Re: Reconstructing data points from a InterpolatingFunction object
- To: mathgroup at smc.vnet.net
- Subject: [mg66538] Re: Reconstructing data points from a InterpolatingFunction object
- From: "Eckhard Schlemm" <e.schlemm at hotmail.de>
- Date: Fri, 19 May 2006 03:39:50 -0400 (EDT)
- References: <e4bits$1a9$1@smc.vnet.net> <e4ella$9o6$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Hello Paul,
Thanks for your answer.
Thanks to your help - and the other answers of course - I managed to get
hold of the data points created by NDSolve to sample the
InterpolatingFunction..But still when I use NonlinearFit[] to fit a model to
these data the outcome is somewhat strange...for a listplot of data and a
plot of the "best fit function" clearly indicates that there are better
paramters to fit the model to the data....I think this problem has nothing
to do with from where I got the data points,,, in my case from the
InterpolatingFunction object but I don't think that is the cause of this
strange behavior.
I attached the code run on a WinXP machine, mathematica version 5.0
Can you tell me, why ff[t] is so much different from the data points of
data?... Oh I almost forgot... it works properly for some values of a and
T... for example (a,T)=(.5 , 30) seems to work.. but others do not....for
instance (a,T)=(.7 , 30) yields a result which I cannot quite belief to be
the best fit....
So Thanks for your answer again
cheers
Eckhard
> I think a concrete example is likely to generate a more useful answer.
>
> > and therefore need to have access to the data points which NDSolve
> > created and from which the InterpolatingFunction is created....
>
> I don't follow the use of therefore here. The data points at which
> NDSolve samples the solution depends on the automatic and optional
> settings supplied to NDSolve -- so I don't see why accessing these
> points is required. You can, of course, just generate a Table of points
> by re-sampling the InterpolatingFunction.
>
> > Is there any fast and direct way to get these data points ?
> > (There must be....)
>
> See the Advanced Documentation for NDSolve. This can be opened directly
> be executing the following command:
>
> NotebookOpen[FrontEnd`FileName[
> {$TopDirectory, "Documentation", "English","RefGuide",
> "AdvancedDocumentation","DifferentialEquations"}, "Packages.nb"]]
>
> Cheers,
> Paul
>
> _______________________________________________________________________
> 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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`
end