5 ms·

It is a positive feedback loop, not a negative feedback loop. See https://en.wikipedia.org/wiki/Positive_feedback https://en.wikipedia.org/wiki/Positive_feedba

by 1e-9 5y ago

It is a positive feedback loop, not a negative feedback loop. See https://en.wikipedia.org/wiki/Positive_feedback https://en.wikipedia.org/wiki/Positive_feedback.

robotresearcher 5y ago
It’s negative WRT the chip production rate.
- tbihl 5y ago
  No, still positive. Negative feedback is self-righting, while positive feedback is amplification (to speak in very broad terms.)
  - deleted 5y ago
    [deleted]
  - throwawaygh 5y ago
    No! It's negative WRT chip production rate! I have a phd in controls and meant what I said; I assume roboticsresearcher also knows some freshman-level control theory ;-). Stability ==== good in undergrad engineering, but not here. We DON'T want production rate to be stable when we have a global supply shortage! Here, a negative feedback loop is stabilizing the system in an undesirable equilibrium. I.e., the function that's being controlled in "supply of chips", the stable state is "saturated supply", and the negative feedback loop that maintains that equilibrium is "starving chip fab suppliers". (meta: people down-voting comments on control theory terminology by two different experts in this field at least makes me feel a bit better about the signal:noise ratio on the vote counts on my other comments in this thread ;))
    - alisonkisk 5y ago
      It's not stabilizing if the economy is in a death spiral of failing interdependent companies who can't produce machines for each other.
      - robotresearcher 5y ago
        In control terms it is. There’s a stable asymptote of ‘we made no machines today’ every day, until some external process breaks the dependency cycle.
    - saltcured 5y ago
      Only partially facetious here: you have mistakenly decided that it it clamps at zero. If we consider the hoarding aspects, the feedback continues into net negative chip availability. Before long, there will be roving gangs of looters taking back the chips you thought you already had! ;-)
      - throwawaygh 5y ago
        Yes, it's fair, I do assume that chip supply/demand isn't subject to the forces of roving gangs of looters :)
    - tbihl 5y ago
      That's fair. I was looking at it wrong.
- a9h74j 5y ago
  It does have negative external effects, as you observe, in the sense of a viscious circle. But even a viscious circle, mathematically, has positive feedback, resulting initially in a positive exponent growing against time, not a negative exponent damping out in time.
  - robotresearcher 5y ago
    Doesn’t positive feedback require a positive loop gain? Right now, not enough chips are available to make new chips. So the loop gain is less than zero, damping the output recursively.
    - throwawaygh 5y ago
      I'm also confused by the confusion here... probably naive pattern matching? Reminds me of TAing undergrad courses where you could get more than half the class to confuse "positive feedback" and "negative feedback" on a midterm by just giving examples where stability = bad :)
      - deleted 5y ago
        [deleted]
      - robotresearcher 5y ago
        Grandparent gives the choices of ‘positive exponent growing against time’ or ‘negative exponent damping out against time’. Here we have a positive exponent damping (reducing) the output over time, because it’s value is less than one, resulting in a negative loop gain. The Wikipedia article linked up thread defines positive feedback as having positive loop gain, and negative feedback negative loop gain.
        a9h74j 5y ago
        IIRC, generally a positive loop gain greater than one will lead to diverging behavior aka instability, whereas even a positive-sign to feedback, if loop gain is "less than one" will not. I might be brain-farting here, but I cannot be precise anyway, which IIRC gets into plotting poles in a complex plane. (Cue joke my applied math professor would tell, about why all the Polish people were asked to sit in the right-hand aisle of an aircraft.)
- freemint 5y ago
  Negative Vs positive is about the eigenvalue of the feed back loop not about the weighting how it affects external signals
- dev_tty01 5y ago
  No, there is a shortage, leading to a shortage, leading to a shortage, ... If it was negative feedback, the "error" (shortage in production) would lead to an error cancelling signal, and therefore an increase in production. Positive feedback has error leading to larger error, shortage leading to more shortage.
- aidenn0 5y ago
  And it's positive WRT the shortage of chips (a small shortage leads to a larger shortage and so on).
- GuB-42 5y ago
  Negative feedback means the feedback coefficient is negative, you are trying to redefine the usual meaning. It is like saying that I tested positive for COVID-19 WRT my health because I don't have the virus, it is not what a positive test means and it will confuse anyone who knows the correct terminology.

