stepinfo

why stepinfo function don't give me any numerical results for

>> q=tf([1 2 ],[ 1 2 3 4 5 7]); >> stepinfo(q)

ans =

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

Answer 1

[Walter Roberson]

1 and 2 are roots of the numerator and are also roots of the denominator. Therefore at 1 and 2, the value of the function is not simply one of the infinities but is instead 0/0 = NaN . Transfer functions that have point singularities like this do not have defined values for the parameters you are looking for.

[ahmed salama]

i don't understand u ... see this

s=tf([1000],[1 3 2 6592 36354 119894 230060 241392 120960])

S = stepinfo(s,'RiseTimeLimits',[0.05,0.95])

S =

RiseTime: NaN

SettlingTime: NaN

SettlingMin: NaN

SettlingMax: NaN

Overshoot: NaN

Undershoot: NaN

Peak: Inf

PeakTime: Inf

it is obvious that this results appears when the denominator is bigger than the forth order

please answer....

[Walter Roberson]

Sorry, I do not have that toolbox available to test.

The documentation shows a 5th order example,

http://www.mathworks.com/help/toolbox/control/ref/stepinfo.html