MATLAB: How do i plot nyquist from experiment data values

MATLABnyquistplotstability

From the code in this page https://www.mathworks.com/help/control/ref/nyquist.html
if true
  % load iddata2 z2;
sys_p = tfest(z2,2);
w = linspace(-10*pi,10*pi,512);
[re, im, ~, sdre, sdim] = nyquist(sys_p,w);
re = squeeze(re);
im = squeeze(im); 
sdre = squeeze(sdre);
sdim = squeeze(sdim);
plot(re,im,'b', re+3*sdre, im+3*sdim, 'k:', re-3*sdre, im-3*sdim, 'k:')
end
Can i ask where is the part i input my experimental data values or the meaning of codes ? Sorry as i'm kind of new to Matlab with little guidance. Any help is appreciated !

Best Answer

If you just want the plot, do a separate nyquist call without any outputs:
figure(1)
nyquist(sys_p,w)
That should produce the plot you want.
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