[HN Gopher] You need to know what right-half-plane zeros are
___________________________________________________________________
You need to know what right-half-plane zeros are
Author : jbay808
Score : 393 points
Date : 2022-06-10 02:40 UTC (20 hours ago)
(HTM) web link (jbconsulting.substack.com)
(TXT) w3m dump (jbconsulting.substack.com)
| bob1029 wrote:
| This stuff is fun. Surprised I haven't seen direct mention of
| state space representation yet:
|
| https://en.wikipedia.org/wiki/State-space_representation
|
| I recall going through this at university and it being a bit of a
| struggle. Looking back at it now, this stuff makes a lot more
| sense. A decade+ of practical experience probably helps.
| lordnacho wrote:
| Shouldn't there be a diagram of the complex plane so that people
| can see what it's the right half plane of? On top of it, there's
| a picture of a plane which is confusing.
|
| Fascinating subject though, in engineering class it was quite
| surprising how this bunch of functions tracing lines and dots on
| the complex plane would be relevant to just about everything.
| Perhaps the first lesson is that even if you know how a system
| works, you can't just take the inverse function to control what
| comes out.
| rhn_mk1 wrote:
| I felt that the article ended just where it was ripe to dig
| into the maths.
| jbay808 wrote:
| > Shouldn't there be a diagram of the complex plane so that
| people can see what it's the right half plane of?
|
| Author here. Yes! Very fair criticism. I was trying to strike a
| balance between making the concept approachable for those who
| don't have a background involving complex numbers, but that
| certainly leaves the name of the concept more confusing. I
| should add it in a footnote at least.
|
| And I did honestly not think about the potential for confusion
| between plane // airplane. An airplane was the most familiar
| example system I could think of to explain the concept. Oops!
|
| > Perhaps the first lesson is that even if you know how a
| system works, you can't just take the inverse function to
| control what comes out.
|
| That's a great point too. It probably even deserves its own
| article.
| l33t2328 wrote:
| > the potential for confusion between plane // airplane
|
| This reminds me of the famous (possibly apocryphal) story of
| the algebraic geometer of middle eastern descent who was
| brought aside by Air Marshals for talking about how a
| particular problem could be solved by "blowing up points on a
| plane"
| wbl wrote:
| At Berkeley the legend is that there was a class on blowing
| up with special application to local problems.
| LeonB wrote:
| Really good article. Make changes and corrections to it,
| sure, but be careful not to over react to the criticism and
| make too many changes such that you then get even more
| critical feedback and make more corrections and get worse
| feedback and bigger corrections and oh god help me worse
| feedback and bigger changes and stop me please worse feedback
| and help bigger changes seriously kill me bigger feedback
| worse changes arggggh
| ehvatum wrote:
| If you haven't read it, I recommend:
| https://www.gutenberg.org/files/6949/6949-h/6949-h.htm
| yesenadam wrote:
| The main thing missing for me: presumably if there's a plane,
| you're graphing something vs something. What are the X and Y?
| (or, uh, the x and y in the x+iy) Talk of a plane remains
| rather vague without knowing that. Maybe I missed it, but I
| looked twice, and read the comments on this page, and
| couldn't see it mentioned at all. There are a couple of
| graphs/planes, but they seem to be a different kind of thing.
| mellavora wrote:
| It is the complex plane, x is real, y is imaginary.
|
| the author should have clarified this, you are correct, as
| the author also makes clear he is writing for a non-
| technical audience.
|
| He probably forgot to mention it because the concept is so
| fundamental to signal processing that he assumed it was
| common knowledge.
| stephen_g wrote:
| Wikipedia has it highlighted on the graph:
| https://en.wikipedia.org/wiki/Right_half-plane
|
| Also see page 4 here:
| https://web.mit.edu/2.14/www/Handouts/PoleZero.pdf
| yesenadam wrote:
| Uh that first link is just a picture of a right complex
| half-plane... I know what that is, having done quite a
| bit of complex maths, but the kind that uses _i_ , not
| the kind that uses _j_ , e.g. I love _Visual Complex
| Analysis_. I just don 't know what things are being
| graphed in the article! Sorry I didn't explain better. Ok
| thanks for the 13pp article, I will have a look sometime
| soon. I was hoping someone could just tell me the answer.
|
| edit: I looked at the first few pages of the paper but I
| feel none the wiser, at all.
|
| edit2: Ah... "the poles and zeros of a transfer function
| may be complex, and the system dynamics may be
| represented graphically by plotting their locations on
| the complex s-plane". The transfer function (whatever
| that is) is a rational function of the complex variable
| _s_ , i.e. (in my words) it's a fraction with complex
| polynomials for numerator and denominator. The _zeros_
| are the roots of the numerator and the _poles_ are the
| roots of the denominator.
|
| Ok, I still don't know what the transfer function is or
| means or comes from, but am much less in the dark, thank
| you! :-)
| jayjader wrote:
| I see that /u/metaphor has given you some formal
| references.
|
| I'd like to chime in with a more intuition-based
| explanation of what transfer functions are, from my
| recollections of college control theory classes in both
| electrical signals and a more general "systems
| engineering" application:
|
| Basically, the transfer function is a different
| perspective on modelling/representing a system's output
| as a function of its input. Classically, when modelling
| and/or reasoning about a system in physics, the
| perspective we adopt is that of "input" being the forward
| advance of time (and sometimes initial conditions) and
| "output" being the amplitude of the physical
| quantity(ies) or dimension(s) of the system that
| interest(s) us. The transfer function, then, is when we
| switch perspectives to consider the "input" to be a
| sinusoidal signal (characterized by amplitude and phase
| over time), and the "output" is the new amplitude and
| phase of that signal [after "traversing" the system]. Of
| course, you're actually working with a closed-loop, but
| most input/output systems can be modeled as a closed-loop
| if you sufficiently broaden the system's boundaries.
|
| This turns out to be useful for/in several
| reasons/contexts:
|
| - many physical phenomena are sine waves (or, thanks to
| Fourier, a sum of sometimes many different sine waves),
| and often times a system's purpose (to us humans) is to
| control such a phenomena precisely along the lines of "do
| this to the amplitude, and/or adjust the phase like so" -
| dampening, feedback loops, more sophisticated processes
| like hysteresis, maintaining a steady state given
| incoming perturbations, etc. In these cases the transfer
| function ends up being the mathematical expression of
| that system's function in the "domain language" of that
| problem, so to speak.
|
| - It turns out that often, when working with systems
| whose "classical" representation involve components like
| exponentials or sine and cosine of time (which are "just"
| complex exponentials of those quantities), the
| corresponding transfer functions are "simple" fractions
| of polynomials. More precisely, passing into the
| Langrange domain allows transforming a differential
| equation problem into a complex polynomial fractions
| problem - often much easier to crunch/solve. Furthermore,
| in the Lagrange domain, de-phasing a signal by pi/2 is
| equivalent to simply adding 1/(j * signal's frequency) to
| that signal (if I recall correctly). This makes much of
| the math more accessible to human intuition, and
| especially on more complex systems that have several
| "moving parts" the linear quality of polynomials becomes
| invaluable.
|
| Personally, I remember quickly adopting, once I'd grokked
| it, the transfer function perspective when trying to
| reason about the effect of introducing a capacitor into
| an existing circuit - analog or DC[0] - as well as things
| like how the material properties of a door contribute to
| its behavior as a low-pass filter on sound waves. Sitting
| down and doing the math, the formulas that I would arrive
| at spoke much more clearly to me. Also, you are sort of
| adopting a "time-agnostic" (or perhaps time-invariant)
| perspective, where the system itself does not change over
| time. Instead, its' input is characterized by how it
| behaves over time, and the transfer function (especially
| when plotted) gives you a clear, direct sense of what the
| output's "behavior over time" will accordingly be.
| Notably, it's here that the zeroes of the OP become so
| meaningful.
|
| [0]: part of what initially started making things "tick"
| for me was when a professor explained that an impulse on
| an input signal (i.e. a quasi-instant variation, then
| back to the preceding "steady state" value of it - i.e. a
| DC current "turning on"), to a transfer function, "looks
| like" a sine wave signal with a constant amplitude but
| monotonously increasing phase offset - again I forget if
| the rate is constant, polynomial, exponential or what.
| yesenadam wrote:
| You had me at "a more intuition-based explanation of what
| transfer functions are". :-) Thank you so much for this.
|
| edit: By "Lagrange" did you possibly mean to write
| "Laplace"? I confuse those two gentlemen too. p.s. I just
| learnt Lagrange was Italian! born Giuseppe Luigi
| Lagrangia.
| metaphor wrote:
| > _I know what that is, having done quite a bit of
| complex maths, but the kind that uses i, not the kind
| that uses j_
|
| Some things in life leave a lasting impression[1].
| :eye_roll:
|
| It sounds like what you're looking for is an explanation
| of root locus analysis[2].
|
| In the simplest control case, a transfer function is
| nothing more than the expression of a continuous closed-
| loop LTI system's output Y(s) over its input X(s) in the
| Laplace domain, conveniently abstracted as its forward
| path G(s) and negative feedback path H(s).
|
| From there, Routh-Hurwitz method[3] can be used to
| determine stability of the system.
|
| ...and I will continue to use _j_ , thanks.
|
| [1] https://youtu.be/1rqJl7Rs6ps?t=1828
|
| [2] https://en.wikipedia.org/wiki/Root_locus
|
| [3] https://en.wikipedia.org/wiki/Routh%E2%80%93Hurwitz_s
| tabilit...
| yesenadam wrote:
| hehehe Thank you very much! :-) Funny video. I'll check
| out that course. Thanks for the links.
|
| edit: Took a lil while to work out that LTI system is
| _Linear time-invariant system_.
|
| https://en.wikipedia.org/wiki/Linear_time-
| invariant_system
| lordnacho wrote:
| I'd definitely read a series about control theory. The first
| time round was very badly presented at my university. A lot
| of math, motivation hidden.
|
| Stuff like Nyquist criterion just sort of appears out of
| nowhere as functions.
|
| I guess the big one is feedback being the magic, and then the
| complex plane tells you where that blows up.
| pid-1 wrote:
| I went down this rabbit hole in grad and my opinion is that
| Control Theory is good for writing academic papers, but has
| few applications besides the classical ones (mostly in
| mechanics).
|
| Techniques often need very strong assumptions about the
| systems being modeled, which severely limits their
| usefulness.
|
| In fact, CT is sort of the antitheses of the currently most
| hyped way of modeling systems: Machine Learning.
| alanbernstein wrote:
| I think you're sweeping a ton of valuable applications
| under the rug by saying "few applications besides the
| classical ones" ?
| jbay808 wrote:
| I hope I will be able to change your mind!
| lagrange77 wrote:
| Interesting username for such an opinion.
|
| Also systems modeling is not the same as control theory.
| You could indeed utilize machine learning to model a
| system, which you could then control by classical
| controllers. On the other hand, _control algorithms that
| use machine learning_ are a thing.
| metaphor wrote:
| > _Interesting username for such an opinion._
|
| Perhaps just a coincidental namespace collision: Process
| ID, not Proportional-Integral-Derivative.
| lagrange77 wrote:
| Yes, probably.
| metaphor wrote:
| > _Stuff like Nyquist criterion just sort of appears out of
| nowhere as functions._
|
| Black's canonical 1934 paper[1] _Stabilized Feedback
| Amplifiers_ , which had an outsized influence on EE
| classical control theory, may have something to do with
| that:
|
| _Results of experiments, however, seemed to indicate
| something more was involved and these matters were
| described to Mr. H. Nyquist, who developed a more general
| criterion for freedom from instability applicable to an
| amplifier having linear positive constants._
|
| ...which directly cites Nyquist 's canonical 1932 paper[2]
| _Regeneration Theory_.
