high precision mathematics

[Carl Banks]

Karl M. Syring wrote:
> "Carl Banks" <idot at vt.edu> schrieb>
> <snip>
>> Flight simulation: The earth's radius is about 20 million feet (about
>> 7 million meters for my SI using friends), and the simulator must
>> resolve, at a minimum, distances of about 0.1 feet.  That's a
>> difference of 9 decimal places.  We then need several more places for
>> numerical robustness.
> <snip>
> 
> You surely are joking, Mr. Banks?
> This is exactly the kind of misuse of floating point that was referred to in
> a previous posting. Every computational geometry software would use a
> rational data type here, although you might get away with simple point data
> binning in this case.


I suspect you don't know what I'm talking about, since what I'm
referring to is nothing like computational geometry.  Nevertheless,
I'll answer this.

No, I'm not joking.

I have seen the source code of maybe a dozen flight simulators, and
I've written several myself (not in Python, though, yet).  Several of
the simulators are used in research, one came out of NASA, and one was
proprietary.  I have yet to see anything stored as a rational number.

High-fidelity, long-period spacecraft simulations might require
something more precise than 64-bit floating point, but for atmospheric
flight, unmodeled disturbances make the extra precision pointless.



sorry-that-this-is-straying-off-topic-but-it-could-be-worse-as-I-
could-be-replying-to-Timothy-Rue-so-I-hope-you'll-forgive-me-and-
is-this-closing-thingie-some-obscure-Monty-Pythonism-or-what'ly yours,

-- 
CARL BANKS                                http://www.aerojockey.com
"Nullum mihi placet tamquam provocatio magna.  Hoc ex eis non est."