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MathGroup Archive 1997

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Re: bug in Interpolation[] of Mma 3.0

  • To: mathgroup at smc.vnet.net
  • Subject: [mg5810] Re: [mg5767] bug in Interpolation[] of Mma 3.0
  • From: Francisco Edmundo de Andrade <edmundo at lia.ufc.br>
  • Date: Wed, 22 Jan 1997 00:44:15 -0500
  • Sender: owner-wri-mathgroup at wolfram.com

On Sat, 18 Jan 1997, Gennady wrote:
> In my calculation of Interpolation[] function with Mathematica 3.0
> I found the following bug.
>  
> If I run a piece of code given below with Mma 3.0 on my PowerPC 9500/120
> and compare the ListPlot of the original array and the Plot
> of its Interpolation function, I see that the interpolation is very
> poor. There is a big bump between values of abscissa 1.6 and 3.4
> which certainly should not be there.
> The integral of the interpolation function (computed in the last line
> of the code) equals 33.838.
> 
> If I run the same code with Mathematica 2.2 (on the same PowerPC),
> I find that the bump disappears, and the visual agreement between
> the ListPlot and the Interpolation function is much better. Also,
> the integral now is 27.0384, rather than 33.838.
> 
> It would be interesting to check if the same bug appears on other
> computers/platforms. I have reported the bug to Wolfram Research.
> 
> Gennady Stupakov.
> 
> (*---- Mathematica code --------*)
> testlist={{0., 4.037}, {1.689, 4.744}, 
>   {3.379, 6.865}, {3.551, 7.637}, 
>   {3.723, 9.563}, {4.157, 17.429}, 
>   {4.251, 19.065}};
> fun=Interpolation[testlist];
> ListPlot[testlist,PlotJoined->True,DisplayFunction->Identity]
> Plot[fun[s],{s,0,4.2},PlotRange->All,DisplayFunction->Identity]
> Show[%,%%,DisplayFunction->$DisplayFunction];
> NIntegrate[fun[s],{s,0,4.251}]
> (*------------------------------*)
> 
> 
Dear Gennady,

I observed that your assertation applies to Mathematica 3.0 for Windows 95.
Maybe it is a general bug of the version 3.0 (?!)

Edmundo



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