editing a nyquist figure

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 ?

Answer 1

[Teja Muppirala]

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.

[mona faraji]

Thank u very much

it works :)

Answer 2

[Nick Dienemann]

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)

[Nick Dienemann]

find https://de.mathworks.com/help/control/ref/nyquistoptions.html for more options concerning the nyquist plot.

Answer 3

[Arnaud Miege]

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

[mona faraji]

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!