[R] What is the difference between prcomp and princomp?

[Peng Yu]

On Sun, Oct 18, 2009 at 10:42 PM, Peng Yu <pengyu.ut at gmail.com> wrote:
> Some webpage has described prcomp and princomp, but I am still not
> quite sure what the major difference between them is. Can they be used
> interchangeably?
>
> In help, it says
>
>     'princomp' only handles so-called R-mode PCA, that is feature
>     extraction of variables.  If a data matrix is supplied (possibly
>     via a formula) it is required that there are at least as many
>     units as variables.  For Q-mode PCA use 'prcomp'.
>
>
> What are R-mode and Q-mode? Are they just too different numerical
> methods to compute PCA?

Also, it seems that 'loadings' of princomp is the same as 'rotation'
of prcomp. I'm wondering whey they have different names in the two
functions.