[Rd] \link to another package

[Ross Boylan]

In the documentation for my package I would like to reference the Rmpi
documentation.  I started with \link{Rmpi}, which caused R CMD check to
complain that it could not resolve the link.  Since Rmpi wasn't loaded,
this isn't surprising.

Ideally the user would see Rmpi, but the link would go to Rmpi's
Rmpi-pkg.  It's not clear to me if this is possible.  I've combined two
documented features to say \link[Rmpi=Rmpi-pkg]{Rmpi}.  Is that OK?

According to the 2.3.1 documentation
\link[Rmpi]{Rmpi} gets me the Rmpi link in the Rmpi package and
\line[=Rmpi-pkg]{Rmpi} gets me Rmpi-pkg.
There is no mention of combining these two syntaxes.

There is also a discussion of \link[Rmpi:bar]{Rmpi}, but that appears to
refer to a *file* bar.html rather than an internal value (i.e.,
\alias{bar}).

Not only R CMD check but some users of the package may not have Rmpi
loaded, so I'd like the documentation to work gracefully in that
situation.  "Gracefully" means that if Rmpi is not loaded the help still
shows; it does not mean that clicking on the link magically produces the
Rmpi documentation.

-- 
Ross Boylan                                      wk:  (415) 514-8146
185 Berry St #5700                               ross at biostat.ucsf.edu
Dept of Epidemiology and Biostatistics           fax: (415) 514-8150
University of California, San Francisco
San Francisco, CA 94107-1739                     hm:  (415) 550-1062