Looping until a solution is found

On May 30, 2009, at 9:36 AM, Uwe Ligges wrote:

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),
                     logk=log(exp(unlist(startvals[4]))+0.2))
   m1 <- mlefun(starvals, data=data)
}

So this implicitly assumes that try() is wrapped around the code 
inside mlefun?


David Winsemius, MD
Heritage Laboratories
West Hartford, CT