[R] optim with constraints

[Steven]

Hi, dear R users

I am a newbie in R and I wantto use the method of meximum likelihood
to fit a Weibull distribution to my survival data. I use "optim" as
follows:


optim(c(1, 0.25),weibull.like,mydata=mydata,method="L-BFGS-B",hessian
= TRUE)

My question is: how do I setup the constraints so that the two
parametrs of Weibull to be pisotive? Or should I use other function
like"nlm"?

Many thanks! Any comments are greatly appreciated!

Steven