Dear R-sig-ecology list,


I am fitting a gamm model(package: mgcv)  in which I have a violation of
independence with regard to temporal autocorrelation due to the fact that
all of my variables have a cyclical seasonal pattern. I have largely
corrected for this by including a AR-2 correlation structure in the
following way:

>corstr <- corARMA(c(0.4, -0.1), p=2, q=0, form = ~ DATE)

I nevertheless continue to have some autocorrelation in the "significant"
range at some of the larger time lags (i.e. year lags) as identified by:

>E <- resid(gamm.fit$lme, type="normalized")
>acf(E)


My guess is that an AR-2 structure can't produce a sin-like correlation
structure, but when I try a higher AR structure(i.e. p=3), the fitting
doesn't converge.

Is anyone familiar with such a problem? Does the fitting need to run for a
longer period of time, or are there other options for me?

Many thanks for you help,
Marc

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