arxdata (System Identification Toolbox)

Extract the ARX parameters from idmodel models.

Syntax

[A,B] = arxdata(m)
[A,B,dA,dB] = arxdata(m)

Description

m is the model as an idarx or idpoly model object. arxdata will work on any idarx model. For idpoly it will give an error unless the underlying model is an ARX model, i.e., the orders nc=nd=nf=0. (See the reference page for idpoly.)

A and B are returned in the standard multivariable ARX format (see idarx), describing the model.

Here and are matrices of dimensions ny-by-ny and ny-by-nu, respectively (ny is the number of outputs, i.e., the dimension of the vector and nu is the number of inputs). See Multivariable ARX Models: The idarx Model in the "Tutorial".

The arguments A and B are 3-D arrays that contain the A matrices and the B matrices of the model in the following way:

A is an ny-by-ny-by-(na+1) array such that

```
A(:,:,k+1) = Ak
A(:,:,1) = eye(ny)
```

Similarly B is an ny-by-nu-by-(nb+1) array with

```
B(:,:,k+1) = Bk
```

Note that A always starts with the identity matrix, and that leading entries in B equal to zero means delays in the model. For a time series B = [].

dA and dB are the estimated standard deviations of A and B.

See Also

idarx

arx arxstruc