thanks it seems to be a good idea. a also find the PK package with the biexp function.
2012/8/23 Peter Ehlers <ehl...@ucalgary.ca> > > Have you checked help(SSbiexp) ? > > Peter Ehlers > > > On 2012-08-23 04:54, vincent guyader wrote: > >> Hi everyone, >> >> I'm trying to perform a bi exponential Fit with the package NLS. the >> plinear algorithm seems to be a good choice >> >> see: >> >> p<-3000 >> q<-1000 >> a<--0.03 >> b<--0.02 >> t<-seq(0:144);t >> y<-p*exp(a*t) + q*exp(b*t)+rnorm(t,sd=0.3*(p* >> exp(a*t) + q*exp(b*t))) >> fittA <- nls(y~cbind(exp(a*t), exp(b*t)), >> algorithm="plinear",start=**list(a=-.1, b=-0.2), data=list(y=y, t=t), >> trace=FALSE);fittA >> >> # a b .lin1 .lin2 >> # -0.003074 -2.777 4512 -2399 >> >> fittB <- nls(y~cbind(exp(a*t), exp(b*t)), >> algorithm="plinear",start=**list(a=-.1, b=-0.3), data=list(y=y, t=t), >> trace=FALSE);fittB >> >> # a b .lin1 .lin2 >> # -0.02248 -0.04684 2414.86017 2052.96601 >> >> >> but >> >> 1 - the initial condition is very sensitive, is there any way to find a >> good start for the parameters? >> 2 - I would like to havre .lin1 >0 ans .lin2 >0 , is there a way to do >> that? >> >> >> thx a lot >> >> [[alternative HTML version deleted]] >> >> ______________________________**________________ >> R-help@r-project.org mailing list >> https://stat.ethz.ch/mailman/**listinfo/r-help<https://stat.ethz.ch/mailman/listinfo/r-help> >> PLEASE do read the posting guide http://www.R-project.org/** >> posting-guide.html <http://www.R-project.org/posting-guide.html> >> and provide commented, minimal, self-contained, reproducible code. >> >> > [[alternative HTML version deleted]] ______________________________________________ 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.
