[Rd] Named parameters in optim()

[Duncan Murdoch]

On 3/2/2006 2:52 PM, Prof Brian Ripley wrote:
> I think the cost is small, and have just added this.

Thank you!

Duncan Murdoch

> 
> On Thu, 2 Mar 2006, Duncan Murdoch wrote:
> 
>> If I name the elements of the vector of initial values passed to
>> optim(), then it attaches the names to the final result, e.g.
>>
>> > f <- function(parms) (parms[1]-1)^2+(parms[2]-2)^2
>> > optim(c(x=3,y=4), f)
>> $par
>>         x         y
>> 0.9999635 2.0003241
>>
>> $value
>> [1] 1.063637e-07
>>
>> $counts
>> function gradient
>>       65       NA
>>
>> $convergence
>> [1] 0
>>
>> $message
>> NULL
>>
>> However, the vector that gets passed to f doesn't have its names attached:
>>
>> > f <- function(parms) {
>> +  print(parms)
>> +  (parms["x"]-1)^2+(parms["y"]-2)^2
>> + }
>> > optim(c(x=3,y=4), f)
>> [1] 3 4
>> Error in optim(c(x = 3, y = 4), f) : function cannot be evaluated at
>> initial parameters
>>
>> Is this something that should be fixed, i.e. could it be fixed without
>> making optim() substantially slower?  If not, it's at least something
>> that should be documented.
>>
>> Duncan Murdoch
>>
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>>
>