Thanks for sending the data... The problem is triggered by only having one observation per district, so that you have a random effect for each datum. This causes the correlation of the parameter estimates/predictions for the smooth term to become so high that covariance matrix of the smooth coefficients is no longer +ve definite. You can easily see the very high correlations by replacing the smooth with a low order polynomial in lon and lat and fitting with glmmPQL --- the correlation for the fixed effect parameters is rather high. I can patch gamm so that it provides an answer anyway: but it will only produce extremely high variance estimates for the smooth, reflecting the fundamental identifiability problem in separating the smooth variation from the random effect for a model with a random effect for each datum.
best, Simon On Tuesday 02 October 2007 15:50, Dae-Jin Lee wrote: > Hi all R users ! > > I'm using gamm function from Simon Wood's mgcv package, to fit a spatial > regression Generalized Additive Mixed Model, as covariates I have the > geographical longitude and latitude locations of indexed data. I include a > random effect for each district (dist) so the code is > > fit <- gamm(y~s(lon,lat,bs="tp", m=2)+offset(log(exp.)), > random=list(dist=~1), family="poisson", niterPQL=30) > > when I run the gamm function I obtain the next error message: > > %%% > Maximum number of PQL iterations: 30 > iteration 1 > iteration 2 > ... > iteration 8 > iteration 9 > iteration 10 > Error in chol(XVX + S) : the leading minor of order 29 is not positive > definite > %%% > > Could be any problem in gamm() ??? > > -- > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html and provide commented, minimal, > self-contained, reproducible code. -- > Simon Wood, Mathematical Sciences, University of Bath, Bath, BA2 7AY UK > +44 1225 386603 www.maths.bath.ac.uk/~sw283 ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
