How to Analyze Data Using the advice Command

You can use the advice command to analyze time- or frequency- domain data before estimating a model. The resulting report informs you about the possible need to preprocess the data and identifies potential restrictions on the model accuracy. You should use these recommendations in combination with plotting the data and validating the models estimated from this data.

Note

advice does not support frequency-response data.

Before applying the advice command to your data, you must have represented your data as an iddata object. For more information, see Representing Time- and Frequency-Domain Data Using iddata Objects.

If you are using the System Identification app, you must export your data to the MATLAB^® workspace before you can use the advice command on this data. For more information about exporting data, see Exporting Models from the App to the MATLAB Workspace.

Use the following syntax to get advice about an iddata object data:

advice(data)

For more information about the advice syntax, see the advice reference page.

Advice provide guidance for these kinds of questions:

• Does it make sense to remove constant offsets and linear trends from the data?

• What are the excitation levels of the signals and how does this affects the model orders?

• Is there an indication of output feedback in the data? When feedback is present in the system, only prediction-error methods work well for estimating closed-loop data.

• Is there an indication of nonlinearity in the process that generated the data?