Re: Math Constants Library formal review results

From: Corwin Joy (cjoy_at_[hidden])
Date: 2001-05-15 00:28:04

--- In boost_at_y..., "Paul A. Bristow" <pbristow_at_h...> wrote:
> There has been a lot of dissention about the format of my proposed
> mathematical constants.
>  <..snip..> e.g.
> a collection of
> namespace math_double_constants
> {
>   const double pi = 31459;
> }

Not to rain on your parade, but as a mathematician I can tell you 
that what you are doing here is a *bad* idea anyway.  If you want to 
do serious numerical work, then I would *strongly* recommend not 
defining PI as a fixed sequence of digits like you do above because 
then you will never be able to take advantage of the full numerical 
accuracy of the machine you are working on. (Plus, it is less 
portable.)  Better, is to use constants that are calculated to the 
precision of the machine you are working on e.g.
const double pi = 4.0 *(atan(0.5) + atan(0.2) + atan(0.125));

If you do something like above
double pi = 3.15; // (rounded to 2 dp)

the numerical analysts will likely be displeased.
This kind of argument goes for many other mathematical constants that 
are transcendental or irrational.

Corwin