talk) 01:41, 5 September 2014 (UTC)

Huh? The negative feedback loop there would be in the reservoir control system where the input is the level measurement and the output is the valve setting. The internal state that is controlled would often be the difference between a function of the spill valve setting and the level input. And it's not necessarily an electronic control system, it could be mechanical or hydraulic; a 'signal' is a very general concept that includes shafts turning, water overflowing into a bucket, virtually anything, provided it indicates something to the mechanism, causes it to do something.GliderMaven (talk) 02:00, 5 September 2014 (UTC)

GliderMaven: There is a problem with your attitude here: while most are searching for a solution, you are busy portraying everyone but yourself as lacking all understanding. That is not conducive to progress.

Another problem is your lofty stance that the proposed definition is 'wrong' , despite its adoption by many, many published authors, of which four are cited and quoted verbatim. Even supposing you were correct about this, WP could report this popular view, and if there were those, like you, who felt there were better alternatives, then those views would be reported too, and sourced. If a balanced view of all published definitions suggested some were preferable to others, possibly the published arguments pro and con could be summarized.

The objective here is to present an accurate portrayal of published opinion, not the most persuasive and compelling opinion devised by the minds of Talk-page editors.

To turn to the substance of your objections, it is sufficient to request that you support them with sources. As matters rest, your description, that feedback does not oppose change, but creates it, is both unsourced and inadequately verbalized. For example, in an error-correcting regulator, the cause of a departure of a system from it's status quo is a disturbance (by definition) and the departure instigates the feedback that corrects for the disturbance, not creating change, but nullifying it. Brews ohare (talk) 03:28, 5 September 2014 (UTC)

Look I'm not the one making the positive claim that this is correct; you are. I'm simply stating I don't understand it, that it at least seems to be quite incorrect, that I cannot explain how this can really be valid. And the first source you are relying on is "Leadership and Change Management". I don't consider that to be in any way, shape or form, a quality source for negative feedback. It's a flimsy 'management theory' pile of shit. This is primarily a hard-technical article, not sociology.

I repeat my question, precisely change from what, when? From an equilibrium? If so you must say that. For if it's not that, if I have an object that is constantly being perturbed, is negative feedback really correcting each of these changes? It isn't. If something moves the temperature down 5 degrees, and something else moves it up 2 degrees, is the feedback really opposing the second change? No, the feedback is still in the same direction and it is NOT opposing it. In fact because feedback can be non linear, the feedback signal may be completely unchanged by the second change; a thermostat is either on or off, and it's on throughout the second change. It's not reacting to the change, it's reacting to the displacement from equilibrium. The definition is wrong.

You said: For example, in an error-correcting regulator, the cause of a departure of a system from it's status quo is a disturbance (by definition) and the departure instigates the feedback that corrects for the disturbance, not creating change, but nullifying it.

But crucially, the definition you favour does not say that it 'corrects disturbances', it says opposes changes. That's not the same thing at all. 'Disturbance' can imply things have an optimum position and it's been moved away (disturbed) from that, whereas a change by definition, unless otherwise specified, is simply any difference, and has no such implication. Different words connote different meanings, otherwise they wouldn't be different words. The definition as it is stated is clearly wrong.GliderMaven (talk) 04:58, 5 September 2014 (UTC)

It is my bad to use the term 'corrects disturbance', which is a presumption that Ashby shows is theoretically impossible. Feedback only opposes the disturbance.

Let's debate sources, not opinions. We know that four sources quoted above use the 'opposes change' description of negative feedback. The other proposals are unsourced. Brews ohare (talk) 05:15, 5 September 2014 (UTC)

Yes, opposing the disturbance is better. Whether or not the other proposals are unsourced, but that particular use of those sources is untrustworthy. We cannot in good faith put material into Wikipedia as true, if we know it to be false.GliderMaven (talk) 10:41, 5 September 2014 (UTC)

Re the reservoir example: yes, I understand what the feedback loop is. My point is that the input to the control system is not the output of the hydroelectric system (outflow water and electricity) but an internal parameter. And the output of the control system does not influence the input to the hydroelectric system. The exact wording was "reduce an input signal of that system." If anything, it would increase an input signal (open the spill valve more). Trevithj (talk) 07:57, 5 September 2014 (UTC)

Yes, I don't think that the dam itself is a feedback loop. The level control system clearly is or can contain a feedback loop; but I don't think the dam is actually inside the loop. There's no control of an input to the dam. The dam and hydroelectric system overall contains a feedback loop to control the spill valve, but it's a fallacy of composition to think that the dam is part of the feedback loop. It's the other way around, the feedback loop is part of the dam. Likewise, just because my car contains feedback loops, doesn't mean my car is a feedback loop. You have to draw the (sub)system boundaries correctly to be able to identify the loop. My car, and the dam is certainly affected by the behavior of feedback loops, speed and level respectively.GliderMaven (talk) 10:41, 5 September 2014 (UTC)

GliderMaven: Regarding the sourced definition¹ that negative feedback is that form of feedback that "opposes change", you say:

"We cannot in good faith put material into Wikipedia as true, if we know it to be false"

Playing with words, to say that 'opposing a disturbance' is not 'opposing a change' it is 'creating a change' is just silly word play. Now, where is the source that says this definition is "false"? Opinion of WP editors is not a basis.

¹Sources supporting the definition are:

• Annabel Beerel (2009). Leadership and Change Management. SAGE Publications Ltd. p. 52. ISBN 9781446205655. A negative or self-correcting feedback loop describes system behavior that opposes change
• Helen E. Allison, Richard J. Hobbs (2006). Science and Policy in Natural Resource Management: Understanding System Complexity. Cambridge University Press. p. 205. ISBN 9781139458603. Balancing or negative feedback counteracts and opposes change
• Santiram Kal (2009). Basic Electronics: Devices, Circuits and IT Fundamentals. PHI Learning Pvt. Ltd. p. 191. ISBN 9788120319523. If the feedback signal reduces the input signal, i.e. it is out of phase with the input [signal], it is called negative feedback.
• Jack Andrew Morton (1971). Organizing for innovation: a systems approach to technical management. McGraw-Hill. p. 13. Negative feedback occurs when a change in input or action of the system is opposed by the output fed back

Brews ohare (talk) 14:31, 5 September 2014 (UTC)

I don't have to come up with specific references to refute individual references, particularly if they're low quality ones that nobody in their right mind would critique. It's not playing with words to point out that your references are poor quality, nor to point out that the definition that you've pulled from those references is inconsistent with the other definitions.

This ultimately goes to your poor judgement. Why would we as a group allow you to edit the article when you continue to show such poor judgement? Referencing a work by management consultants in this context????GliderMaven (talk) 16:01, 5 September 2014 (UTC)

GliderMaven: Your opinion of these references is based upon your own parochial view of the subject that precludes some very common subject areas like education and management. They also include an electronics text, and all refer their definitions to control system usage. You have provided, actually, no references of your own. Brews ohare (talk) 17:11, 5 September 2014 (UTC)

I actually did previously check the electronics source, although it had somewhat similar wording, you have not accurately summarised it. In any case it wouldn't matter if they all used the same wording, that doesn't mean it agrees with the references in the generality.GliderMaven (talk) 17:34, 5 September 2014 (UTC)

So the candidates that aren't obviously wrong right now seem to be:

• In negative feedback, an output signal from a system feeds back so as to reduce an input signal of that system.

• Negative feedback is feedback that opposes disturbances.

• In negative feedback, information about a gap (between a system parameter and a reference value) is used to reduce the gap.

The problem I have with the second one is that it's not entirely mechanistic; it's phenomenological. If there's a feedback loop that isn't a negative feedback loop opposes disturbances then the definition is faulty. Since in the generality feedback includes chaotic systems, it's not clear that it's correct.GliderMaven (talk) 17:34, 5 September 2014 (UTC)

GliderMaven (talk) 17:34, 5 September 2014 (UTC)

Your objection to the second definition, which you have significantly distorted by replacing "change" with "disturbances" thereby eliminating the negative feedback amplifier as an example of negative feedback, is that perhaps an exception can be found - a feedback system that opposes change but isn't negative feedback. Of course, we can come up with other approaches to combat change, like feed-forward systems. However, we are limiting ourselves to distinguishing between feedback systems. The huge number of authors that seem to think the distinction is the contrast between opposition to change versus reinforcement of change, seems to indicate that if there are some odd examples where positive feedback reduces change, they are sufficiently uncommon that the 'opposing-change' definition is not misleading except possibly in some unidentified peculiar circumstances, which could be earmarked if they ever show up. So I think this objection based upon a hypothetical exception is not important.

More references can be added, as Dicklyon has shown. Here are three:

• "Balancing or negative feedback counteracts and opposes change" 1
• "Most environmental systems are dominated by negative feedback, which opposes change." 2
• "Negative feedback is a circular chain of effects that opposes change" 3

Brews ohare (talk) 17:48, 5 September 2014 (UTC)

The second isn't technically incorrect, negative feedback certainly can oppose changes in the context of environmental systems, but I don't read that as a definition of NF. The 3rd of those, is taken it out of context. The next but one sentence defines what they mean by 'change' as "When part of a system changes too much from what it should be..." without that context it's too vague, and as I have already shown, wrong; because it implies something that is not true, that negative feedback opposes all changes, which it certainly doesn't, that's damping, not negative feedback. If you include all the sentences from the third definition, it broadly seems to be correct, although I still have some minor qualms.GliderMaven (talk) 20:41, 5 September 2014 (UTC)

If there is a valid criticism of this definition it is that most of the sources using it are thinking about homeostatic uses of feedback, restoration of status quo, while the negative feedback amplifier is not at all about counteracting disturbances, but about letting disturbances take their course and making the system indifferent to their presence. The definition still applies, but only rather technically speaking, as an opposition to the input signal variation, albeit with a different design motivation than restoration of equilibrium by nulling the input signal. Brews ohare (talk) 18:05, 5 September 2014 (UTC)

I certainly wouldn't say that negative feedback amplifiers aren't about counteracting disturbances, indeed they are specifically used to do that very thing, for example they're used to largely remove cross-over distortion in audio amplifiers, which very much is a type of disturbance.GliderMaven (talk) 20:41, 5 September 2014 (UTC)

GliderMaven: The 'opposes-change' formulation could be reworded to make clear that it's intention is to distinguish between the two types of feedback, positive and negative. It is not suggesting that it opposes all or any change, but that if you are having trouble deciding if the feedback is positive or negative, just ask: "is the feedback reinforcing or opposing the change?"

