zpplot (System Identification Toolbox)

Plot zeros and poles.

zpplot(zepo)
zpplot(zpform(zepo1,zepo2, ..., zepon))
zpplot(zepo,sd,mode,axis)

Description

The zeros and poles specified by zepo (see zepo for the format) are graphed, with o denoting zeros and x denoting poles. Poles and zeros associated with the same input, but different models, are always graphed in the same diagram, and pressing the Return key advances the plot from one model to the next. On color screens poles, zeros and their confidence regions, corresponding to the same model all have the same color. Poles and zeros at infinity are ignored. For discrete-time models, zeros and poles at the origin are also ignored.

If sd has a value larger than zero, confidence regions around the poles and zeros are also graphed. The regions corresponding to sd standard deviations are marked. The default value is sd = 0. Note that the confidence regions may sometimes stretch outside the plot, but they are always symmetric around the indicated zero or pole.

If the poles and zeros are associated with a discrete-time model, a unit circle is also drawn.

When zepo contains information about several different inputs, there are some options:

mode = 'sub' splits the screen into several plots.

mode = 'same' gives all plots in the same diagram. Pressing the Return key advances the plots.

mode = 'sep' erases the previous plot before the next input is treated.

The default value is mode = 'sub'.

axis = [x1 x2 y1 y2] fixes the axis scaling accordingly. axis = m is the same as

axis = [-m m -m m]

Examples

zpbj = th2zp(thbj2);
zpax = th2zp(tharmax4);
zpoe = th2zp(thoe3);
zpplot(zpform(zpoe,zpax,zpbj),3)

show all zeros and poles of three models along with the confidence regions corresponding to three standard deviations.