On Mon, 3 Sep 2007, Nguyen Dinh Nguyen wrote: > Dear all, > I found something strange when calculating sin of pi value
What exactly? Comments below on two guesses as to what. > sin(pi) > [1] 1.224606e-16 That is non-zero due to using finite-precision arithmetic. The number stored as pi is not exactly the mathematics quantity, and so sin(representation of pi) should be non-zero (although there is also rounding error in calculating what it is). Note that sin() is computed by your C runtime, so the exact result will depend on your OS, compiler and possibly CPU. > pi > [1] 3.141593 That is the printout of pi to the default 7 significant digits. R knows pi to higher accuracy: > print(pi, digits=16) [1] 3.141592653589793 > sin(3.141592653589793) [1] 1.224606e-16 but note that printing to 16 digits and reading back in might not have given the same number, but happens to for pi at least on my system: > 3.141592653589793 == pi [1] TRUE > sin(3.141593) > [1] -3.464102e-07 > > Any help and comment should be appreciated. > Regards > Nguyen > > ____________________________ > Nguyen Dinh Nguyen > Garvan Institute of Medical Research > Sydney, Australia > > -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
