System Identification Toolbox

Taking a Look at the Data

The first thing to do after having inserted the data set into the Data Board is to examine it. By checking the Data View item Time plot, a plot of the input and output signals will be shown for the data sets that are selected. You select/deselect the data sets by clicking on them. For multivariable data, the different combinations of input and output signals are chosen under menu item Channel in the plot window. Using the zoom function (drawing rectangles with the left mouse button down) different portions of the data can be examined in more detail.

To examine the frequency contents of the data, check the Data View item Data spectra. The function is analogous to Time plot, but the signals' spectra are shown instead. By default the periodograms of the data are shown, i.e., the absolute square of the Fourier transforms of the data. The plot can be changed to any chosen frequency range and a number of different ways of estimating spectra, by the Options menu item in the spectra window.

The purpose of examining the data in these ways is to find out if there are portions of the data that are not suitable for identification, if the information contents of the data is suitable in the interesting frequency regions, and if the data have to be preprocessed in some way, before using them for estimation.

Getting Input-Output Data into the GUI

Preprocessing Data