StepInfo Outputting NaN for my Transfer Function

I am trying to find the overshoot of a transfer function for a step response but the stepinfo command does not display anything useful. This is the code.

sys=tf(280*[1 1.5 .5], [100 215 30.5 1 0]);

stepinfo(sys)

ans =

        RiseTime: NaN
    SettlingTime: NaN
     SettlingMin: NaN
     SettlingMax: NaN
       Overshoot: NaN
      Undershoot: NaN
            Peak: Inf
        PeakTime: Inf

Answer 1

[Fangjun Jiang]

a=step(sys);
b=stepinfo(a)

Answer 2

[Craig]

Hi Omar,

The system you specified has an integrator and is therefore unstable. This is the reason why NaN's are being returned by stepinfo.

You can see the response by doing

>> step(sys)

-craig

[Fangjun Jiang]

That is the point of my answer. It needs to run step() first to get the step response and then run stepinfo() using the step response as the input.

The existence of an integrator in the system increases the chance of making the system stable. It's usually the derivative that makes the system un-stable.