User`s guide

5 ODE P ara meter Estimation (Grey-Box Modeling)
Choosing idgrey or idnlgrey Model Object
Grey-box m odels require that you specify the structure of the ODE model in
a file. You use this file to create the
idgrey or id nlgrey model object. You
can use both the
idgrey and the idnlgrey objects to model linear systems.
However, you can only represent nonlinear dynamics using the
idnlgrey
model object.
The
idgrey object requires that you write an M-file to describe the linear
dynamics in the state-space form, such that this M-fi le returns the state-space
matrices as a function of your parameters. For more information, see
“Specifying the Linear Grey-Box Model Structure” on page 5-6.
The
idnlgrey object requires that you write an M-file or M EX-file to describe
thedynamicsasasetoffirst-order differential equations, such that this file
returns the output and s tate derivative s as a function of time, input, state,
and p arame ter values . For more information,see“SpecifyingtheNonlinear
Grey-Box Model Structure” on page 5-17.
The following table compares
idgrey and idnlgrey model objects.
Comparison of idgrey and idnlgrey Objects
Settings and
Operations
Supported by
idgrey?
Supported by
idnlgrey?
Set bounds on
parameter values.
No Yes
Handle i n itial states
individually.
No Yes
Perform linear analysis
(e.g., using bode).
Yes No
5-4