Using Matlab, how can I find the value K in the following root locus?

Question

In Matlab, how can I find value of K, in a system that has oscillation?

(system's tf, if needed: (K * (s + 25))/(s^3 + 24 s^2 + 100 s) )

PS. I'm using root locus.

Answer 1

Does the dcgain function do what you need?

Answer 2

I assume this is the plant for a closed-loop system with gain compensation only (that would be K). In that case I would express it as a transfer function and then use the root-locus command to see where it hits on the x-axis:

num = [1 25];
den = [1 24 100 0];

sys=tf(num,den)
rlocus(sys)

Unfortunately your system appears to be stable for all values of K! Doh!