Hello,
I have being trying to estimate the parameters of the generalized exponential
distribution. The random number generation for the GE distribution
is x<-(-log(1-U^(1/p1))/b), where U stands for uniform dist. The data i have
generated to estimate the parameters is right censored and the code is given
below; The problem is that, the newton-Raphson approach isnt working and i do
not know what is wrong. Can somebody suggest something or help in identifying
what the problem might be.
p1<-0.6;b<-2
n=20;rr=5000
U<-runif(n,0,1)
for (i in 1:rr){
x<-(-log(1-U^(1/p1))/b)
meantrue<-gamma(1+(1/p1))*b
meantrue
d<-meantrue/0.30
cen<- runif(n,min=0,max=d)
s<-ifelse(x<=cen,1,0)
q<-c(x,cen)
z<-function(data, p){
shape<-p[1]
scale<-p[2]
log1<-n*sum(s)*log(p[1])+
n*sum(s)*log(p[2])+(p[1]-1)*sum(s)*log(1-((exp(-(p[2])*sum(x)))))
-(p[2])*sum(t) + (p[1])*log((exp(-(p[2])*sum(x))))-
(p[1])*sum(s)*log((exp(-(p[2])*sum(x))))
return(-log1)
}
}
start <- c(1,1)
zz<-optim(start,fn=z,data=q,hessian=T)
zz
m1<-zz$par[2]
p<-zz$par[1]
Thank you
Chris Kelvin
INSPEM. UPM
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