UmbralRaptor changed the topic of #kspacademia to: https://gist.github.com/pdn4kd/164b9b85435d87afbec0c3a7e69d3e6d | Dogs are cats. Spiders are cat interferometers. | Космизм сегодня! | Document well, for tomorrow you may get mauled by a ネコバス. | <UmbralRaptor> … one of the other grad students just compared me to nomal O_o | <ferram4> I shall beat my problems to death with an engineer.
<egg|z|egg> not all tensors the results of tensor products, some are merely linear combinations thereof
<egg|z|egg> also the partial trace is much nicer to eggspress with Einstein notation, a^{ki}_{ji}
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<kmath> <bofh453> Current mood: <@Newpa_Hasai> Is 2017 the series finale or something? <@jgerity> If it's not we're definitely poised mid-air over the shark.
<bofh> egg|z|egg: universal property, IMO. like, it's the vastly less confusing way in the long run.
<egg|z|egg> bofh: yeah, but then for a quick introduction it gets messy...
<bofh> and it's straightforward enough to go over given only linalg, by using tensor-products over modules as a representative system.
<bofh> true, but IMO a lot of that is b/c you need to actually draw the diagrams
<egg|z|egg> bofh: true; over IRC that's hard :-p
<egg|z|egg> bofh: feel free to have another go at shoving tensors into UmbralRaptor btw
* egg|z|egg should zzz
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<bofh> *nods* might try in a bit.
<UmbralRaptor> hrm
<UmbralRaptor> bofh: Also, *way* too evergreen.
<UmbralRaptor> At least it'll stop in 102 days.
<UmbralRaptor> (Or tonight if I had gone with 5777)
<egg|phone|egg> UmbralRaptor: evergreen?
<kmath> <bofh453> Current mood: <@Newpa_Hasai> Is 2017 the series finale or something? <@jgerity> If it's not we're definitely poised mid-air over the shark.
<kmath> <MonaChalabi> Career low: an 8th grader asks to interview you for a school project, you say yes and then the "production team" ch… https://t.co/zbvdsV375N
<egg|phone|egg> Bofh: 貓=猫 ⊗_ℝ ℂ
<UmbralRaptor> egg|phone|egg: AAAAAAAAAAAAAAAAΑA
<egg|phone|egg> UmbralRaptor: cats!
<UmbralRaptor> cat tensor product with "_R C"?
<kmath> <FioraAeterna> Yog-Sothoth knows the gate. Yog-Sothoth is the gate. Yog-Sothoth is the key and guardian of the gate. https://t.co/6ZfBb8oI2U
<bofh> egg|phone|egg: >_>
<bofh> SnoopJeDi: accurate description of Stokes' theorem IMO
<UmbralRaptor> Past, present, future, all are one to Yog-Sothoth.
<egg|phone|egg> Bofh: ネコノミコン!
<egg|phone|egg> UmbralRaptor: complexification
<UmbralRaptor> egg|phone|egg: well, yes.
* UmbralRaptor totally read the "no" as a sentence particle.
<Fiora> i'm glad there is appreciation of uh
<Fiora> that thread
<Fiora> and its spawn
<egg|phone|egg> UmbralRaptor https://en.m.wikipedia.org/wiki/Complexification of the simplified ideograph ?
* egg|phone|egg terrible pun
* UmbralRaptor facepalms
<SnoopJeDi> I should learn not-English, for the wordplay alone.
<bofh> Fiora: one can never go wrong with the Lurker at the Threshold & his demonic hellspawn :P
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<kmath> <eevee> ok i really need to figure out how to get latex's math font to match the prose font, because right now i'm wrapping every prose number in $$
<SnoopJeDi> I have no idea what her book is about but I WANNA KNOW
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<SnoopJeDi> 23:27 < Zensei> <o7 this guy is looking at the solar eclipse
<UmbralRaptor> ?
<SnoopJeDi> emoticon guy with both hands up and I'm just stunned by it
<FluffyFoxeh> hah
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<Technicalfool> "The word "variable" comes from math, where it means almost the exact opposite thing"
<Technicalfool> ...no, it means pretty much the same thing.
