Talk:Positive feedback/Archive 1

message: hello, i was just wondering who the author of this article is?  i need to know for referencing the information for my essay.  thank-you very much.  my e-mail is teenateichroeb@yahoo.com
:Greetings.  There is rarely any one author per se on any given Wikipedia article.  I direct you to this page which talks about the best way to go about citing Wikipedia.  Have fun! RadicalBender 16:35, 8 Mar 2004 (UTC)
thread_title:  The author of this article 

message: Rated "high" as high school/SAT biology content. This article needs biological/biochemical examples of feedback regulation, e.g. of enzyme activity or gene expression. It also needs references. - tameeria 00:19, 19 February 2007 (UTC)
thread_title: Untitled

message: I don't understand the gaming examples. --Abdull 21:33, 21 July 2005 (UTC)
replies: text: I'm not sure how to improve the explanation. The idea is that there's an "upward spiral", where improvement in the player's position leads to more and more rapid improvement. Please feel free to edit it, or maybe visit your bookstore and take a look at the source, Rules of Play. Deco 03:55, 23 July 2005 (UTC)
replies: text: These might be good examples in gaming but they're not very good examples. Why do we need examples specifically from gaming anyway?  I think the rest of the article does fine.  Deleting.  Every name is taken12345 09:22, 4 April 2007 (UTC)
thread_title:  games? 

message: Article says "A system in equilibrium in which there is positive feedback to any change in its current state is said to be in an unstable equilibrium, whereas it is possible for one with negative feedback to be in a stable equilibrium." 
What if the gain is less than one. In climate terms a positive feedback with gain of less than one is considered a stable climate. Is this different in other disciplines? crandles (talk) 16:04, 17 February 2009 (UTC)
replies: text: That makes no sense.  Positive feedback should simply be feedback which self-reinforces.  In simple cases, if the feedback factor is smaller than 1 this means amplification, and the output is greater than the input but does not grow infinitely; if the feedback is greater than 1 then it does grow without limit. Negative feedback is similar, it is feedback which attenuates and if it is between 0 and -1 then it simply means the output is smaller than the input, with unstable oscillations if more negative than -1.  One problem is that phrases like gain and loop gain are used in more than one sense. --Rumping (talk) 22:34, 3 February 2010 (UTC)
thread_title:  Is it unstable if gain is less than one? 

message: The second line of the lede says "it will tend to spiral out of control". This is an inappropriate metaphor for such a prominent position in the article. I would suggest something like, 'Under strong positive feedback, most systems quickly move to a limit state, where the limit is provided by external factors, or into some other new stable state where the positive feedback is somehow negated.' Does anybody here have a better or more general wording that does not involve spiralling or any other unlikely convolutions? --Nigelj (talk) 13:23, 5 March 2010 (UTC)
replies: text: Well a week has gone by and nobody has objected or suggested anything better, so I have made the change. While I was at it I tidied up some other wording in the lede. --Nigelj (talk) 13:35, 13 March 2010 (UTC)
thread_title:  Spiralling 

message: Altered 'in biology' section slightly in order to link to the Ferguson reflex, which is the name of the contractions mentioned. Medical Sciences (Edited by Naish, Revest and Court) is where I found this, in the endocrinology chapter.  —Preceding unsigned comment added by 138.253.88.75 (talk) 22:28, 3 November 2010 (UTC)
thread_title:  Ferguson Reflex 

message: Positive feedback in dynamic systems has a additive or multiplicative effect. A latch built with NAND or NOR gates fails the test for positive feedback in 2 ways. 1: The bubble on the end of the gate is an inverter. Thus, the feedback is negative, not positive. 2: digital (logic) feedback is not accumulative/multiplicative as it is with e.g., thermal runaway. --Bill Huston  (talk)
:That is wrong. I have included that diagram here to help this discussion. First, notice two little bubbles. From the input next to the S, you go through the bottom inverting gate, then the top one before coming back to the input next to the S, that's two inversions of sense and so is positive feedback. Second, who heard of a circuit being held in a limit-state, with all outputs hard against the supply rails, with no input and negative feedback? The only thing that drives every component in a circuit against the rails and keeps it there is positive feedback (or an extreme input, which is not necessary for a latched flip-flop). Third, we think of logic gates as 'digital' with only two states, but they don't know that; they are made entirely of analogue components inside the chips - MOSFETs or other transistors, diodes or resistors. You can make a flip-flop out of any low-gain analogue transistors and it will latch hard against the supply rails as soon as you switch it on, that's only because of the extreme positive feedback having additive and multiplicative effects. Here are two references that support this explicitly:  and  , from a simple google search. I'm going to reinstate the section, per WP:BRD. See if you can find a reference that says flip-flops latch because of negative feedback. --Nigelj (talk) 20:46, 4 November 2010 (UTC)
thread_title:  A flip-flop/latch is NOT positive feedback! 

message: I moved the material on psychology to a new 'In psychology' section.  So revealed, it is sorely lacking, having discussion of two references on gifted children, and nothing else.  What was left in the biology section, I split into physiology and evolutionary biology subsections.  I deleted some editorial asides and original research/synthesis.
Robertmacl (talk) 19:07, 29 December 2010 (UTC)
thread_title:  In biology 

message: I would like to propose that this diagram (in its current form anyway) be moved out of the lead. Despite its implied generality, I believe it is actually quite specific to electronics. It uses a definition of feedback type that is not generic - the sign of the feedback signal (Nyquist and Bode), and is very likely based on Black's and Bode's work related to the negative feedback amplifier. While very important in the development of the concepts of positive/negative feedback, this work introduces some confusion here: this article is specific to positive feedback, while the model is associated with negative feedback.
It also doesn't work easily with examples given. It is not obvious what the inputs/outputs are of a cattle stampede, nor how the β function would apply to the feedback. A simpler two-attribute causal loop diagram would work - e.g., number_of_animals_running and overall_level_of_fear reinforcing each other.
I agree that a clear diagram is a good idea in the lead. The other lead images depict specific examples of positive feedback, not generic models, so I had added the simplest diagram I could find, using the example of compound interest. The diagram was easy to follow, uses a familiar example, and is of a form commonly used in system dynamics literature to explain the concept.
As my initial edit was reversed, I ask for wider opinions on this suggestion. -- Trevithj (talk) 21:58, 18 April 2012 (UTC)
replies: text: Added an example diagram as described above, to illustrate the existing stampede example. -- Trevithj (talk) 23:31, 2 May 2012 (UTC)

text: Moved image as discussed. Added cited text, based on only published reference that I could find for "ideal feedback model" other than wikimedia (W Chen 1993), although likely based on Hendrik Bode's work. -- Trevithj (talk) 21:31, 7 May 2012 (UTC)
thread_title:  Use of 'ideal feedback model'