[R] Derivative of a Function Expression

[Gabor Grothendieck]

Actually in thinking about this its pretty easy to do it without Ryacas too:

Df <- f
body(Df) <- deriv(body(f), "x")
Df


On 9/3/07, Gabor Grothendieck <ggrothendieck at gmail.com> wrote:
> The Ryacas package can do that (but the function must be one line
> and it can't have brace brackets).  The first yacas call below registers f with
> yacas, then we set up a function to act as a template to hold the
> derivative and then we set its body calling yacas again to take the
> derivative.
>
> library(Ryacas)
> f <- function(x)  2*cos(x)^2 + 3*sin(x) +  0.5
> yacas(f) # register f with yacas
> Df <- f
> body(Df) <- yacas(expression(deriv(f(x))))[[1]]
> Df
>
> Here is the output:
>
> > library(Ryacas)
> > f <- function(x)  2*cos(x)^2 + 3*sin(x) +  0.5
> > yacas(f)
> [1] "Starting Yacas!"
> expression(TRUE)
> > Df <- f
> > body(Df) <- yacas(expression(deriv(f(x))))[[1]]
> > Df
> function (x)
> 2 * (-2 * sin(x) * cos(x)) + 3 * cos(x)
>
> Also see:
>
> demo("Ryacas-Function")
>
> and the other demos, vignette and home page:
>   http://ryacas.googlecode.com
>
>
>
> On 9/3/07, Rory Winston <rory.winston at gmail.com> wrote:
> > Hi
> >
> > I am currently (for pedagogical purposes) writing a simple numerical
> > analysis library in R. I have come unstuck when writing a simple
> > Newton-Raphson implementation, that looks like this:
> >
> > f <- function(x) { 2*cos(x)^2 + 3*sin(x) +  0.5  }
> >
> > root <- newton(f, tol=0.0001, N=20, a=1)
> >
> > My issue is calculating the symbolic derivative of f() inside the newton()
> > function. I cant seem to get R to do this...I can of course calculate the
> > derivative by calling D() with an expression object containing the inner
> > function definition, but I would like to just define the function once and
> > then compute the derivative of the existing function. I have tried using
> > deriv() and as.call(), but I am evidently misusing them, as they dont do
> > what I want. Does anyone know how I can define a function, say foo, which
> > manipulates one or more arguments, and then refer to that function later in
> > my code in order to calculate a (partial) derivative?
> >
> > Thanks
> > Rory
> >
> >        [[alternative HTML version deleted]]
> >
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>