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Re: Reconstructing data points from a InterpolatingFunction object


In article <e4bits$1a9$1 at smc.vnet.net>,
 "Eckhard Schlemm" <e.schlemm at hotmail.de> wrote:

> I am nummerically solving a differential equation using NDSolve and then I
> want to apply a NonlinearFit on the resulting InterpolatingFunction
> object....

What do you want the NonlinearFit to do? Note that in Version 5 you can 
use FindFit instead of NonlinearFit. Also, you can use 
InterpolatingFunctions directly, rather than sampling or re-sampling 
them.

I think a concrete example is likely to generate a more useful answer.

> and therefore need to have access to the data points which NDSolve
> created and from which the InterpolatingFunction is created....

I don't follow the use of therefore here. The data points at which 
NDSolve samples the solution depends on the automatic and optional 
settings supplied to NDSolve -- so I don't see why accessing these 
points is required. You can, of course, just generate a Table of points 
by re-sampling the InterpolatingFunction.

> Is there any fast and direct way to get these data points ? 
> (There must be....)

See the Advanced Documentation for NDSolve. This can be opened directly 
be executing the following command:

 NotebookOpen[FrontEnd`FileName[
  {$TopDirectory, "Documentation", "English","RefGuide", 
    "AdvancedDocumentation","DifferentialEquations"}, "Packages.nb"]]

Cheers,
Paul

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Paul Abbott                                      Phone:  61 8 6488 2734
School of Physics, M013                            Fax: +61 8 6488 1014
The University of Western Australia         (CRICOS Provider No 00126G)    
AUSTRALIA                               http://physics.uwa.edu.au/~paul


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