Hello,

could try() work for you? ["|try|is a wrapper to run an expression that 
might fail and allow the user's code to handle error-recovery.", see ?try]

e.g.:

  options(warn=-1)    ## to ignore all warnings
# then, within your simulation:
  model <- try(lmer(...), silent=TRUE)
  model.conv <- ifelse(class(model )[1] =='try-error',0,1)


HTH

Luca


-------------------------------------------
Luca Borger
Postdoctoral Research Fellow
CNRS - Centre d'Etudes Biologiques de Chizé
Villiers-en-Bois
79360 Beauvoir-sur-Niort
France

Tel: +33 (0)549 09 96 13
Fax: +33 (0)549 09 65 26

email: lborger@cebc.cnrs.fr
http://www.researcherid.com/rid/C-6003-2008
http://cnrs.academia.edu/LucaBorger
-------------------------------------------


Le 29/09/2011 09:06, Phil Smith a écrit :
> Hi lmer list-serve people:
>
> I'm using lmer() in a large simulation and get the following error message:
>
> Error in mer_finalize(ans) : Downdated X'X is not positive definite, 8.
>
> Then the simulation quits.
>
> My question is: How do I diagnose that lmer will give this message before I
> call it?
>
> My goal is to determing whether it will and skip the the replication in the
> simulation (noting the frequency of the error), so that the entire
> simulation can complete?
>
> Kindly provide your reply directly to: Phil.Smith.Duluth.GA@gmail.com   ...
> I'm not too skillful at learning how to find replies to my queries
> otherwise.
>
> Many thanks!
> Phil Smith
> Duluth, GA
>
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