if( !require('drc') ){
    install.packages('drce', dependencies=TRUE, repos='http://cran.rstudio.com/')
}
library(drc) # get the dataset S.alba

library(lattice)

xyplot(DryMatter ~ Dose | Herbicide, data=S.alba, scales=list(x=list(log=TRUE)), xlab='Dose(g/ha)', ylab='Dry matter(g/pot)')

# Fit a model like what was introduced in the section 'common control':
#
S.alba.m1 = nls(DryMatter ~ c[Herbicide] +(d-c[Herbicide])/(1+exp(b[Herbicide]*(log(Dose)-log(e[Herbicide])))),
                 data=S.alba,
                 start=list(b=c(2, 2), c=c(500,100), d=1000, e=c(50,100)))
print(summary(S.alba.m1))