nyquistplot (Control System Toolbox)

Plot Nyquist frequency response and return the plot handle

Syntax

h = nyquistplot(sys)

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

sys = rss(5);
h = nicholsplot(sys);
% Change units to Hz 
setoptions(h,'FreqUnits','Hz');

See Also
getoptions Get plot options

nyquist Nyquist frequency response of LTI models

setoptions Set plot options

nyquist obsv