Transforming Between Linear Model Representations
You can transform linear models between state-space and polynomial
forms. You can also transform between frequency-response, state-space,
and polynomial forms.
If you used the System Identification Tool GUI to estimate models,
you must export the models to the MATLAB workspace before converting
models.
For detailed information about each command in the following
table, see the corresponding reference page.
Commands for Transforming Model Representations
| Command | Model
Type to Convert | Usage Example |
|---|
| idfrd | Converts any single- or multiple-output idmodel object
to idfrd model.
If you have the Control System Toolbox product,
this command converts any LTI object. | To get frequency response of m at default
frequencies, use the following command:m_f = idfrd(m)
To get frequency response at specific frequencies,
use the following command:m_f = idfrd(m,f) To
get frequency response for a submodel from input 2 to
output 3, use the following command:m_f = idfrd(m(2,3)) |
| idpoly | Converts single-output idmodel object
to ARMAX representation.
If you have the Control System Toolbox product,
this command converts any single-output LTI object except frd. | To get an ARMAX model from state-space model m_ss,
use the following command:m_p = idpoly(m_ss) |
| idss | Converts any single- or multiple-output idmodel object
to state-space representation.
If you have the Control System Toolbox product,
this command converts any LTI object except frd. | To get a state-space model from an ARX model m_arx,
use the following command:m_ss = idss(m_arx) |
Note
The idss conversion produces warnings when
the continuous-time disturbance model does not have the required white-noise
component. These warnings occur because the underlying state-space
model, which is formed and used by these transformations, is ill defined.
In this case, modify the C-polynomial such that
the degree of the monic C-polynomial in continuous-time
equals the sum of the degrees of the monic A-
and D-polynomials in continuous-time. For example: length(C)-1 = (length(A)-1)+(length(D)-1)
|
 | Transforming Between Discrete-Time and Continuous-Time Representations | | Subreferencing Model Objects |  |
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