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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.

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

To import data into the app:

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

systemIdentification

In the System Identification app window, select

**Import data**>**Freq. domain data**. This action opens the Import Data dialog box.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.

(Optional) In the

**Data Information**area, click**More**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).

**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.Click

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

**Close**to close the Import Data dialog box.

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.

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

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

systemIdentification

In the System Identification app window, select

**Import data**>**Freq. domain data**. This action opens the Import Data dialog box.In the

**Data Format for Signals**list, select**Freq. Function (Complex)**.Specify the following options:

**Response**— Enter the MATLAB variable name or a MATLAB expression that represents the complex frequency-response data*G(e*.^{iw})**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.

(Optional) In the

**Data Information**area, click**More**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.Click

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

**Close**to close the Import Data dialog box.

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

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

systemIdentification

In the System Identification app window, select

**Import data**>**Freq. domain data**. This action opens the Import Data dialog box.In the

**Data Format for Signals**list, select**Freq. Function (Amp/Phase)**.Specify the following options:

**Amplitude**— Enter the MATLAB variable name or a MATLAB expression that represents the amplitude $$\left|G\right|$$.**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.

(Optional) In the

**Data Information**area, click**More**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.Click

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

**Close**to close the Import Data dialog box.

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