From: Doug McIlroy <doug@cs.dartmouth.edu>
To: tuhs@tuhs.org, dbrock@computerhistory.org
Subject: Re: [TUHS] Space Travel, was New: The Earliest UNIX Code
Date: Sat, 19 Oct 2019 10:40:08 -0400 [thread overview]
Message-ID: <201910191440.x9JEe8PB035921@tahoe.cs.Dartmouth.EDU> (raw)
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.
next reply other threads:[~2019-10-19 14:40 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-19 14:40 Doug McIlroy [this message]
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
-- strict thread matches above, loose matches on Subject: below --
2019-10-19 13:13 [TUHS] Space Travel, was New: The Earliest UNIX Code Doug McIlroy
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
2019-10-26 15:10 ` Lars Brinkhoff
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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