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R formula language---a min and max function?

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ivo welch-2

R formula language---a min and max function?

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.

sincerely,

/iaw

______________________________________________
[hidden email] 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

Re: R formula language---a min and max function?

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
>
> ______________________________________________
> [hidden email] 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

______________________________________________
[hidden email] 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.

ivo welch

Re: R formula language---a min and max function?

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 <[hidden email]> 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
>>
>> ______________________________________________
>> [hidden email] 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
>
>

______________________________________________
[hidden email] 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.

Gabor Grothendieck

Re: R formula language---a min and max function?

You need to use set.seed first so that your example is reproducible.
Using set.seed(1) there is no error:

> set.seed(1)
> 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 )
0.001657260 : 2 3 10
0.00153709 : 1.998312 3.000547 9.999568
0.001509616 : 1.996222 3.001117 9.998197
0.001509616 : 1.996222 3.001117 9.998197
> r1
Nonlinear regression model
model: y ~ a + b * pmin(c, x)
data: parent.frame()
a b c
1.996 3.001 9.998
residual sum-of-squares: 0.001510

Number of iterations to convergence: 3
Achieved convergence tolerance: 3.195e-09

On Tue, May 4, 2010 at 3:52 PM, ivo welch <[hidden email]> 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.
>
> regards,
>
> /iaw
>
>
> On Tue, May 4, 2010 at 3:40 PM, David Winsemius <[hidden email]> 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
>>>
>>> ______________________________________________
>>> [hidden email] 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
>>
>>
>
> ______________________________________________
> [hidden email] 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

Re: R formula language---a min and max function?

In reply to this post by ivo welch

On May 4, 2010, at 3:52 PM, ivo welch wrote:

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 <[hidden email]
> > 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
>>>
>>> ______________________________________________
>>> [hidden email] 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
>>
>>

ivo welch

Re: R formula language---a min and max function?

thank you, david and gabor. very much appreciated. I should have
thought of setting the seed. this was only an example, of course.
alas, such intermittent errors could still be of concern to me,
because I need to simulate this nls() to find out its properties under
the NULL, so I can't easily tolerate errors. fortunately, I had the
window still open, so getting my y's out was easy, and the rounded
figures produce the same nls error.

> cbind(x,round(y,3))
x y
[1,] 1 5.017
[2,] 2 7.993
[3,] 3 11.014
[4,] 4 13.998
[5,] 5 17.003
[6,] 6 19.977
[7,] 7 23.011
[8,] 8 25.991
[9,] 9 29.003
[10,] 10 32.014
[11,] 11 31.995
[12,] 12 32.004
[13,] 13 32.012
[14,] 14 31.994
[15,] 15 31.998
[16,] 16 32.000
[17,] 17 32.009
[18,] 18 31.995
[19,] 19 32.000
[20,] 20 31.982

> r1= nls( y~ a+b*pmin(c,x), start=list(a=2, b=3, c=10), trace=TRUE )
0.002138 : 2 3 10
0.002117 : 2.004 3.000 9.999
0.002113 : 2.006 2.999 10.001
0.002082 : 2.005 2.999 10.000
0.002077 : 2.005 2.999 10.000
0.002077 : 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

I really don't care about this example, of course---only about
learning how to avoid nls() from dying on me. so, any advice would be
appreciated.

regards,

/iaw

----
Ivo Welch ([hidden email], [hidden email])

On Tue, May 4, 2010 at 3:59 PM, David Winsemius <[hidden email]> wrote:

>
> 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 <[hidden email]>
>> 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
>>>>
>>>> ______________________________________________
>>>> [hidden email] 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
>>>
>>>
>
> David Winsemius, MD
> West Hartford, CT
>
>

David Winsemius

Re: R formula language---a min and max function?

On May 4, 2010, at 5:25 PM, ivo welch wrote:

> thank you, david and gabor. very much appreciated. I should have
> thought of setting the seed. this was only an example, of course.
> alas, such intermittent errors could still be of concern to me,
> because I need to simulate this nls() to find out its properties under
> the NULL, so I can't easily tolerate errors. fortunately, I had the
> window still open, so getting my y's out was easy, and the rounded
> figures produce the same nls error.

