Hans van Thiel <[EMAIL PROTECTED]> writes: > On Fri, 2007-11-09 at 14:30 -0500, Brent Yorgey wrote: >> >> On Nov 9, 2007 2:08 PM, Hans van Thiel <[EMAIL PROTECTED]> wrote: >> Hello All, >> Can anybody explain the results for 1.0, 2.0 and 3.0 times pi >> below? >> GHCi yields the same results. I did search the Haskell report >> and my >> text books, but to no avail. Thanks in advance, >> Hans van Thiel >> >> Hugs> sin (0.0 * pi) >> 0.0 >> Hugs> sin (0.5 * pi) >> 1.0 >> Hugs> sin (1.0 * pi) >> 1.22460635382238e-16 >> Hugs> sin (1.5 * pi) >> -1.0 >> Hugs> sin (2.0 * pi) >> -2.44921270764475e-16 >> Hugs> sin ( 2.5 * pi) >> 1.0 >> Hugs> sin (3.0 * pi) >> 3.67381906146713e-16 >> Hugs>
> All right, I'd have guessed that myself, if it hadn't been for the exact > computation results for 0, 0.5, 1.5 and 2.5 times pi. So the rounding > errors are only manifest for 1.0, 2.0 and 3.0 times pi. But look at the > difference between sin (1.0 * pi) and sin (3.0 * pi). That's not a > rounding error, but a factor 3 difference.. and sin (as well as cos) are > modulo (2 * pi), right? but sin theta ~ theta for small theta, and the angle you're getting the (approximate) sine of is the difference between 2*pi and 2π. So I'm not too surprised that we have -2*sin pi = sin (2*pi) -- Jón Fairbairn [EMAIL PROTECTED] _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
