Friends

    I'm trying fit a survival model by maximum likelihood estimation using this function:

flver=function(a1,a2,b1,b2)
{

lver=-(sum(st*log(exp(a1*x1+a2*x2)))+sum(st*log(hheft(exp(b1*x1+b2*x2)*t,f.heft)))
-(exp(a1*x1+a2*x2)/exp(b1*x1-b2*x2))*sum(-log(1-pheft(exp(b1*x1+b2*x2)*t,f.heft))))
}
emv=mle(flver,start=list(a1=0,a2=0,b1=0,b2=0))

where hheft and pheft are functions defined in polspline package. 
My variables are:
t: time
st: censor 
x1 and x2: Covariates

I don't find any estimation because an error occurs:

Non finite/finite difference value [0].

Can I treat this error? I try using "SANN" method and this error occurs too. There is another alternative?

Thanks

Olympio Neto



    
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