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 app 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 linear model to an `idfrd` model.If you have the Control System Toolbox™ product, this command converts any numeric LTI model too. | To get frequency response of `m` at default
frequencies, use the following command:m_f = idfrd(m) m_f = idfrd(m,f) `2` to
output `3` , use the following command:m_f = idfrd(m(2,3)) |

`idpoly` | Converts any linear identified model, except `idfrd` ,
to ARMAX representation if the original model has a nontrivial noise
component, or OE if the noise model is trivial ( ).If you have the Control System Toolbox product, this command converts any numeric LTI model, 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 linear identified model, except `idfrd` ,
to state-space representation.If you have the Control System Toolbox product, this command converts any numeric LTI model, except `frd` . | To get a state-space model from an ARX model `m_arx` ,
use the following command:m_ss = idss(m_arx) |

`idtf` | Converts any linear identified model, except `idfrd` ,
to transfer function representation. The noise component of the original
model is lost since an `idtf` object has no elements
to model noise dynamics. If you have the Control System Toolbox product, this command converts any numeric LTI model, except `frd` . | To get a transfer function from a state-space model `m_ss` ,
use the following command:m_tf = idtf(m_ss) |

Conversion of an

`idtf`

model to an`idpoly`

model.Conversion of an

`idgrey`

model to an`idss`

model.

If you want to translate the estimated parameter covariance
during conversion, use |

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