[Rd] Different results for tan(pi/2) and tanpi(1/2)

[John McKown]

On Fri, Sep 9, 2016 at 12:24 PM, Hans W Borchers <hwborchers at 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
>
>
>
​When I do a ?tanpi, I see the following:

     ‘tanpi(0.5)’ is ‘NaN’.  Similarly for other inputs with fractional
     part ‘0.5’.
​


​I don't know why this is, but apparently the function is working as
documented. Whether that is correct or not is not for me to say.​



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Maranatha! <><
John McKown

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