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## Import Frequency-Domain Data into the App

### Importing Frequency-Domain Input/Output Signals into the App

Frequency-domain data consists of Fourier transforms of time-domain data (a function of frequency).

Before you can import frequency-domain data into the System Identification app, you must import the data into the MATLAB® workspace, as described in Frequency-Domain Input/Output Signal Representation.

### Note

The input and output signals must have the same number of data samples.

To import data into the app:

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

`systemIdentification`
2. In the System Identification app window, select Import data > Freq. domain data. This action opens the Import Data dialog box.

3. Specify the following options:

• Input — Enter the MATLAB variable name (column vector or matrix) or a MATLAB expression that represents the input data. The expression must evaluate to a column vector or matrix.

• Output — Enter the MATLAB variable name (column vector or matrix) or a MATLAB expression that represents the output data. The expression must evaluate to a column vector or matrix.

• Frequency — Enter the MATLAB variable name of a vector or a MATLAB expression that represents the frequencies. The expression must evaluate to a column vector.

The frequency vector must have the same number of rows as the input and output signals.

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

• Frequency unit — Enter `Hz` for Hertz or keep the `rad/s` default value.

• Sample time — Enter the actual sample time in the experiment. For continuous-time data, enter `0`. For more information about this setting, see Specifying the Data Sample Time.

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

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 output 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).

### Note

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.

### Note

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.

### Tip

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.

### Tip

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

6. Click to close the Import Data dialog box.

### Importing Frequency-Response Data into the App

#### Prerequisite

Before you can import frequency-response data into the System Identification app, you must import the data into the MATLAB workspace, as described in Frequency-Response Data Representation.

#### Importing Complex-Valued Frequency-Response Data

To import frequency-response data consisting of complex-valued frequency values at specified frequencies:

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

`systemIdentification`
2. In the System Identification app window, select Import data > Freq. domain data. This action opens the Import Data dialog box.

3. In the Data Format for Signals list, select Freq. Function (Complex).

4. Specify the following options:

• Response — Enter the MATLAB variable name or a MATLAB expression that represents the complex frequency-response data G(eiw).

• Frequency — Enter the MATLAB variable name of a vector or a MATLAB expression that represents the frequencies. The expression must evaluate to a column vector.

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

• Frequency unit — Enter `Hz` for Hertz or keep the `rad/s` default value.

• Sample time — Enter the actual sample time in the experiment. For continuous-time data, enter `0`. For more information about this setting, see Specifying the Data Sample Time.

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

Channel Names

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

### Tip

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.

### Tip

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.

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

7. Click to close the Import Data dialog box.

#### Importing Amplitude and Phase Frequency-Response Data

To import frequency-response data consisting of amplitude and phase values at specified frequencies:

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

`systemIdentification`
2. In the System Identification app window, select Import data > Freq. domain data. This action opens the Import Data dialog box.

3. In the Data Format for Signals list, select Freq. Function (Amp/Phase).

4. Specify the following options:

• Amplitude — Enter the MATLAB variable name or a MATLAB expression that represents the amplitude $|G|$.

• Phase (deg) — Enter the MATLAB variable name or a MATLAB expression that represents the phase $\phi =\mathrm{arg}G$.

• Frequency — Enter the MATLAB variable name of a vector or a MATLAB expression that represents the frequencies. The expression must evaluate to a column vector.

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

• Frequency unit — Enter `Hz` for Hertz or keep the `rad/s` default value.

• Sample time — Enter the actual sample time in the experiment. For continuous-time data, enter `0`. For more information about this setting, see Specifying the Data Sample Time.

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

Channel Names

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

### Tip

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.

### Tip

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.

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

7. Click to close the Import Data dialog box.

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