Re: [R] impenetrable warning

Spencer Graves Wed, 22 Sep 2004 10:14:56 -0700

In this case, this trick will identify the specify command in the lme code that produce the error.

If that does not lead you to an answer, have you tried simplifying your lme call to identify more clearly which part (or combination) seems to generate the problem?

     hope this helps.  spencer graves

Liaw, Andy wrote:

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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Spencer Graves, PhD, Senior Development Engineer
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