Hello all! I am trying to estimate four parameters (mu, sigma, theta and lambda) of a model Using the nls package in R, I can only get it to work if I limit the number of parameters to be estimated to three (i.e. mu, sigma and theta) as in the first model - mod1 - below. Including a fourth parameter (lambda) like in the second model - mod2 - returns the following error messages 1. Error in numericDeriv(form[[3L]], names(ind), env): 2. Missing value or an infinity produced when evaluating the model mod1<-nls(germ~1-(exp(-1*((psi-(theta/time)-mu)/sigma))),start=c(mu=-2.7, theta=3, sigma=3), data=ht) mod1 mod2<-nls(germ~1-(exp(-1*((psi-(theta/time)-mu)/sigma)^lambda)),start=c(mu=-2.7, theta=3, sigma=3, lambda=-1.2), data=ht) mod2 Please have a look at my code and tell how I might get it to work. A sample of my data is shown below. It has five levels of psi (0, -0.4, -0.8, -1.2 and -1.6). psi time germ 0 1.333333 0 0 1.416667 0 0 1.5 0.04 0 1.583333 0.04 0 2.083333 0.08 0 2.166667 0.16 0 2.25 0.24 0 2.583333 0.64 0 2.666667 0.72 0 2.916667 1 . . . -1.6 2.916667 0 -1.6 3.166667 0 -1.6 3.666667 0 -1.6 7.666667 0 -1.6 9.666667 0 -1.6 12.66667 0 -1.6 19.66667 0 Dr Onoriode Coast Postdoctoral Fellow Agriculture Flagship CSIRO E onoriode.coast at csiro.au T +61 2 6799 1541 M 0477 386 110 21888 Kamilaroi Highway, Narrabri, NSW, 2390 Australia www.csiro.au [[alternative HTML version deleted]]