[R] a question of etiquette

[Adelchi Azzalini]

The new version of a package which I maintain will include a new function which I have ported to R from Matlab.
The documentation of this R function indicates the authors of the original Matlab code, reference to their paper, URL of the source code.

Question: is this adequate, or should I include them as co-authors of the package, or as contributors, or what else?
Is there a general policy about this matter?

Adelchi Azzalini
http://azzalini.stat.unipd.it/