In addition to Math.PI not being able to store the exact value of pi, the computation of trig functions involves approximations. For example, one definition of a cosine is in terms of an infinite series, and a computer can't calculate an infinite number of terms. Even if the argument passed to Math.cos() is exact, the result generally won't be. - Gordon
________________________________ From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of Jon Bradley Sent: Sunday, September 16, 2007 2:49 PM To: [email protected] Subject: Re: [flexcoders] Math.cos...? That's pretty much it. To a computer Math.cos(Math.PI/2) is not 0. It's really close to 0, because PI is an infinite sequence and a computer can "only" store it as a double precision floating point number (ie, a fixed value). What you get back from this calculation is the error bound of the computer basically, which you can then use for numerical calculations, ie, MathLib.ERROR_BOUND = Math.cos(Math.PI/2). Then you can feasibly use if you need numerical accuracy. IE, if result == MathLib.ERROR_BOUND, result = 0. Numerical accuracy in AS2 is not equivalent to that of AS3. I ran into this while porting the Mersenne Twister algorithm to AS2 - I couldn't even store 2^32 as a hex value in AS2 (0x100000000, which equals 4294967296). At least we can be somewhat numerically accurate now... good luck, jon On Sep 16, 2007, at 5:15 PM, Troy Gilbert wrote: > Why does Math.cos(Math.PI/2) not return zero? Round-off error in the Math libs? It does return a value very close to 0 (1.7xe-17). Troy.
