User`s guide

sigma
11-202
11sigma
Purpose Singular values of the frequency response of LTI models
Syntax sigma(sys)
sigma(sys,w)
sigma(sys,w,type)
sigma(sys1,sys2,...,sysN)
sigma(sys1,sys2,...,sysN,w)
sigma(sys1,sys2,...,sysN,w,type)
sigma(sys1,'PlotStyle1',...,sysN,'PlotStyleN')
[sv,w] = sigma(sys)
sv = sigma(sys,w)
Description sigma calculatesthesingularvaluesof thefrequencyresponse ofanLTI model.
For an FRD model,
sys, sigma computes the singular values of sys.Response
at thefrequencies, sys.frequency. Forcontinuous-timeTF,SS, orZPK models
with transfer function ,
sigma computes the singular values of as
a function of the frequency . For discrete-time TF, SS, or ZPK models with
transfer function and sample time ,
sigma computes the s ingular
values of
for frequencies between 0 and the Nyquist frequency .
The singular values of the frequency response extend the Bode magnitude
response for MIMO systems and are useful in robustness analysis. The
singular value response of a SISO system is identical to its Bode magnitude
response.When invokedwithout output arguments,
sigma produces a singular
value plot o n the screen.
sigma(sys) plots the singular values of the frequency response of an arbitrary
LTI model
sys. This model can b e continuous or discrete, and SISO or MIMO.
The frequency points are chosen automatically based on the system poles and
zeros, or from
sys.frequency if sys is an FRD.
sigma(sys,w) explicitly specifies the frequency range or frequency pointsto be
used for the plot. To focus on a particular frequency interval
[wmin,wmax],set
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