User`s guide

1 Data Processing

Before you can perform this task, you must represent your data as an iddata

object in the M ATLA B workspace, as described in “Representing Time- and

Frequency-Domain Data Using iddata Objects” on page 1-47.

To remove mean values from each channel in

data (which is an iddata

object), use the following syntax:

data = detrend(data);

To subtract one linear trend, use the following syntax:

data = detrend(data,1);

In this case, 1 indicates that a ﬁrs t-order trend is removed from each signal.

Note When you estimate a model from detrended data, you should also

detrend the validation data in the same way.

For more information about detrending options, see the detrend reference

page.

How to Add Detrended Values to the Model Output

Suppose that you estimated the model M using detrended data, w here you

removed

u0 an d y0 from the input and output signals, respectively.

To simulate this model about nonzero e quilibrium values:

1 Subtract u0 from the input signal you want to use to simulate the model.

For example,

Unew=U-u0.

2 Simulate the model using the sim command and the input signal resulting

from step 1.

For example,

Ysim = sim(M,Unew,INIT), where INIT speciﬁes the initial

conditions of the simulation.

3 Add y0 to the simulated model output.

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