thank you, david. indeed. works great (almost). an example for anyone else googling this in the future:
> x=1:20 > y= 2+3*ifelse(x>10, 10, x)+rnorm(20,0,0.01) > r1= nls( y~ a+b*pmin(c,x), start=list(a=2, b=3, c=10), trace=TRUE ) 0.002142 : 2 3 10 0.002115 : 2.004 3.000 10.000 0.002114 : 2.006 2.999 10.001 0.002084 : 2.005 2.999 10.000 ... 0.002079 : 2.005 2.999 10.000 Error in nls(y ~ a + b * pmin(c, x), start = list(a = 2, b = 3, c = 10), : step factor 0.000488281 reduced below 'minFactor' of 0.000976562 strange error, but unrelated to my question. will figure this one out next. regards, /iaw On Tue, May 4, 2010 at 3:40 PM, David Winsemius <dwinsem...@comcast.net> wrote: > > On May 4, 2010, at 3:33 PM, ivo welch wrote: > >> Dear R experts---I would like to estimate a non-linear least squares >> expression that looks something like >> >> y ~ a+b*min(c,x) >> >> where a, b, and c are the three parameters. how do I define a min >> function in the formula language of R? advice appreciated. > > ?pmin > >> >> sincerely, >> >> /iaw >> >> ______________________________________________ >> 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. > > David Winsemius, MD > West Hartford, CT > > ______________________________________________ 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.