<Technicalfool> now equals-as-assignment operator is subtly different, but still not "the exact opposite"
<SnoopJeDi> Technicalfool, except with Python names where they're...pretty much the same thing again :)
<SnoopJeDi> or any other reference-y language I s'pose, I think Java's the same way?
* SnoopJeDi hasn't written Java since the 90s and nothing serious
<Technicalfool> if anything math is the more ambiguous one. I mean where in E=MC^2 is "C" defined as type const? >.>
<Technicalfool> I AM KIDDING BEFORE SOMEONE QUOTES THE ENTIRE DAMN THEORY AT ME.
<FluffyFoxeh> SnoopJeDi: in such languages, variables are essentially labels that store the address of the object they refer to
<FluffyFoxeh> but they can be re-assigned
<FluffyFoxeh> (Usually)
<SnoopJeDi> FluffyFoxeh, that was my point!
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<egg|cell|egg> https://www.rockpapershotgun.de/ Flinte Stein Papier?
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<Iskierka> https://twitter.com/lbent/status/910583945514835969 @egg, do you actually pick your own job title at google?
<kmath> <lbent> @justkelly_ok @yonatanzunger @GoodfellaTaco The ironic part is that he *could* have titled himself "Wizard" at Goog… https://t.co/F90BWBNFQE
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<egg|work|egg> UmbralRaptor: moar delocalized ANBOcat: this time near the office! O_o
<egg|work|egg> something something unitary evolution of cats something
<egg|work|egg> bofh: I wonder whether 貓 = 猫 ⊗ ℂ is too terrible a pun to tweet :-p
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<UmbralRaptor> egg|work|egg: ANBOcat is an eigencat?
<UmbralRaptor> And how would a pun be too terrible to tweet?
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* UmbralRaptor stares at emails.
<UmbralRaptor> "Now you can support Honor Society — and get rewarded when you make a purchase. There is no limit to the amount of rewards you can earn 1 Apply for the Honor Society Visa® card today. In addition to your $100 bonus,1 you'll get these other great benefits:"
<UmbralRaptor> … no
<kmath> <bofh453> I think Jose is lost. https://t.co/aTmocj8Adi
<kmath> <stephentyrone> @bofh453 He's welcome to remain lost as long as he likes.
<FluffyFoxeh> lol
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<APlayer> Hi!
<APlayer> Ellied: Are you online?
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<UmbralRaptor> egg|phone|egg: house guarding cat?
<egg|zzz|egg> apparently
<egg|zzz|egg> UmbralRaptor: note that this cat appears earlier in the same place (but sleeping in the sun instead)
<egg|zzz|egg> no, in the shade
<egg|zzz|egg> UmbralRaptor: but yeah, that's a highly localized cat
<UmbralRaptor> Maybe the cat was tired after a long shift?
<egg|zzz|egg> !wpn bofh
* Qboid gives bofh a symmetric geobukseon
<kmath> <DrPhiltill> Seen at #EPSC2017 https://t.co/5Eb1nYw50n
<UmbralRaptor> (also note the comment about output stability)
<Ellied> APlayer: ahoy
<APlayer> Hi! You were recommended for transistor questions? :-)
<Ellied> aye
<Ellied> what's the application?
<APlayer> So, let me describe that...
<SnoopJeDi> hmm, has anyone claimed the nomme de plume "The Transistor Trans-sister?"
<egg|zzz|egg> bofh: is there some meaning of complexification that applies to categories? so I can make the 貓 = 猫 ⊗ ℂ pun even worse
<APlayer> I have my Raspberry Pi hooked up to a power bank. I want to be able to turn it off and on again without removing any cables. So, to turn it on, I just press a button on the battery pack and it starts delivering current.
<Ellied> right, but then you need to be able to cut it off once it's done powering down.
<APlayer> However, shutting down is more complicated. When I shut down using software, the display and RPi still draw some current, and the battery pack keeps delivering it
<APlayer> I need to fully cut it off for about 12 seconds for the battery to shut down as well
<APlayer> Anyway, I /may/ use a button, but I'd have to hold it down for that time... Or a switch, which would be equally annoying to switch back on.
