[R] Generalized least squares using "gnls" function

[Prof Brian Ripley]

The default argument for varPower's `form' arg is form = ~fitted(.)
I am pretty sure that is the `.' that is not found, and I guess it is an 
S/R difference.

I've always had trouble with this form of varPower (even in S).  I just 
wonder if form = ~fitted(".") might work.


On Thu, 15 Jan 2004, Ravi Varadhan wrote:

> Dear Christian:
> 
> That is not the problem, but thanks for your attempted help. I still 
> don't know what the problem is.  Has anyone encountered this while 
> using "gnls" function in the package "nlme"?
> 
> thanks again for any help,
> 
> Ravi.
> 
> 
> 
> ----- Original Message -----
> From: Christian Mora <christian_mora at vtr.net>
> Date: Wednesday, January 14, 2004 7:15 pm
> Subject: RE: [R] Generalized least squares using "gnls" function
> 
> > Have you tried removing tol=1.e-07 or changing the value considering
> > that the error is Object "." not found
> > 
> > -----Original Message-----
> > From: r-help-bounces+christian_mora=vtr.net at stat.math.ethz.ch
> > [mailto:r-help-bounces+christian_mora=vtr.net at stat.math.ethz.ch] On
> > Behalf Of Ravi Varadhan
> > Sent: Wednesday, January 14, 2004 6:11 PM
> > To: r-help at stat.math.ethz.ch
> > Subject: [R] Generalized least squares using "gnls" function
> > 
> > 
> > Hi:
> > 
> > I have data from an assay in the form of two vectors, one is 
> > response 
> > and the other is a predictor. When I attempt to fit a 5 parameter 
> > logistic model with "nls", I get converged parameter estimates. I 
> > also 
> > get the same answers with "gnls" without specifying the "weights" 
> > argument.
> > 
> > However, when I attempt to use the "gnls" function and try to 
> > estimate 
> > the variance function, as a power function, I get the following 
> > error 
> > message:
> > 
> > > ans51g <- gnls(log(b51) ~ p0 + p1/(1 + exp(-(log(dose)-
> > p2)/p3))^p4, 
> > start=list(p0=3,p1=1,p2=4,p3=2,p4=1.5),control=gnlsControl(tol=1.e-
> > 07),weights=varPower())
> > Error in eval(expr, envir, enclos) : Object "." not found
> > > 
> > 
> > What am I doing wrong here and how can I do a GLS analysis with a 
> > variance function that is estimated from the data?
> > 
> > Here is my data:
> > 
> > > b51 <- c(17447.60674, 7060.37234, 2872.53012,  796.40426,  
> > 454.47222,  260.22340,  120.11905,    83.40196,  51.45745,    
> > 36.87912,  26.73256,    25.18681, 17.97674)
> > > dose <- c( 1.000000e+04, 1.000000e+03, 2.500000e+02, 
> > 6.250000e+01, 
> > 3.125000e+01,  1.562500e+01, 7.812500e+00, 3.906250e+00, 
> > 1.953125e+00, 9.765625e-01, 4.882813e-01, 2.441406e-01, 1.000000e-03)
> > 
> > thanks for the help,
> > Ravi.
> > 
> > ______________________________________________
> > R-help at stat.math.ethz.ch mailing list
> > https://www.stat.math.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide!
> > http://www.R-project.org/posting-guide.html
> > 
> >
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
> 
> 

-- 
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