tanpi(x) should be more accurate than tan(pi*x), especially near multiples of pi/2.
Bill Dunlap TIBCO Software wdunlap tibco.com On Fri, Sep 9, 2016 at 11:55 AM, Hans W Borchers <hwborch...@gmail.com> wrote: > The same argument would hold for tan(pi/2). > I don't say the result 'NaN' is wrong, > but I thought, > tan(pi*x) and tanpi(x) should give the same result. > > Hans Werner > > > On Fri, Sep 9, 2016 at 8:44 PM, William Dunlap <wdun...@tibco.com> wrote: > > It should be the case that tan(pi*x) != tanpi(x) in many cases - that is > why > > it was added. The limits from below and below of the real function > > tan(pi*x) as x approaches 1/2 are different, +Inf and -Inf, so the limit > is > > not well defined. Hence the computer function tanpi(1/2) ought to > return > > Not-a-Number. > > > > Bill Dunlap > > TIBCO Software > > wdunlap tibco.com > > > > On Fri, Sep 9, 2016 at 10:24 AM, Hans W Borchers <hwborch...@gmail.com> > > wrote: > >> > >> As the subject line says, we get different results for tan(pi/2) and > >> tanpi(1/2), though this should not be the case: > >> > >> > tan(pi/2) > >> [1] 1.633124e+16 > >> > >> > tanpi(1/2) > >> [1] NaN > >> Warning message: > >> In tanpi(1/2) : NaNs produced > >> > >> By redefining tanpi with sinpi and cospi, we can get closer: > >> > >> > tanpi <- function(x) sinpi(x) / cospi(x) > >> > >> > tanpi(c(0, 1/2, 1, 3/2, 2)) > >> [1] 0 Inf 0 -Inf 0 > >> > >> Hans Werner > >> > >> ______________________________________________ > >> R-devel@r-project.org mailing list > >> https://stat.ethz.ch/mailman/listinfo/r-devel > > > > > [[alternative HTML version deleted]] ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
