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MathGroup Archive 2007

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Re: Strange interpolation pb

  • To: mathgroup at smc.vnet.net
  • Subject: [mg80533] Re: Strange interpolation pb
  • From: Fred Bartoli <mynamewithAdotinbetween at free.fr>
  • Date: Fri, 24 Aug 2007 02:05:39 -0400 (EDT)
  • References: <fagt7p$8ij$1@smc.vnet.net>

Le Wed, 22 Aug 2007 08:47:53 +0000, Fred a =C3=A9crit:

> Hello,
> I've a strange error with the Interpolation function
>
> In[1]:= $Version
>
> Out[1]= 6.0 for Linux x86 (64-bit) (June 19, 2007)
>
> In[2]:= t=Join[{0},10^Range[-8,-2,0.1]];
>
> y=Interpolation[Transpose[{t,Exp[-10000 t]}]]
>
> LogLinearPlot[y[t],{t,10^-6,0.01},PlotRange->All]
>
> Out[3]= InterpolatingFunction[{{0.,0.01}},<>]
>
> During evaluation of In[2]:= InterpolatingFunction::dmval: Input value
> {-13.8153} lies outside the range of data in the interpolating function .
> Extrapolation will be used. >>
>
> Anyone reproduce or explains it?
>

Some further investigation show that it's a "feature" logarithmic X axis
plot functions.


t = Join[{0}, 10^Range[-8, -2, 0.1]];

y = Interpolation[Transpose[{t, Exp[-10000 t]}]];
a = {};
fplot = LogLinearPlot;
(* strangely this one reports seemingly correct evaluation points while
giving the error*)
Reap[
 fplot[y[t], {t, 10^-6, 0.01}, PlotRange -> All, PlotPoints -> 10,
  MaxRecursion -> 0, PlotRange -> All, EvaluationMonitor :> Sow[t]]]
% // Length[#[[2, 1]]] &

(*and this one tells all the truth and show an added wrong evaluation
point*)
fplot[
 Block[{}, a = Append[a, t]; y[t]], {t, 10^-6, 0.01},
 PlotRange -> All, PlotPoints -> 10, MaxRecursion -> 0,
 PlotRange -> All]
a
a // Length



--
Thanks,
Fred.


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