Hi,
Currently the `gaussian' family's initialization code signals an error if
any response data are zero or negative and a log link is used. Given that
zero or negative response data are perfectly legitimate under the GLM
fitted using `gaussian("log")', this seems a bit unsatisfactory. Might
it be worth changing it?
The current offending code from `gaussian' is:
initialize = expression({
n <- rep.int(1, nobs)
if (is.null(etastart) && is.null(start) && is.null(mustart) &&
((family$link == "inverse" && any(y == 0)) ||
(family$link == "log" && any(y <= 0)))) stop(
"cannot find valid starting values: please specify some")
mustart <- y
})
A possible replacement would be ...
initialize = expression({
n <- rep.int(1, nobs)
if (is.null(etastart) && is.null(start) && is.null(mustart) &&
((family$link == "inverse" && all(y == 0)) ||
(family$link == "log" && all(y <= 0)))) stop(
"cannot find valid starting values: please specify some")
mustart <- y
if (family$link=="log") {
iy <- y<=0
if (sum(iy)) mustart[iy] <- min(y[!iy])*.5
} else if (family$link=="inverse") {
iy <- y==0
if (sum(iy)) mustart[iy] <- min(abs(y[!iy]))*.5
}
})
best,
Simon
>- Simon Wood, Mathematical Sciences, University of Bath, Bath BA2 7AY
>- +44 (0)1225 386603 www.maths.bath.ac.uk/~sw283/
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