Confidence Limits for Non-Linear Regression

Prof Brian D Ripley <ripley at stats.ox.ac.uk> writes:

I had thought if you turn tracing on, you would see the area in parameter
space where profile.nls gets in trouble, but profiling seems to turn it
off.  You could try increasing maxiter in nls.control.

It works if trace = TRUE in the original call to nls that creates the
object being profiled.  Try

example(Bennett5, package = "NISTnls")
pr2 <- profile(fm2)


Dieter: If you fitting a conventional three parameter logistic model
or a four parameter model you may want to try the self-starting model
functions in the nls package (SSlogis or SSfpl).  Those functions use
a parameterization that has proven to be very stable.  Often the
difficulties in assessing the variability in parameter estimates is
due to a poorly chosen parameterization for the model.

If you would be willing to send me one of the problematic data sets I
could try to assess what is going wrong for you.
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._