[R] How to do global curve fitting in R
bgunter.4567 at gmail.com
Wed Sep 9 19:25:27 CEST 2015
1) To add to Duncan's comments, if you create a new "dataset" discrete
factor column to indicate the dataset in the combined data, then you
would fit the model dataset/(corrected denominator).
2) However, there **is** a statistical issue here, for if you have
more than a "few" data sets, say more than 10 or a dozen or so, it
probably makes more sense to fit a mixed effects model where the
dataset factor is random. If so, my prior advice holds.
"Data is not information. Information is not knowledge. And knowledge
is certainly not wisdom."
-- Clifford Stoll
On Wed, Sep 9, 2015 at 9:37 AM, Duncan Murdoch <murdoch.duncan at gmail.com> wrote:
> On 09/09/2015 12:28 PM, Jianling Fan wrote:
>> Hi, Bert
>> Thanks for your reply.
>> 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.
> You might have a typo: x0 and b aren't separately identifiable in that
> model, only the ratio matters.
>> 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?
> The nls() function should do what you want. Your model is partially
> linear ("a" enters linearly), so the "plinear" algorithm should work.
> There's also an example of a "self-starting" logistic regression model
> in ?selfStart.
> Duncan Murdoch
>> On 9 September 2015 at 10:16, Bert Gunter <bgunter.4567 at gmail.com> wrote:
>>> 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
>>> 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!
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