nlme, extract stand deviation value

["Li, Qishan" <qishan@email.arizona.edu>]

Dear s-newsers:
 
I should be grateful for suggestions on how to do the following:

I am using Splus (nlme)  and I want to extract a parameter and use it later.
The parameter value is 4.077946, which is the StdDev of Asym.
                  > My_buffer<-  StdDev of Asym , the value is  4.077946

I do not know which function I should use. I tried
                      >random.effects(fm2)
but, it does not work.

Many thanks.

Qishan Li
---------------------------------------------
>fm2 <- nlme(weight ~ SSlogis(Time, Asym, xmid, scal), data = Soybean,
            fixed = Asym + xmid + scal ~ 1, random = pdDiag(Asym + xmid
~ 1),
            start = c(18, 52, 7.5))

> fm2
Nonlinear mixed-effects model fit by maximum likelihood
  Model: weight ~ SSlogis(Time, Asym, xmid, scal)
  Data: Soybean
  Log-likelihood: -755.7323
  Fixed: Asym + xmid + scal ~ 1
     Asym     xmid    scal
 18.96426 55.14188 8.55292

Random effects:
 Formula: list(Asym ~ 1, xmid ~ 1)
 Level: Plot
 Structure: Diagonal
            Asym    xmid Residual
StdDev: 4.077946 2.52487   1.1924

Number of Observations: 412
Number of Groups: 48
>