System Identification Toolbox

Frequency Function Format: the idfrd model

Frequency functions and spectra are stored as an idfrd (Identified Frequency Response Data) model object (which is not a child of idmodel). This model format is used by spa and etfe to deliver their results. Moreover, any idmodel can be transformed to an idfrd object.

The frequency function and the disturbance spectrum corresponding to an idmodel m is computed by

• h = idfrd(m)
  

This gives G and in (3-11) along with their estimated covariances, which are translated from the covariance matrix of the estimated parameters. If m corresponds to a time-continuous model, the frequency functions are computed accordingly.

The functions are retrieved by h.ResponseData, h.CovarianceData, h.SpectrumData, and h.NoiseCovariance or any case-insensitive abbreviation of the names. The frequency vector is contained in h.Frequency.

In addition, an idfrd model can be defined directly from the frequency functions. See Function Reference, which also contains a list of idfrd properties. The channels of an idfrd model can be manipulated analogously to idmodels.

An alternative is to compute the response functions without storing them as an idfrd object.

• [Response,Frequency,Covariance] = freqresp(m)
  

Parametric Models: idmodel and its children

Graphs of Model Properties