Hi Charlotte ,

I can't reproduce your code, but skimming through it -
It would appear that:
1) in
eqn1<- function(K1, bird)
you didn't define "bird" (you did define it before the function, so I'd
suggest just removing it from the function call like this:
eqn1<- function(K1)

2) you didn't "return" and value at the end of the function.

3) you use different name in optim then in the function you made.

4) I see no point for you to use the for loop.



Consider trying the following code:

b<-1.22
c<-0.55
bird<-bird.density[0] # I assume this exists
eqn<- function(K1, bird) {
               b<-1.22
               c<-0.55
               bird <- 0.55*bird + b*bird*1-b*bird*bird/K
            return(bird)
}

k1<-optim(c(0,10),eqn)



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On Mon, Apr 26, 2010 at 9:00 AM, Charlotte Chang <c.h.w.chang@gmail.com>wrote:

> optim

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