Nyquist plot with additional plot customization options
h = nyquistplot(sys)
nyquistplot(sys,{wmin,wmax})
nyquistplot(sys,w)
nyquistplot(sys1,sys2,...,w)
nyquistplot(AX,...)
nyquistplot(..., plotoptions)
h = nyquistplot(sys)
draws the Nyquist
plot of the dynamic
system model sys
. 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/TimeUnit
,
where TimeUnit
is the time units of the input dynamic
system, specified in the TimeUnit
property
of sys
).
nyquistplot(sys,w)
uses the user-supplied
vector w
of frequencies (in rad/TimeUnit
,
where TimeUnit
is the time units of the input dynamic
system, specified in the TimeUnit
property
of sys
) 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 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.
Customize Nyquist Plot Frequency Units
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');
Compare the frequency responses of identified state-space models
of order 2 and 6 along with their 1-std
confidence
regions rendered at every 50th frequency sample.
load iddata1 sys1 = n4sid(z1, 2) % discrete-time IDSS model of order 2 sys2 = n4sid(z1, 6) % discrete-time IDSS model of order 6
Both models produce about 76% fit to data. However, sys2
shows
higher uncertainty in its frequency response, especially close to Nyquist
frequency
as shown by the plot:
w = linspace(10,10*pi,256); h = nyquistplot(sys1,sys2,w); setoptions(h,'ConfidenceRegionDisplaySpacing',50,'ShowFullContour','off');
Right-click to turn on the confidence region characteristic by using the Characteristics-> Confidence Region.
You can change the properties of your plot, for example the units. For information on the ways to change properties of your plots, see Ways to Customize Plots.