How can I create a root locus plot with additionally highlighted poles for certain gain factors using RLOCUS or RLOCUSPLOT?

I am creating root locus plots using RLOCUSPLOT and I want to emphasize the poles for a certain gain in my plot. I know it is possible to pass a gain vector as third parameter of RLOCUSPLOT but this does not lead to the desired result.

rlocusplot(tf([1 2],[1 2 1]))

hold on

rlocusplot(tf([1 2],[1 2 1]), 1);

How can I create the root locus plot with additionally highlighted poles for a certain gain factor?

Answer 1

[MathWorks Support Team]

The following example uses RLOCUSPLOT to create the complete root locus. In the second step RLOCUS calculates the poles for gain value k=1. Finally the the poles are plotted into the existing root locus plot using red marker "x":

rlocusplot(tf([1 2],[1 2 1]))

hold on

pole=rlocus(tf([1 2],[1 2 1]), 1);

plot(real(pole),imag(pole),'rx','Markersize',10)

hold off

You can adjust the appearance of the highlighted poles according to your preference. For further information refer to the LineSpec documentation:

   docsearch('linespec')