> > 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? > > Well, that's not really true: it says it is unable to find starting > values, and asks you to provide some. I don't really see why your choices > are satisfactory: what happens if all the data are negative for example?
- then the suggested code traps it. > > We could try even harder, but code that is almost never used tends to get > broken whilst no one is testing it. So if you want to pursue it I think > we need a comprehensive test suite. - well, I guess, but I wouldn't have thought that zeros in data modelled using `gaussian("log")' is such a rare occurance is it? [Or did you mean that `gaussian("log")' is almost never used, and should hence be kept simple]. I suppose there are arguments both ways... best, Simon > > > 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/ > > > > ______________________________________________ > > R-devel@r-project.org mailing list > > https://stat.ethz.ch/mailman/listinfo/r-devel > > > > > > -- > Brian D. Ripley, [EMAIL PROTECTED] > Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ > University of Oxford, Tel: +44 1865 272861 (self) > 1 South Parks Road, +44 1865 272866 (PA) > Oxford OX1 3TG, UK Fax: +44 1865 272595 > ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel