[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)