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Function Reference: nyquist

Function File: nyquist (sys)
Function File: nyquist (sys1, sys2, …, sysN)
Function File: nyquist (sys1, sys2, …, sysN, w)
Function File: nyquist (sys1, ’style1’, …, sysN, ’styleN’)
Function File: [re, im, w] = nyquist (sys)
Function File: [re, im, w] = nyquist (sys, w)

Nyquist diagram of frequency response. If no output arguments are given, the response is printed on the screen.

Inputs

sys
LTI system. Must be a single-input and single-output (SISO) system.
w
Optional vector of frequency values. If w is not specified, it is calculated by the zeros and poles of the system. Alternatively, the cell {wmin, wmax} specifies a frequency range, where wmin and wmax denote minimum and maximum frequencies in rad/s.
’style’
Line style and color, e.g. ’r’ for a solid red line or ’-.k’ for a dash-dotted black line. See help plot for details.

Outputs

re
Vector of real parts. Has length of frequency vector w.
im
Vector of imaginary parts. Has length of frequency vector w.
w
Vector of frequency values used.

See also: bode, nichols, sigma

Source Code: nyquist 

 s = tf('s');
 G_1 = 1.2/(s^2/9+0.42*s+1)^2;
 G_2 = 1.2/(s^2/9+0.33*s+1)^2;
 nyquist(G_1,G_2);
plotted figure