Hi ,

   To my knowledge, there're two functions that can do principal component
analysis, princomp and prcomp.

   I don't really know the difference; the only thing I know is that when
the sample size < number of variable, only prcomp will work. Could someone
tell me the difference or where I can find easy-to-read reference?

   To access the first PC using princomp:
     Mpca<-princomp(M, cor=T)
     Mpca$scores[,1]

    How can I access the first PC using prcomp?
    Mpca<-prcomp(M)

    Is there an option for "cor=T"?
    In case where both functions work, will the results be the same?

    Thanks,

Miao

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