[HN Gopher] The Fundamentals of Control Theory
___________________________________________________________________
The Fundamentals of Control Theory
Author : teleforce
Score : 206 points
Date : 2022-10-03 17:51 UTC (5 hours ago)
(HTM) web link (engineeringmedia.com)
(TXT) w3m dump (engineeringmedia.com)
| seiferteric wrote:
| I took control theory in my undergrad EE degree and did fun
| project of making a analog PID control from scratch using OpAmps,
| potentiometers for setting weights for P,I&D signals as well as
| input and output sensing, a motor for output which positioned a
| stick to point in the direction of the input dial. Was great to
| see how it responded when changing or disabling P,I or D.
|
| I only have a basic understanding of machine learning however,
| but am I completely wrong in seeing a lot of overlap in control
| theory? Seems like a ML model is like a bunch of controllers (not
| necessarily PID, or even linear) in parallel with a weight and a
| bunch of outputs in parallel and the difference between your
| desired output and the input is your error signal.
| rcxdude wrote:
| Kinda-sorta. ML is a bit more about optimisation theory, not
| control, but there's a lot of overlap: you can consider
| controllers to be optimisers, and optimisers can be used in
| control (a sub-field called optimal control). One big
| constraint in control is it has to be causal, i.e. it only sees
| part of the function it is trying to optimise (the part that is
| in the past) and only has the ability to influence part of the
| input in the system it is optimising (the part in the future).
| Control also has a huge amount of overlap with signal
| processing, both analog and digital (most of the math is
| basically the same).
| ah27182 wrote:
| Are you responding to the link? I didnt see ML being
| mentioned...
| seiferteric wrote:
| Sorry the ML is just a tangent.
| vitaminCPP wrote:
| Brian Douglas is certainly one of the great teacher of control.
| That said, this books is, to my knowledge, a incomplete and
| abandoned project.
|
| I would recommend checking it's YouTube channel instead.
| kragen wrote:
| You know, the license is CC BY-NC-SA, not BY-NC-SA-ND. You have
| every legal right to finish it. (Did he publish the LaTeX
| source too, or do you have to reverse-engineer it?)
| ubj wrote:
| Yep, looks like you're right that the book is incomplete:
| https://www.patreon.com/posts/book-is-now-free-28313078
|
| Sounds like he's still open to continue working on it in the
| future though:
|
| > Perhaps something will re-motivate me in the future and I'll
| get back to writing this book. In the meantime, I hope it's of
| some use to you.
| amelius wrote:
| I'm worried the field will increasingly become a niche where ML
| takes over cases where accuracy guarantees are not very
| important, time-to-market is important or where complexity rules
| out mathematical modeling.
| belkarx wrote:
| Another source for simple to digest, _useful_ fundamentals:
| https://file.tavsys.net/control/controls-engineering-in-frc....
|
| This was originally created as a guide for high schoolers for
| robotics but goes into relative depth (the subtitle is "Graduate-
| level Control Theory for High Schoolers). I personally found it
| quite useful for intuitive understanding of how control systems
| work.
|
| Prerequisites: linear algebra
| kken wrote:
| Book looks well made. His youtube channel seems to be here:
|
| https://www.youtube.com/controllectures
|
| Control theory is a really fundamental topic that is useful in
| many disciplines. The field has some very pragmatic approaches.
| umutcnkus wrote:
| It is always good to see control theory related posts on HN. (:
|
| I've both BsC and MsC in control and heavily used video lectures
| of Brian, I am probably one of his first patrons. His lecturing
| skills are amazing. If you interested about the topic I also
| suggest to look at 'Steve Brunton' YouTube channel. He is also a
| legendary teacher.
|
| If you want to talk anything about control theory, please feel
| free to contact me.
| lagrange77 wrote:
| What do you mean by BsC and MsC in control? That you wrote your
| Bachelor and Master thesis at the control theory department? No
| front, i'm just curious, because that's what i did, but i
| always referred to my degree as having a M.Sc. in MechE, in my
| case.
| ubj wrote:
| If anyone's studying control theory, you're doing yourself a
| disservice if you don't use Brian Douglas's resources. His videos
| on YouTube are phenomenal at explaining not only the theory and
| techniques, but why you should care in the first place.
|
| Also, why should anyone study control theory? It's the math
| behind making real-world systems perform what you want them to
| do. In particular, robotics and autonomous vehicles rely heavily
| on techniques from control theory.
|
| If you watch Brian's videos, keep in mind that they bifurcated
| into two places: his original videos [1], and his more recent
| MATLAB tech talk videos [2].
|
| [1]: https://www.youtube.com/controllectures
|
| [2]: https://engineeringmedia.com/videos
| lagrange77 wrote:
| > If anyone's studying control theory, you're doing yourself a
| disservice if you don't use Brian Douglas's resources.
|
| The same is true for Steve Brunton. Control theory, systems
| theory, computational engineering and the interface of the
| latter to ML.
