Hello, everyone,
I would like to know the meaning of the error messages of nlme
in order to get converging fits. The application is a simple
non-linear model to a dataset of increasing Apo B.
I use:
platform i386-pc-mingw32
arch i386
os mingw32
system i386, mingw32
status
major 1
minor 5.1
year 2002
month 06
day 17
language R
The non-linear function:
mu2 <- function(k, A, B0, t) {
c0 <- exp(B0)
i <- exp(k)
c1 <- exp(A)
c0 * exp(-i*t) + c1/i * (1-exp(-i*t))
}
For example this error message:
> m2e.1 <- nlme(y ~ mu2(k, A, B0, t), data=thelp,
+ fixed = list(k + A + B0 ~ 1),
+ random = list(id = B0 ~ 1, f = B0 ~ 1),
+ start=c(k=-1.7, A=0.86, B0=1.44))
Error: Singularity in backsolve at level 0, block 1
or:
> m2e.15 <- update(m2e.13, corr = corExp())
Error in as.vector(dist(1:length(x))) : couldn't find function
"dist"
What have I to do to get proper fits? Nevertheless, I get some nice fits
with other models. From my experience with this models, they are relatively
robust against the choose of starting values.
Can somebody explain me the meaning of the error messages?
Kind regards,
Dominik
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