[Rd] 1/tan(-0) != 1/tan(0)
simon.urbanek at r-project.org
Wed Jun 1 19:01:55 CEST 2005
On Jun 1, 2005, at 5:50 AM, (Ted Harding) wrote:
> However, a query: Clearly from the above (ahich I can reproduce
> too), tan() can distinguish between -0 and +0, and return different
> results (otherwise 1/tan() would not return different results).
> But how can the user tell the difference between +0 amnd -0?
That's indeed a good question - by definition (-0)==(+0) is true,
-0<0 is false and signum of both -0 and 0 is 0.
I don't see an obvious way of distinguishing them at R level. Besides
computational ways (like the 1/tan trick) the only (very ugly) way
coming to my mind is something like:
a==0 && substr(sprintf("%f",a),1,1)=="-"
Note that print doesn't display the sign, only printf does.
At C level it's better - you can use the signbit() function/macro
there. Any other ideas?
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