<APlayer> Well, I did some research and figured the RPi has a pin that goes high immediately on boot (3.3 V) and low a few seconds before shutdown, which seems perfect
<Ellied> hmm, which pin is that?
<egg|zzz|egg> bofh: also you need to eggsplain tensors to UmbralRaptor
<Ellied> ahhh yes, good unless you actually use the UART (which you might want to for console access without a display?)
<UmbralRaptor> SnoopJeDi: I've seen variants of the joke, bur not as a Twitter nick or the like.
<APlayer> Now, the plan was to use a circuit with a capacitor that gets charged once the pin goes low and discharges on a transistor for 15 seconds to shut the thing down
<APlayer> Nah, I don't need it
<APlayer> If I ever do, I may just disconnect it, though.
<SnoopJeDi> UmbralRaptor, ah okay, I suspected I was not being terribly original :D
<APlayer> Would it be possible to rig such a thing with two transistors, a fitting capacitor and a virtually unlimited supply of resistances?
<APlayer> Two transistors means 1 PNP one and 1 NPN one
<Ellied> I would use a MOSFET. Bipolar transistors have lower current tolerances and the control terminal draws current, which complicates things.
<APlayer> Uh, how do those work?
<egg|zzz|egg> SnoopJeDi: s/mme/m/
<Qboid> egg|zzz|egg thinks SnoopJeDi meant to say: hmm, has anyone claimed the nom de plume "The Transistor Trans-sister?"
<egg|zzz|egg> (it's pronounced [nɔ̃], not [nɔm])
<egg|zzz|egg> ɔmnɔmnɔm
<SnoopJeDi> désolé, ne parles pas ta langue de la lune
<SnoopJeDi> (merci)
<Ellied> APlayer: basically, you can think of them as a tiny capacitor and a magic switch that turns on whenever the capacitor has at least a certain amount of charge on it, both of which have a common terminal.
<Ellied> The gate is the non-common lead of the capacitor, the drain is the other lead of the switch, and the source is the common lead of both.
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<APlayer> Ah
<Ellied> for your purpose you probably want an external capacitor to wire in parallel with the internal one, since gate capacitances of MOSFETs are by design very tiny
<APlayer> And what about the fact that I need one MOSFET/transistor that allows current to flow when the gate is high and one that allows it when the gate is low?
<Ellied> that's N-channel and P-channel, analogous to NPN and PNP
<APlayer> So you think this is possible?
<Ellied> my guess is you want a big honking P-channel one to act as your high-side switch (and carry the brunt of the current) and a small N-channel one to act as the active-high on-switch.
<Ellied> Using that configuration has the added bonus of increasing the switch-on threshold sensitivity, which makes switching a little simpler
<APlayer> Uh, sorry? What do you mean by high-side switch and active-high on-switch?
<APlayer> Also, how much current do regular transistors typically tolerate? For I am certain I have the necessary transistors, but probably have no MOSFETs.
<APlayer> I am sure I can find them on the internet, but it's no good if I have to pay the tenfold of the item's price for shipping. :P
<Ellied> give me a minute to answer all those questions, I have to do some TA nonsense in the real world
<APlayer> No worries. Actually, on second thought, I will probably have to order the capacitor anyway, so I can likely get all three from the same manufacturer in one package
<Ellied> Okay, back. Let me draw you a diagram.
<APlayer> (Sorry for that, I know next to nothing about EE, and this was just an "experiment"...)
<Ellied> no need to apologize, zero people understand this stuff when they're born. :P
<SnoopJeDi> Helpful to remember that the context is less than 100 years old :)
<UmbralRaptor> Obviously we need to abuse genetic engineering so everyone can be born with an MSc.
<SnoopJeDi> Eugenics for eu and me?
<SnoopJeDi> alternative joke: ewe and me
<APlayer> If you manage to genetically engineer an embryo to be born with a solid understanding of EE, physics, maths or the like... Then you /are/ god.
