User`s guide

3 Linear Model Identification
Extracting Parameter Values from Linear Models
You can extract the numerical param eter values a nd uncertainties of model
objects and store these values using
double data format.
For example, you can extract state-space matrices for state-space models, and
extract polynomials for polynomial models. Yo u can operate on extracted
model data as you would on any other M AT LAB vectors and matrices. You
can also pass these numerical values to Control System Toolbox commands,
for exam ple, or Simulink blocks.
If you specied to estimate model uncertainty data, this information is stored
in the property
Model.CovarianceMatrix in the estimated model. The
covariance matrix is used to compute uncertainties in parameter estimates,
model output plots, Bode plots, residua l plots, and pol e -zero plots.
The most direct method for getting parameter values from linear models is to
use the
get command. For example, get(m,'A') displays the A polynomial
coefcients from model
m. Alternatively, y ou can use dot notation to access
the model properties, as follows:
m.A.
The following table s ummarizes commands for extracting numerical data
from models. All of these commands have the following syntax form:
[G,dG] = command(model)
where G stores model parameters and dG stores standard deviation of
parameters or covariance.
Commands for Extracting Numerical Model Data
Command
Description
Syntax
arxdata
Extracts A RX
parameters from
multiple-output
idarx
or single-o utp ut idpoly
objects that represent
ARX models.
[A,B,dA,dB] = arxdata(m)
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