As for removal of cross-over distortion using the negative feedback amplifier, if a signal exhibiting cross-over distortion is fed as the input signal to the circuit of the lede, that distortion will remain in the output, which ideally is simply an amplified replica of the input.

And as always, I await any presentation of a sourced opinion. Brews ohare (talk) 02:28, 6 September 2014 (UTC)

part 2

Re the reservoir example. It seems the reference for input/output is the control system, rather than the system being controlled. Hmm. Applying the proposed definition to the reservoir control system gives us something like:

• If "an output signal from a system feeds back so as to reduce an input signal of that system"
• and if "the input is the level measurement and the output is the valve setting",
• then the valve setting signal feeds back so as to reduce the level measurement.

That seems another way of saying "opening the spill valve lowers the water level". And it doesn't say anything about stopping the spill once the level is low enough. If we say "so as to reduce the gap between the level measurement and the desired level" then it seems OK. Trevithj (talk) 21:44, 5 September 2014 (UTC)

iIt seems that you object to the 'opposes change' method of identifying negative feedback because you aren't satisfied with mere identification, but want to go further into description. If the only form of negative feedback were error-controlled regulation, the 'gap' approach would work. But now you have the problem of showing that in fact every example of negative feedback is an instance of error-controlled regulation. You may think, despite what I think is conclusive evidence that there is no reduction of any so-called 'gap' in the negative feedback amplifier, that despite the 'error' being I / (1+BA) and no attempt made to push it to zero, this is still a case of error-controlled regulation. However convoluted the argument for such classification in this example, it pales when we look at examples from education, management and psychology. Brews ohare (talk) 04:41, 6 September 2014 (UTC)

The point has been raised that "change" is ambiguous. I'm hoping that identifying a reference point removes that ambiguity. A reference point seems fundamental to the act of measuring anything.

I agree that error-controlled regulation can be described in terms of a gap. It doesn't follow that other forms of regulation cannot be so described. What is a change but a gap between a past measurement and a present one? No gap, no change. Trevithj (talk) 05:53, 6 September 2014 (UTC)

'Change' is not ambiguous, and does not imply a gap. It means that the present is different from the past. Opposition to change means trying to keep the present like the past. So I wear a raincoat that'll work for any forecast; I stay dry. I design for a gain of 1/B now and forever, using a design that doesn't depend on any knowledge of whatever strange A someone sticks in the circuit. I don't need to measure some gap from 1/B and marshal a response to close the gap tailored specifically to what A is doing to the system right now- I don't care what A is doing. I don't need to measure the gain: I trust my theoretical analysis that my design will produce 1/B, and build in no checks. My strategy is fixed and defends against all comers, regardless of their behavior. I stay dry. Brews ohare (talk) 15:08, 6 September 2014 (UTC)

I stand corrected. "Change" is not ambiguous, it is vague. It needs to be clarified by giving it a reference point. For example, your "opposition to change" describes comparing the present value of a parameter of interest to a value it held in the past (the reference point.) If we ignore the past value, how do we know the value has changed? Trevithj (talk) 05:15, 7 September 2014 (UTC)

Two definitions of negative feedback?

A different approach to definition would be to introduce two definitions.

One of these definitions refers to feedback in error-correction, which can take two major forms:

• Homeostasis: Systems where there is no output, where feedback serves only to setting the essential variables of the system to their set point. Examples might be blood pressure, or body temperature where the only 'output' is a reaction that reduces the departure of the system from its proper condition.
• Process control: Systems engaged in manufacturing or producing something, where the factory is kept 'in spec' using feedback, either by setting the essential variables of the system to their set point, or possibly, by adjusting the production system so the monitored quality of the output is held within specs for the product.1 This last approach is much more sophisticated, because the process might vary remarkably to keep the product in spec, for example, in response to changes in the input materials.

A second definition involves feedback in systems that do not monitor system departures from desired operation, and do not attempt to minimize departures by controlling the disturbance. Instead feedback is used to render the system indifferent to disturbances, which have no effect on operation regardless of their presence or exact nature. The poster child for this approach is the negative feedback amplifier. Here is a verbal description of its operation that was once presented on WP:3

"An amplifier with too large an open-loop gain, [say] in a specific frequency range, will additionally produce too large a feedback signal in that same range. This feedback signal, when subtracted from the original input, will act to reduce the original input, also by "too large" an amount. This "too small" input will be amplified again by the "too-large" open-loop gain, creating a signal that is "just right". The net result is a flattening of the amplifier's gain [as a function of frequency] (desensitizing)"

I under-appreciated this description when I first encountered it. On revisiting it, I believe it provides without math a verbal understanding of how the gain 1/B is achieved regardless of open-loop gain differences at different frequencies. The same explanation could be generalized to explain desensitization to variations in open-loop gain of any kind. Of course, there are restrictions upon how well this adjustment works that must be left to mathematical analysis. (For example, step response.) Reference to desensitization as the goal of the feedback in the negative feedback amplifier are readily located. Brews ohare (talk) 21:55, 5 September 2014 (UTC)

The description needs to be appreciated less. It's absurd. Dicklyon (talk) 02:15, 6 September 2014 (UTC)

Well, Dick it's a WP discussion that made it past WP review into print! My initial reaction was like yours, but I think it's accurate. If you follow a signal around the loop, the large open-loop gain amplifies a signal reduced by BO, a larger reduction for larger A, which reduces the input into the open-loop amplifier to a level that is in fact "just right" for amplification by A to obtain O. I think that's what the description says. Care to try wording it better? Brews ohare (talk) 02:42, 6 September 2014 (UTC)

Well, nothing is "too small" or "too large", so the whole basis for the discussion seems silly. It came in here by an anon, years ago, and lasted until you took out some of it here. Dicklyon (talk) 03:53, 6 September 2014 (UTC)

For me the description suggests verbally what happens tracing the feedback loop, and that helps to understand that the feedback is a different operation than one based upon error control. The is no measurement of a departure from 'normal' operation, and no minimizing of such a departure by a regulator. Of course, the mathematical analysis doesn't use those ideas either, but this may be a more intuitive explanation. It seems that grasping the 'design for immunity' use of feedback seen here is hard for some here to separate from the 'fix departures from the norm' use for feedback found in error-controlled regulation. Brews ohare (talk) 04:20, 6 September 2014 (UTC)

To be strictly accurate that is a rough description of how an underdamped negative feedback loop will often operate. But not a critically, or overdamped one.GliderMaven (talk) 12:26, 6 September 2014 (UTC)

'It seems that grasping the 'design for immunity' use of feedback seen here is hard for some here to separate from the 'fix departures from the norm' use for feedback found in error-controlled regulation.' Yeah. Just because you've stuck different labels on the same damn circuit, or because the blocks are implemented differently internally, or if the signals going around the loop are volts instead of water or shafts turning, doesn't mean they're actually logically different if they have the same function in the context of the loop. This topic is not about the words we use to describe it, it's about the mathematical and logical relationships; negative feedback is an identifiable pattern, not something necessarily designed for any human purpose at all, many, many natural processes involve negative feedback.GliderMaven (talk) 12:26, 6 September 2014 (UTC)

Maybe you can explain what exactly is the departure error that is measured in the feedback circuit of the lede? Then you can explain what is the regulator function in this circuit that reduces this error. With sources, preferably. There are neither of these elements present. The circuit simply is designed to produce a gain of 1/B and the circuit is impervious to variations in open-loop gain. Somewhat like GliderMaven does not address arguments, but bypasses them. Brews ohare (talk) 15:22, 6 September 2014 (UTC)

Another try

I had a go at composing a definition for the opening sentence:

"Negative feedback occurs when the output of a system, process or mechanism is fed back into the input in such a way as to reduce or eliminate changes in the output."

And GliderMaven immediately slapped the 'dubious' tag back on it. Could GliderMaven please suggest a wording that he'd be happy with, rather than just tagging or opposing anything anyone else proposes?

Let's see if we can build up a consensus step by step?

1. "Negative feedback when some function of the output of..." - Any alternative suggestions to that?

2. "... of a system, process or mechanism..." - Any alternative suggestions to that?

3. "...is fed back into the input..." - Any alternative suggestions to that?

