[R-sig-ME] nlme question...

[Thompson,Paul]

The model looks odd, very odd.  Are you sure that you mean "k 2K 3K"?
Don't you mean "k, k^2, k^3"?  If you really mean "k 2k 3k", you have
total collinierity.  In addition, if this is an individual growth curve
with 5 parameters, do you have 6+ obs per person?


Paul A. Thompson, Ph.D.

   

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-----Original Message-----
From: r-sig-mixed-models-bounces at r-project.org
[mailto:r-sig-mixed-models-bounces at r-project.org] On Behalf Of Murray
Jorgensen
Sent: Monday, August 30, 2010 2:59 PM
To: Jeffrey Harring
Cc: r-sig-mixed-models at r-project.org
Subject: Re: [R-sig-ME] nlme question...

Maybe you could tell us more about the data and why you wish to 
associate error components with b0 and b1 parameters? It just looks like

a perfectly ordinary nonlinear model that might be fitted using the 
Gauss-Newton or partially linear methods using nls().

Murray Jorgensen

Jeffrey Harring wrote:
>  Hi all,
> 
> Can the algorithm in nlme handle a nonlinear function that is written
as 
> a design matrix and linear coefficients like the following
> 
> The model is a nonlinear growth model with five time points: y = X*b +
> e, where design matrix X is defined as
> 
> X= |  1   0  |
>    |  1   1  |
>    |  1   k  |
>    |  1  2k  |
>    |  1  3k  |
> 
> and parameter vector b = (b0, b1). And where "k" is a parameter to be
> estimated. Of course I also want to estimate the intercept (b0), slope
> (b1). Error variances (e) with 5 free parameters and random effects
> covariance matrix  (2x2: for b0 and b1).
> 
> If anyone has concrete suggestions I would love to hear from you.
> 
> Thanks for your consideration,
> Jeff
> 
> 
> 
> 


-- 
Dr Murray Jorgensen      http://www.stats.waikato.ac.nz/Staff/maj.html
Department of Statistics, University of Waikato, Hamilton, New Zealand
Email: maj at waikato.ac.nz    majorgensen at ihug.co.nz      Fax 7 838 4155
Phone  +64 7 838 4773 wk    Home +64 7 825 0441   Mobile 021 0200 8350

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