Pole Zero plot is giving wrong plot

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Anindya Guha
Anindya Guha 2011-10-17
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/

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采纳的回答

Wayne King
Wayne King 2011-10-17
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

更多回答（1 个）

Honglei Chen
Honglei Chen 2011-10-17
If you look at the ticks of the real axes, you can see that the scale is 10e-16. So practically it is on the imaginary axis. If you want to see a better picture, you can do the following to rescale the axes
axis([-1 1 -5 5])
HTH

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