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Purpose
Frequency response functions (in the xf format) for linear systems.
Syntax
xf = qbode(a,b,c,d,w) xf = qbode(ss,w) xf = qbode(num,den,w) XF = qbode( ... ,'struct') qbode( ... ,'iiplot ...')
Description
For statespace models described by matrices a, b, c, d, or the LTI statespace object sys (see Control System Toolbox), qbode uses an eigenvalue decomposition of a to compute, in a minimum amount of time, all the FRF xf at the frequency points w
xf = [C] (s [^{\} I _{\} ] − [A])^{−1} [B] + [D] 
The result is stored in the xf format . 'iiplot "Test" po reset' can be used to display results in iiplot(see section 2.1.2). The option po is used to save poles in ci.Stack{'IdMain'} so that they can be displayed. reset reinitializes the curve stack.
qbode will not work if your model is not diagonalizable. A specific algorithm was developed to deal with systems with rigidbody modes (double pole at zero associated to nondiagonalizable matrices). This algorithm will not, however, indicate the presence of incoherent b and c matrices. In other cases, you should then use the direct routines res2xf, nor2xf, etc. or the bode function of the Control System Toolbox.
For the polynomial models num, den , qbode computes the FRF at the frequency points w
xf= 

Warnings
See also
demo_fe, res2xf, nor2xf, and bode of the Control System Toolbox