Plotting Root Locus In matlab with K being a positive integar

I have a transfer function of K/(s^3+9s^2+27s+27) and am wondering how to plot the root locus of this as the numerator is a variable. K is gain and has to be a positive integar.

Answer 1

[Paul]

Can use

r = rlocus(sys,K)

where sys is the transfer function with numerator of 1 and K is a vector of positive integers of interest. Then use plot() to plot the imaginary part and real part of r.