|
| [1] http://archive.org/details/bstj13-1-1
|
| [2] http://archive.org/details/bstj11-1-126
| levi_n wrote:
| Thank you for this article and the follow up. The information
| is fascinating, and I eagerly await your next installments.
| woojoo666 wrote:
| Not to mention, it's not just a complex plane. It's the
| s-domain, reached through the laplace transform.
| iandanforth wrote:
| TLDR; If you want to make something go up (or down, or left or
| right) sometimes it goes down (or whatever the opposite is) a bit
| first. If you were to try harder to make it go up at that point,
| the problem gets worse, repeat until your system crashes. Times
| like these are called right-half-plane zeros and any control
| system you build has to be aware of them and designed to avoid
| causing a feedback loop.
| dhosek wrote:
| I lost interest before I got to his political point (about
| inflation), but the comments made me go back and while it's an
| interesting point, it ignores the fact that the current bout of
| inflation is almost certainly a consequence of the Covid stimulus
| plus the supply chain disruptions with a dose of war in Ukraine.
| And it turns out that inflationary pressures seem to be declining
| outside of the volatile food and energy sectors (see
| https://jabberwocking.com/inflationary-pressure-seems-to-be-...).
| I have a bit more faith in domain-specific analysis than abstract
| mathematical approaches.
| civilized wrote:
| It's like "I know math so take me seriously" but then the posts
| don't use the math in any meaningful way.
|
| Not that I think they _should_ use the math. Just skip the
| systems lectures and the "there is math behind this" and go
| straight to the analysis.
| sbf501 wrote:
| Odd that OP would give a grim warning without an equation.
|
| I graduated in 1991 with BSEE and the curriculum was a rush to
| get us to diffeq and linear systems because 90% of the remaining
| three years of classes were taught using S and Z plane analysis.
| My engineering professors were incapable of introducing a concept
| without starting with a differential equation.[1]
|
| For the author to spend so much time explaining control theory,
| then sort of give up on it, was disappointing. Ironically,
| knowledge of control systems and warnings about them should
| pervade the thought process of the thinker and prevent them from
| making grandiose claims. Perhaps OP only has a topical knowledge
| but can spin a good yarn.
|
| [1] I'm a career programmer, but I always start my thoughts with
| a d/dt: whether it's an RTOS project, a graph GraphQL endpoint,
| or USB driver. I guess "if all you have is a hammer..."
| nurettin wrote:
| So sometimes it is better to cut losses rather than double down
| because planes exist.
| GistNoesis wrote:
| Are they still important if you use something like model
| predictive control ?
| jbay808 wrote:
| They are certainly something that your MPC controller will need
| to account for, and they will constrain the theoretical maximum
| performance you can get out of the system no matter how optimal
| your control algorithm is.
| _moof wrote:
| Really should've run this by someone who knows how airplanes
| work, because they don't do what these hypothetical airplanes do.
| First off, "elevator flaps" is a howler. Elevators and flaps are
| two very different things. More importantly, you don't climb with
| the elevator; you climb with excess thrust. You can kinda sorta
| climb a little bit with just elevator, but unless you're making a
| very minor altitude correction, you'll slow way down and your
| climb rate will be really anemic, if you climb at all. But most
| importantly, an airplane won't just keep climbing and do a loop
| like that (unless you've got a thrust-to-weight ratio greater
| than one, which, to put it simply, you don't); the wing will
| stall way before you get anywhere near vertical, and the airplane
| will just stop flying until the angle of attack is reduced.
| tzs wrote:
| > More importantly, you don't climb with the elevator; you
| climb with excess thrust. You can kinda sorta climb a little
| bit with just elevator, but unless you're making a very minor
| altitude correction, you'll slow way down and your climb rate
| will be really anemic, if you climb at all.
|
| So what happens to something like a jet fighter that is in
| level flight with the engines at maximum power if the pilot
| uses the elevators to raise the nose?
| _moof wrote:
| It will climb (and slow down), but again, it's the thrust
| that's producing the climb, and this is an extreme example
| that isn't illustrative. Fighter jets produce enormous thrust
| for their weight with many having thrust-to-weight ratios
| greater than one. If they weren't air-breathing, they could
| literally fly into space. A normal airplane, even if it
| weren't air-breathing, couldn't do that.
|
| Depending on the configuration an F-16 has a T/W a little
| under 1.1, while a transport category aircraft (an airliner)
| will have a T/W somewhere between 0.20 and 0.35. Totally
| different performance characteristics.
| entropicgravity wrote:
| Not to mention poles in the unit circle.
| raydiatian wrote:
| The footnote is nonsense. Needs revision, author is currently
| arguing that poles are indistinguishable from zeros.
| oh_my_goodness wrote:
| The footnote currently appears to be correct.
| jbay808 wrote:
| I'm not aware of what you mean.
| lagrange77 wrote:
| Great article and blog!
|
| I would also mention, that we essentially design controllers to
| shift the poles and zeroes of the total system (which consists of
| the plant system and the controller system) to more desirable
| positions, than those of the plant system alone.
| ali-preview wrote:
| I'm nX 1 too<p>;)\n
| thaumaturgy wrote:
| The danger of "systems thinking" is that it misleads otherwise
| clever people into believing they've found a cheat sheet for
| subjects they don't have deep knowledge in. This article is a
| fine example of that.
|
| I didn't know what right-half-plane zeroes are. I knew some of
| the examples it gave (Veritasium has a fun video on the bicycle
| steering phenomenon), but not that there was a category they all
| fit into. Neat.
|
| But I got squinty when the author said the intended audience was
| everybody, and got a hunch it was going to wander into the
| current economy ... which it did, sort of, except that in this
| case, "wandering" into the subject meant, "wrap it up with a
| graph and then point at it and go, see! See! I can predict the
| economy now!"
|
| The follow-up at https://jbconsulting.substack.com/p/on-shelter-
| futures-part-... goes into more detail and concludes that
| interest rate hikes will increase inflation over the next 5-ish
| years, but there's no "part 2" in the series to be found
| (paywalled?).
|
| There are lots of graphs and the author tries to build a case out
| of several arguments, buuuuut in the end it _feels like_ that
| IASIP conspiracy board meme. I smell a faint whiff of gish
| galloping here and there, but one thing that stands out to me is
| that the author chooses to normalize housing costs against
| inflation, but there 's no mention of wage stagnation anywhere.
|
| Rents and housing costs _can 't_ rise a whole lot more, certainly
| not to the extent the author seems to be predicting, because
| _people can 't afford them_. This is already a conversation
| happening in every housing market in at least several countries.
| In the US, pick literally _any_ local subreddit and ask if anyone
| knows of an affordable place to rent, I dare you. There 's
| already a huge epidemic of unhoused people and van-dwelling is
| more popular than it has ever been, and consumers are currently
| getting squeezed in a lot of directions. Here, one of the things
| in my browser history before this article was this thread:
| https://old.reddit.com/r/news/comments/v8knl5/gas_prices_hit...
|
| So, if wages don't rise to meet these costs, then something big
| is going to break way before the cost increases the article is
| doomsaying.
| robertlagrant wrote:
| > Rents and housing costs can't rise a whole lot more,
| certainly not to the extent the author seems to be predicting,
| because people can't afford them.
|
| House prices are passively controlled because there's only so
| much money to spend on housing?
| ali-preview wrote:
| jokabrink wrote:
| I am not sure what to take from this. The title certainly makes
| sense from a engineers perspective. But from a layman's? I don't
| know.
|
| It seems, that he tries to explain an important concept in
| control theory but does not explain the meaning of "plane" at
| all. Even worse: He uses air _plane_ s as an example.
|
| Isn't it terribly confusing for non-control-theory people? If I
| don't know control theory, then how on earth would I know that he
| means a 2D-plane? And what's this "minimum-phase-system" he
| mentions once? Is a pole a number? And what about RHP poles?
|
| I would be interested in how readers without a background in
| control theory and higher maths understood that article and what
| questions arose.
| zasdffaa wrote:
| Seemed a decent if over-long article to explain something I
| needed to know about feedback theory. Summary: to do x you may
| have to do, or briefly get, anti-x which you need to be aware
| of and account for. Key sentence where the importance clicked
| for me was:
|
| "Let's say our airplane is running in auto-pilot. We've sent a
| request to gain altitude, so the flight controller tilts the
| elevators to initiate a climb. But suddenly the airplane is
| losing altitude, moving farther away from our target? Do we
| pull up even harder?"
|
| It's ok.
| kubanczyk wrote:
| Talk about a borked example.
|
| First of all, I'd call airplane/plane an "aircraft" instead,
| not because that's what aviators and Wikipedia editors do,
| but because it's super confusing in an article about some
| other thing called "plane".
|
| And, as an aviator would probably tell you, in order to climb
| you should care more about the _throttle_ (i.e. increase
| power) than about them elevators! So, in many cases there is
| absolutely no such dip.
|
| And, I know of no aircraft capable of achieving that loopy
| flight path using just elevators. That would require quite a
| bit of kinetic energy, to say the least.
|
| The bike counter-steering example clicked instantly with me,
| but I guess not many people have an intuition about that. I
| rode for decades before learning this and I think most other
| cyclists are not aware as well. (Most motorbike instructors
| teach that however.)
| Sohcahtoa82 wrote:
| > The bike counter-steering example clicked instantly with
| me, but I guess not many people have an intuition about
| that. I rode for decades before learning this and I think
| most other cyclists are not aware as well.
|
| Veritasium did a video on this:
|
| https://youtu.be/9cNmUNHSBac
| brandmeyer wrote:
| > And, as an aviator would probably tell you, in order to
| climb you should care more about the throttle (i.e.
| increase power) than about them elevators! So, in many
| cases there is absolutely no such dip.
|
| An autopilot responds the same way, where an altitude error
| input affects the throttle control. (wincing... when
| implemented with classical SISO controls...).
| padolsey wrote:
| So, to me, this is just calibrating against a continuum.
| Right? I think of this as binary-searching a kinda normal'ish
| distribution? I'm not good at math so I had a hard time once
| the OP article got into differential equations
| noduerme wrote:
| I mean, to a layman like myself, the takeaway is something
| about stateful, irreversible systems where x is on both sides
| of the equation in unequal or inverse measures, and how those
| systems (maybe? sometimes?) progress toward equilibrium by
| going through unexpected phases that seem to contradict what
| you're trying to input. I read the whole thing as a metaphor
| for Fed policies or how we elect Democrats every time the
| economy is about to crash, and Republicans every time it's
| just recovered.
|
| To the degree that some field of math can be best exemplified
| by various types of aircraft stalls, this didn't do a great
| job of explaining either the types of stalls or the feedbacks
| (what you might call negative REPL loops) leading to them.
|
| I agree it's ok.
| jokabrink wrote:
| Fair enough, but then he wouldn't have needed to use control
| theory and just stuck with the examples.
|
| Edit: removed ambiguity
| raydiatian wrote:
| lagrange77 wrote:
| > He uses air _planes_ as an example.
|
| Oh wow, i didn't notice that. It's either pretty clever, or
| unfortunate wording.
| [deleted]
| petesergeant wrote:
| > I am not sure what to take from this
|
| I think the author is using a lot of words to say "things often
| need to get a bit worse in order to start getting better"
| nbadg wrote:
| That's only half of the story. The second half of the story
| is "if the getting worse temporarily cancels out the getting
| better, stop trying to correct, or you're going to crash!"
