User`s guide

Transforming Between Time- and Frequency-Do main Data
high-frequency noise dominates away from frequencies where interesting
system dynamics occur.
Note You cannot transform an idfrd object to a t ime-do main iddata object.
To transform an idfrd object with the name idfrdobj to a frequency-domain
iddata object, use the following syntax:
dataf = iddata(idfrdobj)
The resulting frequency-domain id data object contains values at the same
frequencies as the original
idfrd object.
For the multiple-input case, the toolbox represents frequency-response data
as if each input contributes independently to the entire output of the system
and then combines information. For example, if a system has three inputs,
u1, u2,andu3 and two frequency samples, the input matrix is set to:
100
100
010
010
001
001
⎡
⎣
⎢
⎢
⎢
⎢
⎢
⎢
⎢
⎢
⎤
⎦
⎥
⎥
⎥
⎥
⎥
⎥
⎥
⎥
In general, for nu inputs and ns samples, the input matrix has nu columns
and (
ns
⋅
nu)rows.
If you have
ny outputs, the transformation operation produces an output
matrix has
ny columns a nd (ns
⋅
nu) rows using the values in the complex
frequency response G(iw) matrix (
ny-by-nu-by-ns). In this example, y1 is
determined by unfolding
G(1,1,:), G(1,2,:),andG(1,3,:) into three
column vectors and vertically concatenating these vectors into a single column.
Similarly,
y2 is determined by unfolding G(2,1,:), G( 2,2, :),andG(2,3 ,:)
into three column vectors and v ertically concatenating these vectors.
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