[R] prcomp & eigenvectors
William.Simpson at drdc-rddc.gc.ca
Tue Jun 22 14:44:33 CEST 2004
I have the following situation I want to analyse with prcomp.
Each subject has a curve called the contrast sensitivity function (CSF).
This curve's overall shape is due to the additive output of 3 "channels"
#this shows 3 SF channels; net CSF = c1 + c2+c3
net<-c1*s1 + c2*s2 + c3*s3
Given the CSFs of many subjects, I was hoping that prcomp could show me
the shapes of the constituent channels. I checked this with a simulation.
####simulation where each subject has diff weighting (scores) of channels
#one row per subject, cols represent the csf
for(i in 1:nsim)
csf[i,]<-c1*s1 + c2*s2 + c3*s3
#the cols of out$rotation are the tuning curves of the various
#channels = factor loadings = eigenvectors
1. This plot of the three channels does not look like the original. Am I
correct that the output of prcomp is a linear transformation of the true
channels? If so, can anyone suggest how I might get the real channels out?
Maybe additional info (what?) is needed to be able to do this.
2. I can average all the input CSFs; how do find the average fitted output
CSF using the out object?
Thanks very much for any help
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