Message-ID: <loom.20130314T134120-288@post.gmane.org>
Date: 2013-03-14T12:42:45Z
From: Ben Bolker
Subject: Same eigenvalues but different eigenvectors using 'prcomp' and 'principal' commands
Arlindo Meque <mequitomz <at> yahoo.com.br> writes:
>
>
> Dear all,
>
> I've used the 'prcomp' command to
> calculate the eigenvalues and eigenvectors of a matrix(gg).
>
> Using the command 'principal' from the
> 'psych' package? I've performed the same exercise. I got the same
> eigenvalues but different eigenvectors. Is there any reason for that
> difference?
[snip]
eigenvectors are only defined up to a scale factor. prcomp is
scaling them so that the sum of squares is 1; I haven't bothered
to see how principal() is scaling them (maybe the documention says).
(1,1) and (-1,1) , or (1,1) and (1,-1), would have been
equally valid choices.
Ben Bolker