[R] question regarding variance function in gls

Dear R-help members, I have a question regarding how to use varComb function to specify a variance function for the "weights" in the gls. I need to fit a linear model with heteroscedasticity. The variance function is exp(c0+nu0*W +nu1*W^2) where W is a covariate. Initially I want to use varFu

[R] varComb in gls/lme

Dear R-help members, I have a question regarding how to use varComb function to specify a variance function for the "weights" in the gls. I need to fit a linear model with heteroscedasticity. The variance function is exp(c0+nu0*W +nu1*W^2) where W is a covariate. Initially I want to use va

[R] 2 different colors for 2 groups of lines using xyplot

Hi All, I am trying to use xyplot to plot several lines in one panel with red color for a group of lines, say 3 lines and blue color for another group of lines, say 4. I know this can be easily done using regular plot function. But i could not figure out how to do this in xyplot. Any hel