User`s guide

8 Model Analysis
Using Hamm erstein-Wiener Plots to Validate Models
In this section...
“About Hammerstein-Wiener Plots” on page 8-56
“How to Create Hammerstein-Wiener Plots i n the GUI” on page 8-56
“How to Plot Hammerstein-Wiener Plots at the Command Line” on page
8-58
“Plotting Nonlinear Block Characteristics” on page 8-58
“Plotting Linear B lock Charac teristics” on p age 8-59
About Hammerstein-Wiener Plots
Hammerstein-Wiener model plot lets you explore the characteristics of the
linear bloc k an d the sta tic n onlinearities of the H ammerstein-Wiener model.
For more information about estimating nonlinear Hammerstein-Wiener
models , see “Ident if yi ng H a mmerstein-Wiener Models” on page 4-15.
Examining a Hammerstein-Wiener plot can help you determine whether you
chose an unnecessarily complicated n onlinearity for modeling your system.
For example, if you chose a piece-wise-linear nonlinearity (which is very
general), but the plot indicates saturation behavior, then you can estimate a
new m odel using the simpler saturation nonlinearity instead.
For multivariable systems, you can use the H ammerstein-Wiener p lot
to determine whether to exclud e nonlinear ities for specific channels. If
the nonli n ea r ity for a specific input or output channel does not exhibit
strong nonline ar behavior, yo u can estimate a new model after setting the
nonlinearity at that channel to unit gain.
How to Create Hammerstein-Wiener Plots in the GUI
To create a Hammerstein-WienerplotintheSystemIdentification Tool GUI,
select the Hamm-Wiener check box in the Model Views area. For genera l
information about creating and working w ith plots, see “Working with Plots
in the System Identification Tool GUI” on page 12-15.
8-56