Sorry to report further difficulties with
nls and profiling and constraints ... the problem
this time (which I didn't check for in my last
round of testing) is that the nls profiler doesn't
seem to respect constraints that have been
set when using the port algorithm.
See test code below ...
If I can I will try to hack the code, but I will
probably start by redefining my function with
some workarounds to make the fit quadratically "bad" (but well-defined)
when the parameters are negative ...
As always, please don't hesitate to correct me
if I'm being an idiot ...
y = a*x/(1+a*b*x)+rnorm(npts,sd=0.2)