On May 4, 2010, at 3:52 PM, ivo welch wrote:
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.
I get no error. May be difficult to sort out unless you can reproduce
after setting a random seed.
> 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 )
0.001560045 : 2 3 10
0.001161253 : 2.003824 2.998973 10.000388
0.001161253 : 2.003824 2.998973 10.000388
--
David.
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
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David Winsemius, MD
West Hartford, CT
David Winsemius, MD
West Hartford, CT
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and provide commented, minimal, self-contained, reproducible code.
