[GRASS-stats] Re: [GRASS-user] Testing i.pca ~ prcomp(), m.eigensystem ~ princomp()

Nikos Alexandris nikos.alexandris at felis.uni-freiburg.de
Thu Apr 2 07:28:05 EDT 2009


Nikos:
> > If outputs are not identical, either R or grass do some hidden
> > modification or there is a bug in either grass or R (all within
> > limits, e.g. identical up to the 5th digit in scientific format is
> > fine?).
> > Some textbooks give a rule of thumb for further analysis to use only
> > components with an eigenvalue >=1

> I think this depends on what you are trying to achieve. Of course,
> components with small(-er) eigenvalues include more "noizzze". In my
> change detection project I used *only* components with eigenvalues <
> 1.

Hmm.. Markus, I was too quick yesterday. That's not true. All of the
PC's I've used have "eigenvalue > 1". Sorry :-p



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