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* Re: [TUHS] Space Travel, was New: The Earliest UNIX Code
@ 2019-10-19 14:40 Doug McIlroy
  2019-10-19 18:32 ` Abhinav Rajagopalan
  0 siblings, 1 reply; 19+ messages in thread
From: Doug McIlroy @ 2019-10-19 14:40 UTC (permalink / raw)
  To: tuhs, dbrock

I was about to add a footnote to history about
how the broad interests and collegiality of
Bell Labs staff made Space Travel work, when
I saw that Ken beat me to telling how he got
help from another Turing Award winner.

> 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.

If I remember correctly, the cause of Ken's
difficulty was not roundoff error. It
was discretization error in the integration
formula--probably f(t+dt)=f(t)+f'(t)dt.
Dick saw that the formula did not conserve
energy and found an alternative that did.

^ permalink raw reply	[flat|nested] 19+ messages in thread

end of thread, other threads:[~2019-10-26  2:24 UTC | newest]

Thread overview: 19+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-10-19 14:40 [TUHS] Space Travel, was New: The Earliest UNIX Code 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 19:55       ` [TUHS] Space Travel related question Thomas Paulsen
2019-10-19 20:19         ` Warner Losh
2019-10-19 20:24       ` [TUHS] Space Travel, was New: The Earliest UNIX Code Arthur Krewat
2019-10-19 20:12   ` [TUHS] How to do differential/integral on a PDP-7, was: Space Travel Michael Kjörling
2019-10-19 20:40     ` Arthur Krewat
2019-10-19 21:15       ` Michael Kjörling
2019-10-21  5:14       ` Dave Horsfall
2019-10-21  5:23         ` Lars Brinkhoff
2019-10-21 13:59           ` John P. Linderman
     [not found]             ` <68553366-4E6F-4E17-8903-282C67186D16@humeweb.com>
2019-10-26  2:24               ` Dave Horsfall
2019-10-26  2:09           ` Dave Horsfall
2019-10-21  4:55     ` Dave Horsfall
2019-10-21 19:21       ` Paul Winalski
2019-10-21 19:38         ` Kurt H Maier

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