| Ialdaboth wrote:
| I think "when things get worse we tend to double down on what
| caused things to get worse, until everything around us crash
| and burn" would be more accurate, given the current state of
| affairs.
| noduerme wrote:
| Not sure I share the pessimism. It seems to me that we're
| adjusting to situations pretty rapidly as a species. We're
| definitely at least attempting to find out what inputs lead
| to which short- and long-term outputs, which is a unique
| behavior among mammals.
| Perseids wrote:
| And, critically, you potentially need to ignore the signal of
| "things getting worse". Otherwise you might creature a
| vicious cycle of more corrective action -> more things
| getting worse (at first) -> even more corrective action,
| until your system crashes and you never got into the phase
| where most of the desired result of the corrective action
| materialized.
|
| And a second important point: You mustn't ever get into a
| state where the "things getting worse at first" already
| pushes you over a red line (see the example of the plane that
| loses even more altitude before it rises again. If you hit
| the ground in between you don't care that you theoretically
| would have risen later on).
| chasd00 wrote:
| To me, that immediately sounds like someone making excuses
| for their side and the midterm elections. I don't care how
| much math there is.
| noduerme wrote:
| It really all depends on how low to the ground you are when
| things begin to get worse.
|
| For example, a virus that takes 10 IQ points off people
| who've been infected with it might make China more apt to
| consume Disney movies, while it might plow America straight
| into the ground.
| toomanydoubts wrote:
| At the beginning I didn't understand what the post was about.
| At the ending, it felt like I was at the beginning.
| foxes wrote:
| As a mathematician it is just a lot of fuzzy rambling, until
| they have the actual definition. I really don't know what an
| average person is supposed to take away, you can end up in some
| feedback loop, lol okay. Communicating maths to a wider
| audience you can still be correct but there is zero reason to
| make it fuzzy. It's okay to use an analogy if there is
| something people can latch onto, carry it with them mentally,
| and then you slowly deform it into the correct statement, but
| you have to be careful to not be fuzzy.
|
| If you are writing something just minimise the number of non
| informative sentences. They probably could have explained
| poles, planes, etc all in the same space instead of rambling.
| Cutting to the examples and then giving the definition would
| have been better.
| pizza wrote:
| It's a nice explanation of the phenomenon of "getting tilted"
| in games:
|
| _Tilt originated from Poker and it 's usually a state of
| emotional frustration and confusion._
|
| _It 's most commonly used if you're going on a losing streak
| and then you become so frustrated that you start playing worse
| because you cannot focus anymore._
|
| Part of it, as I see it, is that you are using that frustration
| to fuel further efforts, which ends up in a downward spiral
| feedback loop
|
| https://gaming.stackexchange.com/questions/190507/what-is-th...
| makach wrote:
| Same. I ran to the comments to check my understanding.
| jimnotgym wrote:
| I never studied control theory, but I was fine with this. My
| pure maths education stopped at say first year undergrad. I
| didn't even consider that there were two kinds of plane. I
| thought the example was a good example of the subject.
|
| To answer the confusion about poles...I think the teaching
| method of, 'here are some terms you won't understand until
| later' is very common, isn't it. I bet it even has a name
| loser777 wrote:
| As someone with a rapidly (exponentially?) decaying background
| in engineering, all the article did was create an insufferable
| itch of mathematical fuzziness about why these were called
| zeros until I got to the footnote and the actual article began.
| taneq wrote:
| Thanks for the tip, the rest made way more sense after
| reading that. I don't think I'm particularly poorly read or
| mathematically versed but I've never heard a pole called a
| "right-half-plane zero" before, so maybe the author could
| have lead with that (or even just called it a pole, which I
| _have_ heard of so at least _I 'd_ have been less lost.)
| SilasX wrote:
| The article wasn't doing that, and specifically
| distinguished poles from zeroes:
|
| >> Control theorists like to classify the behaviour of
| dynamical systems based on what we call poles and zeros.
| ... Again roughly speaking, zeros describe mathematically
| how a system reacts to some input in the short term, while
| poles describe how a system reacts in the long term.
| taneq wrote:
| Whoops, adding that to my list of things to read again...
| >.>
| deepsun wrote:
| > Countersteering on a bicycle is another example: To turn right,
| a cyclist will first steer slightly to the left.
|
| It's very visible and pronounced on heavier bikes, like
| motorcycles. Especially if you try riding a very heavy cruiser
| bike -- you'll immediately notice that countersteering is the
| only way to turn it. No matter how you try to lean it, it won't
| respond and will just go straight, but it'll respond very easly
| to handlebar inputs.
| bambax wrote:
| > _the first important lesson of inverse response is: don't ride
| your bicycle on the edge of a cliff_
|
| I don't know if many people often ride their bicycle on cliff
| edges, but many plane (as in airplane) accidents occur because
| it's difficult / impossible to recover from a stall near the
| ground.
| LanceH wrote:
| You can also get your weight to the inside of a turn for a
| bicycle by leaning while riding straight.
|
| Every time this comes up there is a big debate with a bunch of
| people saying counter steering is required. Please, go out and
| try it. Drive perfectly straight along a painted line. Lean
| left, turn left. Lean right, turn right. There is no
| requirement for counter steering.
| bambax wrote:
| I think it's somewhat speed-dependent. I ride motorcycles and
| bikes. On a motorcycle at high speed it's impossible (in my
| experience) to take a turn without counter steering. You
| sometimes have to push really hard on the handle on the side
| where you want to go.
|
| Also, leaning is very similar to counter steering; counter
| steering makes the bike "fall" on the side where you want to
| go.
|
| Interestingly, you can also steer a horse without doing
| anything on the reins; the horse will usually go where you
| put your weight; I think it's because it needs to compensate
| for the weight differential; or maybe it takes it as a hint
| about which way you're looking. In any case it works.
| d--b wrote:
| This is very well explained, but there should be a simpler name
| for this effect than right-half-plane zeros if the author wants
| to spread the concept beyond control theory.
| blauditore wrote:
| Can someone provide a TL;DR? I don't have time to read the whole
| article, and I don't even understand what's the topic based on
| title and reading a few paragraphs, nor from googling "right-
| half-plane zeros".
| a_imho wrote:
| The plane refers to the plane of complex numbers (a+b*i), the
| right half is where the real part (a) is positive. If the zeros
| of your feedback loop are on the right hand side that means it
| is a unstable feedback loop, if they are on the left side it is
| stable feedback loop (this happens because the zeros eventually
| end up in exponents which either tend to infinity or to zero
| with time).
|
| If you squint a little bit most systems looks like a feedback
| loop and my not very confident interpretation is, judging from
| the last picture, that the author thinks we have a runaway
| inflation problem (zeros on the right hand side of the plane)
| and we might or might not have the controls to move them to the
| left hand side to tame it.
| layer8 wrote:
| I thought this would be something about positive zero in a 2D
| coordinate system, but seeing drawings of airplanes in the
| article I concluded "bummer, it's not" and immediately hit
| backspace. Thanks for the summary. :)
| gsliepen wrote:
| > The danger of the right-half-plane zero is that it lures you
| into reacting to it, but that is precisely the wrong thing to do.
| Attempting to apply a new control input to cancel the inverse
| response only sets off an even worse chain of events, where the
| resulting secondary inverse reaction becomes even more severe,
| requiring even more corrective action, until finally you've
| slammed into the ground. > In this situation, the flight
| controller's only option is to ignore the initial misdirection
| and wait patiently until the airplane eventually begins to climb
| as intended.
|
| Of course that is easier said than done; adding a sleep() to your
| control loop to ignore the initial misdirection is also very bad.
| The right way to solve this is to not just tell the control loop
| to "go up", but to plan a realistic trajectory that the control
| loop can execute. That way, the error between the desired
| trajectory and the actual trajectory will be much smaller, and
| the closer the error is to zero, the less chance of a control
| loop to go wild.
| ilayn wrote:
| Always appreciate control theory articles. But this one needs
| some editing. Take ice cream example;that is not zero dynamics
| that's still pretty much convolution. Now zero dynamics examples
| must have no effect on the system. Thus it is not a zero if you
| continuously chugging ice cream. It is indeed a step input that
| you equilibriate at a constant ice cream input and some happiness
| comes out constantly. The moment you stop happiness goes away.
| That is not related to zero.
|
| Also a pure zero action is supposed to cancel the input
| completely. Not at first but completely (restricting the
| discussion to linear systems).
|
| Zeros effects are not so trivial to untangle as the article
| suggests unfortunately but fun read anyways and very nice flow.
| jbay808 wrote:
| > Now zero dynamics examples must have no effect on the system.
| Thus it is not a zero if you continuously chugging ice cream
|
| Thank you for your input! I wonder if you might have misread
| that example. In this system there's indeed a RHP0 in the
| transfer function from ice cream consumption happiness. A
| continuously increasing rate of ice cream intake results in
| exactly no effect on the output.
| ilayn wrote:
| Your happiness shouldn't change if ice cream input has a
| zero. Also it should be independent from the amount of ice
| cream. In other words if we have an ODE say
|
| ddot y + 2 dot y + y = dot u - 2 u
|
| As long as my input is pure C exp(2t) independent of C I see
| no happiness and it's not working on my mood. In your example
| input u effect is cancelled by decay of y cancelling the
| guilt. Making it not a zero.
|
| In my personal case eating celery is a zero i see absolute no
| point eating it :) no harm and no benefit just pointless
| chewing
| tdubhro1 wrote:
| It's a bit disappointing that an article purporting to educate us
| about something we should know but may be unaware of, is
| completely wrong about the example of how an airplane climbs -
| you don't climb by pitching up, you have to increase power.
| jbay808 wrote:
| Fair. Perhaps a glider would have been a better example.
| nosianu wrote:
| How? A glider climbs when the air it is in rises faster than
| the airplane sinks in that air to maintain its forward speed.
|
| If you pitch up you can only exchange speed for a little bit
| of altitude, briefly.
| jacquesm wrote:
| Exactly. A glider in air that doesn't rise is like a yo yo
| on a string, you need to add energy to the system (rising
| air, pulling up on the string at the right moment) to be
| able to overcome the eventual return to the ground state.
| rocqua wrote:
| Just pitching up will have you climb, but at the expense of
| losing velocity right?
| jacquesm wrote:
| Right up to the stall speed limit. You can't just keep
| pitching up, you'd have to apply some power too if you don't
| eventually want to run out of forward (air)speed.
|
| In a glider you can't do that so there when in level flight
| you have a limited amount of forward momentum available to
| help you climb if the air itself isn't moving up, you are
| continuously trading altitude for speed and vv (easy to see
| in a dive: everybody expects you to gain speed in a dive
| because can all relate so something falling, it's obvious the
| reverse has to happen when you climb and the stall speed is a
| design parameter of the aircraft at a given altitude combined
| with a bunch of other factors).
|
| https://aviation.stackexchange.com/questions/27693/how-
| does-...
| jhugo wrote:
| Briefly.
| Linda703 wrote:
| once_inc wrote:
| For those wondering: this article is an introduction into
| inflation of house prices in Canada. You can easily find the next
| article (it's already online) by going to the substack's index.
|
| Very good article, and well worth your time to read.
| dools wrote:
| It's funny as soon as I read the ice cream but I knew where he
| was going with it.
|
| The interesting thing is that his modelling concludes that
| raising interest rates is inflationary which is what Warren
| Mosler also says.
|
| Anyone interested in what to do about inflation would enjoy the
| recent Macro n Cheese podcast episode featuring Randall Wray
| selimthegrim wrote:
| Let's hope Erdogan doesn't read this
| pcthrowaway wrote:
| Link, because I assumed it wasn't out yet since the author
| hadn't provided it: https://jbconsulting.substack.com/p/on-
| shelter-futures-part-...