4. "...in such a way as to reduce or eliminate changes in the output." - Any alternative suggestions to that? DaveApter (talk) 16:10, 6 September 2014 (UTC)

Dave: Happy to have a new voice here. The input/ output formulation seems adapted to process control, but how can it be worded so it is clear how it applies to homeostasis where there is no input/output but only an internal response to defend against some disturbance? Brews ohare (talk) 17:05, 6 September 2014 (UTC)

Another thing to chew on: in the negative feedback amplifier the output is not what is fed back, but a fraction B of the output. And not with the aim of reducing or eliminating changes, but of making the output 1/B times the input, that is, the output is an enlarged version of the input. None of this fits well with the beginning sentence, so what is to be done? Brews ohare (talk) 17:15, 6 September 2014 (UTC)

Brews, since your continued dominance of this talk page makes it impossible for people to hear each other, why don't you try stepping back again and see where this goes? Dicklyon (talk) 17:20, 6 September 2014 (UTC)

OK. I see no evidence of my domination; anyway, I have had no influence in bringing sources to bear. Editors here simply avoid my attempt to discuss sources, and instead present their personal formulations divorced from sources. We have already a very succinct and general definition for distinguishing between positive and negative feedback, one you have endorsed, and one with myriads of sources, but editors want to ornament it like congress attaches pork to straightforward bills. Brews ohare (talk) 17:39, 6 September 2014 (UTC)

The evidence shows that you have made 66% of the edits and have created 60% of the text on this talk page since its inception, almost all very recently. Most of the rest, not much over one-third of the total, is all other editors pushing back against you. Dicklyon (talk) 22:07, 6 September 2014 (UTC)

You measure dominance by number of edits, but if we judge by success I've got nowhere at all. Dick, you are not alone in preferring your unsourced opinion based upon personal intuition to finding what sources say. And where sources have been pointed out that don't agree with you, you are not alone in simply saying the sources got it wrong, or are lacking in some respect, without any source to supports those claims! Brews ohare (talk) 02:14, 7 September 2014 (UTC)

Right, your dominance has proved counterproductive, yet you keep it up. Give it a break, as you said you would. Dicklyon (talk) 02:37, 7 September 2014 (UTC)

Thanks for your questions Brews. The way I see it is that in a homeostatic process, such as temperature regulation, the input is the temperature and the output is the bodily activity to heat it (eg shivering or raising hair fibres to thicken the coat) or cool it (eg perspiration). That output is fed back to the input in either the raising or lowering of temperature to restore it to normal. Do you think a revision of the above wording would help to make this clear?

As for the second point, whether it is all of the output or a fraction of it is covered by my phrasing "... some function of the output". And yes, actually the gain is reduced by the action of the feedback. An op-amp might have an open-loop gain of maybe 10,000, and this is reduced to a gain of 10 if you had for example a 9k and 1k resistor divider network in the feedback loop. DaveApter (talk) 22:00, 6 September 2014 (UTC)

I agree on the amplifier that this works fine; I don't understand Brews's objection. On the homeostasis, I'd take temperature as the output, and heat as the input. If the environment is putting in too much heat, the organism senses increasing temperature and feeds that back to sweat or pant or whatever to let heat out or reduce the excess heat input to reduce the temperature fluctuation. Dicklyon (talk) 22:11, 6 September 2014 (UTC)

Sorry to intrude, but sources could help with vocabulary and concepts. Reading Ashby might help. An 'essential variable' is one that must be held in range for things to work properly. Temperature is an example. An essential variable is compared with a 'setpoint'. It's departure from setpoint is measured as an 'error' and goes to a 'controller' that in turn instructs a 'regulator' to take action. In the case of thermostatic control, the furnace adjusts heat to correct the error and, as Dick says, the heat is input, some of which is corrective feedback. So one might take the 'error' as one form of 'output' and the action taken by the regulator as contributing to 'input'. There is no need to reinvent the wheel here: the vocabulary can be sourced. In the case of the negative feedback amplifier, no source uses this vocabulary. The terms 'error' (I–BO), 'input' (I), and 'output' (O ≈ I/B) have different meanings, and regulation doesn't come up. Brews ohare (talk) 23:20, 6 September 2014 (UTC)

Hi DaveApter. Your proposed definition may work, provided that:

1. the "system, process or mechanism" referred to is actually the control system, and not the system being controlled, and
2. the changes in the output are defined with respect to some explicit reference.

Point 1 is somewhat un-intuitive. I would expect the "system" in the definition to refer to the system-being-controlled. But this produces some confusion and awkwardness.

May I present a possible counter-example: using spill-valves to control water level in a reservoir. Glidermaven and I discussed it (above). If the system is the reservoir then the control is via an internal measurement (water level) being fed "back" to the output (spill valve). That is awkward, but it does work if "system" refers to the control process (see above). A similar point holds with the temperature regulation example: what counts as "input" depends on which system you are talking about. For the control system, input=temperature. For the body system (Dicklyon's point, I believe) input=heat.

Also, Glidermaven made the point that not every change is opposed. After all, a correction is a change too. It would be a pretty poor regulator if it opposed its own corrections. So for that reason, "change" needs to be with respect to a reference point to make this clear. The temperature is compared to a desired internal temperature. The water level is compared to a safe maximum. It is the difference (the "gap" between measures) that is reduced/eliminated, not the absolute level of the output.

Thank you for the fresh input - you have helped me clarify my thinking. Trevithj (talk) 06:11, 7 September 2014 (UTC)

I don't understand why/how you would look at input and output backwards that way, with respect to the thing in the feedback path instead of the intended overall system input/output. Dicklyon (talk) 06:17, 7 September 2014 (UTC)

It is un-intuitive to do so. But take the example of the reservoir: the overall system input is a river. This is not controlled as far as the reservoir is concerned. The overall system output is the spillway. This is not measured. So if the "system" is the reservoir, the proposed definition doesn't fit this example. But it does fit if the "system" is the control system. Input=level measurement, output=signal to control valve. I'm not sure if I personally like it, but it does work. Trevithj (talk) 19:22, 7 September 2014 (UTC)

I don't understand what you meant when you said "Glidermaven made the point that not every change is opposed" - can you give an example? Thanks. DaveApter (talk) 12:35, 7 September 2014 (UTC)

It's because it's wrong. When every change is opposed, a system is subject to damping, not negative feedback. For example a dashpot opposes all changes. If I move a damper down, and then up, the damper opposes it on the up; that's not what negative feedback does. A negative feedback system will help you move it back up.

Consider a room being maintained at 20C by an electric fire/air conditioner on a thermostat. If I open the window, then the room may drop to 15C and the heater will turn on due to negative feedback; the negative feedback is very definitely opposing that particular change. But this is not a general thing, for if I then light the waste paper basket on fire; the room may warm up to 17C, but the negative feedback doesn't oppose that in any way; the thermostat is on, and stays on, since it's trying to push the temperature back to 20C.

So it's not that all changes are opposed by negative feedback, it's that changes from the equilibrium point are opposed by the negative feedback loop; the loop is active when the temperature is away from that equilibrium.GliderMaven (talk) 15:36, 7 September 2014 (UTC)

GliderMaven ignores the point indicated to him before that the definition here is intended only to separate negative from positive feedback. So the "opposes change" is to be contrasted with "reinforces change" in trying to decide what type of feedback is present. There is no intention to make "opposes change" a complete description of negative feedback separating it from all other phenomena found in the universe. It is obvious, for instance, as was also pointed out to GliderMaven before, that feed-forward can oppose change, but is not a form of negative feedback. Brews ohare (talk) 20:00, 7 September 2014 (UTC)

What you're doing is exactly like trying to define cats as being lions. You can say "well, I'm just trying to distinguish cats and dogs", but no, what you're doing is failing to define cats correctly.

If there were only two types of feedback, or even one type of negative feedback, then you might be correct. But as I have pointed out several times now, a feedback system that opposes change is the specific definition of a damping feedback system. Damping can be considered a particular form of negative feedback that attenuates the velocity/state rate change vector. However, most forms of negative feedback are not based on opposing change, thus the definition is too narrow for a general work such as Wikipedia. Note that at least one of three references you rely on further specifies what constitutes a 'change' but you have incorrectly summarised it, and the main one you've used is largely or completely unreliable.GliderMaven (talk) 10:23, 8 September 2014 (UTC)

Not all changes are opposed, and not all that opposes is negative feedback. But we can agree that negative feedback always opposes changes from the reference/equilibrium. True? Trevithj (talk) 20:41, 7 September 2014 (UTC)

In the feedback amplifier 'equilibrium' is not really a consideration. The feedback is negative because it is subtracted from the input to the open-loop amplifier, I–BO, and the 'changes' involved are due to the signal being amplified, which are not normally referred to as disturbances from equilibrium. The opposition in this case refers to the reduction of the input to the open-loop amplifier, I–BO, which reduction brings the output variation down to 1/B from A. Brews ohare (talk) 23:00, 7 September 2014 (UTC)

The case of homeostasis

Having thought a bit more about it, in the example of homeostatic body temperature I would say that the muscular action / sweating etc constitute the mechanism, the output is the actual temperature of the blood, and the inputs are the temperature sensory organs - which I think are within the brainstem and the adrenal glands (as best I understand it; I am not an expert in physiology). The classic reference is Cannon.¹ The conclusion of that chapter states:

"If conditions are such that there is a tendency to tip the organism in one direction, a series of processes are at once set at work which oppose the tendency. And if an opposite tendency develops, another series of processes promptly oppose it. Thus quite automatically the remarkable uniformity of the internal environment is preserved, in opposition to both internal and external disturbing conditions." DaveApter (talk) 12:27, 7 September 2014 (UTC)

¹Walter B. Cannon; The Wisdom of the Body, 1932, pp 177-201

Dave: Your process here, invoking a source, is a most salutary development that has so far been little used on this page. However, the discussion is enlarging beyond the subject here, which is finding a definition that distinguishes negative feedback from positive feedback. Negative feedback does play a role in homeostasis, (see this), so the definition has to work for that instance of negative feedback. But a complete understanding of homeostasis or even process control goes into complexities beyond what is needed to establish how negative feedback is fundamentally different from positive feedback. Perhaps this or this, which must reconcile with this? Brews ohare (talk) 14:34, 7 September 2014 (UTC)

Here is an approach I hadn't seen before due to Li Qiu:

“When feedback modifies an event/phenomenon, the modification will subsequently influence the feedback signal in one of three ways:

1. -the feedback signal increases, leading to more modification. This is known as positive feedback.

2. -the feedback signal decreases, leading to less modification. This is known as negative feedback.

3. -the feedback signal does not change, indicating the phenomenon is in equilibrium.

