User`s guide

1 Data Processing

- If you are working w ith uniformly sampled data, use the actual

sampling interval in your experiment. Each data value is assigned a

sample time, which is calculated from the start time and the sampling

interval. If y ou are working with nonuniformly sampled data at the

command line, y ou can specify a vector of time instants using the

iddata

SamplingInstants

property, as described in “Constructing an iddata

Object for Time-Domain Data” on page 1-48.

For more information about importing data into the M ATL AB workspace, see

the MATLAB documentation.

After you impo rt data, you can import it into the Sy stem Identi ﬁcation Tool

GUI or create a data object for working at the command line. For more

information about importing data into the GUI, see “Importing Time-Domain

Data into the GUI” on page 1-15. To learn more about creating a data object,

see “Representing Time- and Frequency-Domain Data Using iddata Objects”

on page 1-47.

For information about estimating time-series model parameters, see Chapter

6, “Time Series Model Identiﬁcation”.

Importing Frequency-Domain Data into MATLAB

• “What Is Frequency-Domain Data?” on page 1-8

• “How to Import Frequency-Domain Data into MAT L AB” on page 1-9

What Is Frequency-Domain Data?

Frequency-domain data is the Fourier transform of the input a nd output

time-domain signals. For co ntin uo u s-tim e signals, the Fourier transform over

theentiretimeaxisisdeﬁ ned as follows:

Yiw yte dt

Uiw ute dt

iwt

() ()

−

−∞

∞

−

−∞

∞

∫

2π

1-8