| bsedlm wrote:
| can anybody tell me what's f in this scenario?
|
| dy/dt = dx/dt + Ax
|
| is it the case that y = f(x,t)?
|
| thanks
| duped wrote:
| The greatest sin of undergraduate engineering education is
| sequestering signals and systems into electrical engineering
| curricula. I understand why it's done that way (I even had to
| fight to take the course early, sidestepping some prereqs for
| reasons).
|
| But it's really so foundational to understanding concepts of
| stability, resonance, information/energy flow (from the
| conceptual perspective), and the simple analytical tools for
| building a solid conceptual base. It takes a semester to hammer
| home that step response matters, positive feedback bad, negative
| feedback usually good, and topologies are useful.
| nbadg wrote:
| I went to school for mechanical engineering (though I now work
| in software). We were required to take signals and systems, but
| if I remember right it was a weed-out course for most MechEs
| (it certainly was a challenge for me, though I think that had
| more to do with the curriculum than the topic).
|
| Those lessons might have been hard-won on my part, but I
| definitely still use them. The general concepts (feedback loops
| etc) are applicable basically everywhere in life, and I still
| find uses for literal actual math (like using a convolution
| kernel to do rolling window sampling in numpy).
| thrwyoilarticle wrote:
| I can imagine it's used for car suspension?
| dboreham wrote:
| Wasn't control theory invented to understand the dynamic
| behavior of steam engine governors?
| koliber wrote:
| Does anyone know of any courses which could explain concepts of
| stability, resonance, information/energy flow and help build a
| solid conceptual base for managers or entrepreneurs? These
| concepts are crucial when making business decisions. I've been
| building up an understanding of this through experience. If
| there was a way to shortcut this and provide such education
| deliberately, it would allow people to become better decision
| makers quicker.
| Agentlien wrote:
| I took some electrical engineering courses but mainly software
| engineering with a focus on low-level details and graphics.
|
| The more I specialize in graphics the more I realize I need
| much more knowledge about signal processing than we were taught
| at the university.
| AB1908 wrote:
| Could you demonstrate with an example?
| Agentlien wrote:
| I can give a few. In general, the theory behind rendering
| generally treats what's on the screen as a discretization
| of a continuous visual signal. Post processing especially
| is largely about signal processing.
|
| Anti-aliasing (AA) is a very clear example where the lack
| of it leads to moire patterns and jaggies. Understanding a
| lot of AA techniques is simplified by seeing the frame not
| as a discrete set of pixels but as a continuous signal
| being sampled (and can be sampled at multiple sub-pixel
| points per pixel).
|
| A lot of other screen effects are essentially filters
| applied to the graphical signal (sobel, gaussian blur, ...)
| and understanding them from a signal processing view helps
| understanding how to modify and optimize them. A good
| example here is identifying whether your effect is a
| separable filter which can be split into a horizontal and
| vertical pass.
|
| Seeing the image as a continuous signal/field being sampled
| is also the theoretical basis for a lot of visual effects
| used in physically-based rendering and things like screen-
| space ambient occlusion.
|
| Finally, if you want to write your own ray-tracer it really
| helps to be able to take this view of things once you get
| past the basics.
| nabla9 wrote:
| _" signals and systems"_ - covering signals processing, systems
| and control theory is very generic subject.
|
| You need it in economics, biology, chemistry, physics, computer
| science, statistics, electrical engineering, robotics ,
| automation, logistics, ...
|
| It should be taught like calculus or linear algebra, so that
| everyone gets gist of the basics before learning to apply it
| into their specific field.
| trenchgun wrote:
| I was already thinking of taking it this summer, but you
| convinced me to do it for sure.
|
| Thank you!
| Jach wrote:
| I always thought my college education was backwards, with the
| exception that differential equations (and laplace transforms,
| which can help lay the groundwork for other transforms) came
| early enough that I could get by -- though it'd have been
| better if they were earlier, like high school, and if I hadn't
| been able to skip two semesters of calculus thanks to my HS
| calculus then differential equations would have come even later
| in college. But as a CE student at a school nominally more
| about video game making education I ended up first taking as CS
| electives an audio processing course, and then an image
| processing course, before the CE side reached control systems,
| which I had to retake after taking the next digital signal
| processing course, after which control systems made a lot more
| sense. It was only after graduating that I felt like I had
| reached a level of sophistication to go back and really grok
| all the related theory and go deep into applications. Maybe
| that's how graduate students are meant to feel? But I just went
| into full time enterprise work and 'retired' after 6 years of
| that, so I've since forgotten a lot... Still, the concept of
| feedback has proved useful in systems analysis from time to
| time, and it's a framework that I think could yield many low
| hanging fruit in other disciplines. (The book _Behavior: The
| control of perception_ applies control theory to psychology in
| a convincing way but it 's understandably been neglected by
| psychologists who aren't often very sophisticated
| mathematically.)
| codethief wrote:
| Can you recommend any good introductory books on the topics you
| mentioned for someone who studied (theoretical/mathematical)
| physics but never electrical engineering or signal processing?
| (Read this as: I am more or less familiar with Nyquist-
| Shannon's theorem but that's about it.)
| scrlk wrote:
| Signals & Systems by Oppenheim is a classic introductory
| textbook.
| lagrange77 wrote:
| Not a book, but this series on Youtube is excellent.
|
| https://www.youtube.com/watch?v=Pi7l8mMjYVE&list=PLMrJAkhIeN.
| ..
|
| > familiar with Nyquist-Shannon's theorem
|
| BTW: In control theory there is also
| https://en.wikipedia.org/wiki/Nyquist_stability_criterion
| duped wrote:
| ime the books are very loaded on theory and it's hard to
| connect that to practice and concepts. I don't know of any
| book that touches on what poles/zeros _mean_ or why they 're
| useful outside what are (seemingly) contrived properties of
| formulae like stability. It's one of those things that's just
| useful to go through in a university course, even just
| auditing it. The practical problems and lectures are
| extremely useful, particularly due to the overhead of
| notation (the practice is relatively young and derived from a
| different tradition of education, and a lot of contemporary
| notation can seem a little foreign, or is filled with
| shorthand).
|
| Applied Digital Signal Processing by Manolakis & Ingle is the
| book I always turn to for reference and the code examples
| don't suck. Oppenheim & Schafer is a classic but frankly only
| useful as a reference, that tome is a bit dated otherwise.
| The Scientists and Engineer's guide to DSP is also not bad as
| a practical text.
| dukeofdoom wrote:
| If you are going slow on a bicycle, and want to turn right, you
| might have to turn your front wheel left and then right, just so
| you don't fall over and maintain upright balance. Which would be
| a problem if you are riding along a cliff's edge.
| eigart wrote:
| Great read. I've been thinking about how this applies to
| earth/climate change for a while, so I was surprised that the
| system he worries about is inflation/the economy.
| jbay808 wrote:
| Thank you for reading! I agree the Earth is a much worthier
| system to be worried about than the economy, for sure.
| LolWolf wrote:
| Counterpoint: no you don't.
|
| By the time you have a perfectly reasonable model of a system
| that is good enough such that computing the transfer function's
| poles actually tell you something interesting about the system,
| there's way more you can say about the system than "it is
| stable."
|
| There are maybe some lessons to be drawn from basic "classical"
| control theory, but many are better stated by just analyzing the
| system directly.
|
| (As a side note, I'm not saying there's Zero value in analyzing
| transfer functions, just that it's a long way to the top from
| there.)
| lb1lf wrote:
| My signals processing professor apparently knew one joke, and one
| joke only.
|
| "A LOT (Polish airline) airplane is about to land in New York
| City; as they align for final approach, the first officer
| notifies the passengers that those seated on the right can now
| see the Statue of Liberty. A number of passengers get up from
| their seats left of the aisle and lean over the people seated on
| the right to get a glimpse of the statue. Plane promptly crashes.
|
| Why? There were too many Poles in the right half of the plane.
|
| I'll lead myself out.
| l33t2328 wrote:
| I hate to be the guy to ask you to explain the joke, but why
| would that make the plane crash?
|
| I do know what a "pole" refers to, but I don't follow the crash
| bit.
| eftychis wrote:
| tl; dr: The system is unstable as it has positive feedback
| loops. You can "first day of class" think of it as the
| implied series 1/(s-p) -- p the pole, s the Laplace variable
| -- exists and converges. And in particular you want that
| series to converge on the imaginary axis which means it does
| not diverge in the frequency domain (Fourier transform).
| Essentially, that means that you have regions of frequencies
| where your system diverges/amplifies them excessively and
| thus breaks down: is unstable. Filters do the opposite.
|
| P.S. The other note is that for real linear time invariant
| systems the region of convergence of the series/Laplace
| transform of the system must be positive for the system to be
| causal -- and thus real and implementable. So the joke could
| also have been modified to get a magical and unstable plane.
| pcthrowaway wrote:
| > You can "first day of class" think of it as the implied
| series 1/(s-p) -- p the pole, s the Laplace variable --
| exists and converges. And in particular you want that
| series to converge on the imaginary axis which means it
| does not diverge in the frequency domain (Fourier
| transform)
|
| If this was the first day of any class I took, I would have
| dropped it before the second day.
| tinco wrote:
| That makes me think of calculus in freshman's year. The
| first week the prof explained all maths we had learned in
| highschool, and then seemingly continued that same pace
| every week, it was rough. Especially for some of the
| smart kids who had never experienced learning material
| coming at them faster than they could take it in. The
| types who opened their textbook the night before the exam
| and would ace it in highschool got a real test of
| character.
| angry_octet wrote:
| That's why letting kids cruise in high school is a
| terrible mistake. So many school systems are uninterested
| in making sure everyone is challenged, especially in
| maths.
|
| University is good because you'll meet lots of people who
| are smarter than you are.
| Sohcahtoa82 wrote:
| I don't even know how kids cruised in high school and
| still got their diplomas.
|
| I flunked out of high school despite getting A's and B's
| on all my tests because I never did my homework which was
| always at least 50% of our grade.
|
| Trigonometry was so interesting to me as a 15 year old
| that I decided to make it my internet alias. 95+% on
| every test (even trig identities!), still got a C in the
| class, with the teacher taking me aside 1-on-1 to tell me
| "I'm breaking the rules to give you this C when I'm
| supposed to be giving you an F because you only did 2 of
| the 30 homework assignments."
| hdjjhhvvhga wrote:
| That's why I feel it's good to learn a bit about Laplace
| transform for anybody doing anything technical. It has so
| many applications you can hardly get away from it.
| dreamcompiler wrote:
| Acausal systems are implementable. They're common in signal
| processing and even in some rather exotic control systems:
|
| https://www.researchgate.net/publication/253627368_Feedforw
| a...
| Cerium wrote:
| A control system with a pole (in the control systems sense)
| in the right hand half of the plane will be unstable. If the
| system changes during operation, the pole can move around the
| coordinate plane.* As it goes from the left (stable) towards
| the right (unstable) the system will begin to oscillate as
| the pole crosses the Y axis.
|
| In the joke, a Pole (person of Polish origin) was in the left
| of the (air) plane. When they crossed the aisle to look out
| the window, the (air) plane became unstable and crashed (pole
| in the right hand plane).
|
| *My control systems professor loved to explain using an
| example of a driver as a control system. The system (car +
| human driver) seeks to minimize error against the lines on
| the road. If the driver starts drinking, one of the system's
| poles will move right. The car will start overshooting first,
| then will start weaving, before finally crashing when the
| driver is too drunk.
