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From: Lawrence Stewart <stewart@serissa.com>
To: The Eunuchs Hysterical Society <tuhs@tuhs.org>
Subject: Re: [TUHS] Space Travel, was New: The Earliest UNIX Code
Date: Mon, 28 Oct 2019 22:18:46 -0400	[thread overview]
Message-ID: <363F5ECC-7F3E-4441-B9E7-2828BF21F303@serissa.com> (raw)
In-Reply-To: <CAG=a+rgS8iJKnd85wv5kt8JfgZNkOR0u47FySMXYvD+jsOKEZA@mail.gmail.com>


> On 2019, Oct 18, at 6:04 PM, Ken Thompson via TUHS <tuhs@minnie.tuhs.org> wrote:
> 
> while writing "space travel,"
> i could not get the space ship integration
> around a planet to keep from either gaining or
> losing energy due to floating point errors.
> i asked dick hamming if he could help. after
> a couple hours, he came back with a formula.
> i tried it and it worked perfectly. it was some
> weird simple double integration that self
> corrected for fp round off. as near as i can
> ascertain, the formula was never published
> and no one i have asked (including me) has
> been able to recreate it.
> 
> i look forward to the OCR of the code.
> 

I think this must be a variant of “Symplectic Integration”.

My son had an internship at Mitre having something to do with orbit 
determination and I got to reading papers about it.

Symplectic integration is what you want for systems described by a Hamiltonian, 
such as orbits because the usual integrators (Euler, Runge-Kutta) don’t conserve 
the interchange between position and momentum, or something like that.

As far as I can tell, this sort of stuff started getting published in the 1980s, 
so Hamming may well have tossed it off earlier and just not written it up.

Could be a nice historical footnote for the development of orbit calculations.
Could be fun to reverse engineer the code.

-L


  parent reply	other threads:[~2019-10-29  2:19 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-18 11:52 Doug McIlroy
2019-10-18 18:36 ` Steffen Nurpmeso
2019-10-18 20:19   ` SPC
2019-10-18 22:04     ` Ken Thompson via TUHS
2019-10-18 23:20       ` Arthur Krewat
2019-10-19  0:57         ` G. Branden Robinson
2019-10-19  1:11           ` Arthur Krewat
2019-10-29  2:18       ` Lawrence Stewart [this message]
2019-10-26 15:10 ` Lars Brinkhoff
  -- strict thread matches above, loose matches on Subject: below --
2019-10-19 14:40 Doug McIlroy
2019-10-19 18:32 ` Abhinav Rajagopalan
2019-10-19 18:44   ` Abhinav Rajagopalan
2019-10-19 19:19   ` Clem Cole
2019-10-19 19:50     ` Henry Bent
2019-10-19 20:24       ` Arthur Krewat
2019-10-19 13:13 Doug McIlroy
2019-10-17 19:21 [TUHS] New: The Earliest UNIX Code - From the Collection of the Software History Center, Computer History Museum Lyle Bickley
2019-10-17 20:44 ` [TUHS] Space Travel, was New: The Earliest UNIX Code Warren Toomey
2019-10-17 22:39   ` Warner Losh
2019-10-17 22:51     ` Warren Toomey
2019-10-18  5:59       ` Lars Brinkhoff
2019-10-18  9:30         ` SPC
2019-10-18 17:36         ` Nemo
2019-10-18  3:01   ` Warren Toomey
2019-10-18  5:07   ` Lars Brinkhoff
2019-10-18  5:10     ` Lars Brinkhoff
2019-10-18 13:37       ` Warner Losh

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