R help - Sep 2001 - interpolation and numerical differentiation in R ?

Hi,

I'm trying to determine if R is useful to me.  I've browsed 'The
Basics of
S and S-Plus' (Krause & Olson), and like the logic of the language.  
However, I don't see an easy way to do things like this:


* given a set of observations (x,y) (x and y equal-length vectors), and a
2nd set of abscissas x2, interpolate y at the new abscissas x2.  (for now,
I don't really care what kind of interpolation -- linear, some type of
spline, etc.)

* given observations (x,y), (with unequally-spaced x), create vector z
with the numerical derivative of y with respect to x (eg evaluated at the
values x).


I'm sure I could loop over the observations and do the interpolation and
differentiation point-by-point, but that kind of defeats the purpose of a
'vectorized' environment, I think.

I analyze data from solid-state physics experiments, and very little of
the analysis is really *statistical*, so it may be that R is the wrong
tool for me.

If anyone can point me toward documentation covering how to do tasks like
the above in R, I'd appreciate it.

thanks,

-Robert Merithew, PhD			rdm28 at cornell.edu
 LASSP, Cornell University
 Ithaca, NY

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"Robert D. Merithew" <merithew at ccmr.cornell.edu> writes:
> Hi,
> 
> I'm trying to determine if R is useful to me.  I've browsed
'The Basics of
> S and S-Plus' (Krause & Olson), and like the logic of the language.
> However, I don't see an easy way to do things like this:
> 
> 
> * given a set of observations (x,y) (x and y equal-length vectors), and a
> 2nd set of abscissas x2, interpolate y at the new abscissas x2.  (for now,
> I don't really care what kind of interpolation -- linear, some type of
> spline, etc.)
See interpSpline in the splines library.
> * given observations (x,y), (with unequally-spaced x), create vector z
> with the numerical derivative of y with respect to x (eg evaluated at the
> values x).
When evaluating the interpolating spline produced by interpSpline you
can specify that you want derivatives instead of the function value.
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Oh sorry,
The correct address is: http://www.sciviews.org/_passtec
>>>>> "Philippe" == Philippe Grosjean <phgrosje at
ulb.ac.be> writes:
    Philippe> About interpolation, note that a new package is in
    Philippe> construction which will provide some more interpolations
    Philippe> methods, including area method... and also some functions for
    Philippe> calculating best regular interval to keep much of the
    Philippe> irregular serie information (for instance, using turning
    Philippe> points, i.e., information theory). Some code is already
    Philippe> available at http://www.sciviews/_passtec. For the moment, it
    Philippe> is in French only and code is not packaged into a library
    Philippe> yet. But you could get an idea of what it can do at a quick
    Philippe> glance by browsing the manual (if you can read French). Final
    Philippe> library with manual in English will be uploaded to CRAN in 4
    Philippe> or 5 months. It could help or not depending on your
    Philippe> requirements...

Interesting, thank you Philippe!
Since I can read French pretty well, I wanted to look at it.
However, for me,
    http://www.sciviews/_passtec
doesn't seem to be valid.
Have you mis-typed something?

Bonnes salutations,

Martin Maechler <maechler at stat.math.ethz.ch>
http://stat.ethz.ch/~maechler/
Seminar fuer Statistik, ETH-Zentrum  LEO D10	Leonhardstr. 27
ETH (Federal Inst. Technology)	8092 Zurich	SWITZERLAND
phone: x-41-1-632-3408		fax: ...-1228			<><


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