Settling time is not displaying on the step response graph

Question

I am graphing the step response of a closed loop system and I need to display the settling time on the graph for my assignment. Here is my code:

s = tf('s')
L = (20*(s+1))/(10*s*(s-1))
T = L/(1+L)
step(T)

Normally, I would just right click on the graph and in the characteristics hit the settling time option and it displays. It isn't displaying anything. I added this line:

stepinfo(T)

And it gives me the correct step response that is within the bounds of the graph.

Anyone know how to fix it so I can just right click and have it displayed?

Answer 1

The system is unstable, there is a pole in +1.

>> isstable(T)

ans =

  logical

   0

>> pole(T)

ans =

   0.0000 + 0.0000i
  -0.5000 + 1.3229i
  -0.5000 - 1.3229i
   1.0000 + 0.0000i

so according to this :

If sys is unstable, then all step-response characteristics are NaN, except for Peak and PeakTime, which are Inf.

It is weird that stepinfo(T) does output a setlling time though, as it shouldn't.