[R] mcv package gamm function Error in chol(XVX + S)

[Simon Wood]

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() ???
>
> --
>
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-- 
> Simon Wood, Mathematical Sciences, University of Bath, Bath, BA2 7AY UK
> +44 1225 386603  www.maths.bath.ac.uk/~sw283