functions with function inputs and optimisation

Hi all,

Would be great if you could help me get my head around the "further
arguemnts" in the optim function. Let's say we have f and g as shown:

f<-function(x,a,b){(x-a)^2+b}

optim(100,fn=f,gr=NULL,2,5) #the NULL is annoying

g<-function(x,a){2*(x-a)} optim(100,fn=f,gr=g,2,5)


1. How does optim know that 2,5 both go into f whereas g only accepts the
first of those arguments. WHAT IF for some random reason I wanted there to
be no common parameters, what then? so for example the input for g to be 3
s.t. f(x,2,5) and g(x,3)

2. Is there a way for me to skip writing gr=NULL the first time I implement
this? Its quite important for me as I want to implement optimx where the
"further arguments" are the last ones, and I do not want to go setting each
parameter to some sort of default. basically I want to say:

optim(100,fn=f,further_args=c(2,5))

Thanks in advance,
Sachin

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