rlocus (Control System Toolbox)

Evans root locus

Syntax

rlocus(sys)
rlocus(sys,k)

[r,k] = rlocus(sys)
r = rlocus(sys,k)

Description

rlocus

computes the Evans root locus of a SISO open-loop model. The root locus gives the closed-loop pole trajectories as a function of the feedback gain

(assuming negative feedback). Root loci are used to study the effects of varying feedback gains on closed-loop pole locations. In turn, these locations provide indirect information on the time and frequency responses.

rlocus(sys)

calculates and plots the root locus of the open-loop SISO model sys. This function can be applied to any of the following negative feedback loops by setting sys appropriately.

If sys has transfer function

the closed-loop poles are the roots of

rlocus adaptively selects a set of positive gains

to produce a smooth plot. Alternatively,

rlocus(sys,k)

uses the user-specified vector k of gains to plot the root locus.

When invoked with output arguments,

[r,k] = rlocus(sys)
r = rlocus(sys,k)

return the vector k of selected gains and the complex root locations r for these gains. The matrix r has length(k) columns and its jth column lists the closed-loop roots for the gain k(j).

Example

Find and plot the root-locus of the following system.

h = tf([2 5 1],[1 2 3]);
rlocus(h)

For examples, see "Root Locus Design" in the manual and "Hard-Disk Read/Write Head Controller" in the manual.