[R] logistic growth model

[Rubén Roa]

Write the growth formula in an R script.
Define initial par values.
Input the size and age data.
Plot the size and age data as points.
Plot the growth model with the initial par values as a line.
Play with the initial par values until you see a good agreement between the model (the line) and the data (the points).
Optimise.
Re-plot.
Plot a residual histogram.
Plot a residual scatterplot.
Plot a Q-Q residual plot.

HTH

Rubén
____________________________________________________________________________________ 

Dr. Rubén Roa-Ureta
AZTI - Tecnalia / Marine Research Unit
Txatxarramendi Ugartea z/g
48395 Sukarrieta (Bizkaia)
SPAIN



> -----Mensaje original-----
> De: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] En nombre de Renalda
> Enviado el: sábado, 04 de junio de 2011 6:17
> Para: r-help at r-project.org
> Asunto: [R] logistic growth model
> 
> I want to Fit a logistic growth model for y = k 
> *eb0+b1(age)/1 + eb0+b1(age), can some one help on how to get 
> the initial coefficients b0 and b1? I need to estimate in 
> order to do the regression analysis. When I run using b0=0.5 
> and b1=3.4818, I get the following error
> 
> 397443.8 :  0.5 3.4818
> Error in nls(Height ~ k * exp(b1 + b2 * Age)/(1 + exp(b1 + b2 
> * Age)),  :
>    singular gradient
> "please tell me what is wrong with my initials values, and 
> how to get the initial values"
> 
> ______________________________________________
> R-help at r-project.org 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.
>