Please note that R^2 for nonlinear models is nonsense. Search on "R^2 in nonlinear models" for details, e.g.
http://statisticsbyjim.com/regression/r-squared-invalid-nonlinear-regression/ Cheers, Bert Bert Gunter "The trouble with having an open mind is that people keep coming along and sticking things into it." -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip ) On Wed, Aug 15, 2018 at 10:54 AM Francis Boateng < francis.boat...@versantphysics.com> wrote: > Thanks Ellison, I will try it. > > Francis > > > -----Original Message----- > From: S Ellison <s.elli...@lgcgroup.com> > Sent: Thursday, August 9, 2018 8:12 AM > To: Francis Boateng <francis.boat...@versantphysics.com>; > r-help@r-project.org > Subject: RE: exponential day > > > Please, how can I determine parameters from exponential equation > > Example > > one: y = a*exp(-b*x); how do I determine a and b , as well as > > R-square from data sets. And also fitting y = a*exp(-b*x) into the > > data sets Assuming data sets A = (0,2,4,6,8,10) B = > > (1,0.8,0.6,0.4,0.2,0.1) > > For least squares fitting, you could take logs and do a simple linear fit, > if the resduals are reasonably homoscedastic in the log domain (or if you > can sort the weighting out properly). > > For non-linear least squares, look at ?nlm, ?nls or (if you want to roll > your own) ?optim > > For max likelihood, maybe nlme in the nlme package. > > For other ideas, look up 'non-linear fitting with R' on any search engine, > or check the R Task Views > > S Ellison > > > > ******************************************************************* > This email and any attachments are confidential. Any u...{{dropped:18}} ______________________________________________ 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.
