What Is a Root Locus?
The root locus method, developed by W.R. Evans, is widely used in control engineering for the design and analysis of control systems. In this method, the closed-loop system poles are plotted against the value of a system parameter, typically the open-loop transfer function gain.
This method is popular with control system engineers because it lets them quickly and graphically determine how to modify controller poles, zeros, and gain to position dominant closed-loop system poles in the desired locations.
For details, see Control System Toolbox.