 Dear John Nash

Thank  you very much for your inputs on how to fit a non-linear growth curve  without running into "singular gradient". I wasn't aware of the package  "nlmrt" which seems to provide very helpful functions, indeed. I'll try  to figure out how nlxb() can be applied to my data (I am not sure yet  wheter I can actually apply the same initial parameters for all of my  plants) and also how plotting of the fitted curve works with nlxb(). The  easy way of using predict(fit) did not work in this case.

In addition, I am still wondering if there is in fact no way of controlling the step factor in SSweibull.

Best regards, 
Aline Frank


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