Here is one way of getting a reasonable fit: 1. Scale your y's by dividing all values by 1e6. 2. Plot x vs. y. The plot looks like a quadratic function. 3. Fit a quadratic const. + B*x^2 - this a linear regression problem so use lm. 4. Plot the predictions. 5. Eyball the necessary shift - MA is around 0.01. Refit const. + B*(x-.01)^2. Should get const.=1.147 and B=139.144 6. Use start=list(const.= 1.147, A=0, B=1.147, MA=.01). nls should converge in 4 iterations.
In general, good starting points may be crucial to nls convergence. Scaling the y's to reasonable values also helps. Hope this helps, Andy __________________________________ Andy Jaworski 518-1-01 Process Laboratory 3M Corporate Research Laboratory ----- E-mail: [EMAIL PROTECTED] Tel: (651) 733-6092 Fax: (651) 736-3122 "Yu (Warren) Wang" <[EMAIL PROTECTED]> To Sent by: "r-help@stat.math.ethz.ch" [EMAIL PROTECTED] <r-help@stat.math.ethz.ch> at.math.ethz.ch cc Subject 09/05/2007 02:51 [R] question about non-linear least AM squares in R Hi, everyone, My question is: It's not every time that you can get a converged result from the nls function. Is there any solution for me to get a reasonable result? For example: x <- c(-0.06,-0.04,-0.025,-0.015,-0.005,0.005,0.015,0.025,0.04,0.06) y <- c(1866760,1457870,1314960,1250560,1184850,1144920,1158850,1199910,1263850,1452520) fitOup<- nls(y ~ constant + A*(x-MA)^4 + B*(x-MA)^2, start=list(constant=10000000, A=100000000, B=-1000000, MA=0), control=nls.control(maxiter=100, minFactor=1/4096), trace=TRUE) For this one, I cannot get the converged result, how can I reach it? To use another funtion or to modify some settings for nls? Thank you very much! Yours, Warren ______________________________________________ R-help@stat.math.ethz.ch mailing list 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. ______________________________________________ R-help@stat.math.ethz.ch mailing list 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.