[R] Generalized least squares using "gnls" function

[Ravi Varadhan]

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.
> 
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