[TUHS] Space Travel, was New: The Earliest UNIX Code
doug at cs.dartmouth.edu
Sun Oct 20 00:40:08 AEST 2019
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
Dick saw that the formula did not conserve
energy and found an alternative that did.
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