mcv package gamm function Error in chol(XVX + S)
Well, it's certainly a problem detected by gamm, but whether it's a fundamental statistical problem with this model/data combination or something fixable by taking an alternative approach within gamm I can't tell. Would you be able to send me the data used here (I promise not to use it for anything else, of course), so I can figure out where the problem is? best, Simon
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]]
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> Simon Wood, Mathematical Sciences, University of Bath, Bath, BA2 7AY UK > +44 1225 386603 www.maths.bath.ac.uk/~sw283