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Re: ParametricPlot problem

  • To: mathgroup at smc.vnet.net
  • Subject: [mg97811] Re: ParametricPlot problem
  • From: "Sjoerd C. de Vries" <sjoerd.c.devries at gmail.com>
  • Date: Sun, 22 Mar 2009 05:48:55 -0500 (EST)
  • References: <gq2eri$ea1$1@smc.vnet.net>

Hi Jakub,

Instead of f, you could try Exp[f]:

ParametricPlot[{Re[transfer[Exp[f]]], Im[transfer[Exp[f]]]}, {f, 0,
  10}, PlotRange -> All]

You could treat the original plot for f in [0,1] separately (but it
doesn't do much here).

Cheers -- Sjoerd
On Mar 21, 12:17 pm, "Serych Jakub" <Ser... at panska.cz> wrote:
> Dear M users,
> I'm trying to draw phasor characteristic of simple RC low pass filter. Its
> transfer function is:
>
> r = 100;
> c = 0.00001;
> transfer[f_] := 1/(1 + I 2 \[Pi] f r c);
>
> The phasor characteristic should be drawn with:
>
> ParametricPlot[{Re[transfer[f]], Im[transfer[f]]}, {f, 0, Infinity}]
>
> I can understand, that Mathematica has problem with calculation of the
> transfer function for frequency from 0 to Infinity, so I tried to use 10^ 8 in
> the place of infinity. But as the ParametricPlot IMHO subdivides the
> frequency range  into constant intervals, it draws piece of the curve only
> for frequencies near to 10^8.
> I found that the relatively reasonable result is with frequency range 0 to
> 10^3:
>
> ParametricPlot[{Re[transfer[f]], Im[transfer[f]]}, {f, 0, 10^3}]
>
> but there is missing the part of curve near to coordinates origin.
>
> Is there any way to tell the ParametricPlot to divide the interval of the
> frequency in logarithmic manner to have the possibility to draw the phasor
> characteristic in the bigger frequency range?
>
> I tried the PlotPoints and PerformanceGoal options, but it doesn't help (or I
> cannot use it).
>
> Thanks a lot for any help
>
> Jakub



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