[R] R formula language---a min and max function?
ivo.welch at gmail.com
Tue May 4 21:52:09 CEST 2010
thank you, david. indeed. works great (almost). an example for
anyone else googling this in the future:
> 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.
On Tue, May 4, 2010 at 3:40 PM, David Winsemius <dwinsemius at 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.
>> R-help at r-project.org mailing list
>> PLEASE do read the posting guide
>> and provide commented, minimal, self-contained, reproducible code.
> David Winsemius, MD
> West Hartford, CT
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