egg|nomz|egg 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> egg|nomz|egg: generally if your eyes are dewing over, that's not the weather. | <ferram4> I shall beat my problems to death with an engineer.
<SnoopJeDi> awang, the plain-language version is that Integrating Things Is Hard and if you aren't careful you can fail to conserve energy in a system (a lot of egg|anbo|egg's numerical eggsperiments are concerned with this)
<awang> The mathematics gradient between the Principia codebase and my head may prove to be too much for that to work :(
<SnoopJeDi> The Boris pusher splits up the way you move a particle in electrodynamic simulations in a way that avoids this. The n+1/2, n-1/2 business is describing "half" steps
<awang> Although since I have 50% of the things needed to learn graduate math, I suppose it's worth a shot
<SnoopJeDi> it's a *little* like something called the leapfrog method
<SnoopJeDi> numerics are...hard.
<awang> ....Apparently o_O
<awang> That would also explain why a FEA tool at work likes to crash after changing an input by a small amount, I guess?
<awang> FEA involves integration?
<SnoopJeDi> uhhhhh
<SnoopJeDi> sorta? in the sense that you usually build your problems in integral form
<egg|anbo|egg> SnoopJeDi: NewtonDelambreStørmerVerletLeapfrog!
<SnoopJeDi> most of the machinery that makes FEA go is more akin to variational calulus, though
<SnoopJeDi> awang, are you familiar with Newton's method?
<awang> Sort of
<awang> Been a while since I did anything calculus-related
<SnoopJeDi> if you're comfortable with the "update the answer until the answer is good enough" sort of scheme, that's all you *really* have to know in principle. FEA is a very-high-dimensional analogue (and indeed, many solvers in commercial products use things that look a lot like Newton's method!)
<awang> egg|anbo|egg: Where'd the "Leapfrog" part come from?
<awang> Ah
<awang> That's... surprisingly simple
<SnoopJeDi> from a linear algebra standpoint, you're trying to find the closest neighbor to a thing that lives in infinite-dimensional space (the "true" solution)
<SnoopJeDi> where the neighbor lives in finite-dimensional space (your mesh)
<SnoopJeDi> which is incidentally why "mesh it right" is like 99% of the battle haha
<awang> Makes sense
<egg|anbo|egg> awang: trying to describe the fact that your velocities and positions are offset half a step from each other, so advancing one leaps it over the other
<awang> That would also explain some of the conversations around the office talking about meshes
<egg|anbo|egg> (afaict nobody called Leapfrog invented it)
<SnoopJeDi> (as opposed to updating the positions and velocities simultaneously)
<egg|anbo|egg> (but then a lot of people invented it, so you never know)
<SnoopJeDi> oh yeah, meshes are the bane of all FEA
<SnoopJeDi> even if the mesh doesn't make a problem unsolveable, a bad choice can make the problem poorly conditioned and it will fail to converge
<awang> egg|anbo|egg: Ah, that name makes sense
<SnoopJeDi> if you're curious about it, the FEniCS project has a whole book that I believe has some pretty good info on FEM as well as how to use their Python codebase to solve problems
<SnoopJeDi> I learned mine out of a monograph by Peter Monk, "Finite Element Methods for Maxwell's Equations," which is kind of a (very good!) hodgepodge of functional analysis, electrodynamics, numerical analysis, and a few other odds and ends
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<awang> SnoopJeDi: I'll definitely check that out
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<UmbralRaptor> Having lots of access to shiny expensive equipment but struggling with food/housing is very #academicproblems https://twitter.com/diodelass/status/958157690735296512
<kmath> <diodelass> @bofh453 the amusing thing is that these days I can get $100+ worth of electronic parts on the deparment's budget w… https://t.co/p8jqoSPyNQ
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<kmath> <drannawatts> Buoyancy leads to convection. Convection leads to turbulence. Turbulence leads to the dark side. https://t.co/PpRMV207h4
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<UmbralRaptor> ;seen majir
<kmath> UmbralRaptor: I haven't seen majir
<UmbralRaptor> ;seen majiir
<kmath> UmbralRaptor: majiir (~majiir@2601:18c:ca00:a400:211:32ff:fe42:6eda) was last seen idling in somewhere 11 hours and 20 minutes ago
<UmbralRaptor> !seen majiir
<Qboid> UmbralRaptor: I haven't seen the user majiir yet.