| dreamcompiler wrote:
| Because if your poles are not in the left half [of the]
| plane, the system is unstable.
| [deleted]
| ad404b8a372f2b9 wrote:
| The weight imbalance from everybody rushing to the right made
| the plane unstable.
| 2-718-281-828 wrote:
| this is the only answert to the question above and it's
| being downvoted? welcome to hacker news ...
| stephen_g wrote:
| I didn't downvote it, because it's not a bad attempt at
| an answer if you don't know the context, but the actual
| joke is completely different and about calculus and
| control systems. The right side of the plane is double
| meaning for the right half of the _complex_ plane in
| dynamical systems analysis, which is the area where the
| real part of every point is positive. If your poles are
| on the right half of the complex plane, then the system
| is unstable and the output will tend towards exponential
| growth (going out of control) for any change in input.
| ad404b8a372f2b9 wrote:
| The question is about the literal meaning of the joke, he
| knows what a pole is within the context of calculus. He
| didn't understand within the context of the joke what
| lead to the crash.
| lupire wrote:
| It's a joke. There is no cause within the literal
| context. The humor comes from word play.
|
| After the plane crashed, one survivor was stranded in the
| wilderness. Miles from civilization, he cried and
| screamed until he got hoarse. Then he mounted the horse
| and rode back to civilization. Back at home, he found
| himself locked out of his house, since he lost his house
| keys with his luggage on the plane. He sat on the porch
| and sang various lamentations, until he found the right
| key and unlocked the door.
| ad404b8a372f2b9 wrote:
| The joke relies on the fact that keys unlock doors, this
| is the cause, just like the prior one relies on the
| assumption that people rushing to one side crashes the
| plane.
|
| If there are 10 comments explaining what a key is in the
| context of music and I add another that says "I
| understand what the key refers to but how was the door
| opened", one can only assume I lack the knowledge that
| keys open doors.
|
| Sometimes people understand the more complex behaviours
| but somehow miss the simpler explanations, it's happened
| to me before.
| selimthegrim wrote:
| There are enough actual LOT crashes he can form a model
| on his own...
| 22c wrote:
| Interestingly, I recently spoke to a loadmaster who told me
| that left/right side weight distributions are far less
| important than forward/aft, to the point that for the
| majority of aircraft they're loading, imbalance to the left
| or right side of the plane aren't accounted for at all.
| eftychis wrote:
| Yes you want the center of mass to be more forward than
| the center of lift. Otherwise, a small deviation in the
| pitch becomes hard to impossible to recover -- the system
| is unstable and stalls extremely easily. If that is a
| fighter plane of course you want that, so you make sure
| the opposite is true, and have a computer counteract that
| during normal flight.
| cwillu wrote:
| I laughed the first time I made an airplane with the
| centre of mass behind the centre of lift in Kerbal Space
| Program.
| tremon wrote:
| A little bit broader than you asked for, but:
|
| A dynamic control system is modeled by a set of dynamic
| equations, usually expressed as partial derivatives. To
| analyze the behaviour of such a system, the equation is
| solved or approximated in the complex time domain. The
| relevant part of the solution is where the real part of time
| is positive, i.e. the right-half plane.
|
| A pole is a coordinate for which the dynamic equations have
| no solution (y = 1/z has a pole at z=0), which results in
| undefined or uncontrolled behaviour.
|
| (also see https://en.wikipedia.org/wiki/Zeros_and_poles)
| JackFr wrote:
| Honestly, this comment better than the article.
| dreamcompiler wrote:
| Did we have the same professor? Mine loved that joke too.
|
| The students in the classroom next door always knew when Prof
| Lipovski told his joke because everybody along the hallway
| could hear the loud groan emanating from our room.
| Natsu wrote:
| I think all systems professors have the same joke book and
| there's only one page in it :)
| a9h74j wrote:
| Heard a varient at Berkeley from a professor of Applied Math,
| which you would probably no longer hear.
|
| Generic airline, specifically Polish people were asked to
| move to the left side of the plane. Because "Poles in the
| right half plane cause instability."
|
| (As for application in economics, economist Steve Keen, for
| one, explicitly models time delays and dynamics, with results
| worth learning from, AFAIK.)
| ldite wrote:
| And you know why the contour integral of Western Europe is
| zero? Because all the poles are in Central Europe.
|
| (sorry)
| jimnotgym wrote:
| As a resident of post-Brexit Britain, I was horrified as I
| read this expecting it to have the opposite punchline and to
| turn into an anti-immigration joke.
|
| For those that don't know, Polish (and other Eastern
| European) migration was a major issue raised by some in the
| Brexit campaign.
| selimthegrim wrote:
| The real answer is Ilyushin made terribly finicky engines and
| people skimped on maintenance but that's another story.
| cperciva wrote:
| There was nearly a disaster earlier in that flight too, when
| the pilots got sick from food poisoning and the cabin crew had
| to ask if any of the passengers knew how to fly a plane. As it
| turned out, one of the passengers had flown many years
| previously, and offered to try.
|
| When he reached the cockpit, however, he took one look at all
| of the controls on the modern aircraft and realized that he
| wasn't going to be able to operate it. When the chief steward
| asked why, he replied, "I am just a simple Pole in a complex
| plane".
|
| I'll follow lb1lf out.
| [deleted]
| drekipus wrote:
| Now this made me laugh like crazy
| danuker wrote:
| It has a grain of truth to it. Poland could donate MiGs to
| Ukraine, but other countries with US fighters could not,
| because Ukrainian soldiers didn't know how to fly them.
| Tuna-Fish wrote:
| Actually not true. Many Ukrainian fighter pilots have
| received training in the US, where they flew F-16:s. (That
| is, before the current phase of the conflict.)
|
| The hard part is actually the maintenance crews. A modern
| fighter plane requires constant intensive mainentance, they
| generally spend much more time being worked on than they
| spend actually in the air. And this maintenance work
| requires a lot of specific skills that don't necessarily
| translate well or at all between aircraft types.
| jacquesm wrote:
| And a steady supply of parts.
| jacquesm wrote:
| Why did the man from Gdansk marry the woman from Zakopane?
| 'Opposite Poles attract'.
| gugagore wrote:
| The article saying zeros (where the transfer function is 0)
| when it should be saying poles (where the denominator of the
| rational function is zero), right?
| themeiguoren wrote:
| Controls engineer here. The author's control theory knowledge
| is correct - a RHP zero indicates that corrective action will
| begin in the wrong direction (which the article compares well
| with countersteering on a bike). The technical term is a "non
| minimum phase system". It's possible this will lead to
| instability, but in general the long term stability of a
| system is determined by the location of its poles (which is
| more applicable to the author's ice cream example). Poles in
| the RHP will cause a system to blow up.
|
| My gripe with the article is that the author tries to wow you
| with some obscure technical points about a system which is
| unmodeled and he does not understand, to wave his hands at a
| vague conclusion. If he had made the same point using common
| English phrases that encapsulate the idea ("positive feedback
| loop", "we have to let it get worse before it gets better",
| etc), then it would be a lot clearer how wispy his argument
| is.
| [deleted]
| samfriedman wrote:
| The version my professor told was, "Why is politics in Poland
| so volatile? Because all the Poles on the right are unstable!"
| woojoo666 wrote:
| I don't think they should use the term right-half-plane zero if
| they don't explain laplace transform and the s-domain. Just call
| it an unstable system, or unbounded growth.
| oh_my_goodness wrote:
| The point of the article, perhaps not stressed enough, is that
| there are _stable_ systems that can be very difficult to
| control. Zeros in the right half-plane don 't indicate
| instability. They indicate nulls in the transfer function for
| unbounded inputs.
|
| Poles in the right half-plane indicate instability. Zeros in
| the right half-plane indicate something a little more subtle. I
| believe the article is about the latter.
| woojoo666 wrote:
| Good point, I mixed up the two. However, the right-half plane
| still refers to the s-domain so it doesn't make sense to keep
| referring to the a right half plane without explaining what
| plane it is
| jbay808 wrote:
| That would be a right-half-plane pole.
|
| An explanation of the Laplace transform is coming! This is an
| article, not a book.
| parasti wrote:
| This is weird to say, but I've never had this happen before: as
| someone who's never heard of control theory, the initial
| illustrations and the leading icecream example seemed highly
| confusing and put me off from reading the rest.
| magneticnorth wrote:
| The follow-up article on inflation of shelter costs in response
| to mortgage interest rates is also fascinating and worth a read,
| imo [0]. The tl;dr is that in the medium and longer term, higher
| interest rates will decrease inflation, but there's a right-half-
| plane zero effect that will cause higher inflation rates in the
| short term in response to interest rate hikes (with a lot of
| simplifying assumptions).
|
| [0] https://jbconsulting.substack.com/p/on-shelter-futures-
| part-...
| neilwilson wrote:
| It's a little more complex than that because of the potential
| feedback loop via the main price channel.
|
| In other words if you can have a wage/price spiral you can have
| a profit/price spiral and an interest/price spiral for the same
| reasons.
|
| [0]:https://new-wayland.com/blog/interest-price-spiral/
|
| Once you abandon the concepts of general equilibrium and a
| fixed amount of money for what happens in reality, then the
| functional control mechanisms get a whole lot more interesting.
| dukeofdoom wrote:
| I watched this video in preparation for a Drone license test.
| Really interesting stuff.
|
| Human Factors for Drone Pilots
|
| https://www.youtube.com/watch?v=UHYjl0u2UMA
|
| Based on what real pilates need to know about human physiology as
| it relates to steering airplanes.
| [deleted]
| voldacar wrote:
| This is some of the best non-rigorous writing about math that
| I've encountered. Far superior to the awful quanta articles that
| sometimes get posted here.
| cheeselip420 wrote:
| This is fantastic.
| civilized wrote:
| The article claims to be for a broad audience, and contains
| insinuations of political relevance. But right-half-plane zeros
| are a purely technical concept, and they're not explained with
| enough technical detail to be air-dropped into the middle of a
| broad audience piece.
|
| It's almost good. It would be good if it dropped the pretensions
| to technicality.
| whycombinetor wrote:
| The author lost all credibility when he said I have to
| countersteer to turn my bike. The author is a "professional
| engineer and consultant, specializing in feedback systems and
| motors" too. There are >50 million cyclists in the US who would
| presumably immediately recognize this as a false statement and he
| didn't ask a single one of them to proofread.
|
| Edit since some people are confused by this apparently: You can
| steer your bike away from the edge of a cliff by _leaning to
| initiate the turn instead of countersteering_. This makes the
| author 's advice of "Don't ride your bicycle on the edge of a
| cliff" much less critical.
| mk12 wrote:
| I'm curious how you're so confident about this. I think if you
| ask most people (even most cyclists) what happens when you turn
| the handlebars to the right, they'd say you turn to the right.
| I cycle almost every day and I thought this for a long time.
| Have you actually tried it? When I tried it, I found that it
| forces me into a left turn.
| whycombinetor wrote:
| Have you tried leaning to the left while biking in a straight
| line? It results in you turning left without your front wheel
| ever having gone to the right (i.e., turning without
| countersteer).
| kazinator wrote:
| > Have you tried leaning to the left while biking in a
| straight line?
|
| That is impossible. If you lean your body left while biking
| in a straight line, the bike will lean right to keep your
| center of gravity above the track.
|
| For bike and body to be leaning left, the bike must already
| be in a turn. Or else, it must be in the middle of a fall.
|
| Two-track vehicles always begin a turn with a
| countersteering move which induces a fall in the opposite
| direction. Then the steering immediately switches in the
| falling direction, to convert the fall into a turn.
