System Identification Toolbox™

Extracting Parameter Values from Nonlinear Black-Box Models

Nonlinear ARX Parameter Values

You can extract the numerical parameter values of a nonlinear ARX model by accessing the properties of the idnlarx model object.

The nonlinear ARX model parameters you might want to explore include model orders and delays, regressors, nonlinearity estimator parameters, and initial state values. To access the list of standard or custom regressors, you can use the getreg command. For more information, see the getreg reference page.

You can view the parameters of the nonlinearity estimators using the Nonlinearity property. For example:

% Load sample data.
load iddata1
% Estimate a nonlinear ARX model that includes a
% treepartition nonlinearity.
m = nlarx(z1,[2 2 1],'tree');
NL = m.Nonlinearity;
get(NL)
NL.Parameters

For more information about the treepartition nonlinearity, see the corresponding reference page.

To access any properties of a nonlinear ARX model object, use the get command. For more information about nonlinear ARX model properties, see the idnlarx reference page.

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Hammerstein-Wiener Parameter values

You can extract the numerical parameter values of a Hammerstein-Wiener model by accessing the properties of the idnlhw model object.

The Hammerstein-Wiener model parameter you might want to explore include model orders and delays, nonlinearity estimator parameters, and the properties of the linear model.

You can view the parameters of the nonlinearity estimators using the InputNonlinearity and OutputNonlinearity properties. For example:

% Load sample data.
load iddata1
% Estimate a Hammerstein-Wiener model that includes a
% no input nonlinearity and a wavenet output nonlinearity.
m = nlhw(z1,[2 2 1],[],'wav');
% Assign variables to the input and output nonlinearities.
% No input nonlinearity is equivalent to a unitgain nonlienearity.
uNL = m.InputNonlinearity;
yNL = m.OutputNonlinearity;
get(NL)
% Display output nonlinearity parameters.
yNL.Parameters

For more information about the unitgain and wavenet nonlinearities, see the corresponding reference pages.

To access any properties of a Hammerstein-Wiener model object, use the get command. For more information about Hammerstein-Wiener model properties, see the idnlhw reference page.

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Refining Nonlinear Black-Box Models

Next Steps After Estimating Nonlinear Black-Box Models