C Floating point arithmetic

[emjej at uokvax.UUCP]

Sigh...people, including those who feel that C is perfect and thus have
the urge to defend its every jot and tittle to the death, at times have
such a touching faith in double precision! :-)

I am in no wise a numerical analysis guru, but I have studied under one,
and if there is one thing I have learned, that is that if your algorithm
is flawed or your problem ill-conditioned, no amount of precision will
save you.  The fellow commenting on the fuzziness of the input data has an
extremely valid point: an ill-conditioned problem may be such that wildly
different solutions (and hence physical behavior of a system being modeled)
are well within the possible "true" values of the inputs to your number
cruncher.

Also, I recall that in matrix hacking, it turns out that certain
operations are crucial--notably accumulating dot products.  If you do
*these* in high precision, the rest of the stuff can get away with less.
That can make a large difference in storage space and runtime (if you
have hardware that was designed like C so that everything is done in
max precision anyway, the runtime difference is less, I'd agree, but
people beat on some hefty matrices nowadays--thrash, thrash).

						James Jones