Specifications

Creating LTI Models
2-23
Data Retrieval
The functions tf, zpk, ss,andfrd pack the model data and sample time in a
singleLTI object.Conversely,thefollowing commandsprovideconvenientdata
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,theinputargumenttofrdata, can only be an FRD model
You can use any variable names you wantin the outputargument list ofany 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,andz and 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 transfer function from the jthinput to the ithoutput.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}
displays the coefficients of the numerator and denominator of the first input
channel.
ans =
0 1 –1
ans =
Hs
()
s 1–
s
2
2s 10++
-------------------------------
1
s
---
=