User`s guide

2 LTI Models
2-24
Data Retrieval
The functions tf, zpk, ss,andfrd pack the model data and sample time in a
singleLTI object.Conversely,thefollowingcommandsprovide convenientdata
retrieval for any type of TF, SS, or ZPK model
sys,orFRDmodelsysfr.
[num,den,Ts] = tfdata(sys) % Ts = sample time
[z,p,k,Ts] = zpkdata(sys)
[a,b,c,d,Ts] = ssdata(sys)
[a,b,c,d,e,Ts] = dssdata(sys)
[response,frequency,Ts] = frdata(sysfr)
Note that:
•
sys can be any type of LTI object, except an FRD model
•
sysfr, the input argument to frdata, can only be an FRD model
You can use any variable names you want in the output argument list of any of
these functions. The ones listed here correspond to the model property names
described in Tables 2-2 – 2.5.
The output arguments
num and den assigned to tfdata,andzand p assigned
to
zpkdata, are cell arrays, even in the SISO case. These cell arrays have as
many rows as outputs, as many columns as inputs, and their ijth entry
specifies the transferfunction fromthe jthinput to the ith output. For example,
H = [tf([1 –1],[1 2 10]) , tf(1,[1 0])]
creates the one-output/two-input transfer function
Typing
[num,den] = tfdata(H);
num{1,1}, den{1,1}
Hs()
s 1–
s
2
2s 10++
-------------------------------
1
s
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