[R] Beginners Question: Make nlm work

[Peter Dalgaard]

Arne Henningsen <ahenningsen at email.uni-kiel.de> writes:

> Hi,
> 
> did you try "nls" (nonlinear least squares)? "?nlm" says: 
> "For nonlinear regression, 'nls' may be better".
> Another option would be "optim".

Actually, just using nlm  according to specs might help:

> > setwd("~/Biology/R_versuch")
> > mydata<-read.table("YJG45-7_Growth.dat")
> > x<-mydata$V1
> > y<-mydata$V2
> > VH <- function(p) y ~ p[1]/(1+((p[1]-0.008)/0.008)*exp(-(p[2]*x)))

Make that  

VH <- function(p) sum((y - p[1]/(1+((p[1]-0.008)/0.008)*exp(-(p[2]*x))))^2)

> > plot(x, y, xlab="Time (h)",ylab=expression(OD[600][~nm]),las=1)
> > out <- nlm(VH, p = c(3, 4e-3), hessian = TRUE)

I'm quite surprised that the other thing gives a result at all!

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
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