Thanks for taking to time to help me out with this, I really appreciate it!



Quoting "S Ellison-2 [via R]" <ml-node+s789695n4656633h5@n4.nabble.com>:

>
>
>> -----Original Message-----
>> I'd love to write a code that would allow me replace the example code:
>>
>> fit1F <- mle2(LL, fixed=list(xhalf=6))
>>
>> with something like:
>>
>> var<-xhalf
>> val<-6
>>
>> fit1F <- mle2(LL, fixed=list(var=val))
>>
>> or
>>
>> var<-c("xhalf","=")
>> val<-6
>>
>> fit1F <- mle2(LL, fixed=list(var,val))
>>
>> Replacing the value in question is easy enough, but I can't
>> figure out exactly how to replace the identity of the
>> variable that will be held constant.
>
> I'm not sure exactly _where_ in the code you need to replace things.
>
> If it's at the time you call your code (presumably a function)  
> manually, the answer's kind of obvious; write a function that takes  
> a 'fixed' argument and pass that directly to mle2.
>
> If you want to cycle through a set of fixed values, though, you  
> could probably do that by starting with the complete list and then  
> cyclyng through it. A very simple example might look like this:
>
> show.fixed <- function(i, l, a, b, s, fixed) {
> 	#A simple function that takes a 'fixed' parameter in the same  
> format as mle2's 'fixed';
>
> 	cat(paste(i, ":", l, a, b, s, "with", names(fixed), "fixed at",  
> fixed[[1]], "\n"))
> 		#This function just prints out the values provided
>                                 #followed by the name and fixed  
> value of the 'fixed' element
>
> }
>
> #To pass different things to such a function:
>
> #i) Set up a complete list of parameters with their fixed values
> fixed.scope <- list(l=1, a=3, b=5, s=23)
> 	#This could be your starting parameter set if that's convenient
>
> #ii) reference elements of the list inside a loop
> #     I've out such a loop inside the following function:
>
> f <- function(l=0, a=1, b=2, s=3, fs) {
> 	#fs is our complete set of possible fixed values
> 	for(i in 1:4) {
> 		show.fixed(i, l, a, b, s, fixed=fs[i])	 #you would have mle2  
> called here instead of show.fixed
> 			# fs[i] sends the i'th element of fs to the function as a  
> one-element list 	with the right name
> 	}
> }
>
> # iii) call the function with the 'fixed scope' list
> f(fs=fixed.scope)
>         #shows that setting fixed=fs[i] provides the function with  
> the (named) i'th element of the list of fixed parameters
>
> Clearly* you could update the values actually held in fs at each  
> cycle if what you wanted to do was optimise three parameters for  
> different values of each fixed element, or (somewhat dodgy, but I've  
> had to resort to such things with ill-behaved optimisations) do  
> 'three at a time' optimisation to sneak up on a maximum.
> You could also build fs inside your function instead of supplying it  
> from outside.
>
> Steve Ellison
>
> *'clearly' in the usual mathematical sense of "after several years  
> of study and considerable thought one might see that..."
>
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