User`s guide

Representing Frequency-Response Data Using idfrd Objects

The resulting idfrd object data contains the frequency responses from

the s ame inputs in

data1,data2,...,dataN to all the outputs. The

following diagram is a graphical representation of vertical concatenation o f

frequency-response data. The

(j,i,:) vector of the res ulting response data

represents the frequency response from the

ith input to the jth output at all

frequencies.

Data 1

2-by-2-by-nf

Vertical Concatenation

of Data 1 and Data 2

3-by-2-by-nf

Combined

outputs

Same

inputs

Data 1

1-by-2-by-nf

Note Vertical concatenation of idfrd objects requires that they have the

same inputs and frequency vectors. If the input channel names are different

and their dimensions are the same, the concatenation operation uses the

names of input channels in the ﬁrst

idfrd object you listed. Output channels

must have unique names.

Concatenating Noise Spectral Data of idfrd Objects

When the idfrd objects contain the f requency-response data you measured

or constructed manually, the concatenation operation combines only the

ResponseData properties. Because the noise spectral data does not exist

(unless you also entered it manually),

SpectralData is empty in both the

individual

idfrd objects and the concatenated idfrd object.

However, when the

idfrd objects are spectral models that you estimated, the

SpectralData property is not empty and contains the power spectra and

cross spectra of the output noise in the system. For each output channel, the

toolbox es timates one nois e channel toexplainthedifferencebetweenthe

output of the model and the measured output.

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