Thanks Mike. Your suggestion is really helpful.I did with the your instruction , it really works out. What's more,can you use this package http://cran.r-project.org/web/packages/minpack.lm/index.html it use Levenberg-Marquardt algorithm. Can this package do with four parameters? Thanks again
-- View this message in context: http://r.789695.n4.nabble.com/nls-problem-with-R-tp3494454p3508126.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@r-project.org 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.