[R] Looping until a solution is found

Uwe Ligges ligges at statistik.tu-dortmund.de
Sat May 30 15:36:59 CEST 2009

John Poulsen wrote:
> Hello,
> I am using maximum likelihood to find the best parameters for a model.  
> This involves sometimes tweaking the starting values to find a solution 
> that converges.
> I would like to automate the process so that when the optimizer runs 
> into an error it tweaks one of the parameters slightly, tries the fit 
> again, and then continues this until a solution if found.
> I have been using try() to test if a fit will work (see below), but how 
> do I run a loop that says continue until class(m1) is not "try error"?
>   m1<-mlefun(startvals, data=data)
> if(class(m1)=="try-error"){startvals<-list(alpha=10,beta=1,loggamma=log(5),logk=log(exp(unlist(startvals[4]))+0.2)) 
>                  mlefun(starvals, data)}

m1 <- mlefun(starvals, data=data)
while(class(m1) == "try-error"){
     startvals <- list(alpha=10, beta=1, loggamma=log(5),
     m1 <- mlefun(starvals, data=data)

Uwe Ligges

> This seems like it should be easy... but I am stymied.  Thanks for your 
> help
> John
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