Access transfer function data
[num,den] = tfdata(sys)
[num,den,Ts] = tfdata(sys)
[num,den,Ts,sdnum,sdden]=tfdata(sys)
[num,den,Ts,...]=tfdata(sys,J1,...,Jn)
[num,den] = tfdata(sys)
returns the numerator(s) and denominator(s) of the transfer function
for the TF, SS or ZPK model (or LTI array of TF, SS or ZPK models) sys.
For single LTI models, the outputs num and den of tfdata are
cell arrays with the following characteristics:
num and den have
as many rows as outputs and as many columns as inputs.
The (i,j) entries num{i,j} and den{i,j} are
row vectors specifying the numerator and denominator coefficients
of the transfer function from input j to output i.
These coefficients are ordered in descending powers
of s or z.
For arrays sys of LTI models, num and den are
multidimensional cell arrays with the same sizes as sys.
If sys is a state-space or zero-pole-gain
model, it is first converted to transfer function form using tf.
For more information on the format of transfer function model data,
see the tf reference page.
For SISO transfer functions, the syntax
[num,den] = tfdata(sys,'v')
forces tfdata to return the numerator and
denominator directly as row vectors rather than as cell arrays (see
example below).
[num,den,Ts] = tfdata(sys)
also returns the sample time Ts.
[num,den,Ts,sdnum,sdden]=tfdata(sys) also
returns the uncertainties in the numerator and denominator coefficients
of identified system sys. sdnum{i,j}(k) is
the 1 standard uncertainty in the value num{i,j}(k) and sdden{i,j}(k) is
the 1 standard uncertainty in the value den{i,j}(k).
If sys does not contain uncertainty information, sdnum and sdden are
empty ([]).
[num,den,Ts,...]=tfdata(sys,J1,...,Jn) extracts
the data for the (J1,...,JN)entry in the model
array sys.
You can access the remaining LTI properties of sys with get or
by direct referencing, for example,
sys.Ts sys.variable
Given the SISO transfer function
h = tf([1 1],[1 2 5])
you can extract the numerator and denominator coefficients by typing
[num,den] = tfdata(h,'v')
num =
0 1 1
den =
1 2 5
This syntax returns two row vectors.
If you turn h into a MIMO transfer function
by typing
H = [h ; tf(1,[1 1])]
the command
[num,den] = tfdata(H)
now returns two cell arrays with the numerator/denominator data
for each SISO entry. Use celldisp to visualize
this data. Type
celldisp(num)
This command returns the numerator vectors of the entries of H.
num{1} =
0 1 1
num{2} =
0 1
Similarly, for the denominators, type
celldisp(den)
den{1} =
1 2 5
den{2} =
1 1
Extract the numerator, denominator and their standard deviations for a 2-input, 1 output identified transfer function.
load iddata7
transfer function model
sys1 = tfest(z7, 2, 1, 'InputDelay',[1 0]);
an equivalent process model
sys2 = procest(z7, {'P2UZ', 'P2UZ'}, 'InputDelay',[1 0]);
[num1, den1, ~, dnum1, dden1] = tfdata(sys1);
[num2, den2, ~, dnum2, dden2] = tfdata(sys2);