The closed-loop poles are graphically displayed in a
"two-layered root locus" format where "poles track
moving zeros". The migration paths do not adhere to
traditional root locus rules, and exhibit unique features
such as direction reversal on the real axis. Development
of sketching rules to describe and predict these new
features is the major objective of the paper. Recall that
root locus sketching rules associated with scalar-loop
applications are what transform the Evans design
technique from a iterative strategy (albeit graphical) to apowerful tool where clear and concise relationships
between design inputs and resulting effects upon
stability and performance are available. With the new
technique, fully coupled control system architectures can
be designed within an overall framework allowing
simultaneous features to be assessed, while still
retaining an efficient graphical medium.