The "Model Orders" editor is offered for models containing more than one input and/or more than one output channels. Changes made in this dialog for number of poles and zeros are copied over to the edit fields for number of poles and zeros in the transfer function estimation dialog. You can use the table in this dialog for specifying the number of poles and zeros for each I/O pair as a convenient alternative to using the top two edit fields in the transfer function estimation dialog.
The number of poles and zeros must be a nonnegative integers. For continuous-time estimation, the number of zeros must be less than or equal to the number of poles, unless continuous-time frequency domain data is used for estimation. For discrete-time systems, the number of "poles" and "zeros" refer to the roots of "z^-1" in the transfer function NUM(z^-1)/DEN(z^-1).
If you want to use the same settings for all outputs, check the "use same value for all outputs" checkbox. Checking this checkbox causes the number of poles/zeros selected for the current output to be copied to all the other outputs. This option is enabled only for multioutput models.
For discrete-time models, presence of feedthrough can also be chosen
for each I/O pair by checking the corresponding checkboxes in the
column titled "Feedthrough". For example, a discrete-time model with
number of poles = 2 and number of zeros = 3 for a particular I/O pair
takes the following form:
H(z^-1) = (b0 + b1 z^-1 + b2 z^-2 + b3 z^-3) / (1 + a1 z^-1 + z2 z^-2)
When model has direct feedthrough, b0 is a free parameter whose value
is estimated along with the rest of the model parameters (b1, b2, b3, a1, a2).
When model has no feedthrough (default), b0 is fixed to zero value.