User`s guide

1 Data Processing

When you are working w ith transient da ta (such as ste p o r impulse response),

do not remove the mean from the data. With transient data, when the output

atzeroinputisnotzero,youmightwanttosubtracttheconstantvalue

corresponding to the time before the input is applied.

For nonlinear black-box models, detrending data is not alw ay s necessary

because these models can include the trend as part of the m odel.

GUI and Command-Line Alternatives for Detrending

Data

You can detrend d ata using the System Identiﬁcation Tool GUI and at the

command line (using the

detrend command).

Both the G UI and the command line le t you subtract the m ean values a n d one

linear trend from time-domain signals.

However, the

detrend co mmand provides the following additional

functionality not available in the GUI:

• Subtracting several linear trends connected from time-domain data at

speciﬁed breakpoints. A breakpoint is a time value that deﬁnes the

discontinuities between su ccessive linear trends.

• Subtract a m ean v alue from frequency-domain data.

To learn how to detrend data, see one of the following:

• “How to D etrend Data Using the GUI” on p age 1-96

• “How to Detrend Data at the Command Line” on page 1-97

How to Detrend Data Using the GUI

Before you can perform this task, you must i mport data into the System

Identiﬁcation Tool GUI, as described in “Importing Time-Domain Data into

the GUI” on page 1-15.

1-96