There would of course be try()

But ... Again, No error on my device:
> xy <- scan()
1: 1 5.017
3: 2 7.993
5: 3 11.014
7: 4 13.998
9: 5 17.003
11: 6 19.977
13: 7 23.011
15: 8 25.991
17: 9 29.003
19: 10 32.014
21: 11 31.995
23: 12 32.004
25: 13 32.012
27: 14 31.994
29: 15 31.998
31: 16 32.000
33: 17 32.009
35: 18 31.995
37: 19 32.000
39: 20 31.982
41:
Read 40 items
> xym <-matrix(xy, ncol=2, byrow=TRUE)
> colnames(xym)<-c("x","y")
> r1= nls( y~ a+b*pmin(c,x), start=list(a=2, b=3, c=10), trace=TRUE )
0.001505770 : 2 3 10
0.001361737 : 2.003063 2.999924 10.000135

Plotting predict(r1) confirmed a very close fit.

> sessionInfo()
R version 2.10.1 RC (2009-12-09 r50695)
x86_64-apple-darwin9.8.0

locale:
[1] en_US.UTF-8/en_US.UTF-8/C/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
[1] stats graphics grDevices utils datasets methods base

other attached packages:
[1] misc3d_0.7-0 rgl_0.91 spatstat_1.18-3 deldir_0.0-12
[5] mgcv_1.6-1 ks_1.6.12 mvtnorm_0.9-9
KernSmooth_2.23-3
[9] lattice_0.18-3

loaded via a namespace (and not attached):
[1] grid_2.10.1 Matrix_0.999375-38 nlme_3.1-96
tools_2.10.1

>
>> cbind(x,round(y,3))
> x y
> [1,] 1 5.017
> [2,] 2 7.993
> [3,] 3 11.014
> [4,] 4 13.998
> [5,] 5 17.003
> [6,] 6 19.977
> [7,] 7 23.011
> [8,] 8 25.991
> [9,] 9 29.003
> [10,] 10 32.014
> [11,] 11 31.995
> [12,] 12 32.004
> [13,] 13 32.012
> [14,] 14 31.994
> [15,] 15 31.998
> [16,] 16 32.000
> [17,] 17 32.009
> [18,] 18 31.995
> [19,] 19 32.000
> [20,] 20 31.982
>
>> r1= nls( y~ a+b*pmin(c,x), start=list(a=2, b=3, c=10), trace=TRUE )
> 0.002138 : 2 3 10
> 0.002117 : 2.004 3.000 9.999
> 0.002113 : 2.006 2.999 10.001
> 0.002082 : 2.005 2.999 10.000
> 0.002077 : 2.005 2.999 10.000
> 0.002077 : 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
>
> I really don't care about this example, of course---only about
> learning how to avoid nls() from dying on me. so, any advice would be
> appreciated.
>
> regards,
>
> /iaw
>
>
>
> ----
> Ivo Welch ([hidden email], [hidden email])
>
>
>
> On Tue, May 4, 2010 at 3:59 PM, David Winsemius <[hidden email]
> > wrote:
>>
>> 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 <[hidden email]
>>> >
>>> 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
>>
>>

Gabor Grothendieck

Re: R formula language---a min and max function?

In reply to this post by ivo welch

For fixed c, y is linear in pmin(c, x) so the first two statements
find c and the next solves the remaining linear problem

f <- function(c) sum((y - fitted(lm(y ~ pmin(c, x))))^2)
fit.c <- optimize(f, c(0, max(DF$x))); fit.c

lm(y ~ pmin(fit.c$minimum, x))

as a function of c

On Tue, May 4, 2010 at 5:25 PM, ivo welch <[hidden email]> wrote:

