[R] nls

[Prof Brian Ripley]

You problem is x^c for x = 0.  If you intended only c > 1, try a starting 
value meeting that condition (but it seems that the optimal c is about 
0.27 is you increase x slightly).

Why have you used ~~ ?  (Maybe because despite being asked not to, you 
sent HTML mail?)

On Tue, 15 Aug 2006, Xiaodong Jin wrote:

>   Is there anyway to change any y[i] value (i=2,...6) to make following NLS workable? 
>    
>   x <- c(0,5,10,15,20,25,30)
>   y <- c(1.00000,0.82000,0.68000,0.64000,0.66667,0.68667,0.64000)
>   lm(1/y ~~ x)
>   nls(1/y ~~ a+b*x^c, start=list(a=1.16122,b=0.01565,c=1), trace=TRUE)
>    
>   #0.0920573 :  1.16122 0.01565 1.00000 
> #Error in numericDeriv(form[[3]], names(ind), env) : 
> #        Missing value or an infinity produced when evaluating the model
> 
>  			
> ---------------------------------
> 
> 
> 	[[alternative HTML version deleted]]
> 
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595