System Identification Toolbox™

Refining Nonlinear Black-Box Models

How to Refine Nonlinear Black-Box Models in the GUI

The following procedure assumes that the model you want to refine is already in the System Identification Tool GUI. You might have estimated this model in the current session or imported the model into the GUI from the MATLAB workspace. For more information about estimating nonlinear black-box models, see Nonlinear Black-Box Model Identification.

To refine your model:

1. In the System Identification Tool GUI, verify that you have the correct data set in the Working Data area for refining your model.

   If you are using a different data set than the one you used to estimate the model, drag the correct data set into the Working Data area. For more information about specifying estimation data, see Specifying Estimation and Validation Data.

2. Select Estimate > Nonlinear models to open the Nonlinear Models dialog box, if this dialog box is not already open.

3. In the Nonlinear Models dialog box, select the model you want to refine in the Initial model list.

   The list includes only those models that have the selected Model structure and the same number of inputs and outputs as the estimation data in Working Data area.

   Any settings in the Nonlinear Models dialog box related to model structure and estimation algorithms are overridden by the selected initial model.

4. Click Estimate to refine the model.

5. Validate the new model, as described in Model Analysis.

Tip   To continue refining the model directly from the Estimation tab, select the Use last estimated model as initial model for the next estimation check box, and click Estimate. This action automatically selects the most recent model in the Initial model list in the Model Type tab.

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How to Refine Nonlinear Black-Box Models at the Command Line

If you are working at the command line, you can use pem to refine nonlinear black-box models.

The general syntax for refining initial models is as follows:

m = pem(data,init_model)

pem uses the properties of the initial model unless you specify different properties. For more information about specifying model properties directly in the estimator, see Specifying Model Properties for Estimation.

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Supported Nonlinearity Estimators

Extracting Parameter Values from Nonlinear Black-Box Models