Extracting Parameter Values from Linear Models
You can extract the numerical parameter values and 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. You can operate
on extracted model data as you would on any other MATLAB vectors
and matrices. You can also pass these numerical values to Control System Toolbox commands,
for example, or Simulink blocks.
If you specified 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, residual plots,
and pole-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
coefficients from model m. Alternatively, you can
use dot notation to access the model properties, as follows: m.A.
The following table summarizes 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 ARX parameters from multiple-output idarx or
single-output idpoly objects that represent ARX
models. | [A,B,dA,dB] = arxdata(m) |
| freqresp | Extracts frequency-response data from any idmodel or idfrd object. | [H,w,CovH] = freqresp(m)
|
| polydata | Extracts polynomials from any single-output idmodel object. | [A,B,C,D,F,dA,dB,dC,dD,dF] = ...
polydata(m) |
| ssdata | Extracts state-space matrices from any idmodel object. | [A,B,C,D,K,X0,...
dA,dB,dC,dD,dK,dX0] = ...
ssdata(Model) |
| tfdata | Extracts numerator and denominator polynomials from any idmodel object. | [Num,Den,dNum,dDen] = ...
tfdata(Model) |
| zpkdata | Extracts zeros, poles, and transfer function gains from any idmodel object. | [Z,P,K,covZ,covP,covK] = ...
zpkdata(m) |
 | Refining Linear Parametric Models | | Extracting Dynamic Model and Noise Model Separately |  |
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