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MathGroup Archive 1996

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BUG or FEATURE in Interpolation[] ?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg4597] BUG or FEATURE in Interpolation[] ?
  • From: Stefan Schulz <sschulz at chemie.fu-berlin.de>
  • Date: Wed, 21 Aug 1996 03:25:18 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

Dear Mathematica users,

when I typed in the following lines:

xdata = {-1., -0.5, 0., 1., 3., 6., 9.};
ydata = Map[(Exp[-#]-1)^2&, xdata];
data  = Inner[List,xdata,ydata,List];
int   = Interpolation[data];
Plot[int[x], {x,-1,9}]

I found to my surprise, that the function returned by Interpolation 
is not smooth at some of the data points! For this reason I resorted to
write a package Spline1D which returns a smooth cubic spline as a 
pure function, but is naturally slower than the built-in Interpolation 
command. Did I find a bug or is this a feature? If it is a feature
it certainly makes the Interpolation command not suitable to obtain 
smooth curves. I would appreciate your comments an this. Many Thanks
in advance.

Regards,


Stefan

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