# Re: [R] information about a function

From: Prof Brian Ripley <ripley_at_stats.ox.ac.uk>
Date: Mon 17 Jul 2006 - 21:55:42 EST

On Mon, 17 Jul 2006, Holger Flick wrote:

> Hi people,
>
> I am new in this list and could not find a FAQ for it in particular,
> furthermore I could not find my question answered in the official R
> FAQ or docs.
>
> I have simply something like this:
>
> > f<-approxfun(data[,1],data[,2])
>
> and f is:
>
> > f
> function (v)
> .C("R_approx", as.double(x), as.double(y), as.integer(n), xout = as.double(v),
> as.integer(length(v)), as.integer(method), as.double(yleft),
> as.double(yright), as.double(f), NAOK = TRUE, PACKAGE = "base")\$xout
> <environment: 02106C24>
>
> I also used "locPoly".
>
> Both yield either a function or a data frame of values.
>
> Is there a way to get a mathematical representation of the function,
> e.g. a polynomial of any order? Something like
> ax^3+bx^2+cx^1+d or similar if it is of degree 3?

No, because they are not polynomials or any other simple-to-describe function.

Perhaps you should use tools that fit the sort of functions you are interested in: see e.g. lm() and poly().

```--
Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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