UmbralRaptop changed the topic of #principia to: READ THE FAQ: http://goo.gl/gMZF9H; The current version is Διόφαντος. We currently target 1.3.1, and 1.4.x. <scott_manley> anyone that doubts the wisdom of retrograde bop needs to get the hell out | https://xkcd.com/323/ | <egg> calculating the influence of lamont on Pluto is a bit silly…
<novasilisko> https://i.imgur.com/Noh3acF.png better
<egg> novasilisko: no, KSP is unlikely to lead to sanity
<egg> (KSP fora that is)
<novasilisko> no i think your first statement was more correct
<egg> :D
<egg> I'll probably poke at your ellipsoids eventually, or bofh will
<novasilisko> i wonder if it would be possible to approximate gravitation of an oblate body by dividing the force among four points (two per axis) or something
<novasilisko> that sounds like an extremely dangerous path
<egg> no that sounds like a path to silliness
<egg> just do spherical harmonics, it's not that hard
<egg> you can lift the calculations off some shitty fortran or principia or something
<egg> (hell we used some shitty fortran we found to check that we had implemented it correctly)
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<bofh> 00:36:35 <@egg> (hell we used some shitty fortran we found to check that we had implemented it correctly)
<bofh> I am moderately curious which shitty fortran it was.
<bofh> but yes, just do spherical harmonics.
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<egg> bofh: but any idea how to find the point on a triaxial ellipsoid nearest a given point, which is novasilisko's question?
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<bofh> egg: thinking and reading a textbook right now, that's not a trivial question
<bofh> like the "triaxial" bit messes everything up
<bofh> actually is this question equivalent to just asking what the geodesic curves on a triaxial ellipsoid are?
<bofh> "just"
<egg> bofh: hmm how so?
<egg> bofh: question: are sections through an axes ellipses?
<egg> bofh: yeah, any section is an ellipse, right?
<egg> bofh: so now you need sectional eccentricity (spherical longitude) or something, and then you're back to the more pedestrian problem
<egg> bofh: hm wait no, the nearest point doesn't have to be on the plane through any axis
<egg> bofh: argh the lack of symmetry does fuck with things
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<novasilisko> this is like the only place i know that will know what i'm talking about - just messing around, made langton's ant https://i.imgur.com/JOw70HB.gif
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<novasilisko> https://i.imgur.com/8fywWgs.png on a wrapping grid after like 30k iterations or something
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<bofh> 11:02:02 <@egg> bofh: hm wait no, the nearest point doesn't have to be on the plane through any axis
<bofh> yep, eggsactly. which is giving me a headache.
<novasilisko> oh, were you poking at the ellipsoid problem while i was away?
<bofh> yes
<egg> yeah
<egg> novasilisko: you can see the backlog on https://logs.tmsp.io/principia/ or http://esper.irclog.whitequark.org/principia fyi
<novasilisko> oh okay
<egg> bofh: but still, that should be a workable approach: parametrize on spherical longitude, on the ellipse of constant longitude it's classical geodesy, so compute the shortest distance, and minimize over longitude hoping that the derivative isn't too horrid
<egg> not sure what the section eccentricity (λ) is, but that should be feasible too
<bofh> egg: hrm. I suppose that should work, come to think of it, yes.
<bofh> I guess even for nasty values of λ it should still be workable.
<egg> bofh: what do you mean nasty values of λ
<bofh> hm. disregard, I just realized now you're talking *section* eggcentricity and not, like, any global oblateness.
<egg> bofh: yeah by (λ) I mean as a function of λ, i am good with the words,
<egg> !seen awang
<Qboid> egg: Value cannot be null.
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<novasilisko> !wpn
* Qboid gives novasilisko a Molotov semimetal
<novasilisko> today i learned about semimetal
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<novasilisko> automataaaa https://i.imgur.com/f54H9qe.png
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