Estimate Frequency-Response Models at the Command Line
You can use the etfe, spa, and spafdr commands to estimate spectral
            models. The following table provides a brief description of each command and usage
            examples.
The resulting models are stored as idfrd model objects. For detailed information about the commands and
            their arguments, see the corresponding reference page.
Commands for Frequency Response
| Command | Description | Usage | 
|---|---|---|
| etfe | Estimates an empirical transfer function using Fourier analysis. | To estimate a model  m=etfe(data) | 
| spa | Estimates a frequency response with a fixed frequency resolution using spectral analysis. | To estimate a model  m=spa(data) | 
| spafdr | Estimates a frequency response with a variable frequency resolution using spectral analysis. | To estimate a model  m=spafdr(data,R,w) where
                                     | 
Validate the model after estimating it. For more information, see Model Validation.