Help!
nls is killing me!
I am fitting a fairly simple nonlinear model using nls.
Sometimes it goes OK. Sometimes, FOR THE SAME INPUT DATA,
it says 'singular gradient matrix', or 'number of iterations exceeds
maximum, or step below minimum. I have not found a good explanation of
these terms in HELP. I've tried all kind of manipulations with
nls.control. Does not help. Increasing number of iterations up to
50000, or increasing tolerance up to 0.1 or decreasing step down to
0.00001 does not correct the problem. Can anybody explain what is going on
and how to survive this disaster. S+3.3/win98/P400/128
Thank you
S.Rosenfeld
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