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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

CommandDescriptionSyntax
arxdataExtracts ARX parameters from multiple-output idarx or single-output idpoly objects that represent ARX models.
[A,B,dA,dB] = arxdata(m)
freqrespExtracts frequency-response data from any idmodel or idfrd object.
[H,w,CovH] = freqresp(m)
polydataExtracts polynomials from any single-output idmodel object.
[A,B,C,D,F,dA,dB,dC,dD,dF] = ...
       polydata(m)
ssdataExtracts state-space matrices from any idmodel object.
[A,B,C,D,K,X0,...
 dA,dB,dC,dD,dK,dX0] = ...
       ssdata(Model)
tfdataExtracts numerator and denominator polynomials from any idmodel object.
[Num,Den,dNum,dDen] = ...
     tfdata(Model)
zpkdataExtracts zeros, poles, and transfer function gains from any idmodel object.
[Z,P,K,covZ,covP,covK] = ...
     zpkdata(m)

  


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