[R] Function accepted by optim but not mle2 (?)

[Jeff Newmiller]

What is wrong is that you define and use parameters and global data inconsistently in your functions.

v <- 6
f <- function( x ) { x^2 }
g <- function( x ) { v^3 }
f(v) # right answer
g(v) # right answer, accidentally
f(5) # works as expected
g(5) # surprise

You need to go through your functions and confirm for each variable that you either define it in the function before you use it or that it is one of the named parameters. It is possible to use global variables inside your functions, but that is likely to give confusing answers so you should avoid it in most cases (at least until you understand it).
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Sent from my phone. Please excuse my brevity.

Medimel <medimelenglish at gmail.com> wrote:

>Dear Sir/ Madam,
>
>I'm having trouble de-bugging the following - which works perfectly
>well with optim or optimx - but not with mle2.
>I'd be really grateful if someone could show me what is wrong. Many
>thanks in advance. JSC:
>
>gompertz<- function (x,t=data)
>{
>        a3<-x[1]
>        b3<-x[2]
>        shift<-data[1]
>        h.t<-a3*exp(b3*(t-shift))
>        S.t<-exp(a3/b3*(1-exp(b3*(t-shift))))
>	PF<-1-(exp(a3/b3*(1-exp(b3*(data[1]-shift)))))
>	QF<-1-(exp(a3/b3*(1-exp(b3*(data["length"(data)]-shift)))))
>	return(S.t*h.t/(QF-PF))
>}
>
>## GOMPERTZ - maximum likelihood
>gompertz2<-function (x)
>{
>lnlk<-sum(log(gompertz(x,t=data)))
>return(-lnlk)
>}
>
>## this works:
>A<-optimx(c(0.1,0.1),gompertz2,
>method=c("Nelder-Mead"),control=list(fnscale=1))
>
>## this doesn't:
>A <- mle2(gompertz2(x),start=list(a3=0.03,b3=0.1),data=data)
>## Error in gompertz2(x) : object 'x' not found
>
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