Re: ParametricPlot problem

*To*: mathgroup at smc.vnet.net*Subject*: [mg97802] Re: ParametricPlot problem*From*: Bill Rowe <readnews at sbcglobal.net>*Date*: Sun, 22 Mar 2009 05:47:08 -0500 (EST)

On 3/21/09 at 5:17 AM, Serych at panska.cz (Serych Jakub) 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. Are you sure something is missing? Looking at your transfer function I see In[15]:= {Re@#, Im@#} &@transfer[f] /. f -> 0 Out[15]= {1,0} and In[16]:= {Re@#, Im@#} &@transfer[f] /. f -> 1000 Out[16]= {0.0247045,-0.155223} Looking at the plot, I see the right end of the curve at {1,0} and a gap between where the axes cross and the left hand end of the curve. But the left hand end does seem to be at {0.0247045,-0.155223} which indicates Mathematica did plot the curve over the entire range you specified. This is using version 7.01 on Mac OS X