<APlayer> :P
<UmbralRaptor> If you aren't giving the general population godlike powers from time to time…
<Iskierka> Then what's the point of gay space communism? Speaking of, stellaris updated today
<APlayer> You just mentioned two concepts that mutually exclude themselves. :P
<APlayer> each other* seems to fit better here
<SnoopJeDi> homosexuality and communism? They certainly do not, judging by the ?? content of Twitter
<APlayer> (Please correct any grammatical mistakes I make, that's what helps me practice my English)
<SnoopJeDi> unless you mean one very specific realization of communism, in which case carry on Conrad
<UmbralRaptor> !acr -add:FALC Fully Automated Luxury Communism
<Qboid> UmbralRaptor: I added the explanation for this acronym.
<APlayer> I mean the only specific realisation of communism which survived long enough to make some impact in global economics
<UmbralRaptor> !acr -add:FALGSC Fully Automated Luxury Gay Space Communism
<Qboid> UmbralRaptor: I added the explanation for this acronym.
<APlayer> LOL
<UmbralRaptor> The second one is "ha, ha, just serious"
<UmbralRaptor> The first is a real school of thought.
<UmbralRaptor> Anyway, I'm in favor of the state handling a large chunk of healthcare financing, so… ☭?
<Iskierka> according to GOP, worse than ☭
<UmbralRaptor> Do they think that the NHS consists entirely of firing squads?
<kmath> <mbeisen> #NoteToSelf remove answers before printing midterm
<Iskierka> That's probably what theirs would consist of?
<APlayer> First... Ellied++, this is awesome!
<APlayer> (I did not expect so much effort for an answer to a question of mine :D)
<Ellied> the top shows what N and P channel MOSFET symbols look like, for reference. Note the weird convention about drain/source naming; the source goes to the power rail for most applications (and is NOT the one that current "comes out of")
<egg|nomz|egg> !wpn UmbralRaptor
* Qboid gives UmbralRaptor a 50Ω emitter
egg|nomz|egg is now known as egg
<egg> !wpn bofh
* Qboid gives bofh a simple UmbralRaptor
<egg> !wpn Ellied
* Qboid gives Ellied a kappa piston
<Ellied> you overestimate the amount of effort that went into that, I already had all the pens and paper in front of me from the class I just got done with
<egg> !wpn Iskierka
* Qboid gives Iskierka a blue falconet
<UmbralRaptor> egg: Does this mean I have no imaginary components?
<Iskierka> !choose humanoid, machine, mammalian, reptilian, avian, arthropoid, molluscoid, fungoid
<Qboid> Iskierka: Your options are: humanoid, machine, mammalian, reptilian, avian, arthropoid, molluscoid, fungoid. My choice: molluscoid
<APlayer> Uh, is all of that truly necessary for the circuit? Or is a lot of it just proper practice? (I did not imagine it to get this complex)
<Iskierka> !choose humanoid, machine, mammalian, reptilian, avian, arthropoid, molluscoid, fungoid
<Qboid> Iskierka: Your options are: humanoid, machine, mammalian, reptilian, avian, arthropoid, molluscoid, fungoid. My choice: mammalian
<APlayer> Also, as for the effort for the answer... Much less than the complexity of this circuit I expected to see calculated numbers.
<Ellied> APlayer: also note that you can game the values of the resistors and capacitors on the gate of the lower MOSFET; the time constant in the case of most MOSFETs will probably be about the same as the time it takes to turn off, so that's just the product of the resistance and capacitance in seconds. 10MΩ and 0.1µF will give you one second.
<Iskierka> nah I'm gonna ignore that one and pick my own nameset
<APlayer> Uh, sorry?
<Iskierka> welp, looks like we're going with FALGSC lead by cthulhu
<UmbralRaptor> Yay
<kmath> <BaltSymphony> In honor of Gustav Holst's birthday, we bring you: The Planets...as told by Cats. #HappyBirthdayHolst… https://t.co/ADaFKA2fXb
<APlayer> And how does the capacitor work, which is connected between GND and UART TXD?
<APlayer> (This is not the only question I have, it is just the bottommost :P)
<egg> !wpn -add:wpn ctenophore
<Qboid> egg: Weapon added!
<APlayer> !wpn egg
* Qboid gives egg a delta frustum
<Ellied> The lower MOSFET will shut down (and in doing so shut down the upper one) when its gate voltage dips below the part's rated threshold voltage, which is usually around 1-4 volts for modern parts (you want one as low as you can find; 2N7000 is like ~2 ish and very cheap). The capacitor discharges through the resistor after the input pin goes low and holds the MOSFET switched-on for some time
<Ellied> determined by how big the capacitor and resistor are..
