Version 7.4 (R2010a) System Identification Toolbox Software :: System Identification Toolbox Release Notes (System Identification Toolbox™)

Discrete-time Linear Model	Use for Initializing...
Single-output polynomial model of ARX structure (`idpoly`)	Single-output nonlinear ARX model estimation
Multi-output polynomial model of ARX structure (`idarx`)	Multi-output nonlinear ARX model estimation
Single-output polynomial model of Output-Error (OE) structure (`idpoly`) or state-space model with no disturbance component (`idss`) object with K = 0	Single-output Hammerstein-Wiener model estimation
State-space model with no disturbance component (`idss` object with K = 0)	Multi-output Hammerstein-Wiener model estimation

During estimation, the software uses the linear model orders and delay as initial values of the nonlinear model orders and delay. For nonlinear ARX models, this initialization always provides a better fit to the estimation data than the linear ARX model.

You can use a linear model as an alternative approach to using model orders and delay for nonlinear estimation of the same system.

You can estimate or construct the linear model and then use this model for constructing (see idnlarx and idnlhw) or estimating (see nlarx or nlhw) the nonlinear model. For more information, see Using Linear Model for Nonlinear ARX Estimation, and Using Linear Model for Hammerstein-Wiener Estimation in the System Identification Toolbox User's Guide.

New Cell Array Support for B and F Polynomials of Multi-Input Polynomial Models

You can now use cell arrays to specify the B and F polynomials of multi-input polynomial models. The B and F polynomials are represented by the b and f properties of an idpoly object These properties are currently double matrices.

For multi-input polynomial models, these polynomials will be represented by cell arrays only in a future version. If your code performs operations on the b and f properties, make one of the following changes in the code:

When you construct the model using the idpoly command, use cell arrays to specify the B and F polynomials. Using cell arrays causes the b and f properties to be represented by cell arrays.
After you construct or estimate the model, use the new setPolyFormat command to:
- Convert b and f properties to cell arrays.
- Make the model backward compatible to continue using double matrices for b and f properties. This operation ensures that operations on b and f properties that use matrix syntax continue to work without errors in a future version.

When you use cell arrays, you must also update your code to use cell array syntax on b and f properties instead of matrix syntax.

Note For single-input polynomial models, the b and f properties continue to be double row vectors.

Functions and Function Elements Being Removed

Function or Function Element Name	What Happens When you Use the Function or Element?	Use This Instead	Compatibility Considerations
Double matrix support for `b` and `f` properties of multi-input `idpoly` models.	Warns	Use cell array to specify the `b` and `f` properties of multi-input polynomial models.	If your code performs operations on the `b` and `f` properties, update the code to be compatible with a future release. See New Cell Array Support for B and F Polynomials of Multi-Input Polynomial Models.