[R] breakpoints and nonlinear regression

[crimsonengineer87]

Dear Forum,

I have been wracking my head over this problem for the past few days. I have
a dataset of (x,y). I have been able to obtain a nonlinear regression line
using nls. However, we would like to do some statistical analysis. I would
like to obtain a confidence interval for the curve. We thought we could
divide up the curve into piecewise linear regressions and compute CIs from
those portions. There is a package called strucchange that seems helpful,
but I am thoroughly confused.

'breakpoints' is used to calculate the number of breaks in the data for
linear regressions.  I have the following in my script:

bp.pavlu <- breakpoints(Na ~ f(yield, a, b), h=0.15, breaks=3,
data=pavludata)
plot(bp.pavlu)
breakpoints(bp.pavlu)

But I am confused as to how to graph the piecewise functions that make up
the curve. I am not even sure if I am using breakpoints correctly. Do I just
give it a linear relationhip (Na ~ yield), instead of what I have?

Is there an easier way to calculate the confidence interval for a non-linear
regression? 

I am new to R (as I've read in many questions), but I have most certainly
tried many things and am just getting frustrated with the lack of examples
for what I'd like to do with my data... I'd appreciate any insight. I can
also provide more information if I am not clear. Thanks in advance.

Julian

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