by 1e-9 5y ago

It is a positive feedback loop, not a negative feedback loop. See https://en.wikipedia.org/wiki/Positive_feedback https://en.wikipedia.org/wiki/Positive_feedback.

robotresearcher 5y ago

It’s negative WRT the chip production rate.

tbihl 5y ago
No, still positive. Negative feedback is self-righting, while positive feedback is amplification (to speak in very broad terms.)
- deleted 5y ago
  [deleted]
- throwawaygh 5y ago
  No! It's negative WRT chip production rate! I have a phd in controls and meant what I said; I assume roboticsresearcher also knows some freshman-level control theory ;-). Stability ==== good in undergrad engineering, but not here. We DON'T want production rate to be stable when we have a global supply shortage! Here, a negative feedback loop is stabilizing the system in an undesirable equilibrium. I.e., the function that's being controlled in "supply of chips", the stable state is "saturated supply", and the negative feedback loop that maintains that equilibrium is "starving chip fab suppliers". (meta: people down-voting comments on control theory terminology by two different experts in this field at least makes me feel a bit better about the signal:noise ratio on the vote counts on my other comments in this thread ;))
  - alisonkisk 5y ago
    It's not stabilizing if the economy is in a death spiral of failing interdependent companies who can't produce machines for each other.
    - robotresearcher 5y ago
      In control terms it is. There’s a stable asymptote of ‘we made no machines today’ every day, until some external process breaks the dependency cycle.
  - saltcured 5y ago
    Only partially facetious here: you have mistakenly decided that it it clamps at zero. If we consider the hoarding aspects, the feedback continues into net negative chip availability. Before long, there will be roving gangs of looters taking back the chips you thought you already had! ;-)
    - throwawaygh 5y ago
      Yes, it's fair, I do assume that chip supply/demand isn't subject to the forces of roving gangs of looters :)
  - tbihl 5y ago
    That's fair. I was looking at it wrong.
a9h74j 5y ago
It does have negative external effects, as you observe, in the sense of a viscious circle. But even a viscious circle, mathematically, has positive feedback, resulting initially in a positive exponent growing against time, not a negative exponent damping out in time.
- robotresearcher 5y ago
  Doesn’t positive feedback require a positive loop gain? Right now, not enough chips are available to make new chips. So the loop gain is less than zero, damping the output recursively.
  - throwawaygh 5y ago
    I'm also confused by the confusion here... probably naive pattern matching? Reminds me of TAing undergrad courses where you could get more than half the class to confuse "positive feedback" and "negative feedback" on a midterm by just giving examples where stability = bad :)
    - deleted 5y ago
      [deleted]
    - robotresearcher 5y ago
      Grandparent gives the choices of ‘positive exponent growing against time’ or ‘negative exponent damping out against time’. Here we have a positive exponent damping (reducing) the output over time, because it’s value is less than one, resulting in a negative loop gain. The Wikipedia article linked up thread defines positive feedback as having positive loop gain, and negative feedback negative loop gain.
      - a9h74j 5y ago
        IIRC, generally a positive loop gain greater than one will lead to diverging behavior aka instability, whereas even a positive-sign to feedback, if loop gain is "less than one" will not. I might be brain-farting here, but I cannot be precise anyway, which IIRC gets into plotting poles in a complex plane. (Cue joke my applied math professor would tell, about why all the Polish people were asked to sit in the right-hand aisle of an aircraft.)
freemint 5y ago
Negative Vs positive is about the eigenvalue of the feed back loop not about the weighting how it affects external signals
dev_tty01 5y ago
No, there is a shortage, leading to a shortage, leading to a shortage, ... If it was negative feedback, the "error" (shortage in production) would lead to an error cancelling signal, and therefore an increase in production. Positive feedback has error leading to larger error, shortage leading to more shortage.
aidenn0 5y ago
And it's positive WRT the shortage of chips (a small shortage leads to a larger shortage and so on).
GuB-42 5y ago
Negative feedback means the feedback coefficient is negative, you are trying to redefine the usual meaning. It is like saying that I tested positive for COVID-19 WRT my health because I don't have the virus, it is not what a positive test means and it will confuse anyone who knows the correct terminology.