01:37 <queqiao-> ⟨sciencecompliance⟩ Out of curiosity, what basic numerical method does Principia use to calculate trajectories? Euler's or something else?

01:43 <queqiao-> ⟨Al2Me6⟩ https://github.com/mockingbirdnest/Principia/wiki/Principia-configuration-files#definitions-of-scalar-types

08:12 <queqiao-> ⟨egg⟩ https://matrix.mockingbirdnest.com/_matrix/media/r0/download/matrix.mockingbirdnest.com/KYRLxjvwyEJkTEkpMFgSgXKH/unknown.png

08:21 <queqiao-> ⟨sichelgaita⟩ ⟪sciencecompliance⟫ Out of curiosity, what basic numerical […] ⮪ Euler is not even applicable, it's for a first-order equation, we are solving a second-order equation. In the graph above, the vertical axis gives the error and the horizontal axis the cost of the computation. You want to be at the bottom left, and on a steep line. In practice we use "QUINLAN_1999_ORDER_8A" for the history of vessels,...

08:21 <queqiao-> ... "BLANES_MOAN_2002_SRKN_14A" by default for celestials, overridden to "QUINLAN_TREMAINE_1990_ORDER_12" for the RSS system.

09:42 <queqiao-> ⟨Transparent_Elemental⟩ ⟪sichelgaita⟫ Euler is not even applicable, it's for […] ⮪ transform it to a system of first order equations

10:30 <queqiao-> ⟨egg⟩ ⟪Transparent_Elemental⟫ transform it to a system of first order […] ⮪ Yes, or you could transform Euler into the second order method which is equivalent to that. But more importantly, Euler is crap. It would be worse than Newton Delambre Størmer Verlet leapfrog which is the worst in that graph, and more importantly, contrary to all in that graph, it is not symplectic not conjugate symplectic.

10:30 <queqiao-> ⟨egg⟩ * nor

10:31 <queqiao-> ⟨egg⟩ * neither

10:32 <queqiao-> ⟨Farrier⟩ ⟪egg⟫ Yes, or you could transform Euler into […] ⮪ >Euler is crap

10:32 <queqiao-> 😠

13:43 <queqiao-> ⟨Transparent_Elemental⟩ what are symplectic and conjugate symplectic integrators for someone who isn't involved in physical part of the equations?

13:49 <queqiao-> ⟨Soviet Onion⟩ ⟪Transparent_Elemental⟫ transform it to a system of first order […] ⮪ that's what we did when using Euler's to solve a second ODE 😏

13:49 <queqiao-> ⟨Soviet Onion⟩ did the same for RK4 as well

13:58 <queqiao-> ⟨sichelgaita⟩ ⟪Transparent_Elemental⟫ what are symplectic and conjugate […] ⮪ Glossing over the details: they preserve energy. That's kind-of important for the problem at hand, it's silly if your vessels accelerate or slow down without any physical cause.

14:00 <queqiao-> ⟨egg⟩ Explicit Euler gains energy over time. Implicit Euler loses energy over time.

14:34 <queqiao-> ⟨Butcher⟩ ⟪sichelgaita⟫ Glossing over the details: they […] ⮪ Stock calls it a feature.

16:13 <queqiao-> ⟨Al2Me6⟩ I am contemplating opening it up in GIMP and using selection by color.

16:14 <queqiao-> ⟨egg⟩ The slope is the order so that helps a bit

16:19 <raptop> If I'm reading the graph correctly, leapfrog actually beats out the other two 2nd-order ones, and is fairly god if you're restricted in your number of evaluations? (Not that you are)

16:38 <queqiao-> ⟨scimas⟩ ⟪sichelgaita⟫ Euler is not even applicable, it's for […] ⮪ Oh, now the evaluations make sense. I was thinking why would the error improve the further you got from the initial condition.

18:46 <queqiao-> ⟨sciencecompliance⟩ ⟪sichelgaita⟫ Euler is not even applicable, it's for […] ⮪ Very interesting, and, just to be clear, Principia does not include general relativity in its gravitational model, correct?

18:50 <queqiao-> ⟨Quadrupole⟩ This is _Principia_, so right

18:50 <queqiao-> ⟨sciencecompliance⟩ Haha, good point.

18:52 <queqiao-> ⟨Soviet Onion⟩ ⟪sciencecompliance⟫ Very interesting, and, just to be […] ⮪ you want to include relativistic effects in KSP ? 😳

18:52 <queqiao-> ⟨sciencecompliance⟩ I mean, sure, why not?

