[Rd] hypot(x,y) instead of pythag(a,b) ?!

[Prof Brian D Ripley]

> >>>>> Martin Maechler writes:
> 
> > My "theses"
>    
> >    o when hypot() is available, it should be used since it will be 
> >      efficient, precise, etc.
> >    o when it's not available, our "configure" should find out, and set
> >      corresponding "HAVE_HYPOT" to `false'.

Are there any such systems?  After all 1.0.1 requires hypot, and we
have heard no complaints.  I suspect the cause of the confusion is
(plot.c)

#ifdef Macintosh
# define hypot pythag
#endif

so assume that the Mac port did not have hypot. However, a different
version appears in the 1.0.1 sources, and it appears _after_ hypot is first
used, so I am puzzled as to how the current version got there, or why it
would work. (If a system does not have hypot, presumably its headers do not
either!)

> >    o in that case, we should provide a hypot()  {for the above code to
> >      work!}, and we probably should use (an improvement?) of the current
> >      pythag() function [src/appl/pythag.c in R versions <= 1.0.1].
> >    o Hence, we should drop pythag() from the R API and rather say that we
> >      provide hypot() whenever the system's C library 
> >      (or its "math.h", aka libm.*, aka "-m" part, respectively) does *not* 
> >      provide it.

I was puzzled as to why you put it in the API at all.

> >    o I think an R function  hypot() would also make sense.

Don't think so.  What you we is an n-term not 2-term version, and that's
what vecnorm would do (if we had it).

This does all seem to me to be trying to solve a non-existent problem.

-- 
Brian D. Ripley,                  ripley@stats.ox.ac.uk
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 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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