Robust Control Toolbox™

Mouse-based tool for sketching and fitting

Syntax

• [sysout,pts] = drawmag(data) 
  [sysout,pts] = drawmag(data,init_pts) 
  

Description

drawmag interactively uses the mouse in the plot window to create pts (the frd object) and sysout (a stable minimum-phase ss object), which approximately fits the frequency response (magnitude) in pts.

Input arguments:

data	Either a frequency response object that is plotted as a reference, or a constant matrix of the form [xmin xmax ymin ymax] specifying the plot window on the data.
init_pts	Optional frd objects of initial set of points

Output arguments

sysout	Stable, minimum-phase ss object that approximately fits, in magnitude, the pts data.
pts	Frequency response of points.

:

While drawmag is running, all interaction with the program is through the mouse and/or the keyboard. The mouse, if there is one, must be in the plot window. The program recognizes several commands:

• Clicking the mouse button adds a point at the crosshairs. If the crosshairs are outside the plotting window, the points are plotted when the fitting, windowing, or replotting mode is invoked. Typing a is the same as clicking the mouse button.
• Typing r removes the point with frequency nearest that of the crosshairs.
• Typing any integer between 0 and 9 fits the existing points with a transfer function of that order. The fitting routine approximately minimizes the maximum error in a log sense. The new fit is displayed along with the points, and the most recent previous fit, if it exists.
• Typing w uses the crosshair location as the initial point in creating a window. Moving the crosshairs and clicking the mouse or pressing any key then gives a second point at the new crosshair location. These two points define a new window on the data, which is immediately replotted. This is useful in fine tuning parts of the data. You can call windowing repeatedly.
• Typing p simply replots the data using a window that covers all the current data points as well as whatever was specified in in. Typically used after windowing to view all the data.
• Typing k invokes the keyboard using the keyboard command. You should exercise caution when using this option, as it can wreak havoc on the program if variables are changed.

See Also
ginput      Graphically input information from mouse

loglog      Plotting frequency responses on log-log scale

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