Note that an increase or decrease of the feedback signal here refers to the magnitude of the signal's absolute value, without regard to the polarity or sign of the signal.”

Brews ohare (talk) 15:53, 7 September 2014 (UTC)

That's lame; case 3 about equilibrium contradicts the premise that feedback modifies an event/phenomenon. Both positive and negative feedback systems can approach equilibrium, and this tripartite scheme doesn't help understand that. No wonder you haven't seen it before. It's also very vague about what the various increases and decreases actually mean. Dicklyon (talk) 16:55, 7 September 2014 (UTC)

I would need convincing that it is true that "Both positive and negative feedback systems can approach equilibrium," - can you give an example? I should have thought that positive feedback never produces equilibrium except in the degenerate case where the system is driven into saturation (eg an amplifier output is driven to one power rail). DaveApter (talk) 10:33, 8 September 2014 (UTC)

Dick: I don't think we need part 3 as worded. I think the author meant something more along the lines that if feedback is not activated, the system is in equilibrium. In any case, parts 1&2 are one possible solution to separating positive from negative feedback in widely applicable terms. Brews ohare (talk) 17:05, 7 September 2014 (UTC)

As for not spelling out what an increase or decrease in feedback signal means, what is the confusion? Given a system and a feedback signal, won't it be obvious what constitutes an increase/decrease in that feedback signal? Got a confusing example in mind? Brews ohare (talk) 17:16, 7 September 2014 (UTC)

Your remark that positive and negative feedback can both lead to equilibrium does not address the distinction posed, which is that positive feedback leads to increasing modification, and negative feedback to decreasing modification. It fits error-controlled regulation, where negative feedback reduces a measured departure from setpoint, and to the amplifier where a portion B of the output is subtracted, reducing the signal to the open-loop amplifier. This view is very commonly expressed. Do you disagree with it? Brews ohare (talk) 17:32, 7 September 2014 (UTC)

It is my understanding that case 3 may refer to situations where the control has to be continuous in order to keep the parameter in equilibrium. Perturbations/disturbances are not always only momentary. Thoughts? Trevithj (talk) 20:48, 7 September 2014 (UTC)

My guess, only a guess, is that case 3 was meant to read that if feedback wasn't activated (not responding), the system was in equilibrium. But in any event, case 3 is beside the point as interest is in case 1 & 2. Brews ohare (talk) 22:51, 7 September 2014 (UTC)

Let's try fitting the homeostasis example into the proposed definition:

Negative feedback occurs when the [actual blood temperature] output of the [muscular action / sweating] mechanism is fed back into the [temperature sensory organs] input in such a way as to reduce or eliminate changes in the [actual blood temperature] output.

Making allowances for the wording, it sort of works. However I would like to offer an alternative, as a basis for comparison:

Negative feedback occurs when information about a difference between the actual level and a reference level of a system parameter is used to reduce the difference.

This is a variation on an earlier suggestion. Exactly how the information is used doesn't need to be specified. Does it fit the homeostasis case? "System parameter"=blood temperature, "reference level"≈37°C. Trevithj (talk) 06:55, 8 September 2014 (UTC)

OK, it seems to me that we won't get a concise one-sentence definition that covers all cases. But it should be possible to agree on a summary to go into the lead that will give a clear sense of the meaning that will be fleshed out in more detail in the body of the article, with the help of various specific examples and how the principles apply in those cases.

Are we agreed on the clauses 1-3 in my suggestions at the start of this ("Another try") section above? Would replacing clause 4: "...in such a way as to reduce or eliminate changes in the output." with "...with a polarity which tends to reduce the effect of changes in the input"? I'll put that into the article now but leave the 'dubious' tag there. Could GliderMaven please remove the tag if he's now satisfied, or suggest a wording that would suit if not?

btw, I'm not happy with forms of wording suggested above which refer to "subtracting from the input signal" because I'm not convinced that this is always the case - for one example, where the polarity inversion occurs in the amplifying stage rather than in the feedback loop? DaveApter (talk) 10:34, 8 September 2014 (UTC)

Trevithj: To be sure, this subsection is about homeostasis, but the big issue is to find a very general way to distinguish between negative and positive feedback, one that works for homeostasis of course, but includes all cases. For the case of homeostasis, an example of error-controlled regulation, you have presented a couple of ways to fill in the formula:

If feedback modifies a phenomenon, and that modification causes the feedback signal to decrease, leading to less modification, that form of feedback is known as negative feedback.

The purpose of such an exercise is to see if the formula does fit homeostasis. The goal is not to see if some alternative more explicit wording can be found that fits homeostasis.

The original issue was that the lead sentence was focused too narrowly upon error-controlled regulation and did not fit well with different examples, most particularly the negative feedback amplifier.

Dave's present formulation doesn't solve this problem. It requires a non obvious understanding of what is 'input/output', which may have nothing to do with (say) the 'input/output' of a process (like manufacturing cars, or amplifying an electrical signal) and can refer instead to the departure of some essential variable of a monitoring system from its setpoint followed by commands to a regulator. The italicized formulation just above does solve it. Brews ohare (talk) 10:38, 8 September 2014 (UTC)

The widely adopted criterion that negative feedback is feedback that opposes change, while positive feedback reinforces it, seems the best way to go IMO and the main objections to it are that it is limited to the purpose of distinguishing the two forms, and doesn't spell out more specifics. That is like saying a hammer can't saw wood. Brews ohare (talk) 10:53, 8 September 2014 (UTC)

Another source supporting the view that "if increases in the output cause the feedback to decrease the output, the feedback is called negative feedback". Brews ohare (talk) 17:47, 17 September 2014 (UTC)

Another quote

From Wiener, Cybernetics p. 97

"We thus have examples of negative feedbacks to stabilize temperature and negative feedbacks to stablilize velocity...also to stabilize position... The information fed back to the controller tends to oppose the departure of the controlled from the controlling quatity, but it may depend in widely different ways on this departure".

Incidentally I don't subscribe to the view that feedback in an amplifier circuit differs in principle from in a control system or a living organism; the intention of applying feedback in say an audio amplifier is to ensure that the output signal is a more faithful reproduction of the input signal. DaveApter (talk) 16:39, 8 September 2014 (UTC)

Dave: Well, this quote fits error-controlled regulation well, speaking of departures of an essential variable from its setpoint, but is not applicable to amplifiers. Your earlier formulation was good for process control and amplifiers, but not for this.

Your notion of an audio amplifier (or an amplifier in general) is inaccurate. The function of an amplifier is to produce an enlarged exact copy of its input, including any distortion that may happen to be present. See this definition. That includes the negative feedback amplifier, where the output is simply A/(1+BA) times the input, an exact copy of the input, but of different size. Cleaning up a signal is a different function, which can be accomplished in many ways of course, such as filtering. Brews ohare (talk) 17:26, 8 September 2014 (UTC)

Of course, the negative feedback amplifier can introduce distortion, because it isn't an ideal amplifier. See, for example, the article on step response. Brews ohare (talk) 17:36, 8 September 2014 (UTC)

I probably didn't express myself clearly enough. When I said "faithful reproduction of the input signal", I was including the case of it being an enlarged reproduction of the input. And when I said "more faithful" I meant more faithful than it would have been in the absence of negative feedback (ie with a reduced amount of any distortion that would otherwise have been added by the amplifying stage), not that it would have magically eliminated any distortion presented to the input of the amplifier! DaveApter (talk) 19:23, 8 September 2014 (UTC)

I don't know if I have mistaken your meaning. Perhaps we agree that the feedback does not make the negative feedback amplifier 'improve' upon the fidelity of the input signal. The output as noted is AI/(1+BA) and exhibits every flaw present in I. Of course the feedback amplifier introduces less distortion than the open-loop amplifier because it is independent of A, if A is large, and A exhibits more sources of distortion than 1/B.

As you say, the intent of feedback is to reduce the role of unpredictable variations in function, but perhaps you also agree that the way this is done in the amplifier does not rely upon measuring a departure of an essential variable and commanding a regulator to take action to reduce this departure. There is no measured 'error' and no attempt to reduce such an error. Rather than maintain performance by combating the effects of variations in A, the gain simply doesn't depend on A (assuming A is sufficiently large),1 and no monitoring is necessary. Brews ohare (talk) 21:54, 8 September 2014 (UTC)

To date, Dave, the other editors on this page refuse to believe Kal's analysis of the above paragraph captures the role of feedback in the negative feedback amplifier. That opinion is voiced without sources for backup. Yet Kal's is the standard analysis of every electronics text of the last 40 years. Your approach using sources is the only way to cut out unsupported assertions of editor intuition. Brews ohare (talk) 14:47, 9 September 2014 (UTC)

Dave: On my talk page, rather than respond here, you have suggested my participation is counterproductive. You remark that you "did not get the impression that [I] had attentively read what [you] had written, or that [I] had thought through [my] own argument carefully before rushing to the keyboard." That reaction upsets me, as I felt I responded in detail and most cogently to your remarks regarding the role of feedback in the negative feedback amplifier, suggested that perhaps mine coincided with your own, and provided a source 1 to elucidate its analysis. You also suggest that I "Make specific suggestions about changes to the article, rather than maintaining a running debate." I have done so repeatedly, proposing a variety of approaches to the lede. Here is one and here is another.

Much of the unproductive discussion on this Talk page revolves around this original suggestion regarding the lede. You have made some changes to improve this situation.

The prolonged Talk page debate about the lede can be traced directly to the refusal by most participants to discuss sources instead of their opinions, suggesting that textbook treatments of the negative feedback amplifier are somehow incomplete, as they aren't consistent with these editors' personal and unsourced intuitions that every example of negative feedback is a particular implementation of error- controlled regulation.

At this point, I've exhausted all attempts to bring editors to consider sources. I've provided the sources, presented the sources, explained the sources, and yet editors' persist in the notion that their beliefs, if sufficiently lucidly presented, should prevail over published commentary, and have even suggested that sources don't matter.

