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() ???

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