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Re: LogLinearPlot Nintegrate and a strange error message

• To: mathgroup at smc.vnet.net
• Subject: [mg123788] Re: LogLinearPlot Nintegrate and a strange error message
• From: Bob Hanlon <hanlonr357 at gmail.com>
• Date: Mon, 19 Dec 2011 07:19:02 -0500 (EST)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• References: <201112180936.EAA01627@smc.vnet.net>

Doesn't seem to be a problem; however, I recommend that you do the
integration symbolicly.

f1[x_?NumericQ] := NIntegrate[(Sinc[1/x*u]), {u, 0, 1}]

f2[x_] = Integrate[Sinc[u/x], {u, 0, 1}]

x*SinIntegral[1/x]

GraphicsGrid[
 Outer[
  #1[#2[x], {x, 1, 2},
    PlotLabel -> ToString[#1] <> " of " <> ToString[#2],
    ImageSize -> 300] &,
  {Plot, LogLinearPlot},
  {f1, f2}]]


Bob Hanlon


On Sun, Dec 18, 2011 at 4:36 AM, Artur Henrykowski <mantysa at gmail.com> wrote:
> Hello,
>
> I noticed a strange behavior of Mathematica (version 7). I have no
> much experience in using it so probably there is something what I do
> not know (nor understand).
>
> I want to plot some function which is defined as integral, e.g.
>
> f := NIntegrate[(Sinc[1/x*u]), {u, 0, 1}]
>
> then I plotted it
> Plot[f, {x, 1, 2}]
>
> and it seems to be ok.
>
> But when I changed the function to LogLinearPlot
>
> datax = Reap[LogLinearPlot[f, {x, 1, 2}, EvaluationMonitor :> Sow[x]]]
>
> I obtained error message: "NIntegrate::ncvb:"NIntegrate failed to
> converge to prescribed accuracy after..." or other similar (e.g.
> Converge to slowly...) depending on function.
>
> But when I explicitly calculate values of function at points x of
> LogLinearPlot
>
> f /. {x -> datax}
>
> there is no error message.
>
> Why do I obtain this this message after calling LogLinearPlot but not
> in other cases? Are these values and plots reliable?
>
> Artur
>

• References:
  • LogLinearPlot Nintegrate and a strange error message
    • From: Artur Henrykowski <mantysa@gmail.com>