So, as you propose and as I have proposed myself above, I will withdraw, with no optimism that sources will prevail. Brews ohare (talk) 17:44, 9 September 2014 (UTC)

---

Re an earlier comment by DaveApter: it may be a bit hasty to say that there isn't a way to summarize negative feedback in a generic way. I believe there is, but it is difficult to do so in a way where people don't feel an urge to delve into domain-specific details.

I'm beginning to wonder if we should split the article into two pages. I hate the idea, but the discussions in the past do seem to imply there is some sort of basic conceptual conflict. It seems to be an old problem:

From William Ross Ashby, Introduction to Cybernetics (1957) pp 53-54

"On the one side stand those ... whose aim is to get an understanding of the principles behind the multitudinous special mechanisms that exhibit them. To such workers 'feedback' exists between two parts when each affects the other... On the other side stand the practical experimenters and constructors, who want to use the word to refer, when some forward effect from P to R can be taken for granted, to the deliberate condition of some effect back from R to P by some connexion that is physically or materially evident."

Trevithj (talk) 21:32, 9 September 2014 (UTC)

I must admit, I don't really understand what precisely is meant by this, and the link is not loading for me at the moment to find the context.

Anyway, aren't we trying to define what a 'feedback loop' is, not 'feedback' itself? Is it not the case that a positive feedback loop is a loop where when you follow cause-and-effect around the loop, that that cause and effect chain has tended to increase the size of the signal at that point, whereas a negative feedback loop, is when it has tended to decrease it?GliderMaven (talk) 00:34, 11 September 2014 (UTC)

Everything that GM has written about this topic is clear, correct, and helpful. Almost everything else is either unclear, incorrect, or unhelpful. Yes, this is self-referential, and it could lead to feedback instability. Johnuniq (talk) 00:58, 11 September 2014 (UTC)

Hi GliderMaven. Do you mean 'feedback loop' as opposed to 'feedback' the signal? Yes I agree we should define negative feedback with respect to the action of the entire loop. Talking in terms of circular-causality seems more generic than in terms of output-to-input.

Regards the Ashby quote: I'm trying to understand why quite good definitions in the lede seem to get completely rewritten on a regular basis. There does seem to be a debate between theoretical approaches and practical examples - a search of this talk page for "mathematical" may clarify what I mean.

BTW: I understood that you disliked the use of "change" in the existing definition. Is that not true? Trevithj (talk) 01:49, 11 September 2014 (UTC)

While the loop-based view is a good way to distinguish negative from positive, it's not great at making clear what feedback means, which is conceptually tied to the word itself, feeding a signal from an output or sensed state back to an input (a "target" and "error" being optional parts of that, typically included in the feedback part of the loop). Analysis almost always includes a separation between a forward part of the loop and a feedback part of the loop, in both the control and amplifier applications. Dicklyon (talk) 15:13, 11 September 2014 (UTC)

Good point, especially re analysis. Agreed that the output-to-input (R→P) view is a more intuitive way of expressing feedback. On the other hand, it has problems being applied to cases of control where the output of a process is not what is being measured, and/or the input is not what is being influenced. And if an example process involves several components, then it may not always be obvious which of several inputs and outputs are being referred to. The loop-based view (P⇔R) doesn't require these details, and so is easier to apply to other cases. Trevithj (talk) 21:23, 11 September 2014 (UTC)

Typically people will just define what's being measured as an output, and all influences feeding back as inputs. With modern (c. 1970) vector matrix state-space methods, it's all covered. Any state that is "observable" is observed via outputs, and anything that is "controllable" is controlled via inputs. See [6] or [7]. Dicklyon (talk) 00:33, 12 September 2014 (UTC)

I think that the first few sentences in the lead is not really the place to be doing any analysis. We're not trying to define feedback; we're simply trying to identify the topic, to state what a negative feedback loop is.

That seems to be the primary thing, but any initial definition certainly shouldn't preclude the definition or relevant examples of feedforward and feedback mechanisms later in the lead or the article, but they don't seem to be primary thing anyway, nor really are inputs and outputs.GliderMaven (talk) 00:47, 12 September 2014 (UTC)

Good feedback definition

The 1947 book Theory of Servomechanisms, of the MIT Rad Lab series, which I just found in the stack by my bed, has a good definition:

2-21. Characterization of Feedback Systems.—A mechanical or electrical system with feedback is one in which the output of some part of the system is used as an input to the system at a point where this can affect its own value. A servosystem is a feedback system in which the actual output is compared with the input, which is the desired output, and the driving element is activated by the difference of these quantities.

Sure, it's a little narrow with "mechanical or electrical", and "driving element" and such concepts, but it does capture the general case of things (which he calls outputs) being fed back in where they can affect their own value, and the specialization to systems with targets and errors. We need something of this sort, not necessarily these words. We'd have to add some about negative, which that book does not do (since it treats feedback and stability more generally, where in real systems phase often tends to change from negative to positive as frequency increases). Either that or use a much simpler definition of negative feedback, like the one in this book: Negative feedback is a circular change of effects that opposes change. Dicklyon (talk) 05:04, 12 September 2014 (UTC)

This book says In the language of cybernetics, if increases in the output cause the feedback to decrease the output, the feedback is called negative feedback. Something like that combined with something like the servomechanisms characterization seems like it should satisfy all interests here. Dicklyon (talk) 05:13, 12 September 2014 (UTC)

Perhaps something like this would be a good lead:

A system with feedback is one in which the output of some part of the system is used as an input to the system at a point where this output can affect its own value. The feedback is called negative feedback if increases in the output cause the feedback to decrease the output. A common use of negative feedback is in servosystems, or control systems, in which the actual output is compared with an input representing the desired output, and the difference or error signal is used to drive the output in the direction that reduces the error toward zero.

Comments? Dicklyon (talk) 05:22, 12 September 2014 (UTC)

Maybe with less emphasis on "input/output". And perhaps we can join the first two sentences, and use less passive voice. Something like:

A system with negative feedback is one in which a measurement of some part of the system influences the system in a way that keeps the measurement within certain limits.

The servomsystems case looks useful. A nod to the history of the term might not be a bad idea either.

The term originated with the negative feedback amplifier, where an amplifier was controlled by using some of the output to cancel or "negate" its input. The term is also applied to servosystems, or control systems, where a measured output is compared with a reference value representing the desired output, and the difference or error signal is used to drive the output in the direction that reduces the error toward zero.

Hmm. Too wordy? Trevithj (talk) 06:02, 12 September 2014 (UTC)

It's not about useful definitions. We need a very, very general definition. Inputs and outputs only confuses things. How about this:

A negative feedback loop is a closed loop of cause and effect where the overall effect of the loop is to tend to reduce the measurable quantity effecting any point in the loop. GliderMaven (talk) 12:41, 12 September 2014 (UTC)

And a negative feedback signal is the part of the loop that connects a measurement to a point of influence. Trevithj (talk) 20:08, 12 September 2014 (UTC)

"in a way that keeps the measurement within certain limits" is not correct in general, and as far as I know has no basis in sources. And I don't understand the objection to input and output, which is common in sources. That seems to me to be the most common and intuitive way that feedback is defined. And I don't know think "The term originated with the negative feedback amplifier" is correct, but I could be wrong; do we know? Dicklyon (talk) 03:36, 13 September 2014 (UTC)

It's not that we have any problem with inputs and outputs, it's that a feedback loop doesn't necessarily have to have anything that you would normally call an input or an output, and you can add or specify the existence of inputs and outputs willy-nilly, and it doesn't change the essence of it, it was a feedback loop both before and after you added any number of them. For example, an example of a feedback loop with only outputs is called: an oscillator; if you take the output off, it's still an oscillator and a feedback loop.

Inputs and outputs are, practically speaking, very important, but they don't define what a negative/positive feedback loop is, and it's clear that the cause and effect loop is really the real heart of the topic.GliderMaven (talk) 14:17, 13 September 2014 (UTC)

I would argue rather that an oscillator may or may not be built using a feedback loop (as this book supports), and that if it is, then one can identify the path from an output to an input that makes it so (like here). You're right of course that it will continue to oscillate whether or not we identify such an output and input. So what? Dicklyon (talk) 14:25, 13 September 2014 (UTC)

And using "measurements" for outputs and "points of influence" for inputs doesn't really change things, just uses less familiar words for the concepts. Dicklyon (talk) 14:38, 13 September 2014 (UTC)

You don't seem to be quite getting what I'm saying. I'm saying you can build a feedback loop with no signal inputs or outputs at all, and it will do something, oscillate or behave chaotic, or go to zero, depending on the loop. Of course, you can always potentially measure something (add an output on a measurable quantity), but it's still a feedback loop when you're not doing that. So the inputs and outputs are a complete red-herring; they're completely unnecessary to the definition.GliderMaven (talk) 22:39, 13 September 2014 (UTC)

I do understand what you're saying: that it's all about the loop, and the sign of the loop gain. But it's very hard to appreciate what the loop might be, or why it's called feedback, without the notion of "back" meaning from output to input, via a path outside the system that the feedback is "around". But let's try it your way. What lead definition are you proposing? You've proposed a definition of the loop, above, in terms of its effect, as "A negative feedback loop is a closed loop of cause and effect where the overall effect of the loop is to tend to reduce the measurable quantity effecting any point in the loop." Here I assume you mean "affecting", not "effecting", but it's hard to understand what "the measurable quantity affecting any point in the loop" might refer to. Dicklyon (talk) 03:27, 14 September 2014 (UTC)

Re the last point: "familiar" is a relative term. It may be familiar to readers with (eg) an electronics background, but we aren't necessarily aiming the lede at readers who are familiar with that (or any) discipline. Trevithj (talk) 23:59, 13 September 2014 (UTC)