<Ellied> the gate's own capacitance will be negligible compared to the capacitor you're adding, so you can sort of treat it as just a neutral voltage probe.
<APlayer> Uh, wait, I may be fundamentally misunderstanding how capacitors work here. What "way" does it discharge?
* Iskierka laughs at the spiritualist AI advisor voice. Spiritualists consider AI an abomination, and she's totally down with tha- oh, wait
<rqou> hey egg can you help me with "how to have intuition for geometric things?" why do these formulas work? https://i.imgur.com/Tedp69p.png
<rqou> why is there an outer product and a huge mess with cos^{-1}?
<Ellied> APlayer: Through the resistor right next to it. When the input pin is high, 3.3V/10MΩ in current flows through the resistor, which is low enough that it doesn't affect the voltage of the pin much and keeps that capacitor charged to about 3.3V. When the pin goes low, the diode keeps the capacitor from discharging back into the pin, so it has to discharge through the resistor, which takes time;
<Ellied> that time is longer if the capacitor is bigger (more charge to get rid of) or if the resistor is bigger (charge goes away slower).
<rqou> my "geometry-related" intuition is complete garbage
<APlayer> And what does the 10 MOhm resistance do? I assumed it closed the circuit when all else is shut down?
<egg> rqou: "δ can be thought of as a ball" WTF? are they *actively* trying to be confusingly inaccurate or what
<Iskierka> !cchoose ring, elliptical, spiral 2, spiral 4
<Iskierka> !choose ring, elliptical, spiral 2, spiral 4
<Qboid> Iskierka: Your options are: ring, elliptical, spiral 2, spiral 4. My choice: elliptical
<Ellied> It opens the circuit by discharging the capacitor, which lowers the voltage at the MOSFET gate and turns it off. The important thing is that it doesn't turn off until the capacitor has been discharging for some period of time after the input goes low.
<APlayer> So the GND parts are interconnected?
<egg> the equality that involves a δ defines a sphere (the sphere of the ps that satisfies it)
<rqou> egg: you do realize this isn't _actually_ a math class, right?
<Ellied> aye yes, they are. I should maybe have been more specific about that.
<rqou> right, i get that part
<egg> not even a ball, you'd need a >= there
<Ellied> all the grounds are connected to each other, and to ground.
<UmbralRaptor> !choose dE|dSph|compact|BCG
<Qboid> UmbralRaptor: Your options are: dE, dSph, compact, BCG. My choice: BCG
<egg> rqou: yes, but that's no excuse for going out of your way to make things more confusing @#^$%$@#
<Ellied> In this case "ground" really means "negative terminal of battery bank"
<rqou> ok, come here and teach/TA this class :P
<APlayer> Makes sense
<egg> rqou: nah get in the next plane to ZRH so I can teach it to you (also bring UmbralRaptor with you :-p)
<Ellied> oh can I come too
<rqou> anyways, i kinda understand what u and v are
<APlayer> So, UART TXD goes low. The capacitor keeps the N-Ch MOSFET open and delivers a current to the P-Ch one. What happens there?
<rqou> they're basically making that point r on the axis of rotation the new origin
<rqou> right?
<rqou> but then what's that omega*omega^T for?
<egg> I dunno, I have yet to skim through the whole thing :-p
<egg> I just saw that nonsense about a ball and got angry :-p
<rqou> fine, it's a sphere
<rqou> happy now? :P
* egg glares at the arccos on the last page
<APlayer> Let me just /query you to keep the conversations separate...
<UmbralRaptor> egg: let's go. https://photos.app.goo.gl/p3PqE4luZqm7CLVj2
<egg> APlayer: nah, mixed conversations are fine
<rqou> hey, i can't just fly to ZRH, i have other classes to attend
<egg> APlayer: also I'm going to afk to drink smoe tea probably
<egg> rqou: I'll be back in a bit after tea & chocolate
<APlayer> No worries, I just wanted to get that in one place
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* UmbralRaptor offers egg chocolate with hot peppers.
