> While trying to fit a nonlinear model using nls( ), I get an error message
> that says I have a singular gradient matrix. I am not sure what causes
> this problem. Should I try different initial values of the parameters, or
> is the problem something else?
I have found that supplying analytic first derivatives
using deriv() can eliminate this problem (not always,
but sometimes). Supplying analytic derivatives
is well-described in V&R.
Bruce
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