Does anyone know the difference between positive and negative feedback loops and how each of them work? Examples would be awesome, too. I seem to have a sporadic understanding of this concept-- I learn it and then promptly forget it. Thanks in advance everyone! Please Register or Log in to view the hidden image!
*Sorry I don't have time to go in depth on this, but to get things rolling I'll give a basic description.* Initially Feedback Loops enhance or buffer changes that occur in a system. A positive connection is when a change (increase or decrease) in a variable causes the same change in the second variable (increase/increase or decrease/decrease). Since it is a direct proportionality it is considered positive. A negative connection is similiarly when a change (increase or decrease) results in an inverse propotionality change in the second variable (increase/decrease or decrease/increase). When these two connections are combined you have a negative feedback loop due to +(-) = - One must multiply all the signs of all the connections around a loop to find out wether it is a positive or a negative feedback loop in more complicated loop structures. In general Negative feedback loops tend to dampen or buffer changes, tending to hold a system in an equilibrium state, making it more stable. Positive loops on the other hand will result in unlimited growth (until checked) and are considered vicious cycles. So in general positive feedback loops enhance or amplify changes, tending to move a system away from an equilibrium state, making it more unstable. Hope that helps get things started
Good job AMansAmoeba try to simplify though. Here Lets make feedback loops If X>0 X+1 End The result is a positive feed back loop: X keeps getting larger once you have pasted the threshold (>0) and won’t ever stop within the bounds of that loop. A real positive feed back loop that you can make is putting a microphone and speaker together: in under a second the noise will be horribly loud. Here is a negative feed back loop If X>0 X-1 End What ever value you place for X it will minus it off tell it reaches 0 or less then. Bounce a spring or rubber band and it will eventually reach stable.
Generally the whole deal with feedback which isn't clear in either previous posts is that the output is linked to the input. The most common example being "feedback" when you have a microphone that gets too close to the speaker it's attached to and the sound just keeps getting louder. Since an increase in the current loudness of the speaker, leads the future loudness to be greater it is an example of positive feedback. In negative feedback the louder the current volume, the louder you would have to yell into the microphone to make the same noise. In general as mentioned positive feedback leads to choice of state, while negative feedback leads to maintenance of state. In biology cell differentiation into a certain cell type uses positive feedback and homeostatic systems like metabolism involve negative regulation.