<kmath> <BaltSymphony> In honor of Gustav Holst's birthday, we bring you: The Planets...as told by Cats. #HappyBirthdayHolst… https://t.co/ADaFKA2fXb
* egg|tea|egg pokes bofh with UmbralRaptor and tensors
* UmbralRaptor tenses
<egg|tea|egg> bofh: also, <egg|zzz|egg> bofh: is there some meaning of complexification that applies to categories? so I can make the 貓 = 猫 ⊗ ℂ pun even worse
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UmbralRaptor is now known as EigenRaptor
<EigenRaptor> (160 minute long QM class in 55 minutes)
<egg> rqou: so, lemme look at that thing
<rqou> it does work btw
<rqou> blindly applying the formula is good enough for the first problem on the problem set :P
<rqou> (but of course i want to know wtf is actually happening)
<egg> rqou: hm, that arc cos on the last page makes me nervous if you want to evaluate that in floating point arithmetic (sounds like you're trying to summon the devils of ill-conditioning)
<egg> but anyway, back to the ωω^T
<rqou> yeah, i'm not familiar with computational issues that can arise here
<egg> ω^Tv is a trivector (a pseudoscalar), if we write it without silly matrix-heavy notation it's morally ω∧v
<egg> rqou: look for "mangled angles" in Kahan's "mindless"
<rqou> but hey, people who program robots can't even consistently handle gimbal lock :P
<egg> rqou: anyway, so ω∧v is a trivector, and then we multiply it (something something interior product) with a bivector (ω) and get a vector, so this does make sense (i.e. it doesn't depend on the chosen coordinates or on the chosen orientation).
<egg> as for intuition, lemme think a bit
<rqou> ok, you need to teach me n-vectors after i finish the problem set :P
<egg> ah but to do that properly I need to start with the tensor product, which brings us back to EigenRaptor...
<egg> :D
<rqou> wait, is the Kahan that wrote the thing about floating point that you linked me the same Kahan that invented this formula?
<egg> I don't know, never heard about those Paden-Kahan things
<rqou> how do you normally do IK?
<rqou> do you even do IK?
<rqou> does Principia need IK?
<egg> what does IK mean?
<EigenRaptor> IK?
<rqou> inverse kinematics
<egg> "[46] W. Kahan. Lectures on computational aspects of geometry."
<egg> welp, might be him
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<egg> rqou: anyway, read mangled angles, that arccos is suspicious unless the argument is necessarily far from 1
<SnoopJeDi> rqou, what would IK be used for in Principia? The subject is close to the math that drives, say, trajectory planning, but I'm not aware off the top of my head of anything in Principia that would need IK *specifically*
<SnoopJeDi> (I'm also not super familiar with Principia's innards, so)
<rqou> other types of vidya use IK to do things like e.g. figure out how to animate arms/legs/whatever
<egg> tbh we have *a lot* of weird stuff, but we don't have robotic arms
<rqou> i guess Principia doesn't eed that
<rqou> *need
<egg> *heed
<egg> *feed
<SnoopJeDi> if you wanted to solve trajectory optimization problems you'd use some similar maths
<egg> SnoopJeDi: uh
<SnoopJeDi> you'd maybe* use some similar maths
<egg> SnoopJeDi: that's a rather differently constrained optimization problem I think?
<SnoopJeDi> yes, I should think that's a rather obvious thing to say
<SnoopJeDi> but the maths that let you talk about the problem space manifold are the same, no?
<egg> rqou: so, the action (multiplication, cross product, whatever) of a bivector ω (again, think angular velocity or something) with a vector v is a vector orthogonal to v; it's also orthogonal to the angular velocity (which makes sense; you can't say it points in one direction without preferring right-handed or left-handed screws, but you can say that some line is the axis)
<SnoopJeDi> been too long since I've done any diff. geom or (complicated) optimization so maybe I'm out in left field
<rqou> is this all related to tensors?
<egg> distantly?
<egg> rqou: remember the infinitesimal rotations from last time? ω is still one of those
<egg> derivatives of rotations, etc.
<SnoopJeDi> inasmuch as tensors generalize vectors I guess?
