R help - Nov 2008 - plot Principal Components axes on original data

Hello

I'm writing an example PCA analysis for some students.  I've done PCA on
a
2-column matrix to show it at the most simple form (a rotation of two
axes).  I can't, however, figure out how to plot the rotated axes as lines
over top of the original data plotted on the x-y.  Does anyone know how to
do this?  It will be a good way to show how the rotated axes describing the
most variation compared to the original axes.

I've used the princomp function, and here's how I set up the data.

library(MASS)
Sigma<-matrix(c(10,3,3,2),2,2)
dat<-mvrnorm(n=60, mu=c(12,13), Sigma)

plot(dat, xlab="x", ylab="y")

pc.ex<-princomp(dat)


Thanks in advance.

Gareth Campbell
PhD Candidate
The University of Auckland

P    +649 815 3670
M    +6421 256 3511
E   gareth.campbell@esr.cri.nz
    gcam032@gmail.com

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