With regards to the root migration plots in Fig. 2
and associated Eqs. (7)-(8) and (1 1)-(13), all root
migration characteristics, except for 6(s), follow
traditional rules, i.e., these loci are "one-layered".
Therefore, generation of sketching rules for these plots
are unnecessary. Closed-loop pole migration behavior
is governed by a "two-layered'' loci (see Eq. (7) ), and
generation of new sketching rules is necessary here.