Nevertheless, I think we can probably agree that making up new terms makes the concepts less familiar, in general. Dicklyon (talk) 03:29, 14 September 2014 (UTC)

OK, I'm not trying to make up terms. How about: "A negative feedback loop is a closed loop of cause and effect which tends to reduce the quantity acting at each point in the loop.".GliderMaven (talk) 20:34, 14 September 2014 (UTC)

I think "the quantity acting" is not a standard term of art, nor easy to interpret in any way that makes sense. And opposing change is not really related to reducing a quantity. Dicklyon (talk) 21:07, 14 September 2014 (UTC)

By the way, the Britannica definition you quoted kind of misses the mark. It says: In negative feedback, the feedback signal is of a sense opposite to the signal present at the point in the circuit where the feedback signal is applied. The point is rather that the output is fed back to an input in such a way as to oppose changes in the output; there need not be any other (input) signal present at that point of application, so applying it in the opposite sense is not possible in general. Review the quotes from books at the start of this subsection. Also, the hyperphysics definition that you provided did have input and output, and you didn't seem to object at that point. Dicklyon (talk) 00:04, 15 September 2014 (UTC)

As GliderMaven points out, we're not trying to define 'feedback', which has its own article, but negative feedback. It might also help to use sources to supply this distinction, inasmuch as WP is supposed to report what sources say, not WP editors. Brews ohare (talk) 00:22, 14 September 2014 (UTC)

Another try at a lead

Here is another attempt at a synthesis of definitions, focusing on negative, not needing inputs, and defining an output as some measurement of the system's state:

• A system with negative feedback is one in which an output (that is, some measurement of the system's state) is fed back into the system at a point where this output affects its own value in such a way as to oppose changes in the output.

I'm not loving it, but I think it meets most of the objections. Dicklyon (talk) 00:22, 15 September 2014 (UTC)

Doesn't attack 'negative feedback' directly, but as an aspect of a system. Could a system be eg a legal system, an educational or management system, a philosophical system, a notational system? Brews ohare (talk) 05:27, 15 September 2014 (UTC)

Hmm. All measurements are outputs, not all outputs are measurements. I'm unclear why we keep saying "output" when "measurement" is the intended meaning.

• Negative feedback is feedback in which a measurement of a system influences that system in a way that tends to prevent or reduce variations in the measurement.

I would rather say something like "relative variations", since there are many cases where the measurement is not absolute. Trevithj (talk) 08:32, 15 September 2014 (UTC)

Measurements do not take place in the negative feedback amplifier, where a fixed fraction of the output is subtracted from the input signal, regardless of its value, but nothing is measured. Measurement does occur in error-controlled regulation, where the value of an essential variable (e.g. temperature) is measured to determine its departure from its set point to find the error. Brews ohare (talk) 11:43, 15 September 2014 (UTC)

How about using sources? Brews ohare (talk) 11:46, 15 September 2014 (UTC)

In a broader context, little of this discussion applies. Brews ohare (talk) 13:14, 15 September 2014 (UTC)

I guess my objection to "output" comes from a systems analysis point of view, where an output is a flow that crosses the system boundary. If it feeds back externally, that is outside the context of the "system" and so irrelevant to analysis. If it feeds back internally, then the fact that the flow crosses the boundary becomes irrelevant. So "output" kind of grates. Trevithj (talk) 15:17, 15 September 2014 (UTC)

Trevithj: The idea of a system involves drawing a boundary, as you point out, but the placement of the boundary is dependent upon one's purpose. Is the thermostat inside or outside, for example. If the monitor feeds information about the 'system' back to the 'system', the entire feedback 'system' lies outside the system. If the monitor feeds information about the product of the system back to the system, then the information isn't necessarily about the status of the system making the product. For example, the information may be a market analysis - customers want different features. I think this discussion is too narrowly drawn. Brews ohare (talk) 16:01, 15 September 2014 (UTC)

I'm completely with Trevithj on this. This very, very definitely is a systems topic. If you don't define 'input' and 'output' wrt a system boundary, then all inputs are from outputs and all outputs go to inputs anyway. It's inherently redundant to even use the terms 'output' and 'input'. And there's nothing that says you need to take a system output to create a feedback loop; plenty of feedback loops go from some point in the middle of a system and go back to control a system input or even go to some place else in the system that isn't even a system input, but is part of a control loop.

I mean, what are we trying to tell the reader with the use of term 'output' here? Where else would you get a signal from? By specifically mentioning it, you're implying that it's necessarily a system output, but that just isn't true.GliderMaven (talk) 00:42, 16 September 2014 (UTC)

The notion of feedback, in which a signal is "fed back" into the system needs to get it out first. There are at least two relevant systems, or subsystems here: the forward system, which produces the signal that gets fed back, and the closed-loop system that you get by feeding that signal back in where it can affect itself. So, yes, it's a system problem. The "output", or "measurement" if you prefer, is from the forward system. Feeding it back in (often via a feedback loop filter, or controller) makes the closed loop system. The feedback path is outside of the forward subsystem. I think we all understand these things, just getting hung up on words to describe it. I'm almost OK with "Negative feedback is feedback in which a measurement of a system influences that system in a way that tends to prevent or reduce variations in the measurement" except that "measurement of a system" seems awkward or not quite meaningful. Maybe "measurement on a system" or "measurement of a system's state" would be a little more clear, if not less awkward. Anyway, calling it a measurement doesn't make it different than an output; both come outside the system and then get fed back in. Dicklyon (talk) 03:08, 16 September 2014 (UTC)

An 'output' might be measurable or not, and it might measurable and measured or not. Measurement and output are not the same thing. And measurement does not occur in the negative feedback amplifier. Dick, if you think measurement occurs, what is measured and how is it measured? Brews ohare (talk) 03:33, 16 September 2014 (UTC)

Deletion of erroneous material in lede

The sentences claiming a distinction between positive and negative feedback based upon stability considerations are simply mistaken, ignoring entirely the Nyquist stability criterion and the concepts of gain margin and phase margin. The change in wording from 'negative feedback can lead to equilibrium' to 'negative feedback tends to promote a settling to equilibrium' is a backward step inasmuch as amplifiers have nothing to do with settling to equilibrium. I have removed these errors. Brews ohare (talk) 16:34, 19 September 2014 (UTC)

I think ignoring entirely the Nyquist stability criterion in the lead is a good idea, and that "Whereas positive feedback tends to lead to instability via exponential growth or oscillation, negative feedback generally promotes stability" is a pretty fair characterization of their distinction. It doesn't mean all positive feedback systems are unstable, or that a negative feedback system can't go unstable at a frequency where its feedback loop gain is actually positive (Nyquist's point). I care less about the equilibrium part; I was trying to make it more meaningful, but leaving it out of the lead is OK, too. What do others think? Dicklyon (talk) 20:27, 19 September 2014 (UTC)

It possibly confounds the lede to introduce stability. Again, it means different things in different disciplines, especially related to oscillation. Some disciplines regard any oscillation as a sign of instability. Others are only concerned about stability of amplitude or frequency. Best to avoid the subject in the lede, IMO. Trevithj (talk) 01:04, 20 September 2014 (UTC)

OK by me. I just edited what was there to make it more sensible. Dicklyon (talk) 02:11, 20 September 2014 (UTC)

Removing 'dubious' tag

So far as I can see, no one has proposed an alternative to the definition I put in the lead on 8th September, so I am removing the 'dubious' tag that was appended immediately afterwards. If anyone thinks it should be re-applied please could they explain why here first before re-tagging it? And suggest a proposed wording, preferably using the four numbered clauses in my suggestion above (in the section 'Another try'). Thanks. DaveApter (talk) 12:31, 19 September 2014 (UTC)

It could be improved by adding a line that explains 'input/output' can be construed in the normal sense of inventory input/output or in the sense of monitoring (status output) and regulation (status adjustment via input). Brews ohare (talk) 14:24, 19 September 2014 (UTC)

And sources might help to avoid another 4-month Talk-page embroglio down the road, although there is next to no sensitivity to sources exhibited so far. Brews ohare (talk) 14:41, 19 September 2014 (UTC)

I actually think this is among the best lead proposals to date, though I have made a few edits just now that I think help clarify it a bit. The existence of equalibrium, and exponential decay toward it, is not a property that distinguishes positive from negative feedback systems: just stable from unstable ones. We don't need sources referenced in the lead, as long as the lead summarizes what's in the article and there are good sources there. So we need to review and make sure this is indeed a good summary. Maybe augment it with something that will make trevithj happier. Dicklyon (talk) 15:10, 19 September 2014 (UTC)

Thanks, @Dicklyon, and I think your tweaks to the wording are a definite improvement. DaveApter (talk) 16:32, 19 September 2014 (UTC)

The sentences claiming a distinction between positive and negative feedback based upon stability considerations are simply mistaken, ignoring entirely the Nyquist stability criterion and the concepts of gain margin and phase margin. The change in wording from 'negative feedback can lead to equilibrium' to 'negative feedback tends to promote a settling to equilibrium' is a backward step inasmuch as amplifiers have nothing to do with equilibrium. Brews ohare (talk) 15:35, 19 September 2014 (UTC)

While dubious isn't quite the right word, IMO, I must say that I do support the 'dubious' tag. The existing definition isn't a definition. Rather, it is an example, focused on the electronics/control theory POV. It is a good example, and I agree that negative feedback does occur in the case described. However, I do not agree that all cases of negative feedback involve some function of the output of a system, process, or mechanism that is fed back into the input with a polarity that tends to reduce the fluctuations in the output. For example, the following statement is also an example:

• Negative feedback occurs when some function of the state of a system, process, or mechanism is fed to the output with a polarity that tends to reduce the fluctuations in the state.

