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…
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<GregroxMun> I sent US2 a long feedback letter complaining about the bad integrator
<GregroxMun> (and praising some of the other features, I wasn't trying to be mean)
<egg> their reply sounds reasonable
<egg> and Verlet is OK if you're trying to be fast (it's still symplectic so you don't get aberrant behaviour)
<egg> very often used in qualitative studies
<GregroxMun> among these what are their characteristics
<egg> forget the Eulers
<egg> RK2 sounds like a nonsymplectic 2nd order RK, not sure why you'd go with that
<egg> I'm unfamiliar with PEFRL
<egg> seems to be some other symplectic method based on Forest-Ruth
<egg> all that is perfectly reasonable
<GregroxMun> what does symplectic mean
<GregroxMun> is that what he means when he's talking about 2-body with perturbations?
<GregroxMun> or is that totally unrelated
<egg> GregroxMun: symplectic means that it preserves energy in the long run
<GregroxMun> and that would seem to be ideal
<egg> GregroxMun: it's one of the main properties we look for in our integrators, because it guarantees that you don't get bullshit
<egg> GregroxMun: and they do the same
<egg> GregroxMun: their choice of integrator seems fairly reasonable all things considered; I might have gone with a higher order but otherwise it's OK in principle
<GregroxMun> mhm
<GregroxMun> ok
<GregroxMun> So I will keep the integrator and alter the sim settings to get better performance
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<GregroxMun> wow
<GregroxMun> those changes
<GregroxMun> they really really made a difference
<GregroxMun> I'm finding that the orbits are pretty rock hard
<GregroxMun> I'm using substeps, very tiny max allowable error, and the PEFRL integrator
<GregroxMun> Currently about 90 years into a 1000 year long sim and nothing has gone wrong yet
<GregroxMun> of course
<GregroxMun> previously I had been going at least ten times faster
<GregroxMun> sooo uh
<GregroxMun> how's principia dev going
<GregroxMun> or to be more of a nag,
<GregroxMun> please please please do sensible planetary orbit lines!
<GregroxMun> There's a few planetary systems that I really want to make but they require binary orbits that make sense :P
<GregroxMun> It's less me being annoyed at the state it's in now, and more me really looking forward to what I will be able to do when it's fixed.
<GregroxMun> Also
<GregroxMun> so you now have a more complicated gravity model to account for non-spherical worlds, right?
<GregroxMun> can triaxial ellipsoids be simulated?
<GregroxMun> and how difficult would it be to do that?
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<egg> GregroxMun: we're working on fancier gravity, yes
<GregroxMun> I saw in the changelog that you have it working on Earth, right?
<egg> you can eggspand a triaxial ellipsoid in spherical harmonics, sure
<egg> GregroxMun: "working"
<GregroxMun> what do those quotes entail?
<egg> kinda, not ready for release yet
<GregroxMun> hmm
<GregroxMun> anyway
<GregroxMun> Scott Manley wouldn't play WW because he'd already "been there, done that" with demoing oblate gravity on Earth in RSS
<GregroxMun> so of course now I gotta make a working haumea for him so I can get some ADVERTISEMENT
<GregroxMun> :P
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<GregroxMun> egg
<GregroxMun> I found something cool
<GregroxMun> WhirligigWorld's Tyepolbynar system
<GregroxMun> the outermost moon Aerious
<GregroxMun> it is in an unstable orbit
<GregroxMun> because of perturbations from the Sun
<GregroxMun> but it never actually gets lost
<GregroxMun> the orbital elements change wildly
<GregroxMun> but it never actually gets lost
<GregroxMun> after 10 years anyway
<GregroxMun> I'm letting it run longer still.
<GregroxMun> sometimes it looks like it gets sooooo close but then it will circularize a bit and the danger goes away
<GregroxMun> it does seem like it's getting worse with time after 10 years
<GregroxMun> the orbit is, on average, getting more eccentric and distant I think
<GregroxMun> maybe you should take a look at it
<GregroxMun> it reminds me of retrobop in some ways
<GregroxMun> 20 years and it's still there
<GregroxMun> I see no reason why it would go unstable now
* UmbralRaptop 🔪 ☿6 in its lack of moon support.
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