<SnoopJeDi> generalize row vectors*, not the linear algebra-y vectors
<egg> SnoopJeDi: no, there's also the fact that it's a bivector, so the wedge product comes in
<rqou> so what's weird is that in my experience different groups of people have totally different ideas about what tensors are
<rqou> "CS/AI/ML" people --> "it's a big(ger) bag of numbers with higher dimensions"
<rqou> the way i heard of it --> "something something vector spaces and dual spaces"
<rqou> what wikipedia says --> "something something basis-independent transformations"
<SnoopJeDi> egg, right, the idea of an exterior product is definitely relevant too
<SnoopJeDi> rqou, there are a lot of perspectives to understand these sorts of maths from
<SnoopJeDi> c.f. algebraic vs geometric interpretatiosn
<egg> afk a bit reviewing #1569
<Qboid> [#1569] title: Fork the prediction at the end of the psychohistory | We don't really understand what's happening in #1561: the prediction starts *after* the current time of the plugin, which is rather mysterious (I have a hunch that the code that "forgets before" the prediction has something to do with the problem).... | https://github.com/mockingbirdnest/principia/issues/1569
<SnoopJeDi> of course there's something called psychohistory in Principia, heh
<egg> ah but there's a prehistory too
<egg> ferram4 had a comment about that iirc
<SnoopJeDi> that seems more redundant than obtuse
<SnoopJeDi> but naming preferences ¯\_(ツ)_/¯
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<egg> <ferram4> I see that principia is not only simulating gravity, but also shorten the dark ages after the fall of the empire.
<SnoopJeDi> R. D-annealed Olivaw?
* SnoopJeDi struggles for a joke
<egg> rqou: back
<egg> rqou: so you remember this stuff about derivatives of rotations right?
<egg> rqou: that "derivative of a path of rotations" is something that can be called a pseudovector, a bivector, an infinitesimal rotation (and that can be represented as an antisymmetric matrix)
<egg> rqou: ω is one of those
<egg> bofh: I accidentally typed ωq into google search and ended up on http://www.tolypreygel.com/notes/note_silly_hh.pdf Ꙩ_ꙩ
<kmath> <johnregehr> at least he's sharing today, sometimes he wants the whole thing https://t.co/spzegPVKG3
<kmath> <johnregehr> @spun_off https://t.co/gdWtXaDiP3
<egg> !wpn rqou
* Qboid gives rqou a solderless nephroid
<soundnfury> !wpn egg
* Qboid gives egg an osmium insulator
<Ellied> that's an unusual material for an insulator
<soundnfury> maybe it's an acoustic insulator?
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<rqou> whee, my "linear systems" course is now saying "btw, you should take the point set topology course in the math department if you have the time to"
<rqou> gotta have ALL THE MATH
<EigenRaptor> It's insulating you from xrays.
<bofh> https://mobile.twitter.com/martyn_williams/status/910991394419884032 cool, Kim Jong Un just straight-up served Tr*mp
<kmath> <martyn_williams> Extraordinary personal message from Kim Jong Un to Donald Trump on KCNA. I don't think I've ever seen something lik… https://t.co/OUmT4ZfYxU
<bofh> what the hell is happening
<kmath> <bofh453> Current mood: <@Newpa_Hasai> Is 2017 the series finale or something? <@jgerity> If it's not we're definitely poised mid-air over the shark.
<soundnfury> "a frightened dog barks louder" projecting much?
<bofh> like I'm fairly sure if you faced KJU or Tr*mp at a wall you'd have powerpoint slides appear
<rqou> linear systems is great! "let's shove all of diffeqs and other misc stuff into the first half, and then we still have the actual linear systems stuff to teach"
<bofh> yuck, why not just make it require a DEs course?
<bofh> nevermind the fact that any DE in a linear systems course is fully solvable using only laplace transforms
<Ellied> at my uni you just have to take an ODEs course and then a PDEs course before you can take anything interesting
<bofh> I overrode so many reqs in my undergrad, holy shit.
<Ellied> All freshman take the notorious Three Tired Classes (intro classical mechanics, waves, and E&M, the last of which is the First Great Population Bottleneck for physics majors) and then as a sophomore you take modern physics, ODEs, and PDEs, leaving you finally free for whatever else as a Junior.
