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Hi, I have a problem fitting the following Weibull Model to a set of data. The model is this one: a-b*exp(-c*x^d) If I fitted the model with CurveExpert I can find a very nice set of coefficients which create a curve very close to my data, but when I use the nls.lm function in R I can't obtain the same result. My data are these: X Y 15 13 50 13 75 9 90 4 With the commercial software I obtain the following coefficients: Weibull...

...ell into a Weibull model y = a-b*exp(-c*x^d). I want to estimate the parameters of the coefficients a, b, c and d, given x and y. Can you guys help me? Just as an example, I fit the data y <- c(1,2,3,4,10,20) and x <- c(1,7,14,25,29,30) According to this model above, and using the software CurveExpert, and I got the estimates of a (2.95),b (2.90),c (2.82e-2) and d (2.97). This is just a sample data but I would like to do it on R because I can loop multiple times through all my files. I would also like to fit a logistic model y = a/(1+b*exp-c*x) Can you help me???? Thanks -- View this messa...

...nfield.ac.uk To: r-help at r-project.org Date: Mon, 23 Aug 2010 16:01:59 +0100 Subject: [R] Fitting Weibull Model with Levenberg-Marquardt regression method Hi, I have a problem fitting the following Weibull Model to a set of data. The model is this one: a-b*exp(-c*x^d) If I fitted the model with CurveExpert I can find a very nice set of coefficients which create a curve very close to my data, but when I use the nls.lm function in R I can't obtain the same result. My data are these: X Y 15 13 50 13 75 9 90 4 With the commercial software I obtain the following coefficients: Weibull...