a question I assume to know the anser, but none could tell me why. To make it short, I employ an example from Pinheiro & Bates (2000).
library(nlme)
fm1Dial.gnls <- gnls(rate ~ SSasympOff(pressure, Asym, lrc, c0),
data = Dialyzer,
params = list(Asym + lrc ~ QB, c0 ~ 1),
start = c(53.6, 8.6, 0.51, -0.26, 0.225) )
summary(fm1Dial.gnls)
I can find pressure not among the coefficients.
To obtain an coefficient for it, would it be legal to use pressure within params or would I then use a parameter to explain itself? Could this in any way be seen as a hint how pressure affects rate?
fm2Dial.gnls <- gnls( rate ~ SSasympOff(pressure, Asym, lrc, c0),
data = Dialyzer,
params = list(Asym + lrc ~ pressure, c0 ~ 1),
start = c(53.6, 8.6, 0.51, -0.26, 0.225) )
summary(fm2Dial.gnls)
The data is just as an example and has no further meaning. For any answer I would be very grateful.