|
| https://www.youtube.com/channel/UCm5mt-A4w61lknZ9lCsZtBw
| mhh__ wrote:
| Terry Davis did a nice intro to PID controllers when he demoed
| his physics simulator
| scrlk wrote:
| I assume it's this video ("Terry Davis Demos SimStructure
| (2016-08-25)"): https://www.youtube.com/watch?v=25hLohVZdME
|
| He starts talking about PID controllers at around 3:40.
| syntaxing wrote:
| MechE here. Control Theory surprisingly is only mandatorily
| taught to MechE (at least in the US). It was also arguably the
| hardest class I took in my 3 semester of hell (junior year +
| first semester of senior year). Huge props to you if you can
| learn this on your own. A lot of the fundamental math (a ton of
| Laplace transforms) and block diagram analysis is hard to follow
| without some guidance.
|
| Edit: Interesting, I went to a ABET accredited college and my EE
| counterparts did not take control systems. Where we were told
| that we had to take it because of our (MechE) ABET requirements.
| hprotagonist wrote:
| US ABET BME here.
|
| we for sure took mandatory signals and controls, and we
| basically regarded ourselves as EEs whose circuits tended to be
| squishy and alive.
|
| A disgustingly useful class, and damn hard.
| lux_scintilla wrote:
| I think it must vary by institution. For a second data point.
| EE here from an ABET accredited US University. Controls &
| Discrete Controls was mandatory for EE. No other engineering
| major at the school, including MechE, had this requirement.
| jay3ss wrote:
| Nearly the same for me. Continuous controls was a requirement
| for graduating with my BSEE. I don't believe that it was
| required for the MEs.
| soitgoes511 wrote:
| Not exactly true. I have an electrical engineering degree from
| the US and took Systems and Controls. So, this is definitely
| not only taught to ME's..
| runnerup wrote:
| Also is a hard requirement for chemical engineers.
|
| Additionally I find some of controls theory to be relevant
| context for machine learning models, in particular
| backpropagation.
| anthomtb wrote:
| Was it mandatory though? I took a Control Theory class for my
| Electrical and Computer Engineering undergrad degree in the
| US. But it was a senior/graduate-level elective and not
| required to graduate.
|
| Minor aside, the class was the best of all my electives. I
| picked it based on advice from a friend who said "choose your
| electives based on the professor, not the material." One of
| those bits of advice I wish I'd absorbed (I'm sure I'd been
| told) earlier in my school career.
| soitgoes511 wrote:
| Controls was indeed a mandatory EE undergrad class at my
| University (also ABET accredited).
| avindroth wrote:
| It seems like the author assumes that the page is accessed from
| his youtube channel, but as someone who just landed on the
| webpage with no awareness of his channel, some synopsis of the
| book would be nice.
| kragen wrote:
| The book cover has a very quick summary in the form of
| cartoons, but the table of contents (pp 3-4/160) has a list of
| what it covers, the preface (pp. 5-7/160) explains the
| motivations and has a little more color on what it colors, and
| the first chapter (pp. 9-42/160) has a really good overview of
| control theory including cartoons and a dialog with Ctesibios.
| bob1029 wrote:
| I don't recall much about control theory from university, but the
| one thing that did stick was state-space representation.
|
| The part that got me was that you could take this arbitrarily-
| complex LTI system and basically turn it into a matrix that
| encapsulates everything. Any given state the system could exist
| in becomes a simple vector. Lots of crazy compositional
| techniques exist once you get your problems into this kind of
| shape.
| anyfoo wrote:
| Similarly, I like how any LTI system is just poles and zeroes
| in the s-plane. Or, if your system is sampled (DSP, and
| actually most signals you'll deal with in a computer), in the
| z-plane.
|
| But not just every LTI system, ever sampled _signal_ is poles
| and zeroes in the z-plane.
|
| I have used that fact for years, and it still blows me away
| from time to time. Laplace and z-transforms are pretty magical,
| more so than Fourier even (which is basically a special case).
| twawaaay wrote:
| I can highly recommend control theory to all software engineers
| designing high throughput systems.
|
| It is sometimes super useful to think about large systems with
| high traffic of requests/messages as something that can be
| controlled.
| agumonkey wrote:
| Digital computers are turning into analog ones.
| WJW wrote:
| My favorite was a DB project where the DB would accept DELETEs
| faster than the SSD could write them to disk. The eventual
| solution was to implement a proportional controller that looked
| at the "still to be persisted to disk" backlog and kept it at
| ~66% of the value at which the DB would stop accepting queries
| by selectively inserting sleeps into the DELETE-submitting
| process. We could have fixed it at some known-good but low
| value, but implementing a controller enabled us to speed up
| during the night (when there was low user traffic) and still
| not stress the db too much when a lot of users were online.
| twawaaay wrote:
| Yeah, I especially like to use CT for reducing configuration
| parameters or to replace meaningless configuration parameters
| (requests per second, batch sizes) with more meaningful ones
| (acceptable latency, acceptable failure rate).
| lanstin wrote:
| That's a good qualification - if you aren't having to worry
| about these maths, you aren't doing high volume.
___________________________________________________________________
(page generated 2022-10-03 23:00 UTC)