<UmbralRaptor> egg|anbo|egg: found the purrfect circuit?
<egg|anbo|egg> whitequark: ANBOcat saw a cat outside and started hissing at the window and making some weird and loud noises
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<UmbralRaptor> egg|anbo|egg: I recall hearing similar sounds when a cat that preferred living alone was introduced to another cat.
<egg|laptop|egg> ANBOcat tolerates the yellow cat that comes sometimes in the summer
<egg|laptop|egg> but apparently doesn't get along with this one
<egg|laptop|egg> I initially read that as $3 bills https://twitter.com/whitequark/status/958407092573962242
<kmath> <whitequark> *stares at $300 in S3 bills* this is fine
<UmbralRaptor> Hah
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<UmbralRaptor> So, you know how I took 2 qualifying exams on January 17 and 18? Apparently they haven't been graded, and probably won't for another week or 2. So, I should find out if I actually passed Classical and Quantum sometime in mid February.
* UmbralRaptor 🔪 🗡🔪
<SnoopJeDi> >:|
<soundnfury> UmbralRaptor: so, currently you (|passed> + |failed>)/√2 quals?
<UmbralRaptor> Yes
<soundnfury> don't worry, you'll decohere when the results arrive
<soundnfury> or possibly incohere, whatever
<soundnfury> (but you won't collapse ;)
<UmbralRaptor> Probably
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<egg|laptop|egg> bofh: okay, today's episode of "principia development": a benchmark that, if run with profiling, causes the machine to powercycle
<egg|laptop|egg> it's deterministic
<egg|laptop|egg> I have no idea
<APlayer> egg: It is so overwhelmed from the BEAUTIFUL MATHS that it briefly falls unconscious
<APlayer> On a more serious not, the single most foolproof way of crash debugging I know is manually tracking the program flow, installing breakpoints on the way and eventually tracking it down to a single routine, block of code and line.
<APlayer> Might get impractically long in complex flowing programs, though
<bofh> egg|laptop|egg: what the actual fuck?
<egg|laptop|egg> bofh: quite.
<UmbralRaptor> Work the delta function-related problems in Griffiths and Jackson.
<UmbralRaptor> Optional: Find an old graduate E&M textbook. It probably does not introduce the delta function, but it covers topics similar to that covered in both Griffiths and Jackson. How do they handle delta function related problems?
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<UmbralRaptor> ^how is this a single homework problem?
<UmbralRaptor> egg|anbo|egg: coronagraphs are magic.
<UmbralRaptor> (Well, lyot, vortex, etc ones, anyway)
<egg|laptop|egg> might be this
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<egg|laptop|egg> bofh: a spectre is haunting Principia: the spectre of speculative execution.
<SnoopJeDi> egg|laptop|egg, are you familiar with Floquet theory at all? I'm scratching my head a bit at why the transformation is valid for Hill's equation when the varying coefficient κ(s) is nonperiodic
<UmbralRaptor> egg|anbo|egg: will building Principia on my MBA cover my desk in corium?
<egg|laptop|egg> UmbralRaptor: unlikely
<egg|laptop|egg> SnoopJeDi: never heard of it tbh
<SnoopJeDi> I suspect if the coordinate s is on some bounded interval, you do the "normal" trick of copy-pasting κ(s) infinitely to make it periodic and discard the solution outside the interval anyway
<SnoopJeDi> ah okay, figured I'd try my luck :P
<egg|laptop|egg> UmbralRaptor: but you should build principia!
<egg|laptop|egg> SnoopJeDi: try bofh
<SnoopJeDi> the book by the Very Smart Man says the solutions are valid even in the nonperiodic case, but I'm bothered by why and my advisor is being a dismissive dick about it
<awang> Wonder what about the sampling code causes Windows 7 to reboot without any logs or anything
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<bofh> on today's episode of hell, compiling libtiff for windows-i386.
<awang> bofh: Why?
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<UmbralRaptor> Party like it's 1998?
<UmbralRaptor> Or I suppose 2008. *stares at Urvogel*
<awang> Urvogel?
<UmbralRaptor> Context, an old netbook I have (Intel U2500, a Core1Duo).