Dear All:

    I tried to fit negative binomial distribution to data in terms of mean and mean is also a quadratic function of another variable. The likelihood function is:


function (parameters, y1,x11)

{

 

p<-parameters[1]

alpha1<-parameters[1]

beta1<-parameters[2]

delta1<-parameters[3]

 

mu<-alpha1+beta1*(x11)+delta1*(x11^2)

 

ifelse(y1>=0|x11>=0,

 

L<-

      lgamma(y1+p)+p*(log(p)-log(mu+p))+y1*(log(mu)-log(mu+p))

      -lfactorial(y1)-lgamma(p)

 

,Inf)

 

L

 

}



I got outputs even it sounds a problem for delata. Actually, there is a mistake made for the parameters (p & alpha1) set up. If I correct them as:

p<-parameters[1]

alpha1<-parameters[2]

beta1<-parameters[3]

delta1<-parameters[4]



Then error messga there: initial value in 'vmmin' is not finite
In addition: There were 38 warnings (use warnings() to see them).

Could you give some advice please?



Thanks a lot!



Xin Shi

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