|
| (In the absence of wind anyway. A left turn could plausibly
| start without a countersteer if a gust of wind blows over
| the bike into a left lean; the subsequent left steer and
| turn will supply the compensating acceleration to prevent a
| fall.)
|
| A bicycle is always countersteering. A bicycle whose
| steering column is locked out, prevented from turning,
| cannot be ridden. It will fall over.
|
| A bicycle doesn't require a rider in order to maintain
| balance, either. Above a certain speed, a bicycle can
| correct itself. This is due to countersteering. Whenever
| the bicycle accidentally steers slightly to the right, it
| begins to fall to the left, and this provokes a left steer
| which prevents a fall.
|
| A rider who doesn't understand countersteering nevertheless
| intuitively "bootstraps" the turn out of these small
| wobbles, gradually increasing the tilt and and degree of
| turn, through a sequence of small counter-steering
| maneuvers.
| adiM wrote:
| One can always test the hypothesis via an experiment:
|
| https://youtu.be/9cNmUNHSBac
| whycombinetor wrote:
| Indeed. I like this clip where they show bike steering to the
| left, without its front wheel ever going to the right side of
| its original path, by only leaning and no countersteering.
| https://youtu.be/9cNmUNHSBac?t=445
| kazinator wrote:
| The video shows the exact opposite of your claim. The
| bicycle is given an initial push by the experimenter. Its
| steering is initially pointing a bit to the left. Because
| of this, it begins falling to the right, and recovers by
| steering in that direction, away from the guardrail.
|
| The bike seems to be initially leaning to the left, because
| it was induced into motion that way by the experimenter.
| Yet in spite of this, it recovers by tilting to the right.
| whycombinetor wrote:
| Looks to me like 1. The bike is initially rolling
| straight with no handlebar angle, and then starts falling
| over to the left. 2. Due to the mechanic explained in the
| video, this causes the handlebar to turn left.
|
| If there was a human on that bike wanting to turn, here
| they would continue leaning, turning, and pedaling in the
| correct amounts.
|
| But because there's no human to keep their weight leaned
| to the left, then 3. The left turn of the handlebars
| causes the road contact points to move to the left of the
| center of gravity, so that 4. It starts turning right.
| mk12 wrote:
| That's with no rider on the bike. Earlier in the video when
| he attempts to turn with the device that prevents
| countersteering, he falls off every time. It seems unlikely
| that 50M cyclists could easily do this but he could not.
| whycombinetor wrote:
| Now just imagine the possibilities _with_ a rider on the
| bike. Being able to dynamically shift weight to either
| the left or right side of the bike at will! You can even
| do turns while riding with _no hands_.
| kazinator wrote:
| When you shift your weight to the left, the bicycle tilts
| right to keep the center of gravity above the track line.
| whycombinetor wrote:
| If this were the case, you wouldn't be able to turn while
| riding with no hands. Yet reality has us out here riding
| bikes with no hands making turns.
| https://youtu.be/_SWdCutqSWQ?t=73
| kazinator wrote:
| > _That 's with no rider on the bike._
|
| That's irrelevant; bicycles countersteer to keep stable,
| without a rider present (above a certain speed).
|
| If the riderless experiment were repeated with a bike
| whose steering is locked out, it would fall down rather
| quick.
| throwaway290 wrote:
| The bicycle and riding style used in the video do not
| provide a good illustration, I have no idea what he was
| trying to do as he crashed repeatedly, and he did not
| seem (or the frame prevented him) to use the ability of
| his body to lean the bike into the turn, riding naively
| (which didn't prevent them from talking down as if there
| is a clear consensus in the field of bicycle dynamics).
|
| At low speeds on e.g. a light MTB stop pedaling, lift
| your butt off the saddle, lean bike far into desired side
| balancing your body and handlebars to keep going
| straight. You have most of what's needed to turn. You may
| countersteer but your line does not veer into the
| direction of countersteer, counter to illustrations.
|
| Riding edge of a cliff is not a great idea anyway because
| balancing a bicycle tends to require countless small
| adjustments even due to pedaling alone.
| kazinator wrote:
| > _The bicycle and riding style used in the video do not
| provide a good illustration_
|
| It's good enough if you already understand it and know
| what to look for; just not the best for convincing
| someone who doesn't believe the physics.
| dilyevsky wrote:
| Heh was about to reply with the same video. It's really
| counterintuitive even for people who ride a lot
| CamperBob2 wrote:
| It's counterintuitive to cyclists because we don't
| countersteer. We lean instead, generally subconsciously. If
| we didn't lean, it's true that we'd have to countersteer...
| but nobody rides that way, making it a flawed analogy at
| best.
| dilyevsky wrote:
| I'm not good downhill mtb rider but my understanding it's
| really common technique there. Even on road i do that not
| to take a spill in sharp-ish downhill turn going at speed
| kazinator wrote:
| You always countersteer; you're just not doing it
| consciously. Because of that, you're doing it very
| slightly. Because you're doing it slightly, you enter
| into turns slowly. You're not able to take sharp corners
| at a decent speed.
|
| You cannot lean without countersteering first; the lean
| happens because you induced a fall in the desired
| direction, through a tiny countersteering move. With the
| tiny, subconscious counter-steers, you induce only small
| tilts. I suspect it takes multiple small counter-steering
| maneuvers to "build up" a decent tilt for a sharp turn,
| which takes time.
|
| Once I learned to deliberately countersteer, I then
| started doing it all the time. I hardly take any turn
| (big or small) on a bicycle without pushing forward the
| handle-bar on that side.
|
| If you don't make deliberate countersteering your main
| steering method, so that it becomes second nature, you
| will not be able to count on yourself to use it in an
| emergency.
| CamperBob2 wrote:
| Maybe you countersteer. I don't. I checked by riding
| through a puddle, turning right, and then checking the
| resulting trail left by the tires. No overshoot
| whatsoever.
| oh_my_goodness wrote:
| OP: dy/dt = dx/dt + Ax
|
| Comments: The OP is a troubling covert political statement. The
| real issue here seems to be US midterm elections / climate change
| / COVID / appeal to authority.
| draw_down wrote:
| dqft wrote:
| Everything is fine. We are prepared and can handle the
| situation(s). Everything is fine. It's fine. We have it under
| control. Fine. We have the metrics and they're fine. Okay?
| shreyshnaccount wrote:
| My dynamical systems prof loved that xD
| DeathArrow wrote:
| Something I don't understand: on the one hand, people on HN seems
| to enjoy this kind of articles. On the other hand, they upvote
| any article who decries interviews where candidates are asked
| things that involves knowing some theory.
|
| So, if we think knowing theory is useful in cracking hard
| problems, why is it wrong to asses its knowledge in an interview?
| genezeta wrote:
| While I don't claim to have _the_ answer to your question, I
| think there 's a jump you're making that _may_ not be so
| straightforward and somewhat explain things.
|
| You say "people on HN seems to enjoy this kind of articles"
| which seems reasonable, given the comments here. But then you
| jump to "we think knowing theory is useful in cracking hard
| problems".
|
| Going from the first to the second is not quite so clear. That
| is, someone may _enjoy_ such an article and even learning some
| theory, but not necessarily because they think they will
| directly apply it. People sometimes just enjoy learning stuff
| or reading about it and then forgetting it.
|
| You also make a second jump, because other factors may be
| involved. Maybe the theory asked in the interviews is
| completely unrelated to the things involved in the job. The job
| may not even require cracking hard problems. These are frequent
| occurrences -in my experience, at least-, and clearly seem
| compatible with thinking that knowing theory is good in
| general.
| [deleted]
| bee_rider wrote:
| Programming and engineering are neighbors, so it is interesting
| to see what's going on over there. But many engineering
| analysis tools are not really useful for normal programming
| jobs (unless you happen to be working on engineering software,
| control systems, or something like that).
| CamperBob2 wrote:
| HN's readership isn't homogeneous. There's room for both points
| of view.
|
| I've done a lot of useful work in feedback systems without ever
| really grokking Laplacian notation and the notion of complex
| frequency in general. A lot of the actual numerical methods
| used in real life boil down to a few canned formulas. But I
| know enough about the underlying theory to appreciate where the
| canned formulas come from, and fully intend to sit down some
| day and go through the whole process. Articles like this are
| interesting if only for the occasional gems in the comments,
| such as John N.'s pointer to Maxwell's 'On Governors' paper
| that I'd never run across before.
|
| At the same time, I don't see much upside in making hiring
| decisions on the basis of whether someone can regurgitate a
| bunch of textbook math. I'd rather spend the interview talking
| about control problems the candidate has dealt with personally,
| how they were handled, and what the candidate learned from
| them.
| djmips wrote:
| Because programming is rarely about cracking hard problems.
| That's actually why the people HN enjoy the kind of article, it
| takes them away from the drudgery of their job.
| Animats wrote:
| The classic paper, Maxwell's "On governors". (1869) [1] This is
| the first theoretical analysis of feedback.
|
| _It will be seen that the motion of a machine with its governor
| consists in general of a uniform motion, combined with a
| disturbance which may be expressed as the sum of several
| component motions. These components may be of four different
| kinds:-_
|
| (1) The disturbance may continually increase.
|
| (2) It may continually diminish.
|
| (3) It may be an oscillation of continually increasing amplitude.
|
| (4) It may be an oscillation of continually decreasing amplitude.
|
| _The first and third cases are evidently inconsistent with the
| stability of the motion; and the second and fourth alone are
| admissible in a good governor. This condition is mathematically
| equivalent to the condition that all the possible roots, and all
| the possible parts of the impossible roots, of a certain equation
| shall be negative._
|
| That is, in the left half-plane.
|
| (Terminology has changed. Maxwell says "disturbance" where today,
| the term "error" would be used. Today, "disturbance" means an
| input which disturbs stability, while error is an output.)
|
| Maxwell got so much right in that paper, and it was a long time
| before anybody picked up on that result.
|
| Now, where it looks like the author is going is into economic
| territory. Basic economics talks about "economic equilibrium".
| The concept is that restoring forces will bring supply and demand
| into equilibrium. But basic control theory tells us that may not
| happen. Any system with delay in it can potentially be unstable.
| Too much delay, and even simple systems will not stabilize.
|
| [1] https://en.wikisource.org/wiki/On_Governors
| WanderPanda wrote:
| In the real world all exponentials are sigmoids eventually, so
| what we actually get is is a recession with a drastic
| reallocation of resources (creative destruction).
| duped wrote:
| Not really, there are plenty that are sinusoids which are
| just complex exponentials.
|
| The real trouble with sigmoids is when the saturation point
| is beyond physically meaningful quantities of the system. See
| the tacoma narrows bridge collapse.
| [deleted]
| regularfry wrote:
| Isn't it true to say that a theoretical exponential becomes
| a practical sigmoid precisely because some property of the
| system has become saturated and gone nonlinear?
| LeonB wrote:
| (Just trying to get this clear in my own head by writing
| it down.)
|
| When a real world system goes non linear (like the Tacoma
| Narrows case) you don't get a sigmoid but something
| catastrophic.
|
| (If you graph the amplitude of the vibrations they
| increase and increase -- and then -- if it was a sigmoid
| they'd level out and stay at the max amplitude... but in
| reality they go to zero as there is no bridge left to
| vibrate.)
|
| When a company is "growing exponentially" it may saturate
| the market and then the growth slows in a nice sigmoid
| function. That's common. But if, for example, the
| investors insist that the company must maintain the
| growth at all costs... it breaks laws, gets destroyed and
| there's no company left to grow. No exponential curve, no
| sigmoid, no signal at all.
