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Estimate Frequency-Response Models in the App

You must have already imported your data into the app and performed any necessary preprocessing operations. For more information, see Data Preparation.

To estimate frequency-response models in the System Identification app:

  1. In the System Identification app, select Estimate > Spectral models to open the Spectral Model dialog box.

  2. In the Method list, select the spectral analysis method you want to use. For information about each method, see Selecting the Method for Computing Spectral Models.

  3. Specify the frequencies at which to compute the spectral model in one of the following ways:

    • In the Frequencies field, enter either a vector of values, a MATLAB® expression that evaluates to a vector, or a variable name of a vector in the MATLAB workspace. For example, logspace(-1,2,500).

    • Use the combination of Frequency Spacing and Frequencies to construct the frequency vector of values:

      • In the Frequency Spacing list, select Linear or Logarithmic frequency spacing.

        Note

        For etfe, only the Linear option is available.

      • In the Frequencies field, enter the number of frequency points.

      For time-domain data, the frequency ranges from 0 to the Nyquist frequency. For frequency-domain data, the frequency ranges from the smallest to the largest frequency in the data set.

  4. In the Frequency Resolution field, enter the frequency resolution, as described in Controlling Frequency Resolution of Spectral Models. To use the default value, enter default or, equivalently, the empty matrix [].

  5. In the Model Name field, enter the name of the correlation analysis model. The model name should be unique in the Model Board.

  6. Click Estimate to add this model to the Model Board in the System Identification app.

  7. In the Spectral Model dialog box, click Close.

  8. To view the frequency-response plot, select the Frequency resp check box in the System Identification app. For more information about working with this plot, see Frequency Response Plots.

  9. To view the estimated disturbance spectrum, select the Noise spectrum check box in the System Identification app. For more information about working with this plot, see Noise Spectrum Plots.

  10. Validate the model after estimating it. For more information, see Model Validation.

To export the model to the MATLAB workspace, drag it to the To Workspace rectangle in the System Identification app. You can retrieve the responses from the resulting idfrd model object using the bode or nyquist command.

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