The first comment is that will only work on Unix-alikes, since '|' needs a
shell.
So, if this is on a Unix-alike you need to establish if the program is in
the path at run time and cache the result. I have no idea if this would
actually work, but for example system('gp --version') might provide a
suitable test.
On Fri, 27 Apr 2007, Robin Hankin wrote:
> Hello
>
> Quite often I need higher precision, or larger numbers,
> than IEEE double precision allows. One strategy I sometimes
> use is to use system() to call pari/gp, which is not constrained by
> IEEE.
>
> [pari/gp is a GPL high-level mathematical programming language
> geared towards pure mathematics]
>
> Two of my packages contain lines like the following:
>
> > system(" echo '1.12^66' | gp -q f",intern=TRUE)
> [1]
> "1771.697189476241729649767636564084681203806302318041262248838950177194
> 116346432205160921568393661760"
>
> Note the high precision of the answer.
>
> My question is, how to deal with the possibility that pari/gp is not
> installed?
>
> If the system cannot find gp for some reason, I get:
>
> > system(" echo '1.12^66' | gp -q f",intern=TRUE)
> sh: line 1: gp: command not found
> character(0)
> >
>
> What's the recommended way to handle this eventuality gracefully? The
> functions that do use pari/gp have "pure" R equivalents (but much
> slower and less accurate) so I want users to be able to install the
> package without pari/gp.
>
>
> --
> Robin Hankin
> Uncertainty Analyst
> National Oceanography Centre, Southampton
> European Way, Southampton SO14 3ZH, UK
> tel 023-8059-7743
>
> ______________________________________________
> R-devel@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
--
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
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