|
| Both the sigmoid and the total collapse are typical real
| world results of what a simple model would expect to be
| an unbounded exponential curve.
| TheOtherHobbes wrote:
| Control theory assumes the system is linear. As soon as
| you get saturation the system stops being linear.
|
| So in trad undergrad control theory instability implies
| "And then the system blows up" - numerically, literally,
| or sometimes both.
|
| But depending on the system you can end up in regions of
| recursive instability which are better modelled by
| logistic/chaos theory:
|
| https://en.wikipedia.org/wiki/Period-doubling_bifurcation
| mattmaroon wrote:
| I have a feeling this is going to be about interest rates and
| housing.
| steve76 wrote:
| VogonPoetry wrote:
| I think this article is trying to make a political statement,
| "Our leaders have just done something that is going to cause a
| future problem, a crash".
|
| I have only read the linked article, I think the followup might
| be available, but I'm not going to read it before posting this --
| because this article was meant to be clickbait, to get you hooked
| and possibly mis-informed.
|
| The article as it stands (incomplete) contains some classic
| argument fallacies.
|
| It is an "appeal to authority", by attempting to explain control
| theory. This person knows something.
|
| The examples all result in bad things, airplanes crashing, hard
| drives (crashing - perhaps a stretch). Bicycle at the edge of a
| cliff. Eating too much ice cream. Chernobyl. This is a possible
| "appeal to emotion".
|
| The final issue is an "incomplete comparison". The graph at the
| bottom of the article shows housing prices -- all of the previous
| examples have mathematical models which can explain the behavior.
| For the last graph no model (the equations) is presented. Without
| a model you cannot use control theory to analyze the zeros and
| poles.
|
| The last graph wants you to believe in a continuing upward trend,
| the fallacious argument, implies that whatever the Canadian
| political change that has been made is going to make this trend
| to zero, despite the intention to keep it trending upwards.
|
| Background: A long time ago, as a mathematics undergraduate, I
| did take a course in control theory, it was run out of the
| engineering department. It was somewhat awkward as quite a few
| mathematical terms were not-quite-the-same. I get the same unease
| when reading this for poles, zeros and right-half-planes. Any
| engineering textbooks that use j for sqrt(-1) instead of i
| (because that is taken) is an indicator. Yup, this could be
| construed as an "appeal to authority".
| VogonPoetry wrote:
| I have now read the followup article.
|
| There are, to me some language red flags. The followup article
| now uses "we' -- suggesting this is not the work of an
| individual. This was not present in the initial post.
|
| An attempt is made to build a model. Curiously a visual
| programming model is now used. No explicit differential
| equations are given. If the equations are not given there is no
| way to check the model. So "pole" and "zero" analysis is mute.
|
| There are no tests to validate this model against past
| situations - an easy and free test, the past history is known.
| If the model that has been created and can predict the future,
| why would was it not run it against the past and show the
| predictive success?
|
| The built model is only presented against the current situation
| -- is it circumstantial / opinion based.
|
| My understanding of science is -- build a model that can
| predict the future / what happens accurately, i.e. matches the
| measurements. The consensus agrees that this is the (current)
| best model.
|
| Prices are ultimately influenced by a sentiment factor, a value
| derived from a I have no idea what human feeling / property.
| Some power "enabled" humans have been endowed with a much
| higher influence on this parameter. Where is this value
| expressed in the predictive equations?
| PragmaticPulp wrote:
| I agree. The first article was interesting when it was
| talking about control theory, but the hard pivot to economics
| and politics at the end turned the article from potentially
| informative to a disingenuous appeal to authority.
|
| The author clearly knows a lot about control theory, but this
| seems to have led to an idea that he knows a lot about
| everything. This is a theme I see all too frequently in
| people who list "systems thinking" as one of their areas of
| expertise (like this author).
|
| I have the benefit of the doubt and read the second article
| looking for perhaps some actual modeling and references to
| econ literature, but he merely refers to a couple papers and
| then admits that his model was home-grown and will be
| simpler. Some parts of it might be right, but this has too
| many elements of "I'm an expert in one thing therefore I'm
| qualified to talk about everything" for me.
| dukeofdoom wrote:
| Canada does not have 30 year mortgages. Most home owners have
| mortgages with 3-5 year terms. Since 3-5 years ago rates were
| low, and home prices were low, people's mortgage expenses are
| still low. However that's about to end. As people either
| bought at much higher prices in the last 2 years, and/or the
| older mortgages are getting renewed at higher interest rates.
| This will result in drastic increase in what people need to
| pay to stay in their home.... possibly causing a market
| crush.
| VogonPoetry wrote:
| Governments are in a privileged position to get this data
| and they likely have it and have reasonable models.
|
| The classic knob to influence inflation is interest rates.
| This can be also be modeled. Non-politicised civil servants
| have a good record of being able to do a reasonable job at
| this - only if the politics are removed. In my opinion,
| removing all political allegiance for civil servant
| agencies is probably the best way to get better long term
| stability and prosperity.
| Sohcahtoa82 wrote:
| > Most home owners have mortgages with 3-5 year terms.
|
| As an American, this is easily misinterpreted to mean the
| mortgages are expected to be paid off in 3-5 years, which
| would be mind-blowing if true, because it would mean that
| either houses are super cheap, or only the rich are buying.
|
| IMO, adjustable-rate mortgages are almost a scam. Are there
| any legal protections in place to disallow a bank from
| deciding "In the next period, we're going to raise your
| rate to 20% because fuck you the CEO wants another yacht"?
| cecilpl2 wrote:
| You are correct that in Canada we don't do 30-year fixed
| mortgages. We only lock in interest rates for a 5 year
| term.
|
| However, we have what's called a stress-test. In order to
| get a mortgage at the previously low 5-year fixed rates of
| 2%, you still had to qualify as though the rates were >5%.
| This means that if rates go up to 5% everyone should still
| be able to afford their payments.
| jimbob45 wrote:
| 3-5 year mortgage? Aren't the monthly payments totally
| destructive to one's financial health?
| kspacewalk2 wrote:
| The renewal periods are typically 3-5 years. The standard
| mortgage amortization period in Canada is 25 years.
| kspacewalk2 wrote:
| >This will result in drastic increase in what people need
| to pay to stay in their home
|
| This will result in a drastic increase in what _a
| relatively small number_ of homeowners need to pay to stay
| in their home. Specifically, those who bought a house to
| live in in the last 3-4 years.
|
| >possibly causing a market crush.
|
| Before losing their home, this relatively small number of
| people (plus a larger number of those who will experience
| much more moderate mortgage payment increases) will cut
| back on spending for literally everything else. This will
| have a very significant impact on the rest of our economy.
| Which, in fact, is the whole point of inflation targeting -
| cool down the economy when inflation is out of control.
| btilly wrote:
| _Specifically, those who bought a house to live in in the
| last 3-4 years._
|
| Also those who renewed in the last 3-4 years. Which
| realistically means most of those who bought in the last
| 20-25 years.
|
| That's likely over half of all homeowners - not so small
| a fraction after all!
| davidgay wrote:
| Yes, but interest is front-loaded on mortgages, so the
| impact is much lower for those 20-25 years in.
| kspacewalk2 wrote:
| >Also those who renewed in the last 3-4 years.
|
| No. Those who paid the exorbitant prices of the last 3-4
| years. I've renewed recently, and borrowed the ~$100k
| remaining on my mortgage at a historically low rate. If I
| had to renew at twice that rate it would not make a huge
| impact on my finances, because I'm currently paying
| interest on a five-figure principal.
| btilly wrote:
| But it still would impact you.
|
| Across all Canadians, we're talking about $1.5 trillion
| (CAN) in mortgage debt. That's on par with the GDP. If
| you hike the interest rates to match your inflation,
| that's like sucking 5% of your GDP into interest
| payments. This will be a pretty dramatic event, no matter
| how it is distributed.
| kspacewalk2 wrote:
| It will certainly be a dramatic event, but it still
| matters how it is distributed. To make up some numbers by
| way of example, if 4 million people have to pay $50/month
| more, I believe it has a significantly smaller effect on
| the economy than 1 million people having to pay
| $200/month more.
| cecilpl2 wrote:
| > Specifically, those who bought a house to live in in
| the last 3-4 years.
|
| No, everyone in Canada has to renew their mortgage at
| least every 5 years, into whatever the prevailing
| interest rate market is at that time.
| kspacewalk2 wrote:
| The vast majority of 28% of Canadian households who are
| currently carrying a mortgage did not buy their house at
| peak bubble prices, i.e. within the last 3-4 years. They
| carry a much more modest debt load, have paid off more of
| their mortgage, and this will significantly dampen the
| effect of rising rates on their finance.
| trelane wrote:
| Wait, so all mortgages in Canada are ARMs by another name?
| kspacewalk2 wrote:
| I'll be that guy. Please don't hate me.
|
| >So "pole" and "zero" analysis is mute.
|
| Moot.
| VogonPoetry wrote:
| Yup, it should have been moot.
| esquivalience wrote:
| I spotted that but thought your original worked nicely
| anwyay (it is silent on these things)
| taylorius wrote:
| I suppose if pole and zero analysis disagree with you, they
| probably aren't going to say anything.
| relaxing wrote:
| Thank you for taking the time to write these follow-ups. I
| was left with the same uneasy feeling at the end of the
| article, and you've articulated perfectly why.
| mellavora wrote:
| > There are, to me some language red flags. The followup
| article now uses "we' -- suggesting this is not the work of
| an individual. This was not present in the initial post.
|
| First person plural ("we") is normal in technical and
| scientific writing.
| VogonPoetry wrote:
| Yes, agreed. It is a term of inclusivity that is applied to
| observations and models, the testable items. I don't think
| "we" it is acceptably used for individual opinions unless
| it reflects the opinions of multiple authors.
|
| The followup definitely uses the "I" (for opinion)
| initially, but then switches to "we".
|
| As a reader I am not a participant in "we" unless I agree
| with the statements being made. I think it is this is what
| made me frosty and say who is this other person, because it
| isn't me.
| Victerius wrote:
| I call it the "Ian Malcolm syndrome", in reference to the
| character (a mathematician) in Michael Crichton's _Jurassic
| Park_ who tries to apply mathematical concepts to the dinosaur
| attraction to try to show why it is doomed to collapse.
|
| There are a lot of similar posts online about people trying to
| use chaos theory (or what they believe chaos theory is),
| "systems theory", and other obscure concepts to explain why,
| for example, climate change will be the end of us all, or the
| global economy will enter a depression, or any other extremely
| pessimistic macro scenario. I see three reasons why these
| people are doing it. (1) To draw attention to themselves as
| someone with a superior intellect (which they actually aren't)
| (2) To construct an analysis no one has constructed before, in
| a "all these professional economists are saying the same thing,
| but here's why they're all misleading themselves, thanks to my
| ace card of a theory" kind of way, and (3) A love for the
| hyperbole, for dramatic outcomes.
|
| A classic economic prediction like "Inflation pressures will
| potentially slow down growth in the short term, but the
| behavior of the economy over the next 12 months remains
| unpredictable" is not enough. It MUST be "A catastrophic
| economic collapse is inevitable", or "We are going back to the
| Middle Ages by the end of the decade", or "Hundreds of millions
| will die in the next few years".
| sebastos wrote:
| Er, Ian Malcolm, the character who was introduced so that he
| could arrogantly predict that the park would collapse, only
| to get his satisfying come-uppance when... he turns out to be
| completely correct?
| Natsu wrote:
| Why doesn't all the same analysis apply to your making of
| "Ian Malcolm syndrome" itself?
