Control System Toolbox™

nyquistplot - Plot Nyquist frequency responses and return plot handle

Syntax

h = nyquistplot(sys)
nyquistplot(sys,{wmin,wmax})
nyquistplot(sys,w)
nyquistplot(sys1,sys2,...,w)
nyquistplot(AX,...)
nyquistplot(..., plotoptions)

Description

h = nyquistplot(sys) draws the Nyquist plot of the LTI model sys (created with tf, zpk, ss, or frd). It also returns the plot handle h. You can use this handle to customize the plot with the getoptions and setoptions commands. Type

help nyquistoptions 

for a list of available plot options.

The frequency range and number of points are chosen automatically. See bode for details on the notion of frequency in discrete time.

nyquistplot(sys,{wmin,wmax}) draws the Nyquist plot for frequencies between wmin and wmax (in rad/s).

nyquistplot(sys,w) uses the user-supplied vector w of frequencies (in rad/s) at which the Nyquist response is to be evaluated. See logspace to generate logarithmically spaced frequency vectors.

nyquistplot(sys1,sys2,...,w) draws the Nyquist plots of multiple LTI models sys1,sys2,... on a single plot. The frequency vector w is optional. You can also specify a color, line style, and marker for each system, as in

nyquistplot(sys1,'r',sys2,'y--',sys3,'gx')

nyquistplot(AX,...) plots into the axes with handle AX.

nyquistplot(..., plotoptions) plots the Nyquist response with the options specified in plotoptions. Type

help nyquistoptions 

for more details.

Example

Plot the Nyquist frequency response and change the units to rad/s.

sys = rss(5);
h = nyquistplot(sys);
% Change units to radians per second.
setoptions(h,'FreqUnits','rad/s');

See Also

getoptions, nyquist, setoptions

nyquist

obsv