<kmath> <pathogenomenick> Accidentally sequenced a cabbage.
<bofh> whitequark: ^
<Ellied> course subjects are so mixed up in my department that everyone just refers to courses by their numbers in conversation
<Ellied> *writing on the whiteboard* "What course is this for?" "311" "oh god, I'm so sorry"
<bofh> yep, same at both my current & past unis
<rqou> so this class _does_ require a DEs course
<rqou> but our DE course (if you're EE, not math) is apparently pretty unusual
<rqou> it's attached to the intro linalg course, and basically consists of saying "solving a system of linear ODEs is equivalent to finding the kernel of this linear operator"
<rqou> PDEs are then further added on top as "here's the heat equation and fourier transforms"
<rqou> also, this linear systems course deliberately isn't using laplace transforms
<rqou> it's using "modern" (apparently 1960s or so?) state space methods
<egg> bofh: hurricane where-the-hell-is-bermuda-2-the-return http://www.nhc.noaa.gov/graphics_at5.shtml?cone#contents ?
<bofh> rqou: well if you're doibg state space methods, why the hell do you need explict sol'ns of ODEs?
<rqou> fundamentals?
<rqou> idk actually
<bofh> egg: wow that's a strong steering current pushing it up from Hispañola & away from the American mainland.
<bofh> like it seems to be the one good thing that resulted from Irma: essentially a local slight shift of the Southern jet stream there
<bofh> I'm still amused at Jose thougj
<kmath> <generoom> @pathogenomenick I accidentally sequenced the stuff that lives inside a cat's mouth once. Was trying to sequence th… https://t.co/LBSWmhtOFe
<kmath> <ryanhanrahan> If I'm still talking about #Jose on Monday 9/25 I'm finding a new profession. https://t.co/Es5emOP9L9
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<bofh> extremely likely it'll still be a tropical depression, or maybe even still a tropical storm on 9/25
<egg> bofh: you need to tell EigenRaptor about tensor products!
<egg> also possibly rqou because bivectors so wedges :D
<rqou> how come i never learned any of this shit?
<bofh> sure but first I do need to review notes since it has been quite awhile
<egg> rqou: and also numerics, even though it's relevant for you? because we mathematicians get to learn all the good stuff :-p
<rqou> i should have been a math major :P
<egg> but also affine hovels and thick walls in spherical buildings, so,
<rqou> wtf
<rqou> it's not just CS majors that suck at naming things?
<egg> ah but mathematicians suck differently
* soundnfury gives egg a conifer
<egg> >_>
<egg> (yes I named something a conifer in my MSc. thesis)
<egg> it was a tree of cones, essentially :-p
<rqou> goddammit
<soundnfury> rqou: reading maths (or "majoring in math", as you call it) is definitely the best thing
<soundnfury> if you can survive a maths degree without going insane, you can excel in any other career
<soundnfury> and if you _do_ go insane, you can become a mathematician! ;)
<rqou> lol
<rqou> but i was lazy so i just have an EECS degree instead :P
<egg> surely you don't actually get the degree unless go at least somewhat insane
<bofh> ^
<rqou> even for EECS?
<bofh> this seems to be a necessary prereq for a math degree, at least.
<soundnfury> egg: I was mildly insane to start with — cambridge don't let you in otherwise
<soundnfury> but didn't become substantially more insane, hence why I only got a Third
<rqou> ah, another "fancy" school :P
<soundnfury> hey, at least I wasn't a trinmo
<kmath> <whitequark> @AmyZenunim if my three-story-high mom would pick me up and carry around that would be pretty fucked up
EigenRaptor is now known as UmbralRaptor
egg is now known as egg|zzz|egg
<UmbralRaptor> Well, whitequark's mother is too short to be an Eva.
<UmbralRaptor> ;8ball did Arecibo survive?
<kmath> UmbralRaptor: As I see it, yes
<kmath> <NPR> CORRECTION: An earlier tweet misidentified Kim Jong Un as the leader of South Korea. He is the leader of North Kore… https://t.co/PVPDVU11Zy
<soundnfury> "fake news"