This describes several biological examples (eg, regulating body temperature) although "polarity" is an odd choice in that context. BTW: given that at least as many (and possibly more) biology/social pages link to this article as electronic/control pages, maybe an alternative word is in order.

Also, I respectfully suggest that several alternatives have been proposed. I offer one, and as requested, I'll use the four numbered clauses:

1. "Negative feedback when some measured quality..." (not necessarily 'the' output)
2. "... of a process or mechanism..." ('system' has confusions around boundaries)
3. "...is used to influence" (not necessarily 'the' input))
4. "...in a way that maintains the measurement within a relatively narrow range"

Having said all that, re-tagging the lede would be counter-productive to the obvious good will shown here towards reaching a consensus. Please pardon the long post. I didn't have time to make it shorter. Trevithj (talk) 01:54, 20 September 2014 (UTC)

Your concerns are at least partially addressed by this previous proposal of mine: "A system with negative feedback is one in which an output (that is, some measurement of the system's state) is fed back into the system at a point where this output affects its own value in such a way as to oppose changes in the output." Maybe the use of "system" here can be cleaned up. Feel free to propose a new lead sentence or two. Please omit "within a relatively narrow range" as that's too unclear; relative to what? Within a narrower range than the system would have without feedback maybe. Dicklyon (talk) 02:10, 20 September 2014 (UTC)

I agree with your last point. I've suggested in the past using "reduces the gap between the measured value and a reference value", but didn't think that was well received. Main objection is that some cases don't have an explicit reference value. Also, as you pointed out, it is a bit of a circular definition.

As regards the rest - I feel compromise is the wrong way to go. It is a fact that negative feedback originally described using the output of a simple inline process to alter the input. It is also a fact that negative feedback loops are a more generic idea. I feel that we can say that in a succinct way, and are more likely to get consensus. So something like this...

• Negative feedback originally described the practice of feeding some function of the output of a process or mechanism back into the process at a point where this output affects its own value in such a way as to oppose changes in the output. In subsequent usage, negative feedback loops refer to the more general idea of balancing or self-correcting circles of cause-and-effect.

...only perhaps shorter. That's more definite, and there's less compromise in the terminology.Trevithj (talk) 09:48, 20 September 2014 (UTC)

Trevithj, the idea of 'consensus' is not merely 'agreement among a majority of WP editors present on this Talk page at the moment'. To be a meaningful consensus, it should be agreement upon what sources say and it's clear presentation. We have already several well-sourced versions, for example: #An approach, #Earlier proposal and #Proposed change to lede, which you choose to ignore. Apparently you find fault with these sources because they disagree with your own ideas that are not about distinguishing negative feedback in its full generality, but instead attempt to characterize it in terms of a narrow view tied to the 'gap' of error-controlled regulation. Feedback has its own article where your views are prominent. Brews ohare (talk) 12:42, 20 September 2014 (UTC)

If you look at the various subsections of this article, particularly Negative feedback#Negative feedback amplifier and Negative feedback#Error-controlled regulation, the lede should be compatible with both discussions, and also with sources describing management, educational, and psychological uses of the term 'negative feedback'. So far compatibility with the text has been asserted, but not actively investigated. Brews ohare (talk) 12:56, 20 September 2014 (UTC)

Too much noise

Brews, on Aug. 31 you said, "OK folks. I'll leave it to you." Several times since then you've withdrawn again. Yet every time we start to discuss a proposal, and start to find some common ground, you jump in and torpedo the concept and pollute the discussion with excessive noise. You have continued to dominate the talk page, both by number of edits and amount of text, and have done nothing that moves toward convergence. I do my best to ignore you and reply to people with useful suggestions, but you distract them back into arguments. Please take a month or two off and see if things settle. Dicklyon (talk) 16:11, 19 September 2014 (UTC)

Dick, pointing out obvious errors, omissions, and contradictions with sources is 'noise' only to those who prefer their own ideas. Brews ohare (talk) 16:22, 19 September 2014 (UTC)

Speaking very generally, but also to you Dick, no-one here is interested in conveying what sources have to say, but simply restate their personal views without substantiation. You yourself, Dick, have switched back and forth from an amplifier input/output orientation to a stability and equilibrium error-based regulation standpoint without ever twigging that these two uses of feedback are fundamentally different. One bypasses fluctuations and the other combats them. A general definition has to include them both, not to mention the many other applications to things like educational and management theory that do not fit neatly into a engineering framework. Brews ohare (talk) 16:52, 19 September 2014 (UTC)

Trevith has thrown up his hands regarding sources:

"but this hasn't worked very well in the past, even when cited sources are used. (eg:[8][9][10][11][12][13][14][15][16]) People have strong opinions on the subject."

That suggests that some discussion of sources has taken place, but discussion of these sources or any others, for that matter, has not happened, with the exception of Dave's useful reliance upon sources and your doubtful relegation, Dick, of the standard textbook treatment of the feedback amplifier to a secondary effect. 'Strong opinions' are fine if they are sourced, and if they differ, the different views can be summarized and sourced. Brews ohare (talk) 17:06, 19 September 2014 (UTC)

If you could throttle your input even just moderately, say to not more than all other contributors put together, you might have a better chance of making your point. I don't think anyone is reading your walls of rants. Dicklyon (talk) 20:30, 19 September 2014 (UTC)

Dick: My point is made: USE SOURCES. However, your point that no-one is paying attention is quite on target. Brews ohare (talk) 22:59, 19 September 2014 (UTC)

Your percentage of total text on this talk page has increased from 60% to 70% during the last three weeks, after you said you'd back off. You probably aren't using your words very effectively. Try being quiet for a while and see. There are four others here who are actually trying to converge. Dicklyon (talk) 02:17, 20 September 2014 (UTC)

I'll lay off again for a while. However, convergence is not what is happening. What is happening is the misdirected effort by each WP editor to show their own individual opinion, perhaps by virtue of its eloquence or its intuitive obviousness, should trump all published discussion that, as is asserted in various ways, supposedly is not needed anyway. Brews ohare (talk) 14:21, 20 September 2014 (UTC)

An approach

Here is an approach:

Negative feedback is an opposing response of a system or entity that is triggered by a perturbation or disturbance.¹ This opposing response involves a variety of different specifics as to its implementation, triggering, and objectives, all of which details vary from one instance to another. For example, ...

¹Camazine, p. 16, Beerel, Hobbs, Kal Morton

Brews ohare (talk) 16:29, 17 September 2014 (UTC)

The details of applications are provided in the subsections devoted to particular cases. Brews ohare (talk) 17:05, 17 September 2014 (UTC)

To clarify my earlier post, the term "negative feedback" was first used somewhere around the 1920s, by Bell technicians working with electronic amplifiers. (Eg: Harald_T._Friis and A. G. Jensen. "High Frequency Amplifiers." Bell System Technical Journal, April 1924.) It was popularized by Harold Black in the 1930s. According to Mindell, it wasn't until WWII that the term began to be used more broadly to describe control systems.

It is certainly true that control mechanisms were in use long before 1920, but as far as I can tell they weren't called "negative feedback". James Clerk Maxwell never used the term, for example. Neither does the PID control article mentioned above. Trevithj (talk) 01:13, 18 September 2014 (UTC)

So you say the 'term' was coined in 1924 but the technique was in use as described by Bennett as early as 1911, and as a Google search of "PID control"&"negative feedback" shows, these two are often discussed in conjunction. Here is a particular example. The Mindell source you probably refer to is Between Human and Machine, which agrees with Bennett on the early theoretical role of Minorsky and the early practical role of Sperry.

All of which has no bearing upon the proposal immediately above. Brews ohare (talk) 01:33, 18 September 2014 (UTC)

It has a very strong bearing on the proposal above. The last two of the five sources quoted use output-to-input terminology. The first two talk in terms of feedback loops, while the middle source and the newer example given here talk in terms of the overall "balancing" effect. All use the term "negative feedback", which was first coined circa 1920.

The proposal itself aims at a compromise definition. Reasonable, but this hasn't worked very well in the past, even when cited sources are used. (eg:[17][18][19][20][21][22][23][24][25]) People have strong opinions on the subject.

By beginning with an acknowledgement of the output-to-input origins of the term, and then describing the more generic later usage, I hope to better satisfy both sides. Trevithj (talk) 23:12, 18 September 2014 (UTC)

Trevithj: This definition covers the whole subject, and details that vary can be supplied by examples or reference to subsections. I don't think an historical approach will work as easily. So far you haven't provided one that does. Brews ohare (talk) 23:35, 18 September 2014 (UTC)

I like Trevithj's idea, in the sense that it gets the original sense of the term in there, in terms of output being fed back to input. It can then be generalized to systems with loops, whether any point is considered an input or an output or not. Dicklyon (talk) 03:47, 19 September 2014 (UTC)

Maybe this way:

Negative feedback is any balancing or self-correcting circle of cause and effect. The term negative feedback originated in the electronics field, where it described the practice of feeding the output signal of an amplifier back into the input with a sign inversion, with the effect that the net gain of the amplifier was reduced.

