Weighted nls

["Oscar Linares" <olinares@med.umich.edu>]

Dear Colleagues,

I am trying to do weighted nls. I have searched the archives and the white 
book. I tried TBS without success. The data frame and nls invocation are below.

# cs expo fit
csdata<-data.frame(
time=c(0,1,3,9,20),
resp=c(638.697,395.69,199.00,141.58,112.16)
)

# perform nlr
cs.nls<-nls(resp~A1*exp(-a1*time)+A2*exp(-a2*time),
  data=csdata,
  start=list(A1=700,a1=1,A2=100,a2=0.1)
)
cs.nls

I need weighting, e.g., (resp-pred)/sqrt(pred)

Kind Regards,

Oscar A Linares
Molecular Medicine Unit