[R] numeric derivation

Gabor Grothendieck
Sun, 12 Oct 2008 12:36:20 -0000

On Sun, Oct 12, 2008 at 7:24 AM, Oliver Bandel
<oliver at first.in-berlin.de> wrote:
> Hello,
>
>
> I don't understand the description / help-text for the
> numericDeriv() function.
>
> Why is there a new environment used?
>
> And what is meant with an environment here?

?environment

or

http://socserv.mcmaster.ca/jfox/Books/Companion/appendix-scope.pdf

> Is it similar or the same as a local workspace,
> like an environment in functional languages?
>
> And why is it needed here?
>
> numericDeriv could just calculate the difference bewtween two
> values and divide this difference by the distance (which is one
> normally,
> but maybe in timeseries is a different value.

The input to numericDeriv is not values but an expression.
See the Examples section at the end of ?numericDeriv
The expression given as the first arg
ultimately needs to be evaluated at a value so it  needs to
know where to find that value.  Note that it defaults
to the caller's environment so we can leave that argument
out if the variable is known to be there:

X <- 3
numericDeriv(quote(X^2), "X")

>
> Can you please elaborate on that function?
>
> Thanks In Advance,
>                         Oliver
>
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