Hi
I'm trying to fit a mixed effects exponential decay model, in which I
have random effects for the initial value (init), the asymptote (asymp),
and the rate (rate).
The catch is that I'd also like to estimate the correlation between init
and asymp, but not between init and rate, or asymp and rate.
Now using? random = pdDiag(init + asymp + rate ~ 1) has none of the
random effects correlated
And using? random = pdSymm(init + asymp + rate ~ 1) has all three of the
random effects correlated
How do I specify just the correlation I want?
cheers
Chris