[R] Factor Analysis in MASS4

[Ko-Kang Kevin Wang]

Hi,

I had a look at the MASS4 scripts in the MASS package, in Ch 11.3 Factor
Analysis, there is a section of codes like:

  data(ability.cov)

  ability.FA <- factanal(covmat = ability.cov, factors = 1)
  ability.FA
  (ability.FA <- update(ability.FA, factors = 2))
  #summary(ability.FA)
  round(loadings(ability.FA) %*% t(loadings(ability.FA)) +
             diag(ability.FA$uniq), 3)

Unfortunately I still haven't received the book I ordered, so I can't look
this up.

Two questions:

1) What does the update() do?  I mean, what happens if I replace it with 
     factanal(covmat = ability.cov, factors = 2)

2) What does the last command, the formulae in round() mean?  I tried it
and it produced a matrix that looks kind of like correlation matrix of
some sort... 


Cheers,

Kevin

------------------------------------------------------------------------------
Ko-Kang Kevin Wang
Postgraduate PGDipSci Student
Department of Statistics
University of Auckland
New Zealand
Homepage: http://www.stat.auckland.ac.nz/~kwan022


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