Can someone clarify negative feedback for me?

[Seeking Science]

Is feedback negative when AB < 0 or when 1/(1 - AB) < 1? Correspondingly, is feedback positive when AB > 0, or when 1/(1 - AB) > 1? I've found nothing but conflicting information on this.

Also, while species, hormones, nutrients, and even entire populations are governed via negative feedback, how does one determine what A and B are? In a furnace, for example, governed via a thermostat, this is clearly a negative-feedback system. But what is A in this case, what is B, and which equation quantifies it as a negative-feedback system? AB < 0? Or 1/(1 - AB) < 1? According to my calculations, it's not possible for both equations to be valid.

I need to know the answer to this in order to go forward with my work, so I really appreciate any help on this matter.

[timo]

Is AB from a subset of the real numbers and smaller than +1, by chance? In that case, the two expressions are equivalent. Hope that helps. But if you don't even know what A and B is yourself, then I believe you still have very fundamental problems to solve in your work.

Edited March 18, 2013 by timo

[Seeking Science]

I mostly need an example of how the correct equation can be solved and am unable to find one. Understanding how it would be solved for a furnace or any other negative-feedback system would send me in the right direction.

Edited March 18, 2013 by Seeking Science

[Ringer]

There are different ways of how negative feedback work in certain circumstances because there are multiple ways negative feedback can work, but, IIRC, it doesn't get that complicated until you work with electromagnetism (which is all just magic anyway). I don't think that matters in a biological system, either of the two should work.

 

Maybe you should define your variables, because I'm just assuming they're representing production rates or concentrations at a certain time. So A could be t(0)=[hormone] and B could be t(x)=(A - [hormone]). A negative feedback gives a negative for AB.

[Seeking Science]

You mentioned electromagnetism. Can you explain more about how that would involve negative feedback, as that's actually much closer to what I'm trying to quantify than any of the other examples mentioned here. If it's as complicated as you say, maybe you could point me to a book, etc. where I could learn to understand it.

 

Thanks for the earlier info btw. Having suspected that A & B might involve rates as well, it sounds like there's a light at the end of tunnel.