MATLAB: Pole Zero plot is giving wrong plot

controlControl System ToolboxMATLABplot

Hi,
I've used 'pzmap' to create ploe zero plot of a transfer function. According to the transfer function used, all the poles of it should be on the imaginary axis. But this is not the case in the output.
code:- >> num=[3]; >> den=[1 0 10 0 9 0]; >> sys=tf(num,den)
Transfer function: 3 —————— s^5 + 10 s^3 + 9 s
>> pzmap(sys)
output:- http://postimage.org/image/1dx6mev9g/

Best Answer

Hi, The poles are all on the imaginary axis, look at the scale of your real axis, it is 10^{-16}
If you enter:
[p,z] = pzmap(sys);
You'll see the poles are:
      0          
   0.0000 + 3.0000i
   0.0000 - 3.0000i
  -0.0000 + 1.0000i
  -0.0000 - 1.0000i
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