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LogLinearPlot Nintegrate and a strange error message

• To: mathgroup at smc.vnet.net
• Subject: [mg123769] LogLinearPlot Nintegrate and a strange error message
• From: Artur Henrykowski <mantysa at gmail.com>
• Date: Sun, 18 Dec 2011 04:36:03 -0500 (EST)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com

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

• Follow-Ups:
  • Re: LogLinearPlot Nintegrate and a strange error message
    • From: Bob Hanlon <hanlonr357@gmail.com>