3 ms·

More optimal, you deleted a word. Not optimal, but closer to optimal. For the problem we're looking at, the bang bang controller is a far better choice IMHO. I

More optimal, you deleted a word. Not optimal, but closer to optimal. For the problem we're looking at, the bang bang controller is a far better choice IMHO. I'd like to see an example of when you think PID is an ideal choice? I've never found a real usecase. Whenever I've hacked one into anything, I've quickly replaced it with something simpler and better (thermostats being the most obvious example).

ad8e 5y ago
https://diffeq.sciml.ai/dev/extras/timestepping/ https://diffeq.sciml.ai/dev/extras/timestepping/ Current best method for solving ODEs is PI control. (At least, when I checked it a few years ago.)
sackerhews 5y ago
A thermostat is certainly simpler than a PID controller. But it can't solve the problem that a PID does.
srean 5y ago
You are throwing around words like 'better', 'optimal', "mathematically simpler" in a way that does not give me a lot of confidence. Seems padded with weasel to the point of being unfalsifiable and vapid. Engineering is a quantitative field after all. I did not claim PID to be optimal. It was your claim that you found ad hoc methods to be more optimal (whatever that is supposed to mean). Surely you would be able to give examples and in what quantitative way you have found them "better", or "more optimal" and in what ways you have found PID to be mathematically complex.
- jcalvinowens 5y ago
  I gave you an example: a thermostat. It's amusingly common to try and apply PID control to these, and the replies to that parent comment highlight several superior alternatives, both in terms of simplicity and optimality. Simplicity is hard to quantify, but it's one of the most important properties of robust and reliable systems. That's not vapid at all: that's engineering.
  - srean 5y ago
    If thermostats are indeed better why doesnt chemical industry use thermostats to control the temperature of the reagents. PID seems to rule the roost there. What problems does a PID face in comparison to thermostat. Does bang bang track the set point better (in terms of some quantifiable error) than a tuned PID ? I would be surprised if missile guidance, drone guidance use bang bang. My hunch would be they use something more sophisticated than PID. Same for something more banal like cruise control in a car set to some cruising speed.
    - jcalvinowens 5y ago
      PID requires very fragile tuning, and that makes it generally inferior to anything that doesn't. > If thermostats are indeed better why doesnt chemical industry use non-PID to control the temperature of the reagents. PID seems to rule the roost there. For the same reason they still use constant speed compressors: it's how it has been done forever, it's good enough, and all the equipment still works. We know better now, we build new ones with VFDs. I'm not saying "let's tear down everything using PID and rewrite it", it obviously works. But if you're writing new code using PID, you're probably wrong.
      - srean 5y ago
        If you are going to sell me a bang-bang controller for cruise control of a mini car or a trajectory tracking of welding robots, or automated gun/fire control to track a moving target while firing at the same time, blaming the lack of bang bang on institutional inertia, then I unfortunately have to call you out for speaking through a hat. Bang-bangs are just not smooth enough and does not give enough control over tracking. With tuning, PID can at least perform within the desired smoothness envelop. PID have been surprisingly robust even if the gains are set far from optimal. There are satisfactory tools and best practices for tuning PIDs. A stuttering car on bang bang cruise control will certainly not be a pleasant ride. Bang-bangs cannot do the job where you have a low inertia, low damping system that cannot tolerate jerks. PID introduces exactly those properties, inertia and damping, but through the controller.

ad8e 5y ago

https://diffeq.sciml.ai/dev/extras/timestepping/ https://diffeq.sciml.ai/dev/extras/timestepping/ Current best method for solving ODEs is PI control. (At least, when I checked it a few years ago.)

sackerhews 5y ago

A thermostat is certainly simpler than a PID controller. But it can't solve the problem that a PID does.

srean 5y ago

You are throwing around words like 'better', 'optimal', "mathematically simpler" in a way that does not give me a lot of confidence. Seems padded with weasel to the point of being unfalsifiable and vapid. Engineering is a quantitative field after all. I did not claim PID to be optimal. It was your claim that you found ad hoc methods to be more optimal (whatever that is supposed to mean). Surely you would be able to give examples and in what quantitative way you have found them "better", or "more optimal" and in what ways you have found PID to be mathematically complex.

jcalvinowens 5y ago
I gave you an example: a thermostat. It's amusingly common to try and apply PID control to these, and the replies to that parent comment highlight several superior alternatives, both in terms of simplicity and optimality. Simplicity is hard to quantify, but it's one of the most important properties of robust and reliable systems. That's not vapid at all: that's engineering.
- srean 5y ago
  If thermostats are indeed better why doesnt chemical industry use thermostats to control the temperature of the reagents. PID seems to rule the roost there. What problems does a PID face in comparison to thermostat. Does bang bang track the set point better (in terms of some quantifiable error) than a tuned PID ? I would be surprised if missile guidance, drone guidance use bang bang. My hunch would be they use something more sophisticated than PID. Same for something more banal like cruise control in a car set to some cruising speed.
  - jcalvinowens 5y ago
    PID requires very fragile tuning, and that makes it generally inferior to anything that doesn't. > If thermostats are indeed better why doesnt chemical industry use non-PID to control the temperature of the reagents. PID seems to rule the roost there. For the same reason they still use constant speed compressors: it's how it has been done forever, it's good enough, and all the equipment still works. We know better now, we build new ones with VFDs. I'm not saying "let's tear down everything using PID and rewrite it", it obviously works. But if you're writing new code using PID, you're probably wrong.
    - srean 5y ago
      If you are going to sell me a bang-bang controller for cruise control of a mini car or a trajectory tracking of welding robots, or automated gun/fire control to track a moving target while firing at the same time, blaming the lack of bang bang on institutional inertia, then I unfortunately have to call you out for speaking through a hat. Bang-bangs are just not smooth enough and does not give enough control over tracking. With tuning, PID can at least perform within the desired smoothness envelop. PID have been surprisingly robust even if the gains are set far from optimal. There are satisfactory tools and best practices for tuning PIDs. A stuttering car on bang bang cruise control will certainly not be a pleasant ride. Bang-bangs cannot do the job where you have a low inertia, low damping system that cannot tolerate jerks. PID introduces exactly those properties, inertia and damping, but through the controller.