On Sat, 2007-03-03 at 16:30 -0500, Cressoni, Massimo (NIH/NHLBI) [F] wrote: > I am trying to write a function that fits a sigmoid given a X and Y vector > guessing the start parameters. > I use nls. What I did (enclosed) seems to work well with many data points but > if I want to fit small > vectors like : > > pressure <- c(5,15,9,35,45) > gas <- c(1000,2000,3000,4000,5000) > > it do not work. The help page says that it do no not work on zero residual > data. > > Massimo Cressoni
Hi Massimo I think which this script solve your question ------------------------ pressure <- c(5,9,15,35,45) gas <- c(1000,2000,3000,4000,5000) plot(gas,pressure) model.1 <- nls(pressure ~ SSlogis(gas, ASym, xmid, scal))) coef.sig<-coef(summary(model.1))[,1] est.p<-coef.sig[1]/(1+exp((coef.sig[2]-gas)/coef.sig[3])) points(gas,est.p,col=2) ------------------------ If you need more help just need a mail -- Bernardo Rangel Tura,M.D.,Ph.D National Institute of Cardiology Rio de Janeiro - Brazil ______________________________________________ [email protected] 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.
