Re: impulse() giving error

[Lukas Reichlin]

> octave-3.2.3:11> H=tf([2 1],[4 3])
> 
> Transfer function "H" from input "u1" to output ...
>       2 s + 1
>  y1:  -------
>       4 s + 3
> 
> 
> impulse(H) gives a nice graph now.
> 
> step(H) goes wrong now, though:


I warned you in my first mail ;-)
> Warning: Because of a bug in Octave 3.2.x, system sys changes sampling time 
> after the first call of a time response function (lsim, step, impulse, 
> initial). This bug is fixed in current development sources (>= 3.3.51) for 
> Octave 3.4.

You can try step first and impulse afterwards. You will see that now step works 
correctly and impulse fails.

You can check this by

H = tf ([2, 1], [4, 3])
step (H)
H

and you get

octave-3.2.3:2> H = tf ([2, 1], [4, 3])

Transfer function "H" from input "u1" to output ...
      2 s + 1
 y1:  -------
      4 s + 3

octave-3.2.3:3> step (H)
octave-3.2.3:4> H

Transfer function "H" from input "u1" to output ...
      2 s + 1
 y1:  -------
      4 s + 3

Sampling time: 0.14 s
octave-3.2.3:5> 

The last line shows that the model has a sampling time of 0.14 seconds. This 
bug is the reason why I didn't publish control-2.0 so far.