Message-ID: <19981218154050.6295.qmail@www0a.netaddress.usa.net>
Date: 18 Dec 98 10:40:50 EST
From: ADAM SCHROTENBOER <a DOT j DOT schrotenboer AT usa DOT net>
To: Kurt Alstrup <kurt DOT alstrup AT intel DOT com>, djgpp AT delorie DOT com
Subject: Re: [Re: sin() and cos() ???]
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Reply-To: djgpp AT delorie DOT com

It's almost always best to use a constant. If all else fails, cut and paste
the #define PI from math.h and put it into your program. There was a
discussion a few months ago on a NG about the value of PI. And I quote (It may
be somewhat paraphrased) "Leave PI a constant as God intended."

You _can't_ count on the accuracy or precision of trig functions.

And if you do want to get PI from an equation (which I don't suggest) it's
easier to take acos(-1.0), rather than 4 * atan(1.0).

dj-admin AT delorie DOT com wrote:
A better way would be to calculate pi once by eg

 double pi = 4 * atan(1.0);

it should give you pi in a precision suitable for the
math library.

Just my two cents ..

Anton Helm wrote:
> 
> At 18:27 17.12.98 +0000, Arthur wrote:
> 
> >I think in math.h, there is a definition called PI. This is much more
> >accurate than what you've got here.
> >
> >So you can use sin(x*PI/180); instead (easier).
> >
> 
> PI is not ANSI (checked) and as far as I know
> it isn't POSIX either (unchecked).
> 
> So if you want a portable code you should
> have a
> 
> #ifndef PI
> #define PI 3.1415.....
> #endif
> 
> somewhere (well, preferably in a *.h  file) in your program.
> 
> Although PI and M_PI are #defined on lots of systems you
> can't rely on them.
> 
> Tony


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