[R] Problem specifying "function" for "mle" operation

From: Narcyz Ghinea <Narcyz.Ghinea_at_swsahs.nsw.gov.au>
Date: Wed 27 Jul 2005 - 13:01:26 EST

Hello fellow R users,

Below are two cases using the "mle" operation from the stats4 package. In CASE 1 the code runs fine, in CASE 2 errors occur:

CASE 1 x, alpha_current, s, and n are vectors of the same length.

ll_beta<-function(b0=0,b1=0) -sum(s*b0+s*b1*x+s*alpha_current-n*log(1+exp(b0+b1*x+alpha_current)))

fit_beta<-mle(ll_beta)

CASE 2 The error message is as follows => Error in validObject(.Object) : invalid class "mle" object: invalid object for slot "fullcoef" in class "mle": got class "list", should be or extend class "numeric"

x,s,n, and alpha are vectors of the same length (5 dimensions in this specific case).

ll_alpha<-function(alpha=c(0.5,0.5,0.5,0.5,0.5)) -sum(s*b0+s*b1*x+s*alpha-n*log(1+exp(b0+b1*x+alpha))-0.5*(alpha/sigma)^2)

fit_alpha<-mle(ll_alpha)

MY THEORY: I think it has something to do with the fact that the function argument is a vector in CASE 2. Hope this doesn't mean I have to re-write the function in a way that it doesn't require vector inputs.....

Any suggestions on how to make CASE 2 work would be appreciated.

peace

Narcyz.

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