[R] symbolic manipulations
tlumley at u.washington.edu
Sat Apr 7 02:07:29 CEST 2001
On Fri, 6 Apr 2001, Jeff Miller wrote:
> Hi All,
> I copied code from an Splus manual to take symbolic derivatives:
> my.deriv <- function( mathfunc, var )
> tmp <- substitute(mathfunc)
> name <- deparse(substitute(var))
> D(tmp, name)
> (The code also works in R).
> When I try this on x^2 I get
> > my.deriv(x^2, x)
> 2 * x
> Suppose I assign the output of my.deriv(x^2, x) to deriv.xsqr :
> > deriv.xsqr <- my.deriv(x^2, x)
> > deriv.xsqr
> 2 * x
> My question is, how do I take the derivative of deriv.xsqr
> (I want the answer to be 2) ?
FAQ 7.6 explains that this is precisely why the D() function doesn't work
You can do it with
but this is making life unnecessarily difficult for yourself.
Thomas Lumley Asst. Professor, Biostatistics
tlumley at u.washington.edu University of Washington, Seattle
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