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Import Data Objects into the App

You can import the System Identification Toolbox™ iddata and idfrd data objects into the System Identification app.

Before you can import a data object into the System Identification app, you must create the data object in the MATLAB® workspace, as described in Representing Time- and Frequency-Domain Data Using iddata Objects or Representing Frequency-Response Data Using idfrd Objects.


You can also import a Control System Toolbox™ frd object. Importing an frd object converts it to an idfrd object.

Select Import data > Data object to open the Import Data dialog box.

Import iddata, idfrd, or frd (Control System Toolbox) data object in the MATLAB workspace.

To import a data object into the app:

  1. Type the following command in the MATLAB Command Window to open the app:

  2. In the System Identification app window, select Import data > Data object.

    This action opens the Import Data dialog box. IDDATA or IDFRD/FRD is already selected in the Data Format for Signals list.

  3. Specify the following options:

    • Object — Enter the name of the MATLAB variable that represents the data object in the MATLAB workspace. Press Enter.

    • Data name — Enter the name of the data set, which appears in the System Identification app window after the import operation is completed.

    • (Only for time-domain iddata object) Starting time — Enter the starting value of the time axis for time plots.

    • (Only for frequency domain iddata or idfrd object) Frequency unit — Enter the frequency unit for response plots.

    • Sample time — Enter the actual sample time in the experiment. For more information about this setting, see Specifying the Data Sample Time.


      The System Identification Toolbox product uses the sample time during model estimation and to set the horizontal axis on time plots. If you transform a time-domain signal to a frequency-domain signal, the Fourier transforms are computed as discrete Fourier transforms (DFTs) using this sample time.

  4. (Optional) In the Data Information area, click More to expand the dialog box and enter the following optional settings:

    (Only for iddata object) Input Properties

    • InterSample — This options specifies the behavior of the input signals between samples during data acquisition. It is used when transforming models from discrete-time to continuous-time and when resampling the data.

      • zoh (zero-order hold) indicates that the input was piecewise-constant during data acquisition.

      • foh (first-order hold) indicates that the input was piecewise-linear during data acquisition.

      • bl (bandwidth-limited behavior) specifies that the continuous-time input signal has zero power above the Nyquist frequency (equal to the inverse of the sample time).


      See the d2c and c2d reference page for more information about transforming between discrete-time and continuous-time models.

    • Period — Enter Inf to specify a nonperiodic input. If the underlying time-domain data was periodic over an integer number of periods, enter the period of the input signal.


      If your data is periodic, always include a whole number of periods for model estimation.

    Channel Names

    • Input — Enter the name of one or more input channels.


      Naming channels helps you to identify data in plots. For multivariable input and output signals, you can specify the names of individual Input and Output channels, separated by commas.

    • Output — Enter the name of one or more output channels.

    Physical Units of Variables

    • Input — Enter the input units.


      When you have multiple inputs and outputs, enter a comma-separated list of Input and Output units corresponding to each channel.

    • Output — Enter the output units.

    Notes — Enter comments about the experiment or the data. For example, you might enter the experiment name, date, and a description of experimental conditions. Models you estimate from this data inherit your data notes.

  5. Click Import. This action adds a new data icon to the System Identification app window.

  6. Click Close to close the Import Data dialog box.