07:21 <egg> !seen lamont

07:21 <Qboid> egg: I last saw lamont on [30.05.2018 02:19:19] in #principia saying: "can you take say a 4th order symplectic integrator and convert it from 1-body to n-body by updating all the bodies every step?"

17:27 <GH> [Principia] pleroy commented on issue #1839: FTR the relative error in the times is about 2^-48, so it's more than a few ULPs. https://git.io/vhnEf

19:10 <lamont> egg: ^^^ that was just my own curiosity, nothing i’m building in mechjeb

19:10 <egg> lamont: okay

19:11 <egg> then yes, it's just integrating everything together

19:11 <egg> lamont: so btw about that feature request for your latest iteration of the fancylamont guidance, what should we do if backintegrating is too much of a PITA

19:12 <egg> (re <lamont> if you truncate it and t < t0 returns x(t0), v(t0) then it may not intercept correctly and may arrive at x+v at that earlier t < t0)

19:13 <lamont> the impulsive burn approximation i’d think would prevent that from being an issue, but babysitting optimizers is annoying and they tend to find weird soultions if they can…

19:13 <egg> hm

19:14 <lamont> basically i don’t have an answer right now, but i’m chewing on it

19:15 <lamont> i need to finish the work i’m doing on normal ascents, then i can start looking at the node executor and the rendezvous problem (in stock KSP without n-body complications)

19:42 <lamont> having principia integrate a terminal coast might work better for you

19:45 <lamont> the problem them becomes that i’d figure out the x+v at the time of the end of the burn. then principia would need to integrate a coast from that point to some tf, and then also principia would give the desired x, v at tf. that tf just needs to be sufficiently far forwards that the optimizer would never need a negative integration from principia.

19:47 <egg> lamont: tbh we could probably add backward integration in some way, it seems wrong to change the guidance method just to avoid tweaking that plumbing

19:47 <egg> the question is more what we should do in the meantime

19:47 <lamont> well meantime i’m not ready for it yet

19:48 <egg> :D

19:48 <lamont> i’m still dealing with rockets that i tell to launch to the south that get a mind of their own and decide to launch to the north