[R] different forms of nls recommendations

[Dieter Menne]

emorway wrote:
> 
> 
> So I wanted to try a different equation of the general form a/(b+c*x^d)
> 
> US.nls.2<-nls(US.final.values$ECe~(a/(b+c*US.final.values$WTD^d)),data=US.final.values,start=list(a=100.81,b=73.7299,c=0.0565,d=-6.043),trace=TRUE,algorithm="port")
> 
> but that ended with "Convergence failure: false convergence (8)".  I tried
> relaxing the convergence 
> 
> 

You want 4 parameters from a set of data that has a very large variance. Try
to fix d and c to a reasonable constant; it probably will converge.

>From looking at your data and the variances, I would suggest to
log-transform first. If you feel bad about it, you can always fit the
original data later after you have found a good model.

Dieter


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