I have a fair bit of experience with both nls and rating curves. This is
not a nls() problem, this is a model problem. The power law rating curve
favored by hydrologists would not apply to your data as it's based on
the idea that a log-log plot of discharge vs. stage, or state+a in your
case is
If you insist on using nls() for anything that you don't understand
extremely well, you will end up with frustration. nls() uses the same
method K F Gauss used (with good understanding of the details) over
200 years ago. The Gauss-Newton approach inside works very well and
efficiently for problems
Hi
I am not an expert in nonlinear regression, but your data seems to be rather
weird. Last five points has almost linear relationship, the first one is
several times higher. If there is no error in your data, I doubt that you can
model it by power equation.
Cheers
Petr
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