I am trying to fit this data to a weibull distribution: My y variable is:1 1 1 4 7 20 7 14 19 15 18 3 4 1 3 1 1 1 1 1 1 1 1 1
and x variable is:1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 The plot looks like this:http://i.stack.imgur.com/FrIKo.png and I want to fit a weibull curve to it. I am using the nls function in R like this: nls(y ~ ((a/b) * ((x/b)^(a-1)) * exp(- (x/b)^a))) This function always throws up an error saying: Error in numericDeriv(form[[3L]], names(ind), env) : Missing value or an infinity produced when evaluating the model In addition: Warning message: In nls(y ~ ((a/b) * ((x/b)^(a - 1)) * exp(-(x/b)^a))) : No starting values specified for some parameters. Initializing ‘a’, ‘b’ to '1.'. Consider specifying 'start' or using a selfStart model So first I tried different starting values without any success. I cannot understand how to make a "good" guess at the starting values. Then I went with the SSweibull(x, Asym, Drop, lrc, pwr) function which is a selfStart function. Now the SSWeibull function expects values for Asym,Drop,lrc and pwr and I don't have any clue as to what those values might be. I would appreciate if someone could help me figure out how to proceed. Background of the data: I have taken some data from bugzilla and my "y" variable is number of bugs reported in a particular month and "x" variable is the month number after release. ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
