User`s guide

Subtracting Trends from Signals (Detrend ing)
Tip (For linear modeling only) Selec t Preprocess > Quick start to perform
several data cleaning operations, includingremovingthemeanvaluefrom
each signal, splitting data into two halves, specifying the first half as model
estimation data (or Working Data), and specifying the second half as model
Validation Data.
To detrend data using the GUI:
1 In the System Identification Tool, drag the data set you want to detrend to
the Working Data rectangle.
2 Determine if you want to remove both the mean values and the linear
trend from the data.
• If yes, select Preprocess > Remove trends. This creates a new data
setintheDataBoard. Youarefinish ed .
• Ifno,gotostep3.
3 To remove constant offsets from the data, select Preprocess > Remove
means. This sele c tion cre ates a new data set in the System Ide nti fication
Tool GUI.
Note When you estimate a model from detrended data, you should also
detrend the validation data in the same way.
HowtoDetrendDataattheCommandLine
You can use the detrend command to perform the following operations:
• Subtract mean values from time-domain or frequency-domain data.
• Subtract one o r more linear trend s from tim e-domain data at specified
breakpoints, w h ere a breakpoint is a time value that defines the
discontinuities between su ccessive linear trends.
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