[R] create function to solve derivative

[Peter Ehlers]

On 2012-11-16 01:30, Berend Hasselman wrote:
>
> On 16-11-2012, at 09:43, e-letter wrote:
>
>> 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.
>
> Manual "Introduction to R" (http://cran.r-project.org/doc/manuals/r-release/R-intro.html)
> section 2.1 "Vectors and assignment"
> in particular the sentence:  "If an expression is used as a complete command, the value is printed and lost"
>
> Berend

I believe that e-letter is confused by the space-saving
use of the semicolon to place two R expressions on one line.
He neither needs nor wants the ';dx2dx' in his own
expressions.

Peter Ehlers