sigmaplot (Control System Toolbox)

Plot singular values of the frequency response and return the plot handle

Syntax

h = sigmaplot(sys)

h = sigmaplot(sys,{wmin,wmax})
h = sigmaplot(sys,w)
h = sigmaplot(sys,w,type)
h = sigmaplot(sys,[],type)
h = sigmaplot(AX,...)
h = sigmaplot(..., plotoptions)

Discussion

h = sigmaplot(sys) produces a singular value (SV) plot of the frequency response 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 nicholsoptions 
```

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.

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

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

sigmaplot(sys,w,TYPE) or sigmaplot(sys,[],TYPE) draws the following modified SV plots depending on the value of TYPE:

TYPE = 1 --> SV of inv(SYS)

TYPE = 2 --> SV of I + SYS

TYPE = 3 --> SV of I + inv(SYS)

sys should be a square system when using this syntax.

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

sigmaplot(..., plotoptions) plots the singular values with the options specified in plotoptions. Type

```
help sigmaoptions 
```

for more details.

Example

Use the plot handle to change the units to Hz.

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

See Also
getoptions Get plot options

setoptions Set plot options

sigma Singular value plot of LTI models

sigma sisotool