Re: [R] Fitting a model

From: Eik Vettorazzi <E.Vettorazzi_at_uke.uni-hamburg.de>
Date: Thu, 20 Nov 2008 22:08:58 +0100

Actually "drm" as posted before fits a sigmoid curve (a generalized logistic function with 4 parameters, see ?LL.4), so I didn't get the point of your new question.

Dani Valverde schrieb:
> Thank you all for your answers. If you look at the plot resulting from
> my data, it seems that it is some kind of sigmoid function, not only
> polynomial. How could I fit it?
> Best,
>
> Dani
>
> Daniel Valverde Saubí
>
> Grup de Biologia Molecular de Llevats
> Facultat de Veterinària de la Universitat Autònoma de Barcelona
> Edifici V, Campus UAB
> 08193 Cerdanyola del Vallès- SPAIN
>
> Centro de Investigación Biomédica en Red
> en Bioingeniería, Biomateriales y
> Nanomedicina (CIBER-BBN)
>
> Grup d'Aplicacions Biomèdiques de la RMN
> Facultat de Biociències
> Universitat Autònoma de Barcelona
> Edifici Cs, Campus UAB
> 08193 Cerdanyola del Vallès- SPAIN
> +34 93 5814126
>
>
>
> En/na Eik Vettorazzi ha escrit:
>> you might use the drc-package (equivalently you could use nls with an
>> appropriate "selfstart" model like SSlogis)
>>
>> library(drc)
>> mm<-drm(delta~ph,fct=LL.4())
>> plot(mm)
>>
>> From your plot I was assuming that "ph" is the independent variable
>> (as modelled above) - so if you want to predict a ph from delta you
>> will need the "inverse" function of your fitted model - you could
>> toy with ED from the drc package or do a simple grid search with
>> "predict".
>>
>> hth.
>>
>>
>> Dani Valverde schrieb:
>>> Hello,
>>> This is a very basic question, but I don'y know the answer. I have
>>> these data
>>>
>>> delta <-
>>> c(28.6-8.825,28.6-8.828,28.6-8.836,28.6-8.845,28.6-8.897,28.6-8.944,28.6-9.027,28.6-9.091,28.6-9.263,28.6-9.4,28.6-9.7,28.6-9.981,
>>>
>>> 28.6-10.287,28.6-10.48,28.6-10.684,28.6-10.875)
>>> ph <- c(4.4,4.6,4.8,5,5.2,5.4,5.6,5.8,6,6.2,6.4,6.6,6.8,7,7.2,7.4)
>>> plot(ph,delta,ylab=c(expression(Delta*delta)),xlab="pH")
>>>
>>> Which kind of model can I fit on these, so that can I predict for a
>>> given delta the pH of my sample? Once the model is fitted, how can I
>>> plot it on the graph?
>>> Best regards,
>>>
>>> Dani
>>>
>>
>



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