# [R] How to do global curve fitting in R

Jianling Fan fanjianling at gmail.com
Wed Sep 9 19:29:29 CEST 2015

```Thanks very much William,

That's exactly what I need! It is so excellent to do it by a
group-separation by [] syntax.

Thanks again!

Best regards,

Jianling

On 9 September 2015 at 11:15, William Dunlap <wdunlap at tibco.com> wrote:
> You can put all your data in one data.frame along with a column called, say,
> 'group' that says which group each row is in.  Then use the [] syntax in
> nls's
> formula argument to get group-specific estimates for some of the parameters.
> E.g., in the following there is a global parameter 'b' and a group-specific
> parameter
> 'p'.
>
>> d <- transform(data.frame(x=seq(0,1,len=17),
>> group=rep(c("A","B","B","C"),len=17)), y = round(1/(1.4+x^ifelse(group=="A",
>> 2.3, ifelse(group=="B",3.1, 3.5))),2))
>> str(d)
> 'data.frame':   17 obs. of  3 variables:
>  \$ x    : num  0 0.0625 0.125 0.1875 0.25 ...
>  \$ group: Factor w/ 3 levels "A","B","C": 1 2 2 3 1 2 2 3 1 2 ...
>  \$ y    : num  0.71 0.71 0.71 0.71 0.69 0.7 0.69 0.69 0.62 0.64 ...
>> nls(y~1/(b+x^p[group]), data=d, start=list(b=1,
>> p=rep(3,length(levels(d\$group)))))
> Nonlinear regression model
>   model: y ~ 1/(b + x^p[group])
>    data: d
>     b    p1    p2    p3
> 1.406 2.276 3.186 3.601
>  residual sum-of-squares: 9.537e-05
>
> Number of iterations to convergence: 5
> Achieved convergence tolerance: 4.536e-06
>
> issues.)
>
>
> Bill Dunlap
> TIBCO Software
> wdunlap tibco.com
>
> On Wed, Sep 9, 2015 at 9:28 AM, Jianling Fan <fanjianling at gmail.com> wrote:
>>
>> Hi, Bert
>>
>>
>> I am fitting a logistic does response model with 3 parameters as :
>> y=a/(1+(x/x0)b), I have many sets of data. I can fit each of them for
>> the model. but I want them shared the parameter x0 and b, but varied
>> for each a.
>>
>> I don't think it is a  statistics problem. It is a typical global
>> curve fitting problem with shared parameters. And I know how to do it
>> by many other software. But since I am trying to use R, I am wondering
>> is there any package or method to do it in R?
>>
>> Thanks!
>>
>> Jianling
>>
>>
>> On 9 September 2015 at 10:16, Bert Gunter <bgunter.4567 at gmail.com> wrote:
>> > Jianling:
>> >
>> > 1. What models are you trying to fit? Details matter, and it is
>> > impossible to give a good answer without specifics.
>> >
>> > 2. In general terms, to do this one combines all the data and allows
>> > for "appropriate" changes in the model parameters for the different
>> > groups. For example, different intercepts, rate constants, etc. This
>> > is where the specifics matter.
>> >
>> > 3. This is really more a statistics than an R question, and you would
>> > probably do better to pursue these issues either with a local
>> > statistical resource or on a statistics site, like
>> > stats.stackexchange.com.
>> >
>> > Cheers,
>> > Bert
>> > Bert Gunter
>> >
>> > "Data is not information. Information is not knowledge. And knowledge
>> > is certainly not wisdom."
>> >    -- Clifford Stoll
>> >
>> >
>> > On Wed, Sep 9, 2015 at 9:04 AM, Jianling Fan <fanjianling at gmail.com>
>> > wrote:
>> >> Hello all,
>> >>
>> >> I am trying to fit my data to a nls model. I have many sets of data
>> >> and each can fit well for the curve. but I want to fit them at once by
>> >> sharing 2 of 3 parameters of the model. I know it is a typical global
>> >> curve fitting problem, but I don't know how to do it by R?
>> >>
>> >> Does anyone know any package for this??
>> >>
>> >> Thanks a lot!
>> >>
>> >>
>> >> Julian
>> >>
>> >> ______________________________________________
>> >> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> >> https://stat.ethz.ch/mailman/listinfo/r-help
>> >> http://www.R-project.org/posting-guide.html
>> >> and provide commented, minimal, self-contained, reproducible code.
>>
>>
>>
>> --
>> Jianling Fan
>> 樊建凌
>>
>> ______________________________________________
>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
>

--
Jianling Fan

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