[R] create function to solve derivative

[e-letter]

On 16/11/2012, Rolf Turner <rolf.turner at xtra.co.nz> wrote:
>
> Your question makes little sense.  Functions have derivatives --- at
> least some of them do.  Data sets do not have derivatives.  The
> functions D(), deriv() etc. work on specified analytic expressions
> for functions --- data sets do not come into the picture.
>

Is the following procedure correct:

Plot data from data set.

Suppose the resultant graph was linear. The function could be y=mx+c,
so the R function 'lm' could be applied to fit a linear line.

The example in the manual for the help file '?D' shows:

dx2x <- deriv(~ x^2, "x") ; dx2x

So for this example it would be correct to write:

functionname<-deriv(~mx+c,"x");dx2x

What is the significance of ';dx2x'? It would be appreciated to be
referred to the relevant manual sections, thanks.