[R] information about a function

[Prof Brian Ripley]

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.

> Basically, I want to create functions of measured values.

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 at 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