R help - Jul 2010 - how to get higher derivatives with "deriv"

Dear ExpeRts,

I have trouble implementing a function which computes the k-th derivative of a
specified function f and returns it as a function. I tried to adapt what I found
under ?deriv but could not get it to work. Here is how it should look like:

## specify the function
f <- function (x,alpha) x^alpha

## higher derivatives
DD <- function(expr, variable, order = 1) {
   if(order < 1) stop("'order' must be >= 1")
   if(order == 1) deriv(expr, variable)
   else DD(deriv(expr, variable), variable, order - 1)
}

## compute the second derivative of f
f.prime.prime <- DD(f,"x",2)

## evaluate it at x=1 for alpha=0.5
f.prime.prime(1,0.5)


Many thanks,

Marius

## specify the function string
f.str <- "x^alpha"

## higher derivatives 
DD <- function(f.str, x = 2, alpha=3,order = 1){
expr.s <- parse(text=f.str)
while(order>=1) {
expr.s <- D(expr.s,"x")
order <- order-1}
eval(expr.s)
}

compute
DD(f.str,x=1,alpha=0.5,order=1)

-----
A R learner.
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Okay, great. Thanks.

Cheers,

Marius
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