Generally you can set options(warn=2), run the code, then do traceback().
Andy
> From: Simon.Bond
>
> Dear R-help,
>
> Can anyone explain the meaning of the warning,
>
> Singular precision matrix in level -1, block 1
>
> ? Or how to track down where it comes from?
>
> More precisely, using the nlme package, I'm issued with the warning
>
> itt2 <- lme(lrna~rx.nrti+lbrna, random=~1|patid,
> cor=corExp(form=~days|patid,nugget=T), weights=varPower(
> form=~lbrna),data=rna3)
> Warning messages:
> 1: Singular precision matrix in level -1, block 1
> 2: Singular precision matrix in level -1, block 1
>
> the output is:
>
> Linear mixed-effects model fit by REML
> Data: rna3
> Log-restricted-likelihood: -4990.142
> Fixed: lrna ~ rx.nrti + lbrna
> (Intercept) rx.nrtiZDV+3TC rx.nrtiZDV+ABC lbrna
> 2.6597552 0.8589514 0.4259504 0.2929222
>
> Random effects:
> Formula: ~1 | patid
> (Intercept) Residual
> StdDev: 1.251113 0.2105329
>
> Correlation Structure: Exponential spatial correlation
> Formula: ~days | patid
> Parameter estimate(s):
> range nugget
> 204.6422150 0.3349336
> Variance function:
> Structure: Power of variance covariate
> Formula: ~lbrna
> Parameter estimates:
> power
> 0.9733358
> Number of Observations: 2390
> Number of Groups: 124
>
>
>
> Thanks,
>
> Simon Bond.
>
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