Math.cos() (and every other trig function) should check the argument being PI (or any other of its own constants) before calculating, since it would better reflect the mathematical function and maybe even save up on some performance.
On 9/17/07, Gordon Smith <[EMAIL PROTECTED]> wrote: > > 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. > > > >
