System Identification Toolbox

The Plot Windows

The six views all give similar plot windows, with several common features. They have a common menu bar, which covers some basic functions.

First of all, note that there is a zoom function in the plot window. By dragging with the left mouse button down, you can draw rectangles, which will be enlarged when the mouse button is released. By double-clicking, the original axis scales are restored. For plots with two axes, the x-axes scales are locked to each other. A single click on the left mouse button zooms in by a factor of two, while the middle button zooms out. The zoom function can be deactivated if desired. Just select the menu item Zoom under Style.

Second, by pointing to any curve in the plot, and pressing the right mouse button, the curve will be identified with model name and present coordinates.

The common menu bar covers the following functions.

File

File allows you to copy the current figure to another, standard MATLAB figure window. This might be useful, e.g., when you intend to print a customized plot. Other File items cover printing the current plot and closing the plot window.

Options

Options first of all cover actions for setting the axes scaling. This menu item also gives a number of choices that are specific for the plot window in question, like a choice between step response or impulse response in the Transient
response window.

A most important option is the possibility to show confidence intervals. Each estimated model property has some uncertainty. This uncertainty can be estimated from data. By checking Show confidence intervals, a confidence region around the nominal curve (model property) will be marked (by dash-dotted lines). The level of confidence can also be set under this menu item.

Note    Confidence intervals are supported for most models and properties, except models estimated using etfe, and the k-step ahead prediction-property. For n4sid, the covariance properties are actually not fully known. The Cramer-Rao lower limit for the covariance matrix is then used instead.

Style

The style menu gives access to various ways of affecting the plot. You can add gridlines, turn the zoom on and off, and change the linestyles. The menu also covers a number of other options, like choice of units and scale for the axis.

Channel

For multivariate systems, you can choose which input-output channel to examine. The current choice is marked in the figure title.

Help

The Help menu has a number of items, which explain the plot and its options.

Views and Models

Frequency Response and Disturbance Spectra