I am seeking advice on programming a new random effects variance-covariance matrix/structure (pdmat) in R for use in lme()? I've checked out the lme source code (as suggested if you want to program your own pdmat), but remain confused. Does anyone have a good reference? Thanks in advance!

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    $\begingroup$ Pinheiro/Bates is the classic reference but doesn't have the details on how to do this; I had to do it once and basically ended up copying the code from one of the existing structures and changing it to meet my needs. It was trickier than I expected to be, though, and long enough now that I don't quite remember what I did. I too hope someone knows of a better reference. $\endgroup$ – Aaron Dec 16 '11 at 17:58
  • $\begingroup$ Great question. Me too interesting in learning this. Would appreciate @Aaron if you advise us. $\endgroup$ – MYaseen208 Dec 17 '11 at 22:16

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