18:52 <queqiao-> ⟨sciencecompliance⟩ (rhetorical question)

18:52 <queqiao-> ⟨Soviet Onion⟩ computer no smort 😔

18:52 <queqiao-> ⟨Quadrupole⟩ Radiation pressure and Poynting-Robertson have far greater effects than GR

18:54 <queqiao-> ⟨Soviet Onion⟩ yeah, GR is good enough for very highly accurate results only

18:54 <queqiao-> ⟨Soviet Onion⟩ i suppose Principia's suffices for playing KSP

18:56 <queqiao-> ⟨QeDelphyn (Xšayāršā/-ām/-āyā)⟩ radiation pressure would be nice

18:56 <queqiao-> ⟨sciencecompliance⟩ Yeah you could have solar sails

18:58 <queqiao-> ⟨Stonesmile⟩ Maybe leave GR for Principia 2: feldgleichungen

18:58 <queqiao-> ⟨QeDelphyn (Xšayāršā/-ām/-āyā)⟩ atmosphere not ceasing to exist would also be nice, but I fear both of those things would be impractical in terms of computing power required

18:59 <queqiao-> ⟨sciencecompliance⟩ Yeah, makes sense

19:00 <queqiao-> ⟨QeDelphyn (Xšayāršā/-ām/-āyā)⟩ Quick question, is Earth a point mass for the purpose of principia or is it a geoid with varying gravitation?

19:00 <queqiao-> ⟨Quadrupole⟩ ⟪QeDelphyn (Xšayāršā/-ām/-āyā)⟫ atmosphere not ceasing to exist would […] ⮪ The issue with orbital decay is that, a) they break conservation of energy, leading to numerical difficulties, and b) no one want to do station keeping twicr per month.

19:00 <queqiao-> ⟨sciencecompliance⟩ ⟪QeDelphyn (Xšayāršā/-ām/-āyā)⟫ Quick question, is Earth a point mass […] ⮪ I'm told the latter, but I don't know.

19:01 <queqiao-> ⟨Stonesmile⟩ Earth needs to not be a point mass for Sun-Sync orbits to work

19:01 <queqiao-> ⟨sciencecompliance⟩ Of course.

19:02 <queqiao-> ⟨Transparent_Elemental⟩ ~turns out simulating real life is hard when you've only got personal computers~

19:04 <queqiao-> ⟨coffeequaffer⟩ you can up the geopotential definitions in "GameData\Principia\real_solar_system\gravity_model.cfg"

19:15 <queqiao-> ⟨Soviet Onion⟩ ⟪Quadrupole⟫ The issue with orbital decay is that, […] ⮪ imagine you forgot you had a station and timewarped your save for some interplanetary satellite to reach its target body faster 💀

19:16 <queqiao-> ⟨Soviet Onion⟩ you come back home only to find the station burned up in atmosphere, and all the personnel that were inside died

19:55 <queqiao-> ⟨coffeequaffer⟩ +look

20:18 <queqiao-> ⟨sichelgaita⟩ ⟪Quadrupole⟫ The issue with orbital decay is that, […] ⮪ (a) is really just a matter of picking the right integrator with a decent aerodynamic model (b) is a disaster from the playability perspective.

20:27 <queqiao-> ⟨zephyr⟩ Tbh, I see that as an absolute win. Keep your station in a higher orbit

20:28 <queqiao-> ⟨zephyr⟩ * win (though I'm weird like that and working on a way to make stations actually worthwhile so some kind of maintenance would be nice).

20:57 <raptop> ...as for stations, ultimately there's a need for stationkeeping to happen automatically with unfocused craft

20:58 <raptop> And finally, https://github.com/mockingbirdnest/Principia/blob/e27713ccfce53a9ea6238e58782439a1043038fb/astronomy/mercury_perihelion_test.cpp should answer anyone's questions about Principia having GR :D

21:09 <queqiao-> ⟨lamont⟩ you could maybe build orbital decay into principia with some "difficulty" settings to turn it off.

21:10 <queqiao-> ⟨coffeequaffer⟩ i want to see the kerbalism-principia crossover episode "stationkeeping" where y'all add the most important perturbations to orbital calculations, but which can be neutralized with automatic deduction of RCS fuel

21:10 <queqiao-> ⟨lamont⟩ of course then people would run into the mechjeb issues pleading for it to save them from it when mechjeb doesn't remotely have any code similar to what stationkeeping would need and its the wrong place for it

21:11 <queqiao-> ⟨egg⟩ ⟪coffeequaffer⟫ i want to see the kerbalism-principia […] ⮪ That's not how things work.

21:12 <raptop> (insert NEAR vs FAR joke here)

21:13 <queqiao-> ⟨egg⟩ ⟪lamont⟫ of course then people would run into […] ⮪ Well at least it has you who deals with control and optimization problems

21:13 <queqiao-> ⟨lamont⟩ yeah but it needs to run on vessels on rails which MJ doesn't. kerbalism is much closer to the right spot for it.

21:17 <queqiao-> ⟨coffeequaffer⟩ i thought of kerbalism because it already has radiation maps and solar storms.