       ParametricPlot problem

• To: mathgroup at smc.vnet.net
• Subject: [mg97773] ParametricPlot problem
• From: "Serych Jakub" <Serych at panska.cz>
• Date: Sat, 21 Mar 2009 05:17:40 -0500 (EST)

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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