PLOTZP Procedure
Creates a root locus (zero-pole) plot.
Usage
PLOTZP, h
Input Parameters
h—The filter structure.
Keywords
Lines—If present and nonzero, causes lines to be drawn from the origin to the poles and zeros.
Print—If present and nonzero, causes the poles and zeros to be printed to the standard output.
Radius—If present and nonzero, overrides the automatic range calculations and sets the x- and y-ranges of the plot to the specified range [–r, r].
Title—A string containing the title of the plot.
Discussion
For a given filter structure H(z) of the form:
zeros are the values of z, which when used to evaluate the filter structure numerator polynomial return the value zero. The poles are the values of z which return the value zero when used to evaluate the denominator polynomial of the filter structure.
PLOTZP plots the zeros of H(z) with a circular plot symbol (“O”), and uses an “X” to indicate the poles of H(z).
note | It is important to note that PLOTZP uses root finding to obtain the zeros and poles of the filter structure. If either the numerator or the denominator polynomial have repeated roots, the function may generate error messages. |
Example 1
In this example, the poles and zeros of an elliptic filter are plotted. The results are shown in Figure 3-13: PLOTZP Procedure Example 1. The “O”s represent zeros of H(z), and the “X”s represent the poles of H(z).
; Create an elliptical IIR filter.
h = IIRDESIGN(4, .5, .05, .05, /Ellip)
; Plot the poles and zeros of the filter.
PLOTZP, h
 |
Example 2
In this example, PLOTZP prints out the poles and zeros and draws lines from the origin to the poles and zeros. The results are shown in Figure 3-14: PLOTZP Procedure Example 2.
; Create an elliptical IIR filter.
h = IIRDESIGN(4, .5, .05, .05, /Ellip)
PLOTZP, h, /Print, /Lines
; The zeros are at:
; ( -0.752679, 0.658388)( -0.752679, -0.658388)
; ( -0.261730, 0.965141)( -0.261730, -0.965141)
; The poles are at:
; ( -0.0287310, 0.906404)( -0.0287310, -0.906404)
; ( 0.154772, 0.456417)( 0.154772, -0.456417)
; Print the numerical values of the poles and zeros, plot the
; poles and zeros, and draw lines to them from the origin.
 |
See Also
