[R] Same eigenvalues but different eigenvectors using 'prcomp' and 'principal' commands

[Ben Bolker]

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