19 Oct
2019
19 Oct
'19
8:40 p.m.
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.