editing a nyquist figure

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mona faraji
mona faraji 2011-3-28
评论： Nick Dienemann 2022-5-24
How can I edit a nyquist figure or how can I plot a nyquist diagram using MATLAB such that it just consists positive frequencies and not negative ones ?

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Teja Muppirala
Teja Muppirala 2011-3-30
Run the nyquist command as usual:
nyquist([1],[1 2 1])
Then if you right click on the axes (the white part), a context menu will pop up and in the third option you can select not to show the negative frequencies.

更多回答（2 个）

Nick Dienemann
Nick Dienemann 2022-5-24
Ran in:
You can use the following code to turn of plotting of the negative frequencies within your code. Spares you the time to disable them manually in the plot window as suggested by Teja.
num= [-1 1]; %numerator
den= [2 2]; %denominator
G = tf(num,den)
G = -s + 1 ------- 2 s + 2 Continuous-time transfer function.
%-------------- Nyquist diagramm --------------------------
plotoptions= nyquistoptions('cstprefs') ; % default options
plotoptions.ShowFullContour = 'off'; % exclude negative frequencies
nyquist(G,plotoptions)
Arnaud Miege
Arnaud Miege 2011-3-28
Are you using the nyquist function from the Control System Toolbox? According to the documentation:
" nyquist(sys,w) explicitly specifies the frequency range or frequency points to be used for the plot. To focus on a particular frequency interval, set w = {wmin,wmax}. To use particular frequency points, set w to the vector of desired frequencies. Use logspace to generate logarithmically spaced frequency vectors. Frequencies should be specified in rad/sec."
Either specify a positive frequency interval or a vector of positive frequencies.
HTH,
Arnaud
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mona faraji
mona faraji 2011-3-29
Thanks for your answer but...
yes I use nyquist command and however I set wmin and wmax as positive values but the it plots a figure for both positive and negative frequency points!

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