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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