> thank you, david and gabor. very much appreciated. I should have
> thought of setting the seed. this was only an example, of course.
> alas, such intermittent errors could still be of concern to me,
> because I need to simulate this nls() to find out its properties under
> the NULL, so I can't easily tolerate errors. fortunately, I had the
> window still open, so getting my y's out was easy, and the rounded
> figures produce the same nls error.
>
>> cbind(x,round(y,3))
> x y
> [1,] 1 5.017
> [2,] 2 7.993
> [3,] 3 11.014
> [4,] 4 13.998
> [5,] 5 17.003
> [6,] 6 19.977
> [7,] 7 23.011
> [8,] 8 25.991
> [9,] 9 29.003
> [10,] 10 32.014
> [11,] 11 31.995
> [12,] 12 32.004
> [13,] 13 32.012
> [14,] 14 31.994
> [15,] 15 31.998
> [16,] 16 32.000
> [17,] 17 32.009
> [18,] 18 31.995
> [19,] 19 32.000
> [20,] 20 31.982
>
>> r1= nls( y~ a+b*pmin(c,x), start=list(a=2, b=3, c=10), trace=TRUE )
> 0.002138 : 2 3 10
> 0.002117 : 2.004 3.000 9.999
> 0.002113 : 2.006 2.999 10.001
> 0.002082 : 2.005 2.999 10.000
> 0.002077 : 2.005 2.999 10.000
> 0.002077 : 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
>
> I really don't care about this example, of course---only about
> learning how to avoid nls() from dying on me. so, any advice would be
> appreciated.
>
> regards,
>
> /iaw
>
>
>
> ----
> Ivo Welch ([hidden email], [hidden email])
>
>
>
> On Tue, May 4, 2010 at 3:59 PM, David Winsemius <[hidden email]> wrote:
>>
>> 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 <[hidden email]>
>>> 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
>>>>>
>>>>> ______________________________________________
>>>>> [hidden email] 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
>>>>
>>>>
>>
>> David Winsemius, MD
>> West Hartford, CT
>>
>>
>
> ______________________________________________
> [hidden email] 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.
>

Gabor Grothendieck

Re: R formula language---a min and max function?

On Tue, May 4, 2010 at 7:39 PM, Gabor Grothendieck
<[hidden email]> wrote:
> For fixed c, y is linear in pmin(c, x) so the first two statements
> find c and the next solves the remaining linear problem
>

Here is a slightly shorter f:

f <- function(c) sum(resid(lm(y ~ pmin(c, x)))^2)

> f <- function(c) sum((y - fitted(lm(y ~ pmin(c, x))))^2)
> fit.c <- optimize(f, c(0, max(DF$x))); fit.c
>
> lm(y ~ pmin(fit.c$minimum, x))
>
>
> as a function of c
>
> On Tue, May 4, 2010 at 5:25 PM, ivo welch <[hidden email]> wrote:
>> thank you, david and gabor. very much appreciated. I should have
>> thought of setting the seed. this was only an example, of course.
>> alas, such intermittent errors could still be of concern to me,
>> because I need to simulate this nls() to find out its properties under
>> the NULL, so I can't easily tolerate errors. fortunately, I had the
>> window still open, so getting my y's out was easy, and the rounded
>> figures produce the same nls error.
>>
>>> cbind(x,round(y,3))
>> x y
>> [1,] 1 5.017
>> [2,] 2 7.993
>> [3,] 3 11.014
>> [4,] 4 13.998
>> [5,] 5 17.003
>> [6,] 6 19.977
>> [7,] 7 23.011
>> [8,] 8 25.991
>> [9,] 9 29.003
>> [10,] 10 32.014
>> [11,] 11 31.995
>> [12,] 12 32.004
>> [13,] 13 32.012
>> [14,] 14 31.994
>> [15,] 15 31.998
>> [16,] 16 32.000
>> [17,] 17 32.009
>> [18,] 18 31.995
>> [19,] 19 32.000
>> [20,] 20 31.982
>>
>>> r1= nls( y~ a+b*pmin(c,x), start=list(a=2, b=3, c=10), trace=TRUE )
>> 0.002138 : 2 3 10
>> 0.002117 : 2.004 3.000 9.999
>> 0.002113 : 2.006 2.999 10.001
>> 0.002082 : 2.005 2.999 10.000
>> 0.002077 : 2.005 2.999 10.000
>> 0.002077 : 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
>>
>> I really don't care about this example, of course---only about
>> learning how to avoid nls() from dying on me. so, any advice would be
>> appreciated.
>>
>> regards,
>>
>> /iaw
>>
>>
>>
>> ----
>> Ivo Welch ([hidden email], [hidden email])
>>
>>
>>
>> On Tue, May 4, 2010 at 3:59 PM, David Winsemius <[hidden email]> wrote:
>>>
>>> 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 <[hidden email]>
>>>> 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
>>>>>>
>>>>>> ______________________________________________
>>>>>> [hidden email] 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
>>>>>
>>>>>
>>>
>>> David Winsemius, MD
>>> West Hartford, CT
>>>
>>>
>>
>> ______________________________________________
>> [hidden email] 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.
>>
>