[R] Can't get function to run iteratively

[Uzuner, Tolga]

Trying to do something very simple...

> numerical.grad
function(func,x, eps=1e-12) {
#  very simple (crude) numerical approximation
  f <-func(x)
  df <-1:length(x)
  for (i in 1:length(x)) {
    dx <- x
    dx[i] <- dx[i] +eps 
    df[i] <- (func(dx)-f)/eps
   }
df
}
> test<-function(x){x^2}
> y<-seq(0.1,0.5,0.1)
> numerical.grad(test,y)
[1] 0.1999997 0.0000000 0.0000000 0.0000000 0.0000000
Warning messages: 
1: number of items to replace is not a multiple of replacement length 
2: number of items to replace is not a multiple of replacement length 
3: number of items to replace is not a multiple of replacement length 
4: number of items to replace is not a multiple of replacement length 
5: number of items to replace is not a multiple of replacement length 
> 


Any thoughts why this doesn't seem to be working ?


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