R help - Apr 2010 - using varFunc in gnls to replicate Wedderburn-style variance?

Hi,

I'm fitting a gnls on a response that varies from 0 to 1 using a basic
logistic equation (1/(1+e^-bx)).  I'm using gnls because this is spatial
data with correlation in residuals well described by corSpher.  Residual
variance is compressed for fitted values near 0 and 1, and realtively
constant in the 'middle'.  Wedderburn suggested using (1-fitted
value)*fitted value for nonlinear regression with data like mine
(proportions), similar to what is expected for a binomial distribution.  Is
it possible to specify weight using varFunc so that the variance is a
function of the fitted values?  I've only seen examples for varFunc where
covariates are used.

Thanks,
Seth
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