"Long " <longluong_maybach@yahoo.com> wrote in message <ksajbv$4f3$1@newscl01ah.mathworks.com>...
> Hello. I have one simple problem with Matlab Simulink.
>
> u > derivative > derivative > integrator > integrator > output = u
>
> If we take the derivative of an input signal 2 times and then take the integrator 2 times, we are supposed to get the original input signal.
Not necessarily. When you integrate a function you also get an "arbitrary" constant that needs to be evaluated from the initial conditions. If you don't account for this I'm guessing it gets really bad when you do it twice without taking into account the initial condition of the first integral.
>
> But when I use a step signal as the input, in the Simulink scope, the output is not the step signal any more, instead, it has very large value. Maybe because the derivative of step signal has a very large value.
As to how Simulink handles this, I'm not sure. (I don't have that toolbox.)
>
> So how can I solve the problem? I mean in the Simulink simulation, that I can get output = step signal ??? Not the large value.
>
> Thank you very much
