[R-sig-ME] glmer / MuMin : Error in asMethod(object) : not a positive definite matrix

[Rafael Wüest]

Hi Guillaume

You can generate a list of calls by setting evaluate = FALSE in tdredge() and use the resulting list to run the models within a try(). You will just need to extract AIC (or whatever) yourself to rank models. But it should help to pinpoint models that fail.

Something like:

dlist <- dredge(mod_full_CC,rank="AICc",fixed=c("block","year"), evaluate = FALSE)
AICs <- sapply(dlist, function(x) {
  try(AICc(eval(x)))
})

HTH,
Rafi


> On 28 Aug 2020, at 16:37, Ben Bolker <bbolker using gmail.com> wrote:
> 
>   Pretty hard to debug without a reproducible example (and an 8-day run time isn't going to help ...)
> 
>  The error message comes ultimately from the Matrix package (the error message is found in the "dspMatrix" → "dppMatrix" and "dsyMatrix" → "dpoMatrix" coercion methods).  If you run traceback() **immediately** after getting the error message, we might get a little bit more information.
> 
>  What are the warnings?
> 
> If you've got multiple cores, using pdredge() might decrease your run-time.
> 
>  I don't know how to tell dredge() to use a try()-clause or equivalent to skip over models that have problems.
> 
> 
> 
> On 8/28/20 8:40 AM, Guillaume Adeux wrote:
>> Hello everyone,
>> I am currently exploring the relationship between weed biomass during the
>> fallow period and cover crop productivity (in interaction with tillage
>> type, nitrogen fertilization, and cover crop species, as imposed by the
>> 3-way factorial experimental design).
>> This results in a highly complex model which I wish to reduce to achieve
>> parsimony.
>> Hence, I fitted the full model with glmer as:
>> mod_full_CC=glmer(dry_bio_weeds_m2+0.001~
>> *block+year*scale(dry_bio_cover_m2)*tillage*N*CC*
>> +(1|block:tillage)+(1|block:tillage:N)+(1|block:tillage:N:CC)+(1|block:year)+(1|block:year:tillage)+(1|block:year:tillage:N)+(1|block:year:tillage:N:CC),family=gaussian(link="log"),control=glmerControl(optimizer="nloptwrap",optCtrl=list(algorithm="NLOPT_LN_NELDERMEAD")),data=biomassCC_wo_Cbis)
>> and fed it to MuMin::dredge() as:
>> options(na.action = "na.fail")
>> dred_CC=dredge(mod_full_CC,rank="AICc",fixed=c("block","year"))
>> However, I am unable to retrieve my "dred_CC" (after 8 days, arf) object
>> because dredge() stops after returning:
>> *Error in asMethod(object) : not a positive definite matrix*
>> Is this due to a specific problem with one given model? If that's the case,
>> how can I tell the function to simply skip it?
>> To be completely transparent, it also states "In addition: There were 50 or
>> more warnings (use warnings() to see the first 50)" but I don't believe the
>> problem comes from there.
>> I would greatly greatly appreciate it if someone could lend a hand.
>> Thanks for your time.
>> Guillaume ADEUX
>> 	[[alternative HTML version deleted]]
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> 
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