| starkd wrote:
| I admit I was a bit disappointed by the end of the article. But
| I don't think it was strictly an appeal to authority. The
| author is evidently a very good writer, but he might have done
| a better job at summing up a conclusion. It's very difficult to
| tell just what point he was trying to make. He never even said
| just what his inputs and outputs are in his housing model. Even
| if he is saving that for a later article, he should have at
| least mentioned that.
| syntaxfree wrote:
| "the math that I know is THE math to explain inflation,
| political instability and more"
| any1 wrote:
| Textbooks that use j instead of i are an indicator of what? Why
| is slightly different notation awkward? It's not as if notation
| is always consistent within the field of mathematics, right?
| VogonPoetry wrote:
| The context of the writer. Apologies if I implied that the
| notation semantics were important -- letter exchange is free;
| concept change is not. What I indented to mean was the use of
| the terms poles and zeros is a bit wonky. Attempting to be
| cute with a physicist's hat, a pole is a "black hole", an
| entity you must not cross because the calculus will not work.
| It is a discontinuity, a singular value. There are worse
| things in mathematical generalizations; a cut / line in a
| manifold. But tools to cope.
| fluoridation wrote:
| That's not an appeal to authority. An appeal to authority is "P
| is a statement in the topic T. A is an expert in T. A says P is
| true. Therefore P is true." If I draw a parallel between two
| topics and proceed to explain one of them in order to argue
| something about the other one, that's not an appeal to
| authority.
|
| It could be that the reader fails to understand the explanation
| and instead treats the writer as a trustworthy authority. That
| would not make the argument an appeal to authority or even
| fallacious.
|
| It could be that the analogy is poorly justified, which would
| make the argument incomplete, or it could even be that the
| writer failed to understand some subtle aspect of the second
| topic that makes the analogy inappropriate. Neither of these
| would be appeals to authority.
| VogonPoetry wrote:
| In this case the author (A) is setting themselves up as an
| authority in (T). The statement (P) in this article has not
| been revealed, but because (and I suspected separated) is in
| the followup (which I have now read). The followup does refer
| back to the "now you know about poles" -- the appeal to
| authority.
| hmry wrote:
| Setting yourself up as an authority isn't a fallacy. It's a
| rhetorical device. (Though I am not sure what makes you say
| that anyway. The article didn't particularly strike me as
| the author setting themselves up as an authority, beyond
| what is inherent in writing an article that explains
| something.)
|
| If they made the argument "I am an expert in control
| theory, therefore what I think about Canadian politics is
| correct", that would be an appeal to one's own authority.
| But I didn't see anything like that in the article.
| fluoridation wrote:
| >The followup does refer back to the "now you know about
| poles" -- the appeal to authority.
|
| How is that an appeal to authority?
| VogonPoetry wrote:
| In the classic social media sense.
|
| You saw my post on X, now believe what I say on Y.
| fluoridation wrote:
| Would you mind pointing out in the second post the
| sentence where that line of reasoning is implied?
| yt-sdb wrote:
| The person you're replying to already has answered this
| question in a post you've already replied to. But to be
| explicit, consider the first sentence of the follow up
| post [1]:
|
| > Now that you know what right-half-plane zeros are, in
| this article I'm going to begin a deep-dive into a
| control-systems-based analysis of a certain feedback
| system that is drawing particular public attention today:
| inflation.
|
| In my mind, this is explicitly drawing a connection
| between the author's engineering background, particularly
| in control theory, and the current topic, inflation. To
| be clear, it would be fine if the author wanted to make a
| _mathematical_ connection between control theory and
| inflation. However, since the author does not explain
| right-half-plane zeros with any meaningful technical
| detail, the rhetorical effect is an appeal: "just trust
| me on this." Then the author switches topics _and
| explicitly connects the two topics_. I cannot speak for
| the person you're replying to, but this rhetoric is what
| bothers me.
|
| [1] https://jbconsulting.substack.com/p/on-shelter-
| futures-part-...
|
| EDIT: Looks like VogonPoetry already replied while I was
| typing this up.
| VogonPoetry wrote:
| These:
|
| "Now that you know what right-half-plane zeros are, in
| this article I'm going to begin a deep-dive into a
| control-systems-based analysis of a certain feedback
| system that is drawing particular public attention today:
| inflation."
|
| And all of the statements made in the walkback "a bit of
| a preamble" -- basically issuing caveats or disclaiming
| all of what was said before. A classic "I got you here",
| but I'm going to disclaim all of that, you are a fool to
| read anything that follows.
| fluoridation wrote:
| I read that as "now that you know some of the concepts
| and terminology used in systems theory, I can use them to
| make an argument in economics, and you can use that
| knowledge to judge for yourself whether the argument is
| valid or not". It's literally the opposite of a appeal to
| authority. As I see it, the only way it could be
| dishonest would be if the systems theory explanation is
| incorrect or purposely leaves inconvenient things out
| (which it might).
|
| It would be an (incompetent) appeal to authority if it
| said "now that you've seen that I know my stuff when it
| comes to systems theory, you know that this thing I say
| about economics is true".
| dahart wrote:
| > As I see it, the only way it could be dishonest would
| be if the systems theory explanation is incorrect or
| purposely leaves inconvenient things out (which it
| might).
|
| That should be the default assumption, no? Today's
| Control Theory has never been shown to be predictive of
| the economy or politics, wouldn't you agree? The article
| framed the discussion as if control theory is useful,
| purposely implied it's utility, and did not state it's
| _known_ lack of scientific validity, which is indeed
| leaving some very inconvenient facts out, right? Saying
| that they left it open with a 'judge for yourself' is not
| a great counter to the critique of the argument style.
| There is an intentional framing here that fails to list
| the alternatives, tries to establish itself as 'correct'
| via implication, and pivots to a separate topic that is
| unproven to be relevant. Pretending to be unbiased while
| presenting a one-sided set of "information" is a pretty
| common type of appeal to authority.
| fluoridation wrote:
| I'm not particularly interested with whether the argument
| raised by the article is valid or not, which is why I
| left open several possible ways in which it _could_ be
| fallacious. My point is solely that it 's not an appeal
| to authority.
| emaginniss wrote:
| So if a school teacher taught you addition and then later
| used it as the basis for teaching multiplication you'd
| reject it because they were referencing their own work on
| addition?
| VogonPoetry wrote:
| This is complicated. It involves identity, credibility
| (accreditation), reputation and authority.
|
| For me to be taught, my parents ceded authority to the
| school to appoint credible teachers. Those teachers will
| have an identity, qualifications and perhaps a
| reputation. There are consequences for failing or abusing
| this position.
|
| This is the way a lot of traditional things work.
|
| To directly answer your question, no. A teacher that
| taught addition would likely be excellent for teaching
| multiplication.
|
| But, I don't think this is how the internet now works,
| especially in the social media space. There is infinite
| identity, which creates trust problems for reputation and
| credibility. Applying traditional models breaks down. At
| the moment the dominant factor appears to be who can win
| a popularity content.
|
| Hacker News is interesting in that karma is currency to
| build credibility and reputation. This model has flaws
| too. In my opinion, rewarding the most popular is not a
| long term winning strategy for a society or community.
| The demand for change only comes from dissenters.
| Dissenters and different opinions are the engines of
| change for any society / community, otherwise, without
| change, it would stagnate and fall into decline.
|
| But, in the face of infinite identity what is the
| collective actually trying to say?
| fluoridation wrote:
| I find it pretty funny that you're accepting one claim
| _because_ it comes from what you think is an authority,
| while rejecting another because you think it relies on an
| appeal to authority.
| paledot wrote:
| No, but I wouldn't trust them if they referenced their
| math experience as a qualification to teach me SCUBA
| diving.
| relaxing wrote:
| An elementary school teacher doesn't need to rely on
| appeal to authority to teach math. The student can
| quickly verify the method works themselves -- they don't
| have to take the teacher's word for it alone.
|
| In general, appeal to authority as a fallacy applies to
| subjects that are opinion-based or contentious.
| starkd wrote:
| Actually, it seems more an effort to establish credibility.
| "I have a degree in such and such" or "I have worked in
| this field for over 20 years". That seems to be much
| different than appeal to authority.
| throw10920 wrote:
| It seems to only be an appeal to authority when it's a
| person or a position that one disagrees with. Otherwise
| it's "experience" or "consensus".
| Natsu wrote:
| What makes appeal to authority fallacious is that one's
| supposed expertise has no bearing on the truth of the
| things one says. An appeal to authority is when someone
| argues something like, "I'm an expert, I think X and so
| should you" basing their opinion on X on their supposed
| expertise and not actual logic.
|
| When someone gives reasons, their argument rests on those
| reasons, not on their supposed authority as an expert on
| the topic.
| TimPC wrote:
| The follow-up article tries to argue there is an over five year
| lag to interest correcting inflation based on undisclosed
| principles of a model they don't provide equations for. Their
| argument is in effect that the growth of roughly 30% of the
| inflation basket of goods (housing) dominates the shrinking of
| the other 70% of the inflation basket of goods. The analysis is
| suspect as they don't seem to model how much the 70% shrinks or
| slows in growth at all. They also aren't very numerically
| precise on the interest effects on housing prices and
| misanalyze how mortgages work in Canada.
|
| Their analysis argues that roughly 4% of mortgages are replaced
| every year while 96% retain the same rates. This makes it hard
| to argue interest rates have the desired effect size but that
| doesn't stop them from trying.
| jbay808 wrote:
| > The analysis is suspect as they don't seem to model how
| much the 70% shrinks or slows in growth at all.
|
| It doesn't model it at all. The trajectory of ex-shelter CPI
| is taken as an input. For the provided scenarios, all non-
| shelter components are assumed (as a scenario _premise_ , not
| a prediction) to instantly return to a 2% growth rate and
| stay there.
| TimPC wrote:
| I'm curious what the right half plane zero in housing is. In
| general, we correct inflation through interest which we raise
| gradually waiting a month or two to observe the effects of a
| 0.5% raise. I think that should be sufficient to avoid the
| control feedback effects he talks about in this article.
| jbay808 wrote:
| The RHP0 in (Canadian) housing comes from including mortgage
| interest payments -- a term that increases in proportion to
| interest rates -- in the measurement of the CPI.
| CFLAddLoader wrote:
| The author of the article has had their understanding of
| systems eat their understanding of humans. Every time they make
| a realization about people, it immediately gets turned to
| getting more understanding and control over the world. Which
| doesn't leave any room to grow for their understanding of
| humans.
|
| This makes it really hard for them to write an article for non-
| technical people. To do so, they would have to connect the
| human side of things to the systems theory side of things.
| Which they can't do, because they don't understand the human
| side of things.
|
| They aren't using bad-faith arguments to convince you that they
| are correct. They simply have no idea how to talk to you. They
| are in fact trying to be helpful, by presenting what they think
| is really useful information to understand and control the
| world with. Their help is useless to you, but they are trying.
| yt-sdb wrote:
| I agree. The author uses technical jargon but is clearly
| intending the reader to be non-technical. Otherwise, footnote 1
| should just be in the main text. The rhetorical effect,
| intended or otherwise, is an appeal to (the author's)
| authority. As you say, the author then switches to a topic he
| likely much less expertise in (housing prices, inflation, etc.)
| while relying on the reader to believe that this new problem
| shares some mathematical foundations with the original set of
| problems.
| skybrian wrote:
| This seems uncharitable. The author is trying to explain how
| knowing a bit of control theory could be helpful for
| understanding economics. Unfortunately they're having trouble
| writing for a general audience, perhaps due to being too
| comfortable with the math. This doesn't mean anything
| nefarious, just that they could use an editor.
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