Help with Simulink simple double integration problem, seems odd.

Hello! I was having issues with my Simulink model and I think I isolated the problem. This simple test program shows it:

I am providing a signal and processing it this way: double integration - double derivation - double integration. Then, when comparing results at each step there seems to be a problem with the double integration. The original signal compared to the one after double integration-double derivation are pretty much the same. But the two double integrated signals are way off. Could somebody help me solve this issue or explain why this is happening? I have tried many things like changing the solver or sampling time but the result is the same. Also, I need it to be fixed step because for my actual model I am reading a data file.

I am using R2012b version, win7 64 bits. Simulink is running at fixed step (200 Samples/sec), solver is ode5.

Thanks!

Answer 1

[Mischa Kim]

Efrain, it's all about accuracy of the integration/differentiation algorithm. For a fixed-step simulation like the one you are showing you are better off using a discrete derivative block.