[R] nls problem with R

[Andrew Robinson]

The fact that T2 and V2 are of different lengths seems like a likely
culprit.  Other than that, you need to find start points that do not
lead to a singular gradient.  There are several books that provide
advice on obtaining initial parameter estimates for non-linear
models.  Google Books might help you.

Cheers

Andrew




On Tue, May 03, 2011 at 09:08:03PM -0700, sterlesser wrote:
> the original data are
> V2 =c(371000,285000 ,156000, 20600, 4420, 3870, 5500 )
> T2=c( 0.3403 ,0.4181 ,0.4986 ,0.7451 ,1.0069 ,1.553)
> nls2=nls(V2~v0*(1-epi+epi*exp(-cl*(T2-t0))),start=list(v0=10^7,epi=0.9,cl=6.2,t0=8.7))
> after execution error occurs as below
> ################################################################
> Error in nlsModel(formula, mf, start, wts) : 
>   singular gradient matrix at initial parameter estimates
> Error in nlsModel(formula, mf, start, wts) : 
>   singular gradient matrix at initial parameter estimates
> In addition: Warning messages:
> 1: In lhs - rhs :
>   longer object length is not a multiple of shorter object length
> 2: In .swts * attr(rhs, "gradient") :
>   longer object length is not a multiple of shorter object length
> 
> could anyone help me ?thansks
> 
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-- 
Andrew Robinson  
Program Manager, ACERA 
Department of Mathematics and Statistics            Tel: +61-3-8344-6410
University of Melbourne, VIC 3010 Australia               (prefer email)
http://www.ms.unimelb.edu.au/~andrewpr              Fax: +61-3-8344-4599
http://www.acera.unimelb.edu.au/

Forest Analytics with R (Springer, 2011) 
http://www.ms.unimelb.edu.au/FAwR/
Introduction to Scientific Programming and Simulation using R (CRC, 2009): 
http://www.ms.unimelb.edu.au/spuRs/