sgrid (Control System Toolbox)

Generate an s-plane grid of constant damping factors and natural frequencies

Syntax

sgrid
sgrid(z,wn)

Description

sgrid

generates a grid of constant damping factors from zero to one in steps of 0.1 and natural frequencies from zero to 10 rad/sec in steps of one rad/sec, and plots the grid over the current axis. If the current axis contains a continuous s-plane root locus diagram or pole-zero map, sgrid draws the grid over the plot.

sgrid(z,wn)

plots a grid of constant damping factor and natural frequency lines for the damping factors and natural frequencies in the vectors z and wn, respectively. If the current axis contains a continuous s-plane root locus diagram or pole-zero map, sgrid(z,wn) draws the grid over the plot.

Example

Plot s-plane grid lines on the root locus for the following system.

You can do this by typing

H = tf([2 5 1],[1 2 3])
Transfer function:
2 s^2 + 5 s + 1
---------------
 s^2 + 2 s + 3
rlocus(H)
sgrid

Limitations

sgrid plots the grid over the current axis regardless of whether the axis contains a root locus diagram or pole-zero map. Therefore, if the current axes contains, for example, a step response, you may superimpose a meaningless s-plane grid over the plot. In addition, sgrid does not rescale the axis limits of the current axis. Therefore, the s-plane grid may not appear in the plot if the left half of the s-plane is not encompassed by the axis limits.