[R] error using frailty term

[Terry Therneau]

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T
rying to fit a model using the Surv() with a frailty term but get the
following cryptic error message:
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Error in frailty.brent(sqrt(x), y, lower = 0) :
  Ties for max(y), I surrender
Calls: runplots ... coxpenal.fit -> eval -> eval -> <Anonymous> -> frailty.brent
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When I remove the frailty term from the model it runs just fine. Does
anyone know what this error message means?

Thanks,
M.

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 What it means is that the function maximization routine "under the covers" is 
completely befuddled.  (I saw the "I give up" message fairly often in the 
earliest drafts of the code.)
 
  Solution: download the coxme package from CRAN -- superior in every way to 
frailty() terms.  For one thing I made the maximizer much more intelligent: I 
now use optim :-).   
  	
  	Terry Therneau