"Negative feedback is any balancing or self-correcting circle of cause and effect" is inaccurate. It is too general and includes forms of self-correction beyond negative feedback. Use sources. Brews ohare (talk) 05:24, 19 September 2014 (UTC)

I'm unclear on the objection. The quoted passage seems to fit the Camazine and Beerel sources already mentioned above. Then there's Sterman (2000)[26] "negative loops counteract and oppose change" and "processes that seek balance and equilibrium" Trevithj (talk) 10:05, 19 September 2014 (UTC)

Trevithj: If indeed this statement agreed with Camazine and Beerel, the initial proposal that does indeed fit would be preferable as it can be referred to the language of these sources. However, these authors do not suggest all forms of balancing or self-correction fall under 'negative feedback'. Brews ohare (talk) 14:05, 19 September 2014 (UTC)

To this objection might be added that such a description of the use of negative feedback in an amplifier is tortured and muddled at best. Brews ohare (talk) 14:09, 19 September 2014 (UTC)

And additionally, the article already has a substantial history subsection. Brews ohare (talk) 15:13, 20 September 2014 (UTC)

Unfortunate removal of subsection

Dicklyon first, and then Blackburne, have deleted the following addition to the article without discussion on this talk page, certain that their actions require no follow-up:

Psychology. management, and education

In psychology, the term 'negative feedback' is commonly used to label rejection or negative reaction to a subject's response.[1] There is a connection here to the systems view of negative feedback in that such criticism is intended to limit a subject's response and bring it more in line with some objective. However, the term sometimes is used in a variety of organizational settings in a manner more closely related to its use in engineering, such as leadership and management,[2] and education.[3]

Sources

[1] "One type of instruction that may markedly distort individual responses is criticism or negative feedback...The interrogator may make the [subject] adapt himself to the expectations reflected in the interrogator's manner and style of questioning." Gisli H. Gudjonsson, p. 347

[2] "When systems try to change, certain factors support that change (positive feedback) and certain factors counter that change (negative feedback)." Annabel Beerel, p. 52

[3] "[N]egative or corrective feedback is in some instances a necessary condition for second language acquisition." Chun Lai, p. 338

Comments

• In these fields, 'negative feedback' sometimes is used informally to mean "a critical, derogatory, or otherwise negative response", but it also is used more carefully to describe a form of guidance towards an end, much like error-controlled regulation guides a variable to its setpoint. In defense of this addition, no claim is made that it is the best or most complete treatment of this aspect of negative feedback, nor that these sources are the most authoritative or lucid expressions of the role of negative feedback in psychology, management, or education respectively. However the claim is made that these fields do make use of the term 'negative feedback' and frequently cite engineering or cybernetics as its origin in what is unquestionably the topic of this article.

These published views thereby contradict decisively the in-line comment of Blackburne that this contribution "has nothing to do with the topic of this article". Likewise, it seems clear that Dicklyon's in-line comment that this "section exhibits very poor synthesis, including complete misinterpretation of the last source", if merited, should lead to constructive comments about how this addition could be rewritten or better sourced, and should not lead to its summary removal disdaining further comment. Brews ohare (talk) 04:51, 21 September 2014 (UTC)

My view is that it was entirely appropriate to remove that section. It is nothing to do with the topic of this page and it confuses the issue. @Brews, if you really think that the usage in that sense merits inclusion in Wikipedia, then I suggest you create a separate article an put up a disambiguation page. DaveApter (talk) 12:25, 22 September 2014 (UTC)

Dave, I wonder why you think this use of "negative feedback" has nothing to do with article of that name? Two of the cited sources think there is a connection to the systems definition. I believe WP:UNDUE is satisfied by this brief subsection. Brews ohare (talk) 15:16, 22 September 2014 (UTC)

For example Annabel Beerel, p. 52 has an entire section on p. 52 connecting the use of feedback for learning to "system dynamics", apparently drawing upon John D Sterman (2000). Business Dynamics: Systems Thinking and Modeling for a Complex World., a source I do not have access to.

On the other hand, Chun Lai, p. 337 in his article The role of feedback and technology in SLA means by 'negative feedback' the pointing out of student errors in order to alert them to their mistakes and correct them. Personally I don't think that is very different from detecting a 'gap' as a departure of system behavior from its setpoint and using that to correct the system behavior. It might be of interest to note that this concept of negative feedback in learning also is applied in engineering to 'teach' neural networks (also see Bak & Chialvo), with wider applications.

I'll look for more sources, if you think that necessary. Brews ohare (talk) 15:32, 22 September 2014 (UTC)

Your personal odd interpretation of Lai is part of what my edit summary was complaining about. That was clear, was it not? Dicklyon (talk) 17:49, 22 September 2014 (UTC)

Dick: Your opinion is clear, but not your reasoning. Brews ohare (talk) 18:24, 22 September 2014 (UTC)

My reasoning is this: when you say stupid things, it is impossible to talk you out of your odd way of thinking, so I give up. Dicklyon (talk) 19:11, 22 September 2014 (UTC)

Dick: It seems you are too angry to try to make sense. Brews ohare (talk) 19:24, 22 September 2014 (UTC)

No, I'm perfectly fine with how things are going. Dicklyon (talk) 20:02, 22 September 2014 (UTC)

Goodbye, Dick. Brews ohare (talk) 20:11, 22 September 2014 (UTC)

Yes, the form of feedback and the structure of the loop is the same as with negative feedback. But it still isn't negative feedback!

In fact, whole societies were attempted to be constructed based on the idea that this is negative feedback, and they always failed! That's how the hippy community tried to work. They all disbanded, because repeated criticism is, essentially, bullying somebody until they do what you want.

The problem with it isn't the shape of the feedback loop, or the nature of the signal, it's the nature of how the feedback is processed by the humans receiving what is, in the end, criticism.

It turns out that in many cases, humans receiving criticism, overall, get worse at their jobs. That's the opposite of negative feedback in machinery.

And this is not unusual. Management theory is, in many cases, cargo cult science. It takes the forms of science, but very often hasn't been properly tested and very often doesn't work.

Source: All Watched Over by Machines of Loving Grace (TV series)#The_Use_and_Abuse_of_Vegetational_Concepts (the real documentary not the article).GliderMaven (talk) 20:13, 22 September 2014 (UTC)

GliderMaven: You raise the point that although formally a system may follow what looks like negative feedback in determining a performance gap and have in place a system that in theory should reduce the gap, the system may not succeed. I m sure that does happen sometimes. This discussion should appear in this subsection. Brews ohare (talk) 21:32, 22 September 2014 (UTC)

But I'm not convinced it should even be in the article. Most of the references to 'negative feedback' in management theory I've found are solely about criticism, versus 'positive feedback' is about complimenting people. Whereas, in the context of this article, negative feedback should be a mixture of criticism and compliments- in other words they are using 'negative feedback' in a different sense than we are taking it in the rest of the article.

So I would be much happier with a 'for...' at the top to deal with this.GliderMaven (talk) 01:00, 23 September 2014 (UTC)

GliderMaven: Perhaps many times negative feedback is informally used, but this reversion is unwarranted. Brews ohare (talk) 01:06, 23 September 2014 (UTC)

Sourcing Dave's formulation

The formulation in question is:

Negative feedback occurs when some function of the output of a system, process, or mechanism is fed back into the input with a polarity that tends to reduce the fluctuations in the output, whether caused by changes in the input or by other disturbances.

There are some details of wording that could be adjusted. For example, the idea that the definition of 'negative feedback' involves some event or occurrence seems awkward. Maybe a few tweaks like these below would be better:

Negative feedback is the form of feedback in which some function indicative of the performance of a behavior, process, or mechanism is fed back into its operation in a manner that tends to reduce the effect of disturbances upon its output, whatever the origin of these disturbances.

In any case, in the interest of reassuring the reader that this is not a WP invention, but reflective of sources, some sources would be helpful. It seems unlikely that a source that contains this exact wording can be found. A way around this problem would be to present the exact quotes from several sources and indicate how they relate to this WP definition.

Is there any interest in sourcing this lead definition? Brews ohare (talk) 15:23, 19 September 2014 (UTC)

The canard mentioned by Dicklyon: "We don't need sources referenced in the lead, as long as the lead summarizes what's in the article and there are good sources there", however trite, is simply a way to duck this issue of a supportable lead definition. The subsections following in the text illustrate a variety of applications that differ substantially and a general definition that fits all of them is cause of all this brouhaha on the Talk page. Brews ohare (talk) 15:41, 19 September 2014 (UTC)

I've re-added the sentence about equilibrium in the lead, as I'm sure it's broadly accurate, relevant, and useful for giving readers a general sense of the concept. On a related point in the above discussion, I don't agree with the suggestion that there is an essential difference in the concept of negative feedback in the context of an amplifier than in the context of a control system or in biological homeostatic processes. I'll work this idea out in more detail (with refs) shortly. DaveApter (talk) 11:09, 23 September 2014 (UTC)

That there is no "essential difference" between negative feedback in the negative feedback amplifier and that in error-controlled regulation is, of course, not only your belief, Dave, but that of all editors present on this Talk page except for myself. Unfortunately, that consensus is at variance with 40 years of textbook analysis and has no basis in any source, as is made very clear in the subsection on this amplifier. That subsection points out that the so-called 'error signal' in this amplifier has no connection to a 'performance gap' based upon a setpoint, that no 'essential variable' is measured, no setpoint is supplied, and no 'gap' calculated. Instead, this (unrelated) 'error signal' is fixed by the three parameters β. A_OL and the input signal amplitude I, and is in no way minimized or reduced during circuit operation, as is, of course, the entire object of error-controlled regulation, which is devoted to minimizing the 'gap'. Brews ohare (talk) 14:42, 23 September 2014 (UTC)

This operation means that the definition of feedback by Ramaprasad quoted here:

""Feedback is information about the gap between the actual level and the reference level of a system parameter which is used to alter the gap in some way",

does not apply to the negative feedback amplifier. Brews ohare (talk) 16:24, 23 September 2014 (UTC)

To this I add that there is no relation of any kind between the operation of the negative feedback amplifier and homeostasis, because the concept of 'equilibrium' and its maintenance is completely foreign to it. An amplifier's objective, of course, is amplification, not equilibrium. Brews ohare (talk) 14:52, 23 September 2014 (UTC)

It would be desirable that discussion of these points should involve 40 years of textbook analysis, which should not be disparaged (based upon no sources) as a mere 'shadow of what's really going on' and a discussion of 'a secondary effect', both of which claims are based upon personal prejudices and have no basis in fact. Brews ohare (talk) 15:18, 23 September 2014 (UTC)