Hi I keep getting an error like this: Error in `coef<-.corARMA`(`*tmp*`, value = c(18.3113452983211, -1.56626248550284, : Coefficient matrix not invertible or like this: Error in gls(archlogfl ~ co2, correlation = corARMA(p = 3)) : false convergence (8) with the gls function in nlme. The former example was with the model "gls(archlogflfornma~nma,correlation=corARMA(p=3))" where archlogflfornma is "[1] 2.611840 2.618454 2.503317 2.305531 2.180464 2.185764 2.221760 2.211320" and nma is "[1] 138 139 142 148 150 134 137 135". You can see the model in the latter, and archlogfl is "[1] 2.611840 2.618454 2.503317 2.305531 2.180464 2.185764 2.221760 2.211320 [9] 2.105556 2.176747" and co2 is "[1] 597.5778 917.9308 1101.0430 679.7803 886.5347 597.0668 873.4995 [8] 816.3483 1427.0190 423.8917". I'm quite a nube, so sorry, but help most appreciated. I have R 2.13.1. Roland [[alternative HTML version deleted]]