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MathGroup Archive 2000

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Re: [TS 3227] ListInterpolation

  • To: mathgroup at smc.vnet.net
  • Subject: [mg23478] Re: [mg23467] [TS 3227] ListInterpolation
  • From: Matt.Johnson at autolivasp.com
  • Date: Fri, 12 May 2000 22:54:19 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com


Kurt-

per the book:

"Interpolation works by fitting polynomial curves between successive data
points. "

In other words, the curve pases through each data point input.  If you have many
data points, you probably need to increase the PlotPoints to see the noise in
your original data.

As for the derivatives, I have the same problem with my data.  A smoothing
routine that would accurately represent the major trends without the in-between
small variances would be nice.

-matt






Kurt Taretto <Kurt.Taretto at ipe.uni-stuttgart.de> on 05/10/2000 10:54:16 PM

Subject: [mg23478]  [mg23467] [TS 3227]  ListInterpolation




Hi,

I'm using ListInterpolation to get functions that smoothly describe my
data.  So the resulting plots are smooth lines that transverse my noisy
data.  When I try to plot the derivative of this functions, I get very
sharp zig-zags (that I could also get deriving numerically my data).
Mathematica is making an interpolation between my points, and since my
points are noisy distributed, y also get the noise in the derivative.
That's ok, but why do I get smooth plots that cross my data, say, at a
"mean noise value".  I cannot use NonLinearFit because the functions I
need should be case sensitive and I have a large number of data sets, so
choosing a fitting function every time could be extremely tedious.  I'm
sure there's a way out of this, if someone could help